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VAASAN AMMATTIKORKEAKOULU

1. 43 4 3 Interfacing the Transients Independent ADC sesssss 50 4 4 The software environment eeeseseeseesesssisseesetsrtsresstesresrrssresseserssresseser 51 4 4 1 Folders and files naming standard and structure 32 4 4 2 The data storage A container for the information 53 44 3 The ADE7880 Di Vers oerte eee ti teet oe dehet ae cipes pide 54 4 4 4 ADE7880 low level access HAL eceeee 54 4 4 5 Public methods high level access eene 55 4 4 6 SPI hardware access and Middleware layer 58 4 4 7 RTU communications UART control eese 61 448 Real t me clop Eie oen de petii idec le icai end 63 4 5 MATLAB and SIMULINK testing environment 63 xUBuGiimino m 68 S ANALYSIS AND RESULTS 5o sciteet ee d loe Serge guide peri q i pee soni 73 5 1 ADE7880 driver and UART driver performance sess 13 5 2 Testing environment ADE7880 driver and UART driver accuracy 82 5 3 A word about MCU and ADE7880 AFE vs MCU ADCs performance 86 6 COIN GTI STON ta dite a E cae vad lad E oe 89 REE REIN CES eite T tui mta n ted tM aes es 91 APPENDICES sicicoaietneaitnncadletonoes san gyanascslperacuviansadtea tua Ua e R e ELO DES UR MARE 93 LIST OF FIGURES AND TABLES Figure 1 Thre
2. eene 56 Figure 20 ADE7880 SPI Read operation of 32 bit register Datasheet p 79 58 Figure 21 SIMULINK implementation seen 66 Figure 22 MATLAB GUI to control frequencies a b c and d amplitude 67 Figure 23 Terminal console showing the data of a sequence of measures 68 Figure 24 AFE connections Schematic uon iate dee Er eee donde eria 69 Figure 25 Fast acting optolIsolators sample from Isolation circuits schematics 70 Figute 20 PCB Top layer ics ction E uidet ERES eel eats 71 Figure 27 Single SPI reading scope by DSOX2012A see 74 Figure 28 Grouped SPI readings in one cycle scope by DSOX20124A 76 Figure 29 LCD showing the execution times of cases tl t2 and t3 78 Figure 30 LCD execution times when t2 incurs in delay 81 Figure 31 Currents when input of a b c and d frequencies amplitude is 0 5 83 Figure 32 Scope of the test signal four frequencies with an amplitude of 0 5 84 Figure 33 Not filtered testing signal us am ea deseas ee ee et 85 Figure 54 PCB Bottom layer iia eee beides pis aetna deeds aa 102 Ligure 25 PCB Op Ayer aout undated estu c Qu M LIRE ID MUS 102 Figure 36 Silkscreen top layers ia uses eret o cessaneasdeead coundoceds sosdaastcns 102 Figure 37 Silkscreen bottom layer s oo ente eie Use qui ODE qot ree os ip rev tags 102 LIST OF APPE
3. CMT start Registers list access cmd specific call meas specific cal 7 X andier cali j ADE set tx buffer 1 ADE SPI Wrile ADE_SPI_Read get lock lock status ADE get tx buffer Y Figure 19 ADE7880 driver user sequence diagram is the error occurrence which references are contained in error_List_et enumer ation defined into ade788 _configuration h for its identification where 0 means no error and up to 14 different errors are defined This output is propagated along the code from its origin to the caller and by caller we understand the user applica tion that originated the request to the energy meter Regarding the input parameters uint32 t pid belongs to the process identifier a 32 bits integer unique ID that is exclusive of the caller and required to implement the multiple access to the SPI driver from the ADE7880 and the LCD And uint32_t cmd which is a set of indi vidual instructions for configuration processes defined by config_cmd_et enumer ation or measurement options defined by measurement_cmd_et enumeration de fined into ade7880 srv cmd handLer h Regarding the command handler signa 57 ture it additionally requires a variable list of arguments Declared after the com mand instruction different configurations require a different number of o parame ters and the code s documentation or a quick review to each case int
4. Figure 33 Not filtered testing signal The scope above shows the output of the testing environment signal only funda mental is generated before the low pass antialiasing filter and in normal resolution acquisition mode The noise is evident and part of the energy is carried by it The FFT shows the same property of a poor Q factor as another cause of energy loss in the neighbour frequencies 86 5 3 A word about MCU and ADE7880 AFE vs MCU ADCs performance The use of the ADE7880 offers the advantages already seen but at the expense of a higher cost Moreover regarding to frequency component analysis its output is limited to the fundamental and its multiples due to the use of FFT in its DSP com putational block The next lines are intended to give a brief theoretical comparison of an AFE by means of an energy meter versus a MCU to directly interface the power lines The MCU interfacing the power lines through CTs and voltage dividers by means of its embedded ADCs represents a cheaper solution and when requiring to analyse specific frequencies other than harmonics of 45Hz 65HZ the energy meter is not an option anymore Another advantage is the speed at the data is served interfacing the internal ADCs with a DMA channel provides much faster transmission speed than the energy meter SPI On the other hand other requirements have to be ac counted in this option The selected MCU embedded ADCs have to comply with the prerequisites for
5. Figure 7 Even vs Odd function Matlab plot in other words as the electric current is an odd function the Fourier series reduces ro X ps to Equation 11 And coefficient bp where f t is the time domain function n is the harmonic number only odd values of n are required b is the coefficient or regarding harmonics amplitude of the nth harmonic com ponent T is the time period the length of one cycle in seconds Whereas this introduction to the Fourier Transform as a tool to decompose a func tion in the sum of sinusoids an extension of its idea applied to non periodic func tions is the Fourier Transform F g t G f g te dt 28 Equation 12 As a result of the Fourier Transform G f gives the magnitude of g t at a fre quency f For the most known applications there are free sets of look up Transform pair tables that one may use to get G f from g t to reduce the mathematical calculation time To evaluate the Fourier transform the Discrete Fourier Transform is widely used as it can be implemented in computer MCU by numeric algorithms or by dedicated hardware by analysis of a finite amount of data samples taken within the same period It differs from Discrete Time Fourier Transform also called continuous in that is has a finite input with N samples and output resulting in much easier and faster calculations it i271 F x n X k D UDE n n 0 fork 0 1 N 1 Equation 13
6. t3 983438 8 Last event a dJ 44 24014 17 31 Figure 30 LCD execution times when t2 incurs in delay To a further improvement the ADC may trigger an interrupt whenever a reading is made available instead of reading in polling mode Its resultant value evaluated 82 inside the interrupt which deactivates itself in case of the detection of an event As long as the ADC measures will not be needed again upon the end of the measure ments frame when this interrupt has to be enabled again It is recommended to keep the ADC running to avoid its own registers settling time each time it is started This interrupt has to relinquish the control to the MCU s process UART transmission is interrupt driven as well and should have a higher priority allowing the UART trans mission buffer to progress when required Furthermore one may use the available DMA channels to transfer the measured data directly into the UART transmission buffer releasing the processor cycles required to perform the operation and speed ing up the process This is not the case and these optimizations are not implemented being the processing time fast enough to the purpose of this research 5 20 Testing environment ADE7880 driver and UART driver accuracy A set of signals are produced and measured by the energy meter its data transmitted and displayed in the terminal console while an oscilloscope connected to the soundcard output gives the plot of the wave and
7. 0 06 L 0 08 60 Hz 0 1 ye 0 5 10 15 20 fci F1 Time msec x x zi 4 b Frequency Fine Adiust 0 493392 0 114537 0 066079 0 052863 Figure 22 MATLAB 9 GUI to control frequencies a b c and d amplitude The GUI seen in the previous figure facilitates the task of modifying the ampli tudes by providing 4 vertical sliders and a graphical representation of the output signal with its maximum voltage output displayed in the y axis The GUI allows to power on and off the signal generation and although initially was providing the capability to modify the fundamental frequency from 50Hz to 60Hz and fine tune them with a horizontal slider there is no use for them in this research To present the RTU s received data two methodologies can be used One is a ter minal console window displaying the incoming information to the UART RTU port the same MATLAB s computer using a UART to USB converter The second another MATLAB code used to plot in real time the received measures as a graph whereas the energy carried by each frequency can be visually compared The first option was selected as optimal having all the data as lines of strings in the screen 68 Figure 23 Terminal console showing the data of a sequence of measures 4 6 PCB design The schematics and PCB design is performed by means of Mentor Graphics soft ware PADS The PCB is intended to be a portable platform providing support to hold the energy meter its
8. a valid option having a reduced cost while introducing a slightly longer developing time A further recommended research may be conducted by introducing an analysis of the phases and neutral line phase shifting where the drift to capacitive or inductive shift offers richer information of the fault and the faulty line helping to determine the origin and cause of the event 91 REFERENCES Analog Devices 2014 ADE7880 Datasheet Rev C Polyphase Multifunction Energy Metering IC with harmonic monitoring Banks K 2002 The Goertzel Algorithm Retrieved from embedded com Blaza D amp Wilson R 2011 Embedded Market Study Retrieved from Electronics Embedded Ecosystem Embedded com Dobry B K 1993 Programming in C Hawaii wiliki eng hawaii edu Imrs P 2006 TRANSIENT BASED EARTH FAULT LOCATION IN Espoo Doctoral Dissertation M kel J 2013 Fourier series Jarmo M kel Lectures in Advanced Analysis M kinen S 2014 Toroidal Coil in Measuring Alternating Current at a Distance Retrieved from Scientific Research Publishing http www scirp org Mani H 2013 Analog Devices Products Retrieved from Application note AN 639 rev A www analog com Maxim Integrated 2003 01 31 MaximIntegrated Retrieved from Demystifying Delta Sigma ADCs http www maximintegrated com en app notes index mvp id 1870 Moulin E 2003 Measuring Harmonic energy with a solid state energy meter Re
9. where x k a complex number series of N samples such that xo x4 X2 Xy Xy and Xi Xreal t lXimag N number of samples k ranging from 0 to N 1 repeated periodically such that x k x k N To reduce the complexity of the equation above one may refer to Euler s identity for complex numbers analysis stating that for any real number x e cos x i sin x Equation 14 Using known fast Fourier transform FFT algorithms result in shorter time and less processing power Cooley and Turkey introduced this algorithm in 1965 lim iting the input to a power of two size and generating two N 2 sequences to speed 29 up the process the DFT of the even indexed part of x k and the odd indexed part The resultant lecture of this is such that x k gives the value of the Nth fre quency index Referring this to harmonic measurements less calculations are required since only the magnitude of a few frequencies of index N with value x k are required As x k is a complex number it has a real and an imaginary part Z x iy Ze sel x Re IZ e Z cose y Im IZ e Z sine Equation 15 where Z is a complex number x is the Re real part y the Im imaginary part i y 1 i 2 1 Z or Z modulus or the magnitude 0 the phase angle And as in most of the cases when the harmonics are measured not always the phase angle is needed only the magnitude having reduced calculations involved As w
10. 0 55322 0 74390 0 75348 0 00412 Figure 31 Currents when input of a b c and d frequencies amplitude is 0 5 The next Figure 32 Scope of the test signal four frequencies with an amplitude of 0 5 shows the plot of the signal and gives the values of the produced voltage RMS that simulated the current flowing through a Rogovski Coil or a current transformer The collage made at the left of the picture shows two columns The left one shows the data from the cursors Cursors X Y are placed over the fundamental at 50Hz and X2 Y2 over HZ at 350Hz shows AX of 300Hz as expected between both fre quencies AY reveals the attenuation of 4 375dB at the lower frequency with respect to the higher The right column shows measures instead of cursors belonging to the same scope where Freq 1 proves that the frequencies are correctly generated with a fundamental at 50Hz Regarding the amplitudes the FFT shows that the value of the highest frequency Max M is 17 4dBv 84 Agilent Agilent Acquisition Acquisition High R High Re 500kSa 500kSa Channels Channels Cursors Measurements AC RMS Cyo 1 000000Hz 251 9mV Max Figure 32 Scope of the test signal four frequencies with an amplitude of 0 5 As there is no calibration performed during this test the analysis is performed tak ing the total current as the reference for the value of the harmonics Conversion of total current to RMS 7 733A 5 468A V2 RMS Conversion of
11. da y Ee id 4H w ILE T EA ENTAS EN 2 8 E Q 7777 s i E Os 101 Optolsolators i ADE SPI Isolator 3 1 Power Mode amp IRQ signals Isolator ISO 7240M 3IN10UT MCU_ 3 3V ADE Output signals amp reset input Isolator 3 1 MCU_ 3 3V ADE 5V to 3 3V Isolated DC DC converter CONTROLLER SIDE CONTROLLER SIDE 102 Appendix 6 PCB layout and silkscreens real size 62 5mm x 7 45mm Figure 35 PCB Top layer Figure 34 PCB Bottom layer H ILILILILILILI BS AA LI B b10 L N 25 C26 E L ga o 2 ug F1 BN 1 Us Flo Ue Figure 36 Silkscreen top layer Figure 37 Silkscreen bottom layer 103 Appendix 7 Soundcard Datasheet 8 Analog Performance Characteristics Standard test condition Tyabiew 25 C Dvdd 5 0 or 3 3V 5 Avdd 5 0Vt5 Input Voltage Level Logic Low 0 35 Vdd Logic High 0 65Vdd 1KHz input sine wave Sampling frequency 48KHz 0dB 1 Vrms 10K2 50pF load Test bench characterization BW 20Hz 20KHz OdB attenuation tone and 3D disabled Front DAC F version Surround DAC Center LFE DAC S N A weighted DAC Front DAC with headphone amp DAC Surround Center LFE DAC Mic 20dB gain is selected Crosstalk between inputs channels Oo o 70 MIC1 MIC2 PCBEEP PHONE Others LINE CD AUX VIDEO VA SV VD 3 3V 88 36 VA 3 3V VD 3 3V 71 36 Power Supply Current power down mo
12. to the embedded Segger JLink debugger in the YRDKRX63N board allows access not only to the software content but to the CPU and peripheral hardware registers content It is completely integrated in eclipse and works altogether with GDB giving a detailed information Hardware debugging requires of a connected device When there was no possibility to have a connection with the hardware Renesas estudio provides a RX simulation environment that emulates the RX63 hardware and uses GDB useful thou limited compared with a hardware debugging session The Re lease build is used only for demonstrating purposes To write the RX63N highly hardware dependent code and drivers the RX63N Group hardware user s manual Renesas Electronics 2014 is needed providing the information to all of the available MCU registers and their properties The start up environment both by Renesas or Kpit provide with the lowest level hardware ac cess a set of functions and header files with IO definitions to program and start running the CPU in a way that the entry point to the programming becomes already the user code 52 The following code manages all the required MCU hardware ADE7880 communi cations and RTU communications The required peripheral drivers are initialized and started immediately if needed All the drivers but three have very low level access and their flow diagram is very direct retrieving the content of a specific register in a single function Th
13. 3600 0 Normal signals Palsionals e DSP T Ba 1 Sine Wave To Audio 53 Device wa i Source Block Parameters Sine Wave Sink Block Parameters To Audio Device xa Sine Wave mask link To Audio Device Output samples of a sinusoid To generate more than one sinusoid Send sound data to your computer s audio device simultaneously enter a vector of values for the Amplitude Frequency and Phase offset parameters Parameters Main Data Types Device Speakers High Definition Audio Device x Amplitude 7 Inherit sample rate from input abcd Device data type Determine from input data type z Frequency Hz 50 150 250 350 7 Automatically determine buffer size Queue duration seconds 1 0 Phase offset rad o 7 Use default mapping between Data and Device Output Channels Sample mode Discrete 19 Cancel Help Apply Output complexity Real xj Computation method Trigonometric fcn z Sample time 1 192000 Samples per frame 1 Resetting states when re enabled Restart at time zero x 9 Sl Ready 100 ode45 Figure 21 SIMULINK implementation El gen c s Untitled 1 ODD Harmonic Sine Wave Generator 0 1 E ae Amplitude 4 F xa 5h 7th us ou H H H 0 04 N A A A D R R R 0 02 Frequency A M M M 5 M Oo o o 3 0 ix E N N N 0 02 N I H c 0 04 EI c
14. From the power line to the RTU different components are involved but all has to begin from a connection of the power line to the energy meter front end The meth ods are differentiated as direct physically connected to the line or indirect no physical connection and regarding the technology as resistive direct transistor direct and Magnetic indirect 2 2 1 Indirect current measurement methods Indirect current measurement means that there is no physical connection with the measured voltage line the sensor is isolated from the line and it is an accurate method when the current is too high to be measured with a directly connected in strument There are three main technologies where the measurement device pro vides isolation from the line current transformers CT Rogowski Coil and Hall 16 Effect devices All of them provide a voltage level signal at the output that is pro portional to the current flowing through the line under scope CTs are useful when measuring AC transients or switching mode DC since it CN S ANN CESS NS A Figure 3 CT senses the changing magnetic field produced by the AC oscillation The CTs use the power line as the primary of a transformer with 1 to a few turns that its flowing current I in Figure 1 induces an alternating magnetic field in the core B in Figure 1 producing an alternating current in the secondary As the induced current is the result of the relations
15. Len int32 t result uint32 t pid error List et ADE SPI write uinti16 t target register uint32 t value uint8 t reg Len uint32 t pid These functions call in their code lines to the known middleware layer methods to access to the SPI hardware driver without knowing about them To achieve this two function pointers are declared locally with the names of ADE SPI WRITE CALLBACK and ADE SPI READ CALLBACK into the driver s file ade7880 spi protocol c int8 t ADE SPI WRITE CALLBACK uint8 t data uint8 t usBytes uint32 t pid int8 t ADE SPI READ CALLBACK uint8_t data uint8 t usBytes uint32 t pid Two other public functions receive the address of the targeted outsider function as parameter and assign it void ADE SPI WRITE callback set int8 t func uint8 t data uint8 t usBytes uint32 t pid void ADE_SPI_READ_callback_set ADE_SPI_WRITE_CALLBACK func 61 int8 t func uint8 t data uint8 t usBytes uint32_t pid ADE SPI READ CALLBACK func The compiler does not complain because they are locally known but their memory addresses content are initially undetermined remaining disconnected before they are initialized by calling ADE SPI READ callback set with the address of the function amp R ADE SPI Read as its only required parameter and calling ADE SPI WRITE callback set with amp R ADE SPI Write as its parameter Then at some point in the code whenever the driver is ini
16. Max M in dBv to a scalar magnitude 20logi9 G 17 4dBv 17 4 G 10 20 0 135 Current RMS of the 7 harmonic component at 350Hz 5 468x0 135 0 738A m Current at 350Hz as the 7 harmonic shown by the energy meter is 0 753Ams and analysis of the signal produced by the testing environment without calibration shows 0 738Ams The error found is the 2 while the datasheet confirms that the maximum error is of 196 in a dynamic range of 1 1000 Although MATLAB is 85 producing the expected result the linked soundcard hardware was not the ideal en vironment having the software executed in a remote machine with a different hard ware adding a delay to the response time Moreover it is difficult to determine if errors are introduced by one or another as in the case of the frequencies the span more than 50Hz having a high Q factor meaning that the frequency range of 50Hz of the centre frequency has elevated energy when what it is needed is higher energy concentration in the frequencies of interest this may be due to a probable output bandwidth limitation in the lower frequencies of the audio range of 20Hz to 20KHz However the use of a software solution to implement the testing environment pro vides portability and a quick adaptability to new test conditions 79 608 5 0008 156 Agilent Acquisition Normal 1 0 Channels Measurements MS Save to file scope Save Recall Default Erase Press to d We id Save
17. affecting the signal filtering and therefore the measurements MATLAB and SIMULINK software offered in Technobotnia facilities under VAMK s license are installed in a remote application server a different machine with a different hardware and probably not recognising properly the sound hard ware of the local machine where it is actually running The testing environment is built from the basis of MATLAB with SIMULINK and a soundcard Realtek 6 channels ALC662 It does produce the four waves alt hough not including advanced capabilities As said limitations in the soundcard s output probably caused by having the software running in a remote machine did not allow to output different signal through different output channels Other issue is the noise appearing at the output of the soundcard signals which is almost irrel evant since most of this noise has a very high bandwidth that is cut by the filters and although they add energy to the total current the FFT result at the given fre quencies is not altered To produce the signals SIMULINK is used implementing only two source block objects a sine wave DSP and a To Audio Device The former requires little config uration see picture Figure 21 SIMULINK implementation where in the Ampli tude section the amplitudes may be input as an array of four variables a b c d the Frequency section receives an array of the same length with the values of the fre quencies of interest 5
18. can be activated 15 16 T7 If Rogowski coils are used enable the digital integrators in the phase and neutral currents Bit O INTEN set to 1 in the CONFIG register Initialize the DICOEFF register to OxFF8000 before setting the INTEN bit in the CONFIG register Start the DSP by setting Run register to 1 Read the registers in which the harmonic information is stored using the burst or regular reading mode at high to low transitions of CFZ HREADY pin 98 18 CF2 HREADY pin can be programmed as an interrupt read Datasheet Con figuring Harmonic Calculations Update rate p 63 64 and its value is stored and can be read in STATUSO register OXE502 32bits 19 For neutral line monitoring read to HXIRMS OxE889 32bits HYIRMS OxE891 32bits and HZIRMS OxE899 32bits before proceeding with a reading one must follow the procedure to initialize and turn on the ADE7880 DSP 99 Appendix 4 SPI driver access from ADE7880 driver main file import ade7880 driver h A drivers initialization R_ADE_ADE7880_driverCallbacks J Portability through middware layer Legend BLUE Initialize ADE7880 SPI callback functions GREEN pass the address of the ADE7880 middware SPI function to link with the SPI driver ORANGE A pointer function locally declared receives the address of the ADE7880 middware RED The ADE7880 driver uses a detached Jocal function that once initialized references the extemal S
19. comparison of interfacing the power lines with a MCU interfacing an energy meter dedicated DSP versus directly with MCU The comparison shows that this solution is valid for the purpose and at a lower cost If there exists a need to evaluate other frequencies than harmonics the former is not a valid option being this last the choice Although the drawbacks have to be accounted and the use of a DSP library has a learning curve Moreover there is a No research was procured 88 greater need of knowing the theory or mathematical background behind it further more there is additional work to select the proper MCU and ADCs to keep the required accuracy and precision and other signal filtering study is required to properly interface these elements 89 6 CONCLUSION This paper has shown a method to solve the problem presented by VASPEC Oy by interfacing a power line with an ADE7880 energy meter as a front end and a Renesas RX63N microcontroller to retrieve and store in a short term the phase and neutral currents of the power lines fundamental 50Hz and their 3 5 and 7 harmonic component values The selected microcontroller facilitates the communi cations with the ADE7880 by using a SPI channel at 2Mbps and to a remote termi nal unit by means of UART channel at 115200Kbps It is proved that the selected approach can effectively and precisely measure the fundamental and harmonics frequencies altogether with each phase RMS current and
20. fetch the data immediately the SPI communications might be a bot tleneck in tight timing requirements for which my recommendation is to select a MCU with an ADC that meets the accuracy precision and speed among its pe ripherals and fetch the readings using a DMA channel As the given timing specifi cations are relatively relaxed for the RX63N there was no need to implement DMA in the design fulfilling any task under any circumstance into the expected timing 51 However an independent 16bit ADC is given by the specifications as a valid reso lution although a 12bit ADC available on the YRDKR63N board is accepted and will be used for testing 4 4 The software environment The software solution is implemented in C language built in eclipse environment e studio using only generic C99 specification instructions and libraries The propri etary RXC toolchain the set of compiler assembler and linker in use are provided by Renesas as an evaluation version with a limitation of 128KB of linkable object for non commercial software although a GNU solution is available under the name of GNURX by KPIT The software project uses Apache Subversion SVN repository as a version control system stored in VAMK dependencies It includes three differ ent build options Debug using a RX GDB simulator Hardware debugging using Segger JLink hardware debugger and Release Hardware debugging is the most extensively used mode that thanks to a connection
21. for line frequencies between 45 Hz and 66 Hz Neutral currents can also be analysed simultaneously with the sum of the phase currents Figure 82 at p 58 of the Data Sheet presents a synthesized diagram of the harmonic engine its settings and its output registers Working in its normal power mode it draws a 36 maximum current of 5 8mA at 3 3V Other reduced power modes can be selected but not used since the wake up delay affects significantly to the measurements 3 3 Selecting an MCU The YRKRX63N board equipped with a Renesas RX63N R5F5631BDDFP MCU 100MHz 32 bit MCU with on chip FPU 165 DMIPS 1 65 DMIPS MHz with a price rounding 13 Digi key electronics Finland May 2015 was selected for pro totyping Joins all the required capabilities in one MCU due to the availability at the moment of selection and the VASPEC s predilection for Renesas MCU for their long product longevity This IC provides enough communication controllers while UART and SPI are used and Ethernet planned for a possible future implementation Includes PMOD connectors to support a variety of generic PMOD devices and will be the port in use to interface the AFE A later independent PCB design was not necessary The board is also equipped with a Segger J Link hardware debugger that offers valuable information for example to optimize the hardware software inter face or to trace the SPI communication by visualizing the registers content A DSP library is provide
22. individually for each function ADC and DSP are implemented as individual entities giving liberty to select the components given a required accuracy Although a high quality and flexible device can be developed this kind of implementation is expensive and more complicated A third option is a solid state Energy Meter interfaced with an MCU Since the apparition of electronic energy meters they evolved from a single phase voltage meter to a polyphase multifunction energy metering with DSP and harmonic mon itoring These meters can be reduced to two types analog front end AFE ICs and System on Chip SOC meters The first kind provide the front end to the power line allowing an external MCU to control them The second includes a microcon troller Each have benefits as cost is in the case of a SOC and flexibility in AFE ICs and cons like upgradeability the SOC cannot be modified easily Mani 2013 And when referring to different manufacturers they share similar architectures A set of inputs to interface with voltage and current sensors ADC to convert the signal value a DSP to process the information and a MCU to manage the process and peripherals Discarding the SOC a single energy meter can be interfaced by a low cost MCU to handle the communications task 2 3 Microcontroller Unit MCU The MCU should be chosen after the AFE selection if not embedded into it Since it is not the same CPU load to receive the processed values from
23. make the information available for processing in a RTU in 574 us and repeat the measures every half a fundamental cycle until a selected timeframe is consumed or a counter measure action taken However the measuring process can be dynam ically adapted for example until the tamper situation is finished or handled The frequencies are generated by the testing environment provided with MATLAB and SIMULINK and the RTU receives and displays the measurements triggered by the testing frequencies total current surpassing the selected threshold voltage Although the use of Microsoft remote application server and MATLAB in a re mote session where both have a different hardware configuration is not recommend able the related amplitudes require to be reconfigured and calibrated for each dif ferent hardware Other implantations were studied and theoretically proved as effective as the one shown here where the front end in use is provided by the same microcontroller yet the solid and precise ADE7880 energy meter avoids further mathematical calcula tions simplifying the code and saving valuable processing time However the lim itations of the ADE7880 regarding the neutral line harmonics engine and the use FFT to perform the harmonics analysis represent a drawback whenever i e other frequencies than multiples of the fundamental are involved in which case if the processing time is not an impediment and MCU with adequate integrated ADCS is 90
24. mapped in the file ade7880 registers h that follows the hardware datasheet registers list section preserving the naming convention Registers bit length varies 8 16 24 and 32 bits signed or unsigned Wherever possible bit access level is provided to favour the 55 access to configuration registers This is achieved by generating unions as new var iable definitions as follows CONFIG Register address and structure define CONFIG xE618 ADE788 configuration register See Table 47 DS Rey A Page 97 of 104 define CONFIG_DEFAULT exeoo2 Constant macro for its default value gt typedef union 1 uinti6 t REG ALL e struct 1 bit Def Val uintl6 t INTEN Sis e uintl16 t RESERVED 1 1 1 uint16 t CF2DIS 1 2 e uint16 t SWAP ss 3 e uint16 t MOD1SHORT 1 4 e uintl6 t MOD2SHORT 1 5 e uint16 t HSDCEN e A 6 e uinti16 t SWRST 15 7 e uint16 t VTOIA 25 9 8 e uintl16 t VTOIB 25 11 10 e uint16 t VTOIC 25 13 12 uint16 t RESERVED2 25 15 14 0 pbits JCONFIG reg u End of CONFIG Figure 18 ADE7880 Hardware registers access example Defining the address of the register with a name offers readability to the code and simplifies the hardware access A default value can be defined simplifying the task of writing to the defined address The bit access is provided by a new variable def inition CONFIG reg u resultant of the union of the two members one for whole acc
25. register initially as 0 Additionally selecting the desired harmonics at each index is done here One should pay attention that the EM Absolute Maximum Number of Harmonic indexes is 63 actually 2800 Fundamental line frequency This is due to its properties in 97 which its Measurement Bandwidth 3 dB is 3 3KHz Read the EM data sheet for more information 10 11 12 13 14 Select phase or neutral line to monitor Options NEUTRAL_LINE PHASE_A PHASE_B or PHASE_C Number of samples per reading From one single reading to as many as de sired and the average of the total readings is calculated in the following way sum up all the readings number of readings Set CF2DIS bit in CONFIG to 1 to use CF2 HREADY pin to wait for a new calculation to be completed and its register has settle for HRCFG amp HSTIME Set HRCFG bit in HCONFIG O Default 2 waits HSTIME to settle and triggers HREADY 1 Triggers HREADY immediately Set HSTIME bits in HCONFIG Default 01 2 750ms of settle time 500ms 00 1 sec 10 1250 ms 11 Set HRATE bits in HCONFIG Default 000 the update rate of the har monic registers 000 8kHz Set ACTPHSEL bits in HCONFIG Default 00 phase A to select the phase voltage used as time base for harmonic calculations The selected phase has to be connected to its input pins Regarding to the Integrator in case of using a di dt current sensor the EM has its own integrator which
26. required hardware reads an ADC and compares its value with a maximum threshold value Two methods are implemented to get the ADC readings by means of the external ADC peripheral or by means of the ADE7880 this can be selected by modifying a definition in the header file named definitions h Whenever the threshold value is crossed a time stamp is retrieved from the RTC the CMT is turned on counting up to 10ms the time of half of a cycle of the fundamental frequency triggering an interrupt at the end where all the required values are read from the ADE7880 This is repeated during a predeter mined amount of time set to 100ms During this time the retrieved information is available to be evaluated with the possibility to trigger a reaction If no reaction is taken the CMT will consume all the specified time frame The information is placed in the transmissions buffer and transferred to an RTU as soon as it is made available The RTU in this case is a computer receiving UART data that can be formatted to be displayed on a terminal screen by sending strings of ASCII charac ters or retrieved stored and plot in Matlab by sending floating point values Other peripherals are used The LCD uses SPI peripheral channel 0 and SSL3 and it displays the RTC time information about the last event and the threshold value Regarding the switches are programmed to set a new threshold value and to simu late a spike triggering all the measurement events A
27. section is divided by a comment block defining itself system and project includes block macro definitions block local function declarations global variables and a new block per each func tion in the file Not always all the blocks are needed The function header block 38 comment includes the name a description list of arguments and return A header file h includes blocks for macro definitions variable type definition and public function declarations The ADE7880 driver is documented by means Doxygen to facilitate its maintaina bility and understanding Doxygen facilitates the code documenting by means of selected tags around the inline comments Although a powerful tool to ease the task the code should be clearly architected from the beginning and changes carefully implemented by accounting the comments as well otherwise Doxygen code might become a second maintenance task The portability of the ADE7880 driver becomes a high concern because the final MCU target might differ from the initial prototype Regarding to the AFE this is completely achieved by implementing a driver without specific CPU compiler in structions and isolating the hardware both AFE and SPI communications by im plementing their respective HAL This is not performed for the other peripheral drivers since they are highly bound to the MCU and their specific registers with single access and single register access to retrieve data for example an ADC re
28. the implementation of the ISFO503A a single output dc to dc voltage regulator with isolation up to 1000Vdc that requires an input voltage from 4 5 to 5 5Vdc and outputs a 3 3V up to 0 3A enough for the ADE7880 and having a cost rounding 6 Farnell Finland May 2015 This will allow to externally supply the power from any popular 5V 0 5A converter Moreover all the external connections to the ADE7880 have to be iso lated being those the SPI communication paths and other signals with a high band width The addition of Silicon Dioxide Isolators with a high signal rate of 25MHz provides the required high voltage block and GND isolation barrier preventing noisy currents to enter the other side of the circuitry 3 2 Features of interest The ADE7880 is compatible with 3 phase for 4 wire Delta or Wye This is espe cially relevant for the experimentation since the neutral line is the carrier of most of the information but the three phases are sensed simultaneously as well Having 35 an independent computational block for harmonic information on neutral current and phase data path the output registers content can be fetched simultaneously Supplies RMS active reactive and apparent powers power factor THD and har monic distortion of all harmonics within 2 8 kHz pass band up to the 63 harmonic on phase or neutral current and voltage which is beyond the 7 harmonic as the highest index of interest Although the harmonic ca
29. top folder one may find subfolders named by the peripheral s name ade7880 indicating that this is an external peripheral with its HAL and driver Files starting by the peripheral name ade7880_ are specific HAL and hardware related code build to be independent to the uC and portable C code such in a way that only a set of files in the parent folder are required as middleware to allow other systems specific code interact with the driver Files starting by r_ followed by 53 the peripheral s name as r ade7880 belong to the middleware that provides ac cess to and from the Renesas MCU with the ADE7880 IC see Appendix 1 4 4 2 The data storage A container for the information A place to store it is provided as an object This is a structure that provides memory location for all valuable data This container offers a place for the data that may be collected from the energy meter and the time stamp of the measurement keeping an easy and known form to retrieve what it is needed An example of it can be seen in the Appendix 2 The structure is defined only once and local variable declarations to store the same information are not needed The container is allocated when the application is cre ated and is passed as a reference to other functions One memory location provides light code avoiding the allocation of extra memory to store the same data each function call reducing significantly the memory requirements of the applicatio
30. with approxi mately 6dB to the Dynamic range An ideal meter with a dynamic range of 2000 1 with a precision of 0 1 of the units in use and a specified maximum error of 0 1 requires a minimum dynamic range of 146dB or an analog ADC with at least 25 bits of resolution 2000 146dB Equation 6 146dB DM T5 amp its dB 6 7 bit The noise floor of the system becomes relevant to satisfy the specifications To have good accuracy the noise floor of the selected system should lay over the bit resolution or the system won t satisfy the accuracy conditions This is especially relevant when evaluating signals arriving from a CT or Rogowski Coil since their inducted voltage levels can be as low as microamperes falling into the noise floor 21 level For example a system like an energy meter DSP whose maximum ADC in put voltage is 0 5V and the noise floor is lu Vy then the dynamic range is 500075 52 1 or 114dB requiring at least 19 bit ADC 0 5 20 log 114dB 114dB i8nH its dB 607 f vit A different ADC technique is the sigma delta ADCs 1 bit ADC where the final result comes from the successive bit approximation of the sampled value These ADCs have the attribute of oversampling sampling multiple times faster than a traditional ADC This favours the sample quality because while the SNR is the same as before its energy is spread over a larger frequency range As a result of this the RMS nois
31. 0 150 250 350 The use of variables at this point will help the task of varying them dynamically by assigning them directly in MATLAB s input console or by the help of a GUI built for the same purpose In the sample time box the maximum allowed by the soundcard is set The other block requires less configuration where device can only be set to the one found by the OS the OS s primary and Speakers selection being them all located in the remote computer and not allowing to select the local machine s soundcard The length of the queue and 66 the length the waves are played in time can be set and pressing play in the toolbar will start generating the waves The amplitudes as they are meant to play in the soundcard are hardware dependent therefore one signal of a determined amplitude will have a different level using a different soundcard requiring to be corrected to obtain the same output The result ant wave is a voltage signal therefore its output should never be higher than the AFE limitations in the range of 0 5V Although the ADE7880 can stand up to 1V as a maximum transient limit nevertheless its ADC 24bit registers cannot go further than 5 326 737 from 0x AEB86F to 0x514791 nominal values at the full scaled input signal of 0 5V Hence the amplitude should be monitored to avoid AFE damages Py signals Eee ts File Edit View Display Diagram Simulation Analysis Code Tools Help w M
32. 2 1 Three Phase four Wire system decet tette beret ie run ena en sa O S Po esae UU 14 2 2 Interfacing POWER LIMES acetic a toe ut Du cua Que EUR PO PEU NU AREE ur ege 15 2 2 1 Indirect current measurement methods sess 15 2 2 2 Direct voltage measurement method esses 18 2 2 3 Evaluating voltage level signals ees 19 2 2 4 Analog Front End AFE sci ad opt ect ec deena 22 2 3 Microcontroller Unit MCU sess 25 2 4 Evaluating harmornics see reme ot loveaacaovecacounadeedescadaasedesds 24 2 4 1 Fourier series backeround ee ee ettet e te poca 25 2 5 Evaluating transients i iret Seaeescaavseaceisedcadeaspsonasesuvenccassneadeancaesdeadoede 29 3 SELECTED RESOURCES 55 ocior ror PE MS ta EIS HIN pEi 31 3 1 Hardware and Software resources iren tct et dietis te arteriis duae 31 2 2 Selecanedtlie AFE Soa oe ath e aL d S 33 32t Feat res of iMerest 121 254 cea o E edes 34 3 3 SCIONS am MCU as ett atha estadio e tates opp ame E N 36 33 SON Ware envirODTDe llb oe eei Geli ciet eedem uio oue tendis 37 313 Whe Codes sued angi eiie 37 3 6 Communications protocols sessssssesssesesseeessressessseesssetesseesseesseesseeeeseee 39 3 7 Testing environment isere t Roe a TER aE R 39 4 METHODOLOGY AND IMPLEMENTATION eene 40 4 1 Explaining portability Renesas MCU or ARM eene 43 4 2 Prototyping the AFE ADE7880 input channels
33. 28 04 15 14 13 e1100620 a callback c es a 13 e1100620 pated Ak DEPRI 94 r ade7880 1 r ade7880 config h 2 src 3 ade driver h 4 ade7880 5 ade7880 registers 6 ade7880 configuration 7 ade spi protocol 8 ade src cmd handler 9 r ade7880 drv 10 r ade gpio 11 1 Folder containing middleware driver and HAL Qo eS SOV 10 11 Renesas SPI to ADE Hook configuration file This file provides different definitions to serve as ADE7880 general standard configuration values for its two main different working modes as an energy meter or as a harmonics meter To understand what these values refer to one should cross check them with the datasheet Any change here will directly affect to any ADE7880 measurement for that reason is highly recommended to read the document before manipulating the values The values here are standard to measure currents with a C T and one may use them as they are but to a proper accuracy and performance the device should be calibrated as men tioned in the datasheet Driver s source folder Provides access to the driver from outside To implement this driver in an application granting the access to the public functions one should include the file ade7880_driver h into the application requiring of it Driver and HAL folder HAL definitions Specific ADE7880 IC configuration definitions Builds the transmission and Reception buffers and communicates via
34. 6 Appendix 3 Recommended approach for managing Harmonic Calculations with ADE7880 The recommended approach to manage the ADE7880 harmonic calculations is the following 1 Follow boot up procedure and SPI selected as communications protocol 2 Set up Bit 2 CF2DIS in the CONFIG register Set CF2DIS bit to 1 to use the CF2 HREADY pin to signal when the harmonic calculations have set tled and are updated The high to low transition of HREADY signal indi cates when to read the harmonic registers Use the burst reading mode to read the harmonic registers as it is the most efficient way to read them This is done in the following way 1 Set bit 2 of CONFIG register ad dress OxE618 as 1 so CONFIG 0x0006 CONFIG register is 16bits Write the register at least twice in case you write the register individually if sequentially write twice only the last Read the last written register to check that it was a successful write 3 Choose the harmonics to be monitored by setting HX HY and HZ a Write HX OXEAOS 8bits with the desired harmonic index i e 1 for Fundamental b Write HY OXEAOO 8bits as i e 5 to measure the 5th harmonic c Write HZ OxEAOA 8bits as 7 7th harmonic 4 Select all the HCONFIG register bits 5 Write HCONFIG OxE900 16bit i e with update rate of 1ms HCONFIG 0x0047 6 Initialize the gain registers used in the calculations Leave the offset regis ters to 0 7 Write GAIN OxE60F 16bits
35. 9 VAASAN AMMATTIKORKEAKOULU 9 0 x Se VASA YRKESHOGSKOLA d UNIVERSITY OF APPLIED SCIENCES Luis Alvarez Iglesias HARMONICS OVER POWER LINES MEASUREMENT Algorithm in C and testing environment Information Technology Embedded systems 2015 ACKNOWLEDGEMENTS I would like to take this opportunity to show gratitude to my thesis supervisor Jukka Matila Senior Lecturer in Vaasan Ammattikorkeakoulu University of Applied Sci ences for his continuous encouragement to learn and support in any stage of this and any other project Also I would like to present my most sincere gratitude to all VAMK s teachers for the valuable guidance in our learnings Thank you for these years certainly the most valuable and enrichment experience so far VAASAN AMMATTIKORKEAKOULU UNIVERSITY OF APPLIED SCIENCES Information Technology ABSTRACT Author Luis Alvarez Iglesias Title Measure Harmonics over power lines algorithm in C and testing environment Year 2015 Language English Pages 105 Name of Supervisor Jukka Matila This paper is intended to give an overview of measuring harmonic phenomena over the neutral line in 3 phase 4 wire substation network when an earth fault is origi nated It requires electrical and microcontroller interfacing background but little knowledge of harmonics The company VASPEC Oy sponsors the research and belongs to a project owned by the same company to develop a reliable earth fault detection and l
36. ERS SELECT THE HARMONICS TO MONITOR HRATE BITS HCONFIG 7 5 SELECT THE UPDATE RATE OF HARMONIC REGISTERS HSTIME BITS HCONFIG 4 3 SELECT THE DELAY IN TRIGGERING HREADY INTERRUPT HRCFG BIT CE SELECTS IF HREADY FLAG IN ST S0 IS SET IMMEDIATELY OF AFTER HSTIME ISUM IN ISUM IN RESULTS RESULTS RESULTS RESULTS Figure 11 Harmonic engine block diagram fromADE7880 datasheet When using the ADE7880 the sample rate is fixed at 1024 kSPS meaning that any frequency higher than 512 kHz will generate aliases and the antialiasing input filter has to take it into account hence the input passive low pass filters are calculated at this stage These filters have to meet two requirements by one hand cut the non wanted high frequencies and by the other avoid as much as possible the phase shift With the help of LTSpice these filters can be simulated to find the best approach For testing purposes an analog LPF with a cutoff frequency is calculated at 15 kHz having attenuation of 31dB at 512 kHz and a phase shift of 1 5 The ADE7880 recommends a cutoff of 5kHz Analog Devices 2014 one may observe that such a filter can be built with an RC where R 15Q and C 2 2uF Its 0 attenuation band width does not go further than 300Hz and producing a phase shift of 4 at the fre quency of the 7 harmonic and up to 40 in the bandwidth of interest while having a 40dB attenuation at 512kHz Two different approaches may follow a first one the sele
37. ESET REFwwour VDD AGND AVDD DVDD DGND ADE7880 CLKIN Po CLKOUT 23 Pm REF HPFEN OF DIGITAL CONFIG3 INTEGRATOR AIGAIN mang is l Laa 0 GJ cF1 AWATTOS ve Ld te e eer el T AFWATTOS 64 CFZ HREAD IBP COMPUTATIONAL CF3DEN BLOCK FOR REACTIVE POWER 5 65 CF3 HSCLK COMPUTATIONAL IRo BLOCK FOR ORV INFORMATION ON Ra PHASE A CURRENT Rai ICN EE AND VOLTAGE iC SEE PHASE A FOR DETAILED DATA PATH MOSI SDA COMPUTATIONAL BLOCK FOR HARMONIC INFORMATION ON NEUTRAL CURRENT HPFEN OF DIGITAL CONFIG3 INTEGRATOR NIRMSOS e Li ULT TE niema siena PROCESSOR o Neutral current processing path Figure 10 Functional block diagram from ADE7880 datasheet In the functional block one may observe that the neutral current measurements en gine follows an independent path Phase energy values share a common computa tional engine in which the neutra
38. NDICES Appendix 1 Appendix 2 Appendix 3 Appendix 4 Appendix 5 Appendix 6 Appendix 7 Code structure and naming convention Data container Recommended approach for Harmonic Calculations SPI driver access from ADE7880 driver PCB Schematics ADE7880 and connector socket Optolsolators PCB layout and silkscreens Soundcard Datasheet 97 98 96 99 100 100 101 102 103 10 LIST OF ABBREVIATIONS ACRONYMS SYMBOLS ADC AFE CAN CLCK CMOS CMT CS CT dB DFT DMA DMIPS DSP ESD FFT GND HAL IAN IAP Analog to Digital Converter Analog Front End Controller Area Network Clock refers to signal or pin Complementary metal oxide semiconductor Compare Match Timer Channel select Current Transformer decibels Discrete Fourier Transform Direct Memory Access Dhrystone Millions of Instructions per Second Digital Signal Processor Electrostatic discharge Fast Fourier Transform Ground Hardware Abstraction Layer Current Phase A where A can be A B C or Neutral Negative Current Phase A Positive IDE MCU or pC MISO MOSI MSB MSPS NMOS PCB RMS RTC RTU SMD SNR SPI UART 11 Integrated Development Environment Microcontroller unit Master In Slave Out Master Out Slave In Most Significant Bit Mega Samples per Second Negative channel Metal Oxide Semiconductor Printed Circuit Boa
39. On the other hand this choice requires a deeper level of understanding of harmon ics FFT and a DSP library for the selected MCU if available and deserves to men tion a word about the MCU ADC s quality whenever a low floor noise and higher precision is required the selectable number of MCU decreases and the price raises 34 The ADE7880 energy meter was proposed and accepted before starting the devel opment of the project by all the parts and its analysis in this paper is articled post factum It has proven satisfactorily the energy and harmonic meter capabilities ful filling all the demands response time precision and accuracy Comprehensive un derstanding of the harmonics is required but no mathematical implementation is required as this AFE outputs the processed value The ADE7880 retail price of one unit in the market is 11 84 Farnell Oy May 2015 The cost may represent the most important drawback of this IC and a further research to compare with the performance of the select MCU DSP instructions re garding to the required selected input currents in the given timeframe with the mul tiple outputs of the energy meter at a 125kSPS The ADE7880 requires isolated environment since the neutral voltage input GND is internally connected to the IC GND This means that the ADE7880 GND level is the same as the measured neutral power line level and a serious risk since they represent a fatal health hazard The result of this is
40. PI driver ADE7880 folder RX63N ADE7880 Midware R_ADE_ADE788 _driverCallbacks ADE SPI WRITE collback set amp R ADE SPI Write DE SPI READ callback set BR ADE SPI Read middware SP function to link with the SPI driver int8 t RADE SPI Read uint8 t dota vint t usBytes uint32 t pid Attempt to lock the SPI peripheral Woit until lock is given up or x cycles if Clocked The lock has been obtained assert the CS Read Write Date R SPI Read dotc usBytes pid SPI Driver Call Deselect the CS Release the lock R SPI Unlock pid return possible error End of function AD SPI reod ADE7880 portable driver including HAL function prototyping int8_t C ADE_SPI_READ_CALLBACK uint8_t date uint8 t usBytes uint32 t pid Local Declaration only read repeat procedure for writing void ADE SPI READ callback set int8 t func uint8 t date uint amp t usBytes uint32_t pid ADE_SPT_READ_CALLBACK func ADE788 SPI call error et ADE_SPI_read uinti6_t target_register int32 t value vint8 t reg len vint32 t pid Call the SPI routine by means of the ADE788 driver middware ADE SPI READ CALLBACK Cuint8 t amp tx buffer msg cll tx length pid 100 ics Schemat Appendix 5 ADE7880 and connector socket RENESAS PMOD Connector MCU_ 3 3V Raspbeny Pi B Connector 40 Pin Header BH 666 25 E pee B E EEE EN 4 UT TOL 86 232 Pu n
41. S is 3 766 572 0x39792C when the integrator is not in use and the gains are set to 0 Using the proportionality equation throws a result of 171uV at the AFE input which now have to be converted to the real RMS current by knowing the properties of the CT in use to interface the power line 30A input 1V output giving a result of 5 13mA flowing in the power line at the moment of the measurement In Figure 27 Single SPI reading scope by DSOX2012A one may see that the time for the SPI transmission required was approximately 39us almost 8 divisions at 5us div While the SPI clock is 2MHz and theoretically 7 bytes at this speed should be transferred in 28s what we see is the delay caused for the reload of the SPI registers whenever a byte is shifted in This process time if critical may be reduced by using the whole SPI register space where RX63N offers 4 long word registers of 32 bits instead of shifting byte by byte which is the simplest implementation but not the best in terms of performance One complete single cycle set of SPI requests measuring the currents and harmon ics seven values once can be seen in the next scope where the total time for this cycle can be calculated as approximately 290us almost 6 divisions at 5Ous div 76 Although compressed in the picture the clock signal Di follows the same byte pat tern showing the MOSI and MISO bytes of each measure The signal in CS Do shows the transitions from high to low wh
42. SPI by means of the function pointers received from the middleware layer Provides public functions to interact with the IC Middleware driver layer to allow ADE7880 access to the SPI driver by means of callback functions passed as pointers to the driver Middleware driver layer to allow ADE7880 driver access the GPIO pins Appendix 2 Data container ENERGY MEASUREMENT ATTRIBUTES Individual data typedef struct t float value Measured Data uint64 t timestamp Time stamp jem tval st Phase related data storage typedef struct t em tval st IRMS Current RMS em tval st VRMS Voltage RMS em_tval_st WH Watts hour em tval st POWER instantaneous power in Watts em phase t Neutral line related data storage typedef struct 1 em tval st IN IRMS Neutral current RMS value em tval st INSTANT IN Instantaneous Neutral current Neutral current Harmonics RMS values em tval st IN HXIRMS em tval st IN HYIRMS em tval st IN HZIRMS Neutral current Harmonic distortion em tval st IN HXIHD em tval st IN HYIHD em tval st IN HZIHD ISUM RMS values em tval st ISUM HXVRMS em tval st ISUM HYVRMS em tval st ISUM HZVRMS ISUM Harmonics distortion em tval st ISUM HXVHD em tval st ISUM HYVHD em tval st ISUM HZVHD em neutral t Global container typedef struct em_phase_t phase_a em_phase_t phase_b em_phase_t phase_c em_neutral_t neutral_line em data t 9
43. al conductors carrying symmetric alternate current where the phases are shifted one third of the period or 120 and an additional neutral line as a reference line where the sum of the three voltage vectors in an ideal case of a balanced sys tem is zero Phase 1 Phase 2 Phase3 Vz Figure 1 Three phase normalized waveforms and voltage vectors This system have properties that favours its implementation One of them is that any imbalanced load in any phase will reflect the unbalanced current over the neu tral line As a result better voltage regulation is achieved and the system may con tinue working even in case of fault condition In this manner any fault can be ex posed by sensing the neutral line 15 Figure 2 Three phase four wire configuration In the case of a low impedance fault such as a shortcut the grid requires to be protected in the shortest possible time due to the high current drawn and the damage that may occur Actual protective devices may react in microseconds to secure the grid When a high impedance fault occurs the drawn current levels are lower and they may be in acceptable levels avoiding a shutdown of the faulty network This behaviour difficult the diagnosis of the problem and the cause of the fault cannot be easily determined and as long as this exists other signals may appear as a side effect that can reduce the efficiency of the transported power 2 2 Interfacing power lines
44. an Energy Meter and transmit it or to have to process harmonic calculations in a determined time frame The first may be accomplished by a low cost 8 bit MCU and the second may require an MCU with DSP and floating point capabilities Other aspects to consider 24 regarding the performance are like the use of an Operating System if needed with real time capabilities fault handling and diagnosis code or communications CRC validation Other constraints are cost size or environment An implementation of an MCU interfacing an AFE requires peripherals and digital I O of which is relevant to know its type CMOS NMOS or Open Drain Control Pull up Resistor control Peripherals in a MCU include ADC that whenever plan ning to use these should meet the requirements as mentioned It is highly recom mended that these peripherals include the required communications controllers that will be further used like UART SPI CAN Ethernet Parallel Data Capture unit and DMA that will release the CPU load Other parameters are regarding to the CPU architecture the available memory space word length clock generation circuit In terrupts Control unit internal busses and pipelines Whenever there are time con strains these parameters become crucial to control the application flow and perform the task in the given time frame Whenever the MCU AFE are ADCs and having time constraints it is important to count with DSP instructions that will reduce the proce
45. ary as related to prototyping and PCB design and thirdly as related to the testing environment First the selected AFE to prototype in breadboard and later to implement in a PCB and a Renesas YRDKRX63N MCU board ADE7880 Renesas YRDKRX63N MCU board CT Yhdc SCT 013 030 30A input 1V output The selected MCU resources have a code implementation 32 MCU start up code SPI interface 2 independent interfaces UART interface 1 interface RTC CMT 2 units ADC 12 bit Digital I O The selected external resources have a code implementation ADE7880 Energy Meter Switches LEDs Okaya display Other tools related to the MCU used to code and debug were Eclipse based Renesas e2studio IDE Segger J Link hardware debugger Second the testing environment which is based in MATLAB to generate the 50Hz fundamental with harmonic waves with a final implementation using SIM ULINK A multichannel sound card Realtek ACL650 Appendix 7 Soundcard Datasheet appendix 7 5 is used to output the signals for at least as many AFE inputs as used three phases and neutral line currents and one phase voltage Third prototyping and PCB design An initial design over breadboard is proto typed all the components placed include Input current passive low pass RC filters with a f of 14KHz and a maxi mum phase shift of 1 4 degrees in the frequency range of the 7 harmonic 350Hz Voltage line voltag
46. asure ment operation Basically the first operation is unidirectional the MCU sending a bit stream with a write command byte 1 byte as 0x00 in hexadecimal notation the destination memory address byte and a value to write to the ADE7880 register ad dress Whereas the second is a bidirectional communication that follows the same pattern but sending a read command byte 1 byte as 0x01 in hexadecimal notation and an address to read from expecting something in return from the ADE7880 im mediately after this sequence see Figure 20 This transmission is handled by the hardware registers of both devices energy meter and MCU The drivers provide a safe and exclusive access to these registers Therefore the AFE driver has to be aware of the MCU SPI hardware driver ss e ULL ULL UL 1 1 1 1 1 1 1 1 1 1 ENS i 115 14 Lato p MOSI i REGISTER ADDRESS 0 0 O O O O O 1 S ERR poi Rene 1311301 11 01 MISO REGISTER wee Figure 20 ADE7880 SPI Read operation of 32 bit register Datasheet p 79 59 The AFE driver is unaware of the hardware SPI driver this is masked by an inter mediate middleware layer between both of them This layer is bound to the given hardware and its SPI driver requiring some additional rework to port it to another platform Provides GPIO translation and ADE7880 boot up sequence until SPI is stablished and locked into its configurations as the communication protocol The major functio
47. b which corresponds to 0x71 this is because the device ID is assigned to be 0x70 in case of having multiple AFE and using I2C protocol Notice that it is recommended to avoid using this combination upper seven bits as 0111000b to avoid confusion when not using I C protocol although it is not relevant while only using SPI in 4 wire mode where CS pin exclusively targets one destination The 75 next two bytes are the target register and they content is 01000011b and 11000000b which in hexadecimal notation is 0x43C0 and as the datasheet indicates refers to the AIRMS memory register referring to phase A current RMS value Immediately after the last address bit has shifted into the AFE the MISO line starts transmitting back to the MCU when the next SCLK high to low transition occurs While the first two bytes contain only 0 the next two are 00000101b and 00000110b representing 0x00000506 which in decimal notation represents the number 1286 The datasheet in the registers list specifies that this register is a 24 bit signed or unsigned register that is transmitted as a 32 bit word with four or eight MSBs respectively padded with Os And the Current RMS Calculation section specifies that this is a 24 bit signed registers accessed as 32 bit registers with the eight MSBs padded with Os The same section specifies that at the full scale input signal of 0 5V the ADCs produce an output code of approximately 5 326 737 where the equivalent RM
48. bly but not con firmed reloading 64 Before adopting this environment other solutions where examined A first testing environment was built with a second MCU and a4 channel 16bit DAC with parallel input for quick data transfers An interrupt sets the indexes of the sine lookup tables to feed the output pins with the resultant amplitude The main drawback with this implementation is the additional required hardware and the limitations of a uC re garding high speed processes Other proven issues were the asynchronies or delays added by the latencies of the interrupts handlers that distorted the wave generation The idea initially simple was having a concept problem while an interrupt with a higher priority is being serviced avoid other lower priority interrupts to take place losing its turn and showing at a different frequency lower than expected This was practiced with a Renesas MC16 62P 24MHz MCU A pre emptive RT OS could be used but the available MC16 uC OS II was not made precisely for the 62P series needing to port the code A simplest approach with the same MCU was to calculate the least common multiple of the four involved frequencies which for 50 150 250 and 350 is 5250 and use a single timer with a single interrupt where the four fre quencies indexes where processed 5250 times per second this means once every 191 57us Although feasible it is a challenging speed to the mentioned MCU Changing the MCU for a faster model or us
49. ccording to the content of the RTC registers available as a MCU peripheral Using the main clock or a sub clock pre scaled to 128Hz as counting source it can generate an interrupt as fast as 1 256 seconds sufficient precision for the 10Hz of maximum event frequency in the system alt hough the resolution in use is given in seconds The registers can be read at any moment Having independent registers for each value seconds minute hour day month and year all of them are read sequentially with the events occurrence no interrupt is required despite a method was imple mented for this purpose to program possible periodic actions All the registers are of 8 bits unsigned or less but the year which is 16 bit unsigned and a structure is defined to store them all and provide space for a string built with all the registers content formatted with the use of sprint to retrieve and print or transmit the complete date time at once 4 55 MATLABO and SIMULINKO testing environment The MATLAB license of VAMK s school allowed its use for the research and its implementation took place by using the same concept Setting timers to populate the result of the mathematical formulae of the respective sine waves to the sound card This showed a problem regarding to the timers reload and the output to the soundcard that could not be solved and the result was the disappearance of the out put during an undefined interval of time while timers were proba
50. cted for testing purposes having a relaxed RC values but allowing a higher bandwidth respecting the original signal properties 46 RI out u 5 1k C1 H ac dec 20 1 10000000 AC 1 2 2e 3p Figure 12 Input current path low pass filter simulation schematic Vout BdB 12dB 18dB 24dB 30dB 36dB 42dB 48dB 54dB B e a 1 1 f 90 1Hz 10Hz 100Hz 1KHz 10KHz 100KHz 1MHz 10MHz Figure 13 Current low pass filter simulation Bode diagram R 5 1k C 2 2nF With the given RC values of 5 1kQ and 2 2nF the cut off frequency is 15 kHz not affecting the input bandwidth of the IC of 3 3 kHz Having 30dB attenuation The target of these selected relaxed RC values is to avoid possible future testing envi ronment limitations when the case is to select higher harmonics indexes than the 7 and keeping the original properties of the wave at higher frequencies In a second approach the RC values have been analysed to fit specifically a meas urement up to the 7 harmonic In a final design with a fixed value of the 7 index as the maximum harmonic the recommended RC filter implements a resistor of 47 22kQ and a capacitor of 2 2nF having then an attenuation of 27mdB with a phase shift of 5 4 at 350Hz and an attenuation of 44dB at 512kHz R1 V1 22k C1 AC 1 0 0022p ac dec 20 1 1000000 Figure 14 Optimal current input low pass filter for a highest 7th ha
51. d by the manufacturer with 5 different categories of func tions like filtering or transforms like DFT or FFT optimized to work with the MCU and their compilers The code is light the largest function is less than 1kByte and the largest stack memory requirements are less than 100 Bytes These give opti mized code for interfacing directly with the CPU DSP instructions resulting in the lesser CPU clock cycles per function Other relevant properties are its large built in flash memory of IMB and RAM of 256kB or the availability of several Real time OS like FreeRTOS EmbOS or uC OS II and uC OS III This option an RT OS is not in use at this level of the project The retail cost of 1 unit of this MCU rounds 11 in the market Other options are quickly assessed and with a similar price and characteristics was selected an ARM Cortex M4 STM32FA05RGT6 MCU a 32bit RISC 168MHz MCU 210 DMIPS 1 25 DMIPS MHz perfectly capable for DSP instructions and 37 a price rounding 12 Farnell Finland May 2015 The immediate availability of the YRDK63N board for prototyping was the reason to select this latest 3 4 Software environment One of the project s requirements dictates the language all MCU implementation has to be written in C Although regarding MCUs programming language where the language limitations come due to the available compilers C or embedded C is the most universal language in the industry environment Blaza amp Wils
52. dd an extra overhead of about 400 bytes resolving to a total transferred data of 2 71KB With a transmission speed of 115 2Ksps the buffer should empty in 23 5ms in a window of 100ms between events The transmission buffer is a circular buffer where any string can be placed at any time A global variable follows the index to position any incoming new byte and the number of bytes to transmit When the transmission register is empty it begins by placing the next byte in the index order into the UART transmission register and storing the remaining bytes The UART bus is programmed to start transmitting automatically whenever a byte is placed in its register and triggering an interrupt whenever the last bit in the register has shifted out The service of this interrupt will place the next buffer s byte in the register following the index order and de creasing the number of bytes to transmit As strings are transmitted a flag controls 63 when any new string should be shifted immediately into the register or placed in the buffer When the last byte in the buffer is put into the register by the interrupt the flag is released Under the previously estimated conditions the buffer should never be full although in that case new information is hold in queue until the IRQ released a new position This is a blocking situation that should never happen or should be handled as required 4 4 8 Real time clock The time the events occur is recorded a
53. de VA 5V VD 3 3V 0 5 10 VA 3 3V VD 3 3V 0 2 10 Six Channel AC 97 2 3 Audio Codec 33 Rev1 3
54. e Other methods were eval uated but discarded due to the simplicity and effectiveness of the chosen Once the SIMULINK model was implemented only a cable soldered to a Jack connector plugged into the soundcard s output was needed to feed the AFE input pins 40 4 METHODOLOGY AND IMPLEMENTATION Four different frequencies are generated by Simulink and output from the sound card of a computer as an analog signal Having then a fundamental of 50Hz and 34 5 and 7 index harmonics with a maximum amplitude of 1V p and the possibility to control the amplitude of each frequency independently or to modify the harmonic indexes The signal is presented to the AFE neutral current differential input INP and INN The same signal is used to feed the phase A B and C current differential inputs IAP IAN IBP IBN and ICP ICN This is only for testing purposes to verify that the data from the phase inputs is correctly read Since only one signal is generated it is impossible to simulate a 3 phase 4 wire environment In a real environment reading each phase and neutral line will allow to determine the faulty line and ana lyse the missing current with the neutral line current as well as the phase angle of each of them to approximate the origin of the fault To finalize the same signal is presented at one of the phases voltage differential inputs phase A is selected VAN VAP This is an ADE7880 requirement to use the signal as a time base for t
55. e a DSP could be a solution too but the idea was discarded in early stages Additionally this type of implementation is noise sensitive A first MATLAB approach was built using timers to calculate the instantaneous vector of the waveform and throwing its result to the soundcard Some issues merged in this implementation for an unknown reason the wave generation was halted for a short period of time but enough to distort the result perhaps the OS was affecting the process And based in the previous schema this time implementing a third party DSP library Solving partially the problems of the previous others arise with the use of a 32bit DSP in a 64bit machine Additionally a GUI was built to dynamically control the required frequencies and amplitudes Finally SIMULINK proved itself as effective as simple although not exempt of issues that have no solution at the moment Those do not affect the output wave and its apparent continuous signal but limiting the available channels of the soundcard 65 The odd frequencies in the array list were output through the front right channel of the soundcard and the even through the front left while the remaining output chan nels were silent This forced the use of both channels as only one to every input of the AFE and despite having a single multichannel soundcard its output can be only considered as a mono signal and the same single signal was connected in par allel to the AFE inputs
56. e divider circuit with a parasitic filter Required ADE7880 circuitry as specified in Datasheet 33 3 3 V linear regulated power supply based in AMS1117 3 3 to power up the breadboard 3 3 V dc dc isolated regulated power supply ISF 0503A to power up the AFE in the PCB Renesas YRDKRX63N board PMODI port interface CT will be used for testing purposes Rogowski Coil will be used in a real environment requiring an Integrator The PCB prototype was completely designed with PADS in a dual layer board of 75mm x 62mm and completely manually routed for efficiency containing as mayor clusters A socket to insert an ADE7880 previously soldered to a 2 x 20 inline pins board body All the required input filters 3 high speed quad line digital Isolators one ISO7240 with 4 out lines and two ISO7241 with 1 input and 3 output lines to isolate the ADE7880 side of the board from the MCU side A 40 pin socket connector to interface with the Renesas PMOD connector and Raspberry Pi compatible Independent and isolated 5V to fixed 3 3V DC DC converter ISF0503A to power the ADE7880 3 2 Selecting the AFE The option of an MCU fetching the data with ADC and processing it to obtain fun damental and harmonic values is a valid option and reduced cost Whenever the conditions of a high impedance fault and consequently allowing longer time gaps for processing are the target of the implementation this can be the primary option
57. e is less after filtering the signal Maxim Integrated 2003 All the input signals should be filtered to avoid aliasing An aliased signal is pre sent in all sampled systems regardless the ADC architecture It means that any sampled signal higher than the half of the sampling frequency will get a wrong sampled digital value in the frequency below half the sampling rate GO 1 2 3 4 5 6 7 8 10 Figure 5 Aliasing Two different waves having the same sampled values When using a passive first order RC filter one has to consider that their attenua tion of 20dB dec must be sufficiently high at the half of the sampling frequency However when using a Rogowski Coil these sensors have a 20dB dec gain that voids the 20dB dec attenuation of the first order filter thus the attenuation must 22 be offset again Designing the LPF as a cascade set of filters or a second order fil ter will establish the attenuation again On the other hand it is known that Rogowski Coil output requires an integration of its output yet an integration pro duces a result in frequency domain of 20dB dec and a 90 phase shift that have to be accounted Analog integrators design are easy to implement by means of an OpAmp but its design requires special care and the environmental conditions have an important role in the operating lifetime Rr Vout Figure 6 Analog integrator using OpAmp Implementing a digital integrator is possible by processing the sam
58. e phase normalized waveforms and voltage vectors 14 Figure 2 Three phase four wire configuration eee 15 Figure 3 e los 16 Figure 4 Rogowski Coil scheraties uto ies ante cic Ip petu om te 17 Figure 5 Aliasing Two different waves having the same sampled values 21 Figure 6 Analog integrator using OpAmp eene 22 Figure 7 Even vs Odd function Matlab plot eee 27 Figure Plot of a dransient iuo uide tectus ERES dota unia aos 30 Figure 9 Graphical representation of the system esee 42 Figure 10 Functional block diagram from ADE7880 datasheet 44 Figure 11 Harmonic engine block diagram fromADE7880 datasheet 45 Figure 12 Input current path low pass filter simulation schematic 46 Figure 13 Current low pass filter simulation Bode diagram R 5 1k C 2 2nF 46 Figure 14 Optimal current input low pass filter for a highest 7th harmonic index47 Figure 15 Optimal current low pass filter Bode diagram with cuttoff at 3 5kHz 47 Figure 16 Current input antialiasing filters schematic sees 48 Figure 17 Voltage input antialiasing filters schematic esses 48 Figure 18 ADE7880 Hardware registers access example sesssss 55 Figure 19 ADE7880 driver user sequence diagram
59. enever a new AFE register is retrieved The slight delay that can be seen in between each low period is the transition time that the MCU spends in returning from the call to the ADE7880 driver to obtain a value to the next call to obtain another value which is a fraction of each time divi sion B t B t B t B t e Figure 28 Grouped SPI readings in one cycle scope by DSOX2012A This scope Figure 28 Grouped SPI readings in one cycle scope by DSOX2012Amay determine the effectivity of the implemented ADE7880 driver where the time that requires to access to a register return and access again to an other register in both read operations take less than 10us To evaluate the performance of the communications to a RTU the transmission buffer and UART communications a timer counter is enabled to measure different actions time of execution By one hand a first scope let s call it t1 where the T11 performance of the driver is measured by counting the time of one grouped SPI transmission this serves to confirm by another method what so far was seen in Figure 27 Single SPI reading scope by DSOX2012A Another scope t2 is set to measure the time of the same grouped transmission until the UART driver returns after placing the last byte in the transmissions buffer measuring in this way the time that takes to measure and make the information available in a RTU A last scope t3 is set from t
60. er is explained in further improvements The analysis of the data over 200 events offered the next statistical results Sample size n 200 Frequency table for t1 AR 79 295 5 200 1 Frequency table for t2 m of i 574 0 200 1 Frequency table for t3 Xm fm fm 99210 3 1 0 005 98338 8 190 0 95 98338 3 1 0 005 97150 7 1 0 005 97099 3 2 0 01 97098 7 3 0 015 97098 2 1 0 005 97096 5 1 0 005 Where Xz is the list of observed values fz is the number of times the value is observed f Pris the relative frequency The mean value for t1 nays gt Je 3 172985 295 5ms The mean value for t2 u t2 2 x 1 574 0 574 0ms The mean value for t3 80 u t3 gt fan 0 005 99210 3 0 95 98338 8 0 005 98338 3 0 005 97150 7 0 01 97099 3 0 015 97098 7 0 005 97098 2 0 005 97096 5 98293 8035ms The variance for t1 veris as xy w t1 2 1 295 5 295 5 0 The variance for t2 var t2 fi Qu wle2 0 The variance for t3 var t3 gt fin Xm i t3 0 005 99210 3 98293 8035 0 95 98338 8 98293 8035 0 005 98338 3 98293 8035 0 005 97150 7 98293 8035 0 01 97099 3 98293 8035 0 015 97098 7 98293 8035 0 005 97098 2 98293 8035 0 005 97096 5 98293 8035 62674 096 Standard dev
61. ess and one for bit access The first gives all bit range named uint16_t REG ALL in the previous figure announces that it is a 16 bits register and provides access to the whole content at once Next line after it is the declaration of the second member of the union a structure named bits which provides a name to each bit available in the register 4 4 5 Public methods high level access The two most important operations are writing the ADE7880 configurations and reading the measurement from it For this reason the driver offers two public func tions to handle the access to the energy meter These hide lower level access like registers or SPI communications form the user side They are performed by the 56 functions ADE_command_handLer which perform configuration operations and ADE_measure that retrieves the measured values Their signatures are as follows error_List_et ADE command handLer uint32 t pid uint32 t cmd uint8 t arg J error List et ADE measure uint32 t pid uint8 t cmd uint8 t channeL uint16_t samples void resuLlt The public functions share common features in their signature The output or return ADE7880 drv src High level public functions ADE7880 drv E7880 ADE7880 ADE7880 drv MCU SPI drv local functions SPI protocol handle SPI buffer builder Middware Middware MCU SPI drv declare measurement storage location
62. gisters h 19 13 10 14 10 27 e1100620 gj ade7880 spi protocol c 24 13 10 14 21 06 e1100620 ade7880 spi protocol h 19 13 10 14 10 27 1100620 in ade7880 srv cmd handler c 52 28 04 15 21 13 e1100620 fj ade7880 srv cmd handler h 45 16 11 14 23 11 e1100620 Preamble h 1 28 09 14 18 12 e1100620 iq r ade7880 drv c 52 28 04 15 21313 e1100620 nj r ade7880 drv h 52 28 04 15 21 13 1100620 gt rade7880 gpio c 46 17 11 14 22 43 e1100620 gt rade7880 config h 51 28 04 15 14313 e1100620 gt gy r bsp gt gy rglyph 4 zy r rspi rx600 4 zy src gt r rspi nx600 c 44 12 11 14 19 43 e1100620 gt r rspi x600 h 44 12 11 14 19 43 e1100620 gt r rspi X600 config h 44 12 11 14 19 43 e1100620 5j readme txt i 28 09 14 18 12 e1100620 4 zy r rtclock b Le rrtc c 49 19 11 14 19 15 e1100620 p m r rtc h 47 18 11 14 22 41 e1100620 4 zy r switches 4 zy src gt r switches c 44 12 11 14 19 43 e1100620 gt m r switches h 44 12 11 14 19 43 1100620 gt r switches config h 49 19 11 14 19 15 e1100620 Ej readme txt 1 28 09 14 18 12 e1100620 4 r timer gt r cmt counter c 51 28 04 15 14 13 e1100620 b Ir r cmt counter h 51 28 04 15 14 13 e1100620 gt r cmt oneshot c 51 28 04 15 14313 e1100620 gt r cmt oneshot h 51 28 04 15 14 13 e1100620 4 zy r uart rs232 gt r uart c 47 18 11 14 22 41 e1100620 nj r uart h 36 06 11 14 23 02 e1100620 dtd de Vv Vv definitions h 51 28 04 15 14 13 e1100620 main c 51
63. he ADE7880 and the LCD This latest is used for onsite debugging displaying RT information and allowing to set the voltage threshold value not needed in a final implementation In the second place the communications with remote devices the computer used for the testing environment that receives plots and stores the data in case of an anomaly and an RTU running SCADA that receives the information The computer receives UART signals meanwhile the SCADA RTU requires Ether net that is not required at the moment and so not implemented in this project 3 7 Testing environment A testing environment is required in order to assess the implementation on a re duced scale For safety and legal reasons students are not allowed to work with voltage levels over 50V and the conditions had to be simulated at a smaller scale The test environment requires a computer running MATLAB and a professional sound card to generate the significant waves The specifications state fixed frequencies the fundamental of the AC current is 50Hz and harmonic frequencies appear at decimal multiples of a fundamental fre quency being the harmonics of the 3 order 3 times 50Hz resulting in the compo nent of 150Hz the 5 resulting in 250Hz and 7 equals to 350Hz The selected method was by means of SIMULINK blocks One block needed as DSP with a matrix of 4 frequencies with independent amplitudes and the output connected to a second block as the default audio devic
64. he harmonic calculations engine All the required LPF are calculated and placed to each input The AFE is a SPI slave of the RX63N MCU with a 4 wire diagram Only SPI pro tocol is used for all the communications despite the selected energy additionally offers I2C and HSDC High Speed Data Capture To configure the ADE7880 to perform harmonics calculations one may when from power off follow the power up procedure establish SPI as the communications protocol and follow the recom mended approach for managing Harmonic Calculations Regarding to the RX63N MCU and because the YRDKRX63N prototyping board is used no MCU PCB is designed for this research The RX63N PMOD port is configured to allow SPI communications by means of the SPI peripheral number 1 and the Signal Select Line 0 requiring four lines CS CLCK MOSI and MISO The ADE7880 power mode select input pins PMO and PM1 are connected to and controlled by MCU digital output pins driven to the same PMOD port as well as 41 the ADE7880 reset input and HREADY output pins The same POMD port offers 3 3Vcc and GND to power the MCU side of the Isolators The Raspberry Pi con nector offers IRQO IRQ1 and CFI pins as well All these signals are interfaced through the required Isolators and the PCB design presents 3 additional pins ADE_CF1 ADE_CF2 and ADE_CF2 as energy to frequency conversion output pins that may be later used for calibrating purposes The software enables all the
65. he event detection until the UART driver call returns after placing the last byte in the transmission buffer This means the total time of the ten grouped transmissions from the event triggering action to the moment the last re quested value of the last measurement cycle is placed in the output transmission buffer is shown The conditions are for each test case t as follows Measuring t1 the fifth meas urements cycle out of ten was randomly chosen The time counter starts measuring when the measurements cycle function is called and ends after the last call to the ADE7880 driver has returned To measure t2 the first cycle right after an event is detected is chosen to avoid any data from previous measurements in the UART transmission buffer that could have an influence in its performance The third case t3 measures from the moment an event is detected until the call to transmit measures to RTU function has returned The LCD shows the results although the write operation is performed at the end of the whole process to avoid computing its processing time The additional MCU s 16bit timer is configured as an up counter using the periph eral clock PCLK 48MHz prescaled by 8 giving a precision of 1 6 us per clock period counting up to 60000 clock cycles triggering an interrupt every 10ms that when serviced adds one to the global variable that holds the number of timer inter rupts counter The values are shown in F
66. hip between the primary s number of turns single turn and secondary s turns N the output current A in Figure 1 is calculated zie lout Equation 1 where Tout 1s the output current at both ends of the secondary in a closed circuit N is the number of turns of the secondary I is the current flowing through the power line Placing a low value burden resistor in parallel with the load and closing the sec ondary winding circuit will convert the given current to a voltage signal that can be calculated knowing the desired output voltage by ohms law Vout lout Rpuraen Equation 2 17 where Vout is the voltage drop over the burden resistor Tout is the current flowing through the secondary winding Rpurden 1s the value in ohms of the resistor closing the secondary circuit A voltage level is easier to read for any instrumentation device or the input of an ADC Notice that if this burden resistor is not in place and the secondary winding terminals are left open circuit while there is a current flowing over the primary the secondary will store the energy creating a high voltage and a dangerous situation Care is taken by the manufacturers design to efficiently couple primary and sec ondary circuits and to avoid core saturation by choosing the wrong burden resistor In this manner CTs can provide in theory a lossless current measurement and the signal voltage in a power line is large providing a noise immunity
67. iation of t1 t1 Jvar t1 0 Standard deviation of t2 6 t2 Jvar t2 0 Standard deviation of t3 81 6 t3 4 var t3 250 348ms This information reveals that the SPI transfers use exactly the same amount of CPU clock cycles for each transmission This is the expected result due to the fact that this operation is mostly performed by the SPI peripheral and its memory registers involving little CPU load By the other hand reveals that whenever the UART trans mission is involved to transmit a single set of measurements performs as good as the SPI peripheral Although when several sets of measurements are performed case t3 making higher use of the UART transmission buffer the performance is slightly reduced increasing the total time in 8ms from the expected 90 5ms the tenth and last measurements cycle is triggered after 90ms of the event expecting to add no more than 0 5ms of a single transmission up to 98 3ms To confirm the delay added by the UART transmission buffer the same test is per formed but tl case is executed in the second cycle of measurements execution after 10ms of the event and t2 case is performed during the fifth cycle after 40ms of the event The result seen in Figure 30 LCD execution times when t2 incurs in delay shows the UART transmission buffer as the responsible of the delay requir ing almost 1ms more in the same operation BDET7S88B SPI EL 295 2 iz 1456 2
68. id data corrup tion This may appear for example when having concurrent access requests at the same time to the same memory location one access may be writing what the other is reading When non handled interrupts may occur or using an OS with multiple threads accessing the driver one should protect the access to this memory location with any of the known techniques i e disabling interrupts setting flags or locking mechanisms like semaphores when using OS This is not happening in the imple mentation proposed here since event interrupts don t occur while in the window frame of an event s information retrieval The transients ADC readings relinquish the execution to the information retrieval algorithm segment and is not attained again until the process finish 4 4 5 The ADE7880 Driver Provides high level access to all the available registers of the ADE7880 While the individual registers can be read or write independently at the low level access it provides two public functions at a higher level that perform all the operations needed for this implementation and most of the common operations for an energy meter not including operations like energy to frequency measurements or calibra tion registers access although any register can still be read individually 4 4 4 ADE7880 low level access HAL The ADE7880 provides known hardware memory locations or registers infor mation which is provided by the manufacturer These registers are
69. iewed This DSP is controlled by a higher level MCU using SPI communications protocol Other MCU functionalities imple mented are to control a 16bit ADC that measures transients over the neutral line and to transmit the recorded data altogether with a time stamp given by a real time clock to a remote terminal the information is served to the remote terminal unit in 0 5ms 13 2 LITERATURE REVIEW The application of electronics to substitute the old electro mechanic devices to measure power over the grid has brought accuracy and simplified grid quality con trol and management It is not a long time ago when the MCUs became an important component in substation automation at the end of last century and nowadays it is difficult to imagine a design without implementing them Smart meters demand has grown rapidly and with it the development of energy meters Energy meters provide information about power and power quality and all the re quired information about the energy of the line under scope More advanced meters provide more than one phase sensing and harmonic calculations Harmonics measurement over power lines in substation networks help not only to keep track of healthy lines but provide useful information in case of failures that can help to determine their origin and location As harmonics are spread all over the network in all directions they can be read in the nearest substation or by a device for this purpose in the proximi
70. igure 29 LCD showing the where t1 t2 and t3 match the scopes described above and their values are execution time in us of each scope 78 Figure 29 LCD showing the execution times of cases tl t2 and t3 The first line displaying tl 295 5us confirms the oscilloscope s data having ad ditional us that may come from the extra processing clock cycles required by the calculations Being t2 574 0us the most significant figure showing that the time of 0 574ms to serve the seven measured values to an RTU In this implementation means that there are 9 4ms available to evaluate the data and execute the desired action before the next avalanche of measurements is executed and transferred The next row shows t3 99210 3us scope displaying the total time in us of ten cycles of measuring and transmitting corresponding to the chosen window frame of 100ms measuring 10 times starting from time 0 plus the transmission time of all the measures and extra formatting characters Although the requirements specify an available frame as long as 150ms and to effectively measure the harmonics at least once this solution provides with ten times more information in 2 3 of the time If only one measure is accounted the time is reduced by 1 100 Despite complying with the requirements the gap of 0 2ms between the data is gathered by SPI in approximately 0 3ms and served to the RTU in 0 5ms may be reduced significantly as lat
71. implement an algorithm that performs the Discrete Fourier Transform calculation shown in the theory chapter 2 4 1 to the value given by the ADC and obtain the magnitude of the frequency at that index According to RX63N and the RX DSP library documentation its FFT algorithm may perform a complete Discrete Fourier Transform of real valued input array in 151110 clock cycles without error checking and 175483 with error checking RENESAS n d Analysing the worst scenario from the detection of an event until a value is stored into the MCU memory the time required taking 50Hz as the base frequency is 20ms to sample the data and another 1 83ms required by the DSP library with the MCU working at 96MHz its maximum clock frequency At this point 21 83ms are spent in the process The process of data retrieval and storage may take additional CPU clock cycles that are not evaluated but accounting them by rounding up to 22ms Whereas this is still in the range of 150ms provided by the specifications representing a valid solution Additional optimizations may be ap plied as the signal s fundamental is a periodic and odd function the second half of the period is the same but inverted as the first half therefore discarding it the sampling time may substantially be reduced to the half 10ms making a transform in 12ms As stated this approach is theoretical and not a definite statement no test was prac ticed only tries to show a preview of a
72. inux and OS programming Having this in mind the AFE driver was designed to be completely portable and not bound to any particular CPU or specific compiler instruction It can be implemented in a standalone system or in an OS It can run in Renesas or ARM Raspberry Pi is ARM v7 as it is not bound to any of them Only requires a middleware layer implementation that can be easily written by following the same schema as shown here The PCB design reflects the same procedure and tries to follow the Raspberry Pi compatibility by having a similar size 62 5mm width and 74 5 height with smaller area and with a female 40 pin header that fits on the Raspberry Pi v2 IO male pin header A prototype carrying a compatible connector may be attached to a Rasp berry Pi connector and the Renesas PMOD connector using the latest an adapter cable made by following the schematics in Appendix 5 Schematics ADE7880 and connector socket 4 2 Prototyping the AFE ADE7880 input channels Before the PCB was designed a prototype of the AFE board input filters connect ors and power source were located over a breadboard having all the required input and output pins clearly distributed Seven differential inputs of which five are re quired fourteen lines to interface the MCU PMOD port and all the filtering capac itors and resistors were placed on top of it to start the MCU interface Care should be taken regarding ESD 44 FUNCTIONAL BLOCK DIAGRAM R
73. isolated power source and every other component re quired to have an ADE7880 testing board and providing a 40 pin female connector compatible with Raspberry Pi and Renesas PMOD port this latest requiring an ad ditional adapter all in a dual layer format of 75mm x 62mm Presented in a dual layer format all components are SMD with the exception of the pin headers and high voltage input connectors Both layers use intentionally a dif ferent plane the bottom layer where the AFE and its PSU altogether with power related traces are placed is flooded with ground plane to allow a same reference potential and reduce the conductive noise by reducing the ground connections im pedance The top layer where all communications traces and the fast acting optol solators are is flooded with a power plane adding in this way a distributed inter plane capacitance between both planes and therefore better high frequency decou pling Each plane is divided in two different planes to provide electrical isolation One part of each plane belongs to the AFE isolated powered supply side and another to the MCU powered side The Optolsolators electrically divide both AFE and MCU sides of the planes in both layers and therefore the planes are physically divided under the location of the optoIsolators and being a mirror one to each other layer Regardless these measurements the PCB should be placed in an isolating case and avoid direct contact when in use due to the ri
74. ith the FFT there are available algorithms to implement in this case A remark to the Goertzel algorithm that can perform frequency detection using less computational power than the FFT Banks 2002 2 5 Evaluating transients Transients in power lines are transitory non lasting bursts or oscillations of energy as a response to a change from a previous state Generally called spikes they can be voltage current or energy and they disappear if the power is disconnected for a short period of time There are many situations that cause overvoltage transients 30 lightning strikes shortcut trip of a circuit breaker a tree occasionally touching the line or an animal contact among other Earth faults as the shortcuts are sources of transients in their initial instants from microseconds to a few milliseconds The main characteristic is the overvoltage spike with a very high bandwidth and a very short time span Transient Figure 8 Plot of a transient These overcurrent or overvoltage signals carry information that can be analysed by measuring devices They require a very high bandwidth and amplitude tolerance and in general different circuitry and signal processing properties than the harmon ics Due to the random nature the variability of the sources and the difficulties to define their amplitude duration and energy content they are not analysed in this paper and only their amplitude is measured altogether with their time s
75. l current does not interfere and regarding the har monics this last has its own This is could be a relative drawback in other kind of implementations than this since the ADE7880 has one DSP meaning that either one phase or neutral line harmonics can be measured at a time The computational block for harmonics calculations will allow to obtain a reading of the neutral current RMS value This is important since the engine can output three harmonics indexes at a time but four are needed the named 3 5 and 7 and the fundamental as well The fundamental component and related THD are only calculated for the phases they cannot be measured by the neutral line engine obtaining the total RMS current instead by reading the NIRMS register There is no output either to the THD value of the neutral current Although there is no need to retrieve these values following 45 the given specifications they can provide valuable information therefore appearing as a relevant limitation for data analytics HPHASE BITS ACTPHSEL BITS HCONFIG 9 8 SELECT THE PHASE USED TO AS TIME BASE OUTPUT REGISTERS USED WHEN ONE OF PHASES A B C IS ANALYZED HCONFIG 2 1 ENG MONITORED rus rns rwarr rvan eva fr vino m9 eyes parvus seus WATT sowas reva ser WHO WARD CALCULATIONS IC VC HXVHD HXVRMS HARMS HXVHD HXIHD urpu REGISTERS USED WHEN NEUTRAL IN ISUM HYVRMS HYIRMS HYVHD HYIHD ODE HEUTE HX HY HZ REGIST
76. lculations are limited to one phase or neutral at a time due DSP limitation this is not a drawback since only neutral current harmonics are of the interest of this analysis Supplies RMS and harmonic distortions of all harmonics within 2 8 kHz pass band on neutral current with less than 1 error in harmonic current and voltage RMS harmonic active and reactive powers over a dynamic range of 2000 to 1 at TA 25 C Regarding to the ADC equips 7 Sigma delta Z A 24bit ADCs with a sampling rate of 1 024MHz The ADC outputs are signed twos complement 24 bit data words and are available at a rate of 8 KSPS or every 125us For communications it offers serial interfaces I2C SPI or HSDC For harmonics reading HSDC in burst mode reading is recommended although not used since it burst into the line the content of all the registers in a row while only seven are needed three harmonic indexes of neutral current RMS neutral current and three phase RMS current Regarding its working modes of interest as energy meter where all fundamental apparent reactive or accumulated instantaneous or RMS phase powers and their components are calculated and many different properties of the signal not relevant to the research can be computed As a harmonic meter contains a harmonic engine that analyses one phase at a time Harmonic information is computed with a no attenuation pass band of 2 8 kHz corresponding to a 3 dB bandwidth of 3 3 kHz and it is specified
77. measurement Yarborough 2012 The output has relatively low phase shift from tenths of de grees to a few degrees in lower quality CTs allowing a direct connection with the measuring device Although the phase shift does not affect the measurement when these are magnitudes Designers have to ensure that the CT dynamic range is large enough according to the requirements Figure 4 Rogowski Coil schematics 18 The Rogowski Coil shares the CT principles an isolated line whose current flow induces a proportional current in a secondary coil The main difference resides in the core Rogowski Coil s core is air with a lower inductance faster signal response and very linear output Another useful property is that theoretically no matter the distance or location the Rogowski Coil is placed relative to the conductor line whenever the signal line passes through the toroid M kinen 2014 and it does not saturate However the output signal of a Rogowski coil is proportional to the time derivative of the current therefore requires an Integrator or using the non integrated signal and process it to adjust magnitudes and phase shift the signal by 90 This due to the properties of the Rogowski coil where the induced voltage in the coil is proportional to the cur rent rate of change and integration is required to obtain a voltage level proportional to the current waveform ug AN di t Veoil l dt Equation 3 where A is the tu
78. monics regarding the fundamental or how much of the current or voltage be longs to the harmonics in a power line From the mathematical point of view a harmonic answers to the question of how much component of an index x there is over a fundamental frequency y and trans lating it to power lines it gives the amount of energy that is carried by each fre quency This can be achieved by decomposing the original waveform into all of its frequency components by means of the Fourier series 2 4 1 Fourier series background Fourier series shows how any periodic function can be plotted by the sum of sinus oid functions Whenever having a periodic function such that f t T f t Equation 7 For all t maybe written as a Fourier series 1 co f z X lan cos nwt b sin not Equation 8 where Ls o w TU nf and the numbers aj a4 An b4 b2 b are known as the coefficients of the se ries Having different coefficients for different functions f t 26 The Fourier series coefficients can be calculated as follows T 2 2 an f Ocos not dt n 0 1 2 z2 Equation 9 and T 2 2 by f Dsin not dt n 0 1 2 2 Equation 10 If f t is even meaning f t f t T i an Mic cos nwt dt n 0 1 2 0 b 0 and If f t is odd meaning f t f t a 0 T 4 2 b f t sin nwt dt n 0 1 2 0 M kel 2013 27 Even finction
79. n and the clock cycles required to process the allocation and deallocation of each variable and process therefore obtaining a faster execution Another consideration is that the object is allocated only once and in the stack memory which is of faster access than the heap Dobry 1993 Other positive aspect is the flexibility Since the object is a parameter in all the functions calls to the ADE7880 driver access the functions always return the error occurrence therefore having more information than returning a single local variable value Moreover the container makes the data always fully available wherever needed avoiding a long list of parameters in each function declarations with each individual value The object allocates memory for one event s data does not audit the history of events because each event is transmitted immediately to an RTU where this will be processed relying then in the communications buffer When required one may al ways declare the object as a buffer as an array of objects which its iterations may have to be handled This will do the work of a local and volatile storage requiring 54 larger amount of memory If necessary an external and non volatile memory ac cess like an SD card where to save the information to a file should be imple mented There are drawbacks of having one object for everything that matters and all along the code The access to this object has to be handled carefully to avo
80. n voltages VCCI1 and VCC2 and ground levels Two of these Isolators are bidirectional hav ing three and one channel in each direction selected due to the characteristics of the SPI protocol having signal select SS MOSI and clock as MCU outputs and MISO as input as well as other input and output signals 71 The 40 pin header is compatible with the new Raspberry Pi 2 and older Raspberry Pi 2 B being always backwards compatible with the help of an adapter needed as well to connect to the YRDKRX63N board The PCB board provides a standard female micro usb type B jack connector as in put power and requires only one external power supply of 5V of at least 5 00mA The integrated voltage regulator provides an isolated GND and an output of 3 3V up to 300mA although the AFE requires only 28mA working in normal mode Traces are of two different widths power related traces width is 0 500mm and all other traces are 0 250mm Clearance rules allow a minimum separation of 0 250mm the maximum angle for the traces is 45 degrees and pads include thermals where required Figure 26 PCB Top layer In Figure 26 PCB Top layer the separated power planes are easily seen with the MCU power plane at the left and the bigger ADE7880 power plane to the right side separated under the fast acting optoIsolators The ADE7880 comes in a 40 lead lead frame chip scale package LFCSP and the PCB offers a 0 5mm Pitch 40 Pin DIP 12 SMD socket to mount
81. nother CMT timer is config ured additionally to measure the time spent in each SPI communication and the total time of each cycle from the detection of an over voltage to the moment the last byte is shifted into the UART transmission register A led is used to signal the events staying on until the information is transmitted to the RTU 42 The next figure shows the graphical representation of the relationship of different hardware parts and the MCU application with the software drivers to perform the required actions CREATE TASK YRDKRX63N Display info Changes with event or switch action Measure Neutral Transients every ips Simulate events and set threshold level Event starts CMT IRQ every 10ms x10 End put data to Tx Buffer RTU POWER LINE ii 7 a x SS oI ADE7880 DSP Isolators Figure 9 Graphical representation of the system 43 4 1 Explaining portability Renesas MCU or ARM The ADE7880 driver prototyped here has its roots in a preliminary approach by Sami Mahamoud Mahamoed for interfacing the ADE7880 with a Raspberry Pi to retrieve power related values Later was passed to in earlier stages of the project This has affected the design of this implementation The Raspberry Pi is widely used for educational purposes in VAMK as it may serve as an introduction to MCU embedded coding L
82. ns provided by this middleware layer are SPI driver read or write int8 t R ADE SPI Read uint8 t data uint8 t usBytes uint32_t pid int8 t R ADE SPI Write uint8 t data uint8 t usBytes uint32 t pid They are implemented into r ade7880 drv c with other required functions and under the same folder r ade7880 gpio c holds the GPIO configuration Other The architecture of the SPI reads or write functions is simple First step tries to obtain a channel s lock to the SPI peripheral this lock mechanism is implemented in the peripherals driver returning true or false and as the LCD uses a different channel this is true unless the call is originated by an IRQ or it is an OS with mul tiple applications requiring access to the same SPI channel Secondly when the channel s lock is obtained assert the required RX SPI channel Signal Select pin the LCD uses a different one therefore the ADE7880 SPI channel CS pin should always be inactive before this operation Third step proceeds to read or write to the SPI driver and when this execution finalizes the CS pin is deselected and finally the lock is released The CS pin is asserted manually for the freedom that gives to choose any of the I O pins but it could be also triggered automatically by config uring the MCU SPI registers to perform that operation skipping then steps two and four The SPI hardware access is controlled into the SPI hardware driver After initiali zation it offer
83. o this function gives the information about the correct set arguments The distinct measurements parameters are unambiguous requiring in this order the channel uint8 t chan nel referring to one of the three phases A B or C or the neutral line uint16_t sampLes referring to the number of times the measurement is read and later aver aged and one last float resuLt which is a float pointer to the memory location where the measured value is stored The measured values are always stored in the provided container whose location is passed as a reference all along the code to the ADE7880 SPI received buffer where the measured value is extracted from the received SPI bit stream and placed in the given location Passing a pointer to the measurement as an input parameter gives the freedom to use the output return to signal the occurrence of errors and produces a lighter code Precautions have to be taken when working with an OS to protect the access to this memory location with a semaphore to avoid data corruption or using atomic access This is not the case in the RX63N application where the im plementation follows a determined sequence after an IRQ occurrence which fin ishes before the next IRQ can be triggered Inside the IRQ when reading the meas urements follows a sequence with no possibility to corrupt the data Additionally gives the freedom to build an object a structure variable in C language with capac ity to all the requi
84. ocation device Is based on Seppo Pettissalo s original idea and the result of the collaboration of the named person and company together with VAMK and Technobotnia laborato ries during the last quarter of the year 2014 The paper offers a solution to the need of a software algorithm in C language to measure transients and rms currents over the 3 phases and fundamental 3rd 5th and 7th harmonic currents over the neutral line in 3 Phase 4 wire configuration Store and transmit the information altogether with the event s timestamp given by a real time clock It includes hardware software and a testing environment solution An approach to the use of a Renesas RX63N microcontroller interfacing an ADC and an ADE7880 energy meter will be discussed in this document and alternative methods are discussed It will gather the required information providing the values in less than 300 microseconds process transmit and serve the lectures to be dis played in a remote terminal in 0 6ms repeating the process during a time period of 100ms is proved The testing environment is provided by means of a desktop com puter s soundcard and the use of MATLAB to generate the fundamental and har monic waves Keywords fundamental harmonics energy meter power lines neutral line driver CONTENTS 1 INTRODUCTION a ahd le ela cde eddy See Pa Ei vo Mente eben i ae 11 2 LITERATURE REVIEW doite ie ee Doane vea Paseo rtu bue se mea t e oon 13
85. on 2011 followed by C with less than the half of the designs compared to C For this one may find C C compilers for all of the most used MCU on the market and this is the case for Renesas having toolchains for these languages in their products Renesas provides the complete software environment by providing IDEs with their compiler and linker into them One is their relatively new eclipse based e Studio IDE integrating their proprietary compiler and linker into the large eclipse IDE en vironment and providing communication with the hardware debuggers The KPIT GNU toolchain is a solution to the economic limitation of the proprietary solution A version control system Apache Subversion software mostly known as SVN is used as a centralized repository following the traces of all the changes branches and trunks The project files repository is stored in VAMKS server and no installa tion is required as it is already integrated in schools IT services 3 5 The code The code requires special attention whenever the source code has to be maintained along the time or delivered and maintained by third part teams Most of the code is commented using block comments and the less by inline comments this avoids the possibility to comment big portions of the code allowing a clear debugging Every file has a header text introducing the name the version and description of its con tent After this in the case of a source file c file each
86. pan 31 3 SELECTED RESOURCES Here is stated a method to solve the problem proposed by VASPEC Oy when trying to find an efficient low cost digital method to measure transient currents and har monics in power lines on earth fault conditions The research had to include an MCU to perform the calculations and the communications written in C language interface the signals by ADCS and provide a low current testing environment mean ing to provide the signals at the ADC input voltage level The solution presented in this research was built by means of an ADE7880 solid state Energy Meter an Analog Devices Inc product interfaced with a Renesas YRDKRX63N board with a RX63N MCU by means of SPI communication at 2MSPS The MCU transmits the data over UART to an RTU and the faulty condi tions are simulated by means of a PC running MATLAB and a soundcard used to output a wave signal composed of a fundamental frequency of 50Hz carrying a 3 5 and 7 harmonics generated by the SIMULINK DSP and transmitted through a wire connected to the soundcard s jack input to the ADE7880 The software so lution is Eclipse based Renesas e2studio Integrated Development Environment IDE and the project s code written in C The solution works as expected meeting all the requirements specified by VASPEC Oy 3 Hardware and Software resources The resources required for all the stages of the research are identified firstly as related to the AFE and MCU second
87. pled output of the Rogowski coil Having these models a closer output to the ideal avoiding the need of extra analog circuitry thus more stable over the time In this manner allows its use as a CT but remembering to implement a second order filter at the input William Koon Analog Devices Inc 2001 2 2 4 Analog Front End AFE The selection of the required front end hardware presents different options and spe cial considerations have to be taken when measuring harmonics This will affect to the performance accuracy reliability complexity and cost Whenever a decision has to be taken regarding the price the MCU with built in ADCs is the solution It has the lowest prices and easy implementation due to a little number of extra components needed to implement reducing cost complexity and the time to market The selection of the MCU becomes important as it is required to have a good DSP processing capability and ADC high sampling rate Whenever 23 using MCU DSP the software complexity grows as it is needed to have a good understanding of digital filtering and the manufacturer does not provide a DSP li brary or this is not free Manufactures should provide with the information about it as well as detailed information of the DSP processing performance As a result the flexibility of the system is reduced as it may require an entire redesign to implement an upgraded MCU In case of aiming performance the components can be selected
88. quires to write once several MCU specific registers to be configured and turned on and only one MCU specific register is read in order to collect the information Other measurements are adopted to facilitate the reading and understanding of each part of it Individual folders for each driver HAL in those which require it naming convention to identify each section The code s file naming follows a predefined structure such as each driver is wrapped into its own folder where the name identi fies the peripheral s driver and its dependence A folder s name of a driver package related to a Renesas built in SPI controller is called r spi rx600 The initial r_ means that the driver targets a Renesas RX peripheral and the spi rx600 is the name of the peripheral and is exclusive for the rx600 series Other driver folder s name is ade7880 identifies a driver for the ADE7880 IC No reference notation at the beginning of the name means that the code inside is unbound to the hardware portable requiring a HAL implementation and providing the hook code found as r ade7880 on the top of it 39 3 6 Communications protocols There are several different communication protocols required In the first place the communications that take place among MCU and peripherals in a very short range less than 10cm that require of a protocol In this case SPI is selected for being versatile and common providing high speed communications SPI is used by t
89. rd Root Mean Square Real Time Clock Remote Terminal Unit Surface Mounted Device Signal to Noise Ratio Serial Peripheral Interface Universal Asynchronous Receiver Transmitter 11 1 INTRODUCTION Measuring ground fault currents is part of the protection devices of the power lines in a substation network The current magnitudes of these faults depend on the im pedance of the fault and the grounding solidity and resistance There are effective protection devices for low impedance faults which produce a high fault current and require the isolation of the line to avoid any further damage On the other hand high impedance faults on multigrounded systems still represent a challenge for pro tective devices Its lower current may allow the line to continue to operate and the unbalanced currents may be tolerated by the asymmetry of the power lines In any of the cases a quick evaluation of the possible fault is necessary Measuring faulty current harmonics can extend the available information and ex hibit detailed information about the power lines state Harmonics are certainly a common measure to determine the quality of the power in the grid They offer val uable information to evaluate a fault or the origin of an asymmetry For this reason a reliable harmonic measurement is needed in any protective device Moreover the faster the better In case of a fault should the line be isolated there is a small time gap between the faul
90. red information avoiding the creation of individual variables with each portion of data The data container is a set of new type definitions linked from a lower to a higher level The file definitions h provides with a specific example of modelling this data object The following is the structure in a human readable form for stored measurements and its related timestamp Appendix 0 container which phase phase specific measurement measured value container which phase phase specific measurement time stamp 58 This favours the use of a pointer to the location of the container offering the access to store to or retrieve required data from anywhere the pointer is referenced This pointer is casted as a null pointer allowing the user to build its own container without modifying the code but requires to understand how the transmission and reception SPI buffers are built otherwise follows the pattern given here 4 4 6 SPI hardware access and Middleware layer The ADE7880 driver has to be bounded with the hardware SPI driver Having de fined an action like read a measurement or write a configuration command the ADE7880 driver s SPI buffer have to be build the access to the SPI hardware driver has to be safely acquired and granted and the ADE7880 driver s transmission buffer transferred to the hardware SPI buffer registers in a command operation and read back the hardware SPI registers from the ADE7880 receiver buffer for a me
91. ree other drivers require of a low level access to the hardware or HAL and middleware software layer to read or write to the peripheral offering a set of public functions that can be call when inserting the driver in an application They are ADE7880 SPI and LCD drivers although LCD is not part of this research since it will not be part of any final solution The ADE7880 driver can be ported to another environment with little to nothing to modify Requires to implant a software layer following the same routines shown by this code Special care is taken with the SPI hardware driver since has to meets the requirements to work in an OS or having several devices accessing to it at the same time It is re entrant and non blocking at a basic level two or more different de vices and with or without OS can be calling seamlessly the SPI driver There is no OS in this solution but re entrancy is required to handle the ADE7880 and the LCD screen SPI simultaneous access It was successfully tested in Renesas RX63N with no OS and Raspberry Pi ARM v7 with Linux Raspbian OS 4 4 1 Folders and files naming standard and structure Following the same structure as all along the code folders starting by r are specific Renesas application drivers to operate the peripheral indicated by the tail name As in this case r_ade7880 indicates that is the driver that provides control and a set of functions and callbacks to drive the ADE7880 IC Inside the
92. rent to ground during the ADE7880 power up time otherwise unpredict able AFE behaviour may occur If this condition cannot be granted one may trigger 70 the ADE7880 hardware reset after MCU boot up by setting reset pin ADE_RE SET to low at least 10us Said this having this short period for a reset signal is very recommendable to pull up this pin up and filter any noise that may trigger a fake reset signal by adding additional circuitry in Figure 24 AFE connections sche matic resistor R24 is placed to pull up the pin and capacitor C29 as filter Addi tionally the socket J8 for ADE_CF1 ADE_CF2 and ADE CF3 is placed as a pulse output since the power measures may be converted to frequency and measured from these outputs and helping the calibration process Additionally AFE IO volt age high level is 3 3 volts the same as RX63N and Raspberry Pi for other MCUs with other voltage levels they should be translated to this level to avoid IO hard ware damage Figure 25 Fast acting optolIsolators sample from Isolation circuits schematics The four channels optoIsolators have a bandwidth of 25MHz while the selected SPI transmission speed is set to 2MHz although the maximum allowed by the ADE7880 is 2 5MHz At this speed there were neither detected communications loss nor trans mission errors Figure 25 Fast acting optolsolators represents the schematics of one of the three in use where both sides are clearly identified with their ow
93. rmation of the original continuous signal allowing any wave to be reconstructed Relevant characteristics have to be satisfied when selecting an ADC for energy me tering purposes e The analog input bandwidth will define the frequency limit above which the signal is attenuated When measuring harmonics of higher orders they should not be cut by the ADC limitations A 50th order harmonic in 50Hz will require at least a 2 5 KHz bandwidth Moulin 2003 e The sampling frequency should be at least twice the desired bandwidth or the signal will suffer aliasing an effect for which higher frequencies cannot be correctly read and get a wrong digital equivalent sample Moulin 2003 e The LSB precision accuracy and the noise floor Known the voltage range under scope and the ADC resolution we have the precision which is TR Equation 4 where V input voltage range b bit resolution 20 This gives the value of the ideal resolution of the ADC in use A different value is given by the Dynamic Range or SNR of the signal and values are better read in dB In this manner with the quantization error ideally uniformly distributed be tween i and of the LSB in all quantization levels translated to dB the Signal to quantization noise ratio SQNR is SQNR 20logi9 2 6 02 b Equation 5 where SQNR Signal to quantization noise ratio b bit resolution Which is the same as to say that each bit of resolution contributes
94. rmonic index V n002 1Hz 10Hz 100Hz 1KHz 10KHz 100KHz 1MHz Figure 15 Optimal current low pass filter Bode diagram with cuttoff at 3 5kHz 48 ADE_GND 5 1k Where INP Neutral current positive differential input INN Neutral current negative differential input ADE GND ADE7880 GND Voltage level IAP amp IAN IBP amp IBN and ICP amp ICN have the same configuration Figure 16 Current input antialiasing filters schematic lt ADE_GND 2 2nF Ci3 C VN lt C ve C 1 ADE GND Where VN Neutral line Voltage input VCP Phase C Voltage input VAP and VBP voltage inputs have the same configuration as VCP Figure 17 Voltage input antialiasing filters schematic The ADE7880 ADCs have differential inputs that accept a maximum range of X0 5V to preserve the precision and accuracy specified in its documentation In 49 fact they support sporadic maximum differential voltages of 2V but anything above X0 5V cannot be accepted as an accurate measure Hence the CT or Rogowski Coil outputs should be translated to values in this range before its output is sourced to the ADE7880 current input pins And the voltage inputs require an external resistor placed in series and forming a voltage divider with the filter s resistor R14 or R17 in Figure 17 Voltage input antialiasing filters schematic calculated as follows R kQ 10 2V 5 1 10V R kQ amp 7V ms Where R resistance in kQ of the required input resi
95. rn Area N is the number of turns Lis the length of the winding Ho is the air permeability constant di t ES is the rate of change of the current through the loop Hall Effect devices the last listed method is not analysed in this document as it is not involved in this research 2 2 2 Direct voltage measurement method When directly measuring voltage levels it is necessary to construct an attenuation network of resistors in a voltage divider implementation to accommodate the volt age level to the required input and limit the current flow Although for security 19 reasons it is recommended to split the value of the inline resistor in a series of re sistors and calculate the related power dissipation 2 2 3 Evaluating voltage level signals In an ADC one or more input voltage levels who should be in between two input reference voltage values are translated in digital information This voltage level is compared in steps given by its resolution in bits its value digitized in a binary for mat and output as a discrete value of an instantaneous input A use may be applied to record individual instantaneous values which give a description of the element under scope Nyquist Shannon s sampling theorem Smith 1999 stablishes that all the sampling process maybe repeated at a sample rate at least twice faster than the maximum frequency of the signal under scope to obtain data samples enough forming a discrete signal with all the info
96. s 1V range making them suitable to be directly connected to the energy meter This project has tested a CT which outputs 1V at a maximum current of 30A directly connected with controlled maximum currents up to 3 Amps The Appendix 6 Optolsolators in the PCB design section shows the schematics of the required isolation circuitry as they are in the PCB which can work in any con dition testing or real with the only need of implementing the series resistor to the voltage lines input 4 3 Interfacing the Transients Independent ADC The transients appear whenever an event occur in the line they are of unbalanced nature and so they might occur on an individual line not affecting the other As a 3phase 4 wire always tries to reach a steady state these unbalances are always re flected over the neutral line For this reason one fast and sensitive ADC is sensing the neutral permanently A threshold level is set by software that whenever crossed sets a flag that will trigger an avalanche of measurements to evaluate the situation The ADE7880 ADCs can perform measurements at IMHz implementing internal registers to set threshold values to signal over currents and voltages in each phase Associated to the threshold level an interrupt is triggered when any phase drops below or grows more than the selected level Additionally voltage and current peak detection register hold the respective named values Although the interrupt signal can be used to
97. s direct hardware access in read or write functions These functions receive a pointer to the location of the transmission buffer and in case of a reading operation another pointer to the storage s location for the incoming data Around these functions a simple traffic control is built that follows the simplicity of Peter son s algorithm The turn is managed with a global variable as a flag that is set in 60 an atomic instruction and the inside control is given by an array as long as the num ber of channels 3 in this case that if the semaphore is obtained and its channel slot is free stores the application ID that obtained the semaphore into its channel slot In this manner the driver is re entrant and non blocking as other SPI hardware channels are allowed to write to their independent hardware registers while their slot is free More complex algorithms like Bakery algorithm Shankar 2013 are not implemented These middleware layer functions are made available to the AFE driver by means of function pointers and it is mandatory to initialize them before the driver is made available The diagram shown in Error No se encuentra el origen de la referen cia reveals the methodology implemented to maintain the driver unaware of the link to a dedicated SPI hardware driver The ADE7880 SPI handling occurs inside ade788 _spi_protocol c and has as main functions error List et ADE_SPI_read uinti16 t target register uint8 t reg
98. shows the resultant FFT in the same scope The test conditions are in all the cases the mentioned signals interfaced to the INP and NN AFE s input pins and the same signal to the VAP and VAN input pins to serve as the base signal for the DSP Nothing is connected to the phases input Console scopes show idx as the index of the of each set of measurements occur ring every 10ms followed by the seven measured values JN TOTAL as neutral line total current HX HY and HZ RMS as the RMS values of the three harmonics indexes and PA A Ph B and Ph C IRMS as the RMS current of the three phases these latest are not connected for this test as only current and harmonics over the neutral are required Oscilloscope scopes show the analog signal in probe no 1 in a yellow trace and its related FFT in magenta colour The test case shows the result of a measurement where the amplitudes of the fre quencies a b c and d are set to the same dimensionless value of 0 5 This evidences the necessity of amplitudes calibration by showing slightly different results again probably due to hardware limitations in this case in the lower frequencies range as 83 these present a slight attenuation The selected configuration simulates a total RMS current of 7 73 A where the 3 harmonic has a value of 0 55322 the 5 0 74390 and the seventh 0 75348 as seen in Figure 31 Currents when input of a b c and d frequencies amplitude is 0 5 i 2 7 732870
99. sk of shock An EMI test was 69 not executed as this is a standalone device for testing purposes and bypass capaci tors are placed regarding device manufacturer recommendations ADE 43 3V 16MHz T lt ADE 43 0 E RREEREEE 3 gessi ADE7880 Module Figure 24 AFE connections schematic Regarding the AFE connections a number of issues have to be addressed One has to account that the ADE7880 requires an external 16 384MHz crystal to set the clock of its DSP To save space and keep it and its load capacitors near this is placed in the bottom layer under the centre of the ADE7880 socket having in this manner a reduced path The power mode pins PMO and PM 1 are internally pulled and therefore when setting each one of them to a low state by an MCU IO pin current will be sank to ground for that reason it is recommended use and enable pins with pull down resistors although the current that ADE7880 IO draw is as low as 80nA This is not a problem with many modern MCUS such as RX63N that use tristate IO pins sinking out current to ground when low or sourcing it when high having additional pull up and down resistors This acquires relevance when booting up the energy meter since this pins have to be kept in high state during this process and before any communication can be established In case of a simultaneous boot up MCU has to grant that IO can be kept high or in high impedance state not sinking cur
100. ssing time 2 4 Evaluating harmonics A harmonic component of a fundamental frequency is another frequency that is an integer multiple of this latest Accordingly to this any European power line trans porting electricity at 50Hz of fundamental frequency will present harmonics at 100Hz 150Hz 200Hz and so on As a consequence of this the harmonics may be identified by their index that is the integer multiple of the fundamental ergo the 3 harmonic index of a fundamental of 50Hz refers to the 150Hz component They are clearly differentiated from transients or spikes as a wave x times shorter than the reference wave Harmonic analysis of the currents in power lines is the best method to measure the quality of the transported energy They give a description of the distortion of the fundamental frequency and in an ideal environment they are not present Hence in areal environment harmonics indicate the real state of a transmission line For this reason we can understand harmonics as a continuous source of valuable data about 25 the instantaneous real state of a power line Harmonic s effects on the power line are traduced as an increased RMS current needed to source any load and therefore producing losses dissipated as heat Another figure related to the harmonics is the Harmonic Distortion and the Total Harmonic Distortion The first gives the relative deviation of the signal respect the fundamental the second is the percentage of the har
101. stor V maximum instantaneous input voltage V input rms voltage In the testing environment they are unnecessary since the input signals are pro vided by SIMULINK and the amplitudes are a software variable Other I O of interest are the communication paths MOSI MISO clock signal SCLK and signal select SS the power mode PMO and PM1 interrupts HREADY and RESET pins all sourced to the MCU through the PMOD port Whenever this IC is measuring power lines requires isolation thus extra circuitry is required Since in this project there is already a 5V power supply that provide the system with energy the same is used and a dc to dc isolated regulator is placed to power the energy meter Additionally Texas Instruments ISO7240 high speed Iso lators are placed to protect the signal traces The required protection circuitry is not necessary when working with a testing en vironment The test signals are according to the ADE7880 ACD inputs in the range of 0 5V and absolutely harmless thus the energy meter receives the power form the YRDKRX63N PMOD port which outputs 5V and a common AMS1117 3 3V is used to convert the voltage level With the same the optoIsolators are not required 50 and not implemented in the testing prototype establishing a direct connection be tween the MCU and ADE7880 Regarding the current inputs in a real case most of the CT and Rogowski coil in the market work with low output voltages many inasmuch a
102. t detection and the reaction and it is vital to retrieve as much information as possible to determine the origin And further the more harmonic indexes under scope the better A property of a 3 Phase 4 Wire network is that every disturbance in any single phase will appear reflected in the neutral line This may be exploded to simplify the complexity of any sensing device by sensing the current and harmonics over the neutral line Additionally any ground fault low or high impedance generates tran sients These transients are spikes produced by the capacitance charge discharge produced whenever a line contacts a grounded object favouring the discharge of the line capacitance and charging whenever the contact is removed They can have a very high frequency and they have to be measured at a high sample rate Imrs 2006 and they will be used as the trigger event of the evaluation measurements The research establishes an accurate method to retrieve in the case where transients appear followed by asymmetric faults the mentioned information 12 fundamental rms current values of the 3 phases neutral line transients peak instantaneous current value Total current 3 5 and 7 harmonic currents over neutral line This information is fetched and made ready to evaluate in a time period lesser than 300us The model presented here includes an energy meter as DSP to interface the power lines although other approaches are rev
103. t of the MOSI has shifted in the MOSI line carries the overhead bytes con sisting of one byte with the type of operation read or write and two bytes with the target register address The next scope shows this sequence where Do in red is the Channel Select line which enables the slave device the AFE SPI transmission and is active low Above this D shows the SPI transmission clock set to 2MHz where from each bit can be counted in each byte D2 is the MOSI line and Dsis the MISO 74 D D DT DO TQ DU IM wv Figure 27 Single SPI reading scope by DSOX2012A D The transmission endianness is MSB first one may read the transmission starting from left to the right as a human reads a number As the transmission starts by CS shifting from high lo low followed by the SCLK signal and the first MOSI byte we start analysing the MOSI line D A look to Di the SCLK signal one may count the 7 bytes easily thanks to the delay introduced between each byte The master sets data on the MOSI line starting with the first high to low transition of SCLK and the SPI of the ADE7880 samples data on the low to high transitions of SCLK The first byte in D from the left to the right after CS goes from high to low indicates the operation type bit 0 which is a 1 means a read operation as the datasheet specifies 1 for read operations and O for writing The total bit sequence is 01110001
104. this task precision accuracy and speed because if one has to interface external dedicated ADCs the cost raises been higher that a single energy meter When the MCU is selected the required front end circuitry has to be de signed accordingly The development process may be longer since more mathemat ical calculations are involved having a higher risk of error and buggy code Regarding to the processing time most of the actual MCU come with an integrated DSP and public software libraries which will speed up the process otherwise one may implement the analysis based in the theory presented in chapter 2 3 of this research At this point using an FFT library which they usually implement an op timized version of the known algorithms like Cooley and Turkey s algorithm one is still limited by the number of points in the transform which is of the power of two number that defines the number indexes and the frequencies under scope may lay in these indexes The other approach whenever only a few values and not a full FFT set of magnitudes is needed and or a frequency other than the harmonics is involved is to find suitable sampling frequency decide the indexes number one may construct a set of constant cosine lookup tables only the real part is needed 87 and by means of a timer triggering an interrupt at this given fundamental frequency keep track of the index that whenever it matches an index multiple of a frequency under scope
105. tialized and before the SPI hard ware is made available to it the ADE SPI xxxx callback set functions have to be called in the ADE7880 SPI middleware layer void R ADE ADE7880 driverCallbacks void ADE_SPI_WRITE_callback_set amp R_ADE_SPI_Write ADE_SPI_READ_callback_set amp R_ADE_SPI_Read At this point ADE_SPI_read the driver s internal SPI read function uses ADE SPI READ CALLBACK to communicate with the SPI hardware that its memory address targets R_ADE_SPI_Read that will execute and follow the five mentioned steps to achieve SPI hardware access 4 4 4 RTU communications UART control The driver built on top of the UART hardware registers allows bidirectional buff ered byte transfer at 115200sps Interrupts are triggered when the transmission reg ister is empty placing buffered data into it and when the reception buffer is full for retrieving the incoming byte though there is no use for this latest at the moment Any data sent to the driver is treated as a byte stream one may use it to transmit ASCII characters to display in a terminal screen or a binary transmission sent byte after byte As the measured values are real numbers the use of floating point vari ables is extensive to allocate them and their ASCII representation and transmission may represent a challenge and inefficient communications For that reason the data 62 which is meant to be received and interpreted by MATLAB sof
106. trieved from METERING INTERNATIONAL issue 3 2003 WWw metering com Renesas Electronics 2014 RX63N Group User s Hardwar Manual Rev 1 80 Retrieved from RENESAS 32 Bit MCU RX Family RX600 series RENESAS n d RX DSP Library version 3 0 CCRX for High performance Embedded Workshop Application note ROIAN1SOOESO100 Rev 1 00 92 Smith S W 1999 The scientist and enginee s guide to Digital Signal Processing California California Technical Publishing ToolsPractice M E 2010 IoT amp Embedded Software Development Retrieved from What languages do you use to develop software http blog vdcresearch com embedded_sw 2010 09 what languages do you use to develop software html William Koon Analog Devices Inc 2001 04 12 Current sensing for energy metering Retrieved from analog com media http www analog com media en technical documentation technical articles 161745061556071IC Paper pdf Yarborough B 2012 01 06 Components and Methods for Current Measurement Retrieved from Power Electronics http powerelectronics com power electronics systems components and methods current measurement 93 APPENDICES Appendix 1 Code structure and naming convention gt Hardware Debug 4 zy r adc 12b p r adc 12b c45 16 11 14 23 11 e1100620 p r adc 12b h 46 17 11 14 22 43 e1100620 4 zy r ade7880 4 zy src 4 zy ade7880 i ade7880 configuration h 52 28 04 15 21 13 e1100620 ade7880 re
107. tware is sent as floating point of 32bit resolution in binary format four bytes of binary data To obtain a byte division a new variable is defined as the union of a float member and a string of 4 bytes giving the flexibility to manipulate the data as a float and send it to the UART buffer as a string Otherwise data transmitted to a terminal screen is initially formatted and buffered to a string by means of sprint C library func tion and the resultant formatted string is thrown to the UART buffer The transmission buffer is initially set to 4092 bytes this does not represent a prob lem for its allocation and can be safely increased as the MCU has up to 128KB of RAM memory and the code itself uses only 22KB The buffer is calculated and big enough to handle all the possible incoming data As the code inserts no delay be tween an event and the next while expecting the situation to be handled at any mo ment data is continuously gathered and placed to the transmissions buffer in se quences of 10ms during 100ms Data transmitted to MATLAB consist of at an estimated amount of 7 different float values the three phases plus neutral currents and three harmonic currents indexes of 4 bytes each plus a delimiter character mak ing a total of 35 bytes while each data string transmitted to a terminal program have an average of 25 bytes times 7 making 175 bytes per event having 11 events per sequence of 100ms plus the formatting strings that a
108. ty Due to the high cost of a switch gear whose life is reduced every time it trips and the possible economical repercussion to the affected area the false trips have to be avoided Although the timeframe to trigger a counter action has to be granted as short as microseconds in the case of a low impedance fault the gathered specific amount information is a valuable tool to provide the correct reaction A high im pedance fault allows more relaxed time of reaction and in many cases can be toler ated by the network but damages may occur if the normality is not restored An important part of this information is given by the harmonics over the power lines it is essential not only to measure the quality of the power harmonics can be analysed for a wide range of reasons like to avoid damages to power systems due to the overheating produced by the rise of the apparent power or to help to determine the origin of a fault This latest is the area that drove to the case of study in this paper Although a high impedance is initially assumed and a timeframe of 150ms 14 is given it is worth to consider lower impedance faults with a reduced reaction time interval 2 1 Three Phase four Wire system A system where the three phases have their independent lines and an additional neutral or returning line is known as three phase four wire system It is a common method in distributed electric power networks Is characterized for having three electric
109. with the ADE7880 previously soldered to a 0 5mm Pitch 40 Pin 20x2 QFP QFN to DIP adapter that takes the most of the space but provides flexibility easing the task of replacing an energy meter This socket is pin to pin compatible with other energy meters ADE7854 ADE7858 ADE7868 and ADE7878 from the same manufacturer 73 5 ANALYSIS AND RESULTS Measuring the effectiveness of the implementation is achieved by several processes The goal is to measure the SPI speed and signal quality the single measure time the grouped measured time and the total window frame time from the event is trig gered to the moment the last byte of information is placed in the output UART register buffer The testing environment generated wave is seen as well 5 1 ADE7880 driver and UART driver performance The SPI transmission is seen with the help of the digital analyser of a DSOX2012A oscilloscope where the speed of a single transmission only one register reading from the AFE and a group of them seven registers in total which are the total current three harmonics and three phases current are shown A single register read ing always involve three bytes of overhead and two or four bytes of payload de pending on the targeted register Measurements are stored in four bytes registers so a single SPI transmission always requires 7 bytes The payload is always what the slave device places in the MISO line in this case in the next clock cycle after the last bi

VAASAN AMMATTIKORKEAKOULU

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