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ENG460 ENGINEERING THESIS FINAL REPORT

1. Volts V Figure 33 IV curve of BZX79C6V8 diode Figure 33 displays the IV curve of a BZX79C6V8 reverse biased diode The BZX79C6V8 behaves like an ordinary forward biased diode and conducts at approximately 0 7V when it is made to work in the forward region However it is designed to specifically to operate in the reverse region and is always installed reversed The Zener diode starts conducting when its breakdown voltage is met and it can be seen that the BZX79C6V8 diode is breaking down at 6 8V as displayed by the IV curve When the breakdown voltage is met the Zener diode limits the voltage of the circuit Therefore a Zener diode is used to reduce voltages and is often employed for voltage regulation 7 55 Compilation of IV curves of individual diodes IV characteristics of individual diodes 100 90 ml BZX79C2V7 80 E BZX85C3V9 1N4148 ds BZ X79C3VO zg ep 0 82X79C3V3 A 50 la BZXBSCAV3 E 40 BZX85C5V1 BZX79C6V8 m 1N4002 20 BZX85C6V2 10 BZX79C8V2 o BZX79C7V5S o 1 2 3 4 5 6 7 8 9 Orange LED Volts V Figure 34 IV characteristics of individual diodes Figure 34 displays the IV curves of 13 diodes that were being used to configure the eight strings located in the PV simulator It can be observed that for all the diodes tested the applied voltage is limited when it reaches the rated forward or reverse breakdown voltage of
2. Figure 7 Circuitry depicting first contribution to 2 5 2 Second Contribution to I Figure 8 explains the second contribution to This contribution is the current that goes across the diode strings The circuit below is separated into five parts 1 The input V is the input voltage of the DUT Prior to this stage the actual voltage that is coming from the DUT would have already been through Voltage divider amp filter Therefore V is just the signal that is in proportional to the actual 20 2 Vis reduced using voltage divider rule and its polarity inverted to produce V3 The equation of this operation is shown below R4 VS B34 RA xV V3 4 3 V3 is fed into the positive terminal of an operational amplifier This operation does not introduce any gain or inversion and it is believed that buffering occurs at this stage Therefore the input and output are equal V3 V4 5 4 V4 is fed into the negative terminal of an operational amplifier with an electronically controlled gain The resistance R6 consists of a fixed resistor in series with a potentiometer that can be adjusted by the user via Labview The adjustment controls the gain of the output of the operational amplifier and with that the voltage across the diode strings V5 The equation depicting this operation is displayed below V5 a R6 VD 6 X Rs 6 5 Rearranging and expanding of the above equation would display the relations
3. RESLab 2005 17 Daystar Inc DS 100C I V CURVE TRACER User Manual New Mexico s n 2006 18 Comparison of electrical characteristics of silicon solar cells L A Dobrzanski L Wosinska B Dolzanska A Drygala 1 2 Poland Silesian University of Technology 2006 Vol 18 19 Calais Martina Report on Visit on 06 10 03 at the PV laboratory at the Hochschule fuer Technik und Architektur Burgdorf as part of the RESLab PV Simulator project 2003 20 Hewes John Diodes Online The Electronics Club 2011 Cited 12 October 2011 http www kpsec freeuk com components diode htm 21 ANALOG DEVICES AD826 High Speed Low Power Dual Operational Amplifier Datasheet Catalog Online Cited 1 November 2011 http www datasheetcatalog org datasheet analogdevices AD826AR pdf 22 Bhawani Amit What is EEPROM Online 15 June 2009 Cited 15 November 2011 http www amitbhawani com blog eeprom memory 77
4. Define Parameters must then be selected to confirm the parameters TUNE MODE In this mode the current sources are ramped up to follow the set current selected for the IV curve However at this stage the DUT contractors remain open This is to allow for the display of Vin Voltage input from DC generator and V Voltage output of PV array Simulator in the Labview programme Vin and V has a 50V difference due to the voltage drop across the current sources Therefore the Vin must be adjusted to be 50V larger The desired Vout can then be adjusted under Tuning Parameters by adjusting the R option and selecting SAVE in Labview The correct Vout will be displayed only after SAVE is selected RUN MODE When this mode is selected the DUT is connected and an operating voltage is fed into the simulator The current sources are ramped up as well to the selected current setting This puts the PV simulator into operation If any adjustments are required the user can select STOP and move on to either DEFINE or TUNE to make changes 33 3 2 Producing And Recording of IV curves The completed setup that was achieved and concurrently used for the tests is reflected in Figure 16 AC power is required to run the simulator s components and must be connected prior to the test The Labview programme PVSimulator v7 needs to be running prior to any inputs from the DC generator The Field Power Supply connected to the generator is used for
5. the adjusting of DC voltage DC Generator Set Power Connection Communication Connection mu PV Array Simulator Field Power Supply Labview Interface sj HVout IV Curve Tracer Figure 16 Physical connection during the setup 34 Before running the DC generator it must be ensured that the Field Power Supply is adjusted to 0 The required DC output voltage should only be increased after it is running It must be noted that the current limit of the Field Power Supply needs to be adjusted to allow for the unrestricted supply In addition the user has to take into account the 50V voltage drop across the current blocks This means that if the user wants to achieve an open circuit voltage Voc of 100V the DC output voltage Vdc would have to be adjusted to 150V Although there is no danger if this is not followed an insufficient voltage drop would produce an incorrect output of the PV array simulator On the other hand it must be ensured that the user keeps the voltage below the simulator s rating 750V 1 3 Operating the simulator is straightforward with the full set up in place the user selects the number of current sources which are physically located at the top right corner of the machine The current sources are arranged in parallel and have output currents of 4A each Three of the CSBs located in the simulator are shown in Figure 17 In the simulator there are ten CSBs connected in parallel E
6. 19 43 A A ee Saree A e ioe Loe 7 0 00 100 00 200 00 300 00 400 00 500 00 600 00 700 00 800 00 Spannung V Figure 23 IV curve of Test 2 f u kW P 452 00 480 00 500 00 520 00 540 00 560 00 577 89 Spannung V Figure 24 Zoom ins of current ripple E ir gt E t Se RITO NT FASE if 612 44 615 00 617 50 620 00 622 50 625 00 627 50 630 00 634 23 Spannung V Figure 25 Zoom ins of power ripple 44 v n s 1 v Mj 1 v n 1 Chapter Four Analysis of the IV curve production In electronics a diode acts like pressured flow valve in an electrical cable The general usage is to create a blockage and only allows current to pass through if it reaches the diode s conducting voltage Diodes are utilised in many electronic circuits and are often used for protection or regulation in a circuit For a diode to conduct the magnitude of the voltage applied must be high enough to collapse the depletion region of the diode A typical silicon diode conducts at approximately 0 7V while forward biased and allows current to pass through in the circuit If a reverse voltage is applied onto the diode it does not conduct and creates a blockage All diodes have a reverse voltage threshold which is of considerable magnitude generally 50V and above However if the applied voltage goes beyond the breakdown voltage of the diode a breakdown would occur Since the diode is not designed to work in that
7. 2 and terminal 1 at Figure 40 Value of resistance was obtained from the PV Simulator Technical Manual In accordance to Figure 40 connect the output from the diode strings to terminal 2 Connect terminal 3 to the negative terminal of the power source Connect a 15V DC power supply to terminal 4 and terminal 8 Toggle DC power supply connected to diode strings Measure output voltage by connecting DMM to terminal 1 and terminal 3 69 Appendix B Measurement of Voltage and Current across the diode strings PCB Aims and Objectives To measure the voltage and current of the diode string PCB while the simulator is in operation Equipment 2 X UT803 high precision DMM Leads Diode string PCB PV Array Simulator Set up Figure 42 Ammeter connection leads 70 Procedure A modification would have to be done before hand to the diode string PCB Firstly the connection at each diode string has to be broken This is done by slitting the PCB board as seen in Figure 42 It will then be possible to connect an ammeter in series This is done for all the diode strings Two leads for a voltmeter would also be needed and they are soldered between the two ends of the diode strings This connection can be observed in Figure 41 The steps are as follows Replace the original diode string PCB in the PV Array Simulator with the modified PCB Operate the simulator as per normal Do not fiddle with the internal components with the sim
8. FAIRCHILD SEMICONDUCTOR BZX79C 3V3 33 Series Half Watt Zeners Data Sheet Catalog Online Cited 6 October 2011 http www datasheetcatalog org datasheets 37 114302_DS pdf 8 VISHAY BZX85 Series BZX85 Datasheet Vishay Siliconix Online 31 May 2007 Cited 6 October 2011 http www soiseek com VISHAY BZX85 index htm 9 Orange LED 3mm 5000mcd ALAN S ELECTRONIC PROJECTS Online Cited 6 October 2011 http alan parekh vstore ca orange 5000mcd p 75 html 10 NXP Semiconductors 1N4148 1N4448 High speed diodes DISCRETE SEMICONDUCTORS Online 10 August 2004 Cited 6 October 2011 http www nxp com documents data_sheet 1N4148_1N4448 pdf 11 Philips Semiconductors 1N4001G TO 1N4007G DISCRETE SEMICONDUCTORS Online 24 May 1996 Cited 6 October 2011 http www datasheetcatalog org datasheet philips 1N4005 pdf 12 Popadic M Lorito G and Nanver L K Analytical Model of l V Characteristics of Arbitrariliy Shallow p n Junctions s l IEEE Electron Devices Society 2008 IEEE 13 Rozenblat Lazar HOW AN ELECTRIC GENERATOR WORKS Online 2008 Cited 25 August 2011 http www generatorguide net howgeneratorworks html 14 Wolfe Joe Electric motors and generators PHYSCLIPS Online Cited 25 August 2011 http www animations physics unsw edu au jw electricmotors html 15 Ruscoe Andrew DC Genset Operating Instructions s l RESLab 2006 76 16 DC Genset Maintenance Instructions s l
9. Ted BackgroUNd redadas nia a traia ss 3 1 1 1 Initiative of the PV Array Simulator ooooooccnnccccononononnnnonnnanonononnnnnonnnanononnnnnnnnnonanononnss 3 1 1 2 The 25kW PV Array Simulator reen a a R EAE a EA EEE 3 ASA NKA AEE E E E E E inn 4 1 2 1 Fundamentals of the solar cell ssssssssssssssssssrsssrsssrsssrrssesssessserssesssesssesssessseesseessees 4 1 2 2 How the PV array simulator simulates a PV array ccccconocoonnnnnnononanonannnnnnnnnananenanoss 5 LODO Vii ee ee ee eee ee 6 Chapter Two Familiarisation with PV array Simulator coconcocccccncnocanononnnnnnnononnnonannnnonnnnnnann conos 8 2 1 CUECA A a 9 2 1 1 Current Source blocks CSB zasne o ai 9 2 1 2 1Q 50 SB Current Source Circuits osee seca o a sedate ceases ete de pelas telde 9 2 11 23 ESB Control CI CUIt 2 se civsls axes save vans od cxgues AA Rienda 10 2 2 Main Controls is 10 2 2 1 Voltage divider amp filte arrinin a a a a aa 12 2 2 2 Op amp digital Hotsen esinin iaeia a ea aa i a a a a aa ai kiia 12 2 2 32 Array Short Circuit CUMPENK ieena a e sed aes aa EA ansia dd 12 2 2 4 Diode OEM a N a aaa 12 2 3 Supervisory Operational Control cccononocooccnnnnnnanononanonononocananononnnoncnnonnnnrnnnnnnnnanonnnns 14 2 3 1 Labview Control Software oo ceecccssscceesseceesceceecceceeneeesaeceeaaeceeaaeseaeeesaaeceeaaeseeaeeenaees 14 2 3 2 Field Point Un Soi a A ta 14 2 4 Diode Strings PCB ies dieses ted Bei a As e
10. and the temperature test respectively Both tests are explained and discussed in the paragraphs below 3 3 1 Time Drift Test This test was initiated for two purposes One was to find out if the simulator had a warm up period and if there was a need to run the machine for a certain duration before it could produce an accurate output The other purpose was to observe if the simulator would produce consistent results over a time period a few hours and if there was a time limit in which the simulator could be left running before irregularities occur The 8 curves were observed and captured every 10 minutes with 10 tests performed Once they were obtained Microsoft Excel was used to arrange the curves for comparison It was realised that running the machine over a prolonged period did not affect the output of the curves In addition the simulator did not require a warm up period as well with the first curve identical to the rest of the curves Figure 21 showing Curve 3 displays the 10 curves It can be inferred that the outputs were identical and each curve was overlapping the other An electronic copy of the data collected for the Time Drift Test is available in Appendix E I V Curve Comparison for Curve 4 45 Curve 3 2 35 E y A 3 4 3 fos amp E 2f 5 lt i A K 6 iE 7 0 5 0 t 1 t J 0 20 40 60 80 100 120 9 Vol
11. in this test was not imperative because there was now a strong basis of the maximum operating voltage of the control The test procedure is discussed in detail in Appendix A 48 4 1 2 Measurement of Voltage and Current across the diode strings PCB The previous test Section 4 1 1 did not present an output However it was learnt that the operating voltage range would not be higher than 11V due to the contrains presented by the operational amplifier and the 11V Zener diode Continuing on with the study another test was devised to realise the actual voltage and current that was applied passed through the PCB during the curve production Only then would there be a closure as how the PCB is working with the control system of the simulator For this test the connection was broken by slitting the wiring lining on the PCB This was done for all the strings This provided an open circuit where two leads for an ammeter was soldered in The ammeter would be used to measure the current passing through the strings during the curve production In addition to monitor the voltage across the string two leads was soldered over the two points as illustrated in Figure 28 Figure 28 Circuit of diode strings in the test 49 The simulator was powered up and the IV curve tracer was used to generate a waveform As the IV curve tracer sets the operational voltage across the string of diodes an observation was made on the voltmeter and ammeter
12. the V knob on the left of the field power supply The A knob or the current control was increased to allow for the appropriate amount of voltage to be fed to the simulator As the voltage is being increased the PV Simulator input DC genset output panel was observed for the desired DC voltage input from the DC genset The PV Array Simulator has a 50V drop across its current sources Therefore if 100V is required from the simulator output 150V must be fed into the simulator s input via the DC genset 15 To turn off the DC generator the field supply is reduced to O by turning the V knob anti clockwise and switching the supply off This brings the DC genset s voltage down to 4V To stop the motor the red stop button Figure 11 is pressed The motor takes a few minutes before coming to a complete halt 15 2 6 2 Maintenance The DC genset must be maintained so that top performance as well as a longer lifespan can be achieved Currently maintenance is being conducted by staff of the School of Engineering amp Energy on an annual basis As part of the project requirements maintenance was conducted under the supervision of Wayne Clarke and documented in the below sections The steps taken were in accordance to the DC Genset Maintenance Instructions located on the RISE network The three main components of the maintenance are 16 Checking of the DC genset air filter Lubrication of the DC generator a
13. the diode It can be seen that the each curve portrays an inverted PV array IV curve It was also clear that each diode had a specific characteristic which meant that curves of different fill factors can be generated 56 4 2 2 Diode Strings It was observed from the test of individual diodes that each curve provided a specific set of IV characteristics To continue the study another test was conducted to observe how diodes behave when they are placed in series After analysing the diode strings it was realised that the total voltage drop across the diodes in all of the strings was larger than the input voltage of 10V more information regarding the voltage drops of the diode strings are included in Section 2 4 1 Diodes require the applied voltage to be higher than the forward or reverse breakdown voltages to allow current flow Therefore in theory if that voltage was not met the current would not be able to pass through This led to the consideration that the diode strings were operating low currents close to the knee of their IV curves Due to the fact that the diode strings had a larger voltage drop than the input voltage of 10V the test current did not reach 10014 which was achieved earlier in the individual diode test Therefore the resistance was adjusted to allow for the highest possible current range possible for this test Figure 35 demonstrates a test being conducted to observe the IV curve on String 7 To adjust
14. upgrade would contribute significantly to DUTs such as inverters and MPPT charge controllers that are being analysed 66 Conclusion This thesis has successfully accomplished the objectives that were initiated by Murdoch University supervisor Associate Professor Graeme Cole as well as co supervisor Doctor Martina Calais The three main objectives tasked were The familiarization of the PV Array Simulator and its control options in terms of its I V curves produced Operation of the PV Array Simulator and the comparison of test results under different test conditions Further analysis of the IV curve production of the PV Array Simulator For the first objective a thorough explanation is included in the thesis describing the involved components as well as their operating functions in the PV Array Simulator The information was derived from the PV Simulator Technical Manual 1 which was written by Andrew Ruscoe It was also learnt that the simulator was designed to operate like an actual PV array The Main Control which is a subsidiary of the System Control was programmed to mimic the single diode model on which the PV array is implemented In addition functions of the Main Control were presented mathematically which further explained how the IV curve was generated A successful set up and operation of the simulator was achieved during the course of the project In addition measurements of the eight different IV curve options w
15. 4 2 6 1 Operating the DC genset The DC genset is capable of producing up to 800VDC and utmost precaution must be taken while working on it As a rule of thumb no connections should be made while the DC genset is running Within the DC genset panel in the engine room there are four series pairs of 9200uF SOOVDC capacitors Although they discharge rapidly through the genset windings a fault might cause large amounts of voltages to remain Therefore due care must be taken while replacing or maintaining them One way of reducing a shock hazard would be to measure the voltage between the capacitors before any work is done An emergency stop switch is also located at the top of the AC circuit breaker on the DC genset panel 15 To vary the DC genset output a field power supply is needed The field power supply is located on the right hand side of the simulator and is marked DC Genset Field Supply Before any connection is made the field power supply switch has to be in the OFF position and the voltage and current knob are turned completely anti clockwise fully reduced Refer to Figure 9 15 DC GENSET FIELD SUPPLY PS 0014 Figure 9 The Field Power Supply Left and the DC GENSET FIELD SUPPLY output Right 25 The PV Array Simulator must then be connected to the DC genset s output in the PV Simulator INPUT DC GENSET OUTPUT panel which is located above the DC GENSET FIELD SUPPLY output This is d
16. 40 60 80 100 120 0 20 40 60 80 100 120 Volts V Volts V IV curve of Curve 5 IV curve of Curve 6 IV curve of Curve 7 40 60 80 100 120 Volts V 0 5 0 5 0 20 IV curve of Curve 8 40 60 80 100 120 Volts V Figure 20 IV curves acquired from the PV simulator 38 3 2 2 Classification of the IV curve options to various cell technologies As the simulator is used for the testing of applications associated with PV modules research was done to attain further information on the cell technology that is being replicated The table below gives an approximate classification on the fill factors of each cell technology Using this material the curves were sorted according to their fill factors This gives the user additional information when interpreting the results of the test 18 Table 5 Classification of the IV curve options to various cell technologies Cell Technology Fill Factor Curve No Monocrystalline silicon solar cell 83 86 1 2 7 Polycrystalline silicon solar cell 87 89 3 5 Amorphous silicon solar cell 63 66 4 6 8 39 3 3 Investigation of repeatability of tests under different conditions As it was not certain how stable the simulator was in terms of its operational stability the simulator was tested under conditions that might affect its performance There were namely two different tests that were suggested by Andrew during his visit to RISE the time drift test
17. 9 Figure 29 IV curve with broken cONNectiON occccccconononocnnononnnnnnnonncnnnncnnnnnnnnnnnnnnnnnnnnnnnonnnnnnnnos 50 Figure 30 Connection for the forward biased diode occccconononooncnnononanonanncncnncnnnnnnnannnncnnnos 52 Figure 31 Connection for the reverse biased diode oo cccccccononooooncnnonnnanonannnncnncnnnnnnanonononnnos 52 Figure 32 IV curve Of 1N4148 diode ccccoconococonononoconononnnnnononnnnnnnnnnoncnnnnnonnnnnononnnnnnnnnannnonnnnnnnos 54 Figure 33 IV curve of BZX79C6V8 diode ccoconococcccnococonononooncnnoncnnnnnrnnoncnncononannnonononnnnnnnnnnnnnonnnnnos 55 Figure 34 IV characteristics of individual diodes ococoooocccncncnanononoannnnonnnanononnnncnncnnnnannnnnnnnnnnos 56 Figure 35 Experimental setup for diode StriNgS coconcooooccncnonanononnnnnnncnnnnnononnnncnnnnnnanonannnnnnnnos 57 Figure 36 IV curves of diode StriNgS cccoconocococnnnnoconononannnononnnnnanenonnnnncononnnnnononnnnnnnnnnnnnnnonnnnnos 58 Figure 37 Calculated IV curve of the diode strings cc cccccccsssesessececececesseseaeseeeessessestsaeeeeess 61 Figure 38 Physical test And SPICE simulation of 1N4148 diode ccccccnnonooocncnnonnnanonannnnnonons 62 vii Figure 39 Physical test And SPICE simulation of BZX79C6V8 diode ccconococoonccncnocanonaonnnnnnons 63 Figure 40 Connection diagram of the AD826 amp set up cirCUit oooooocccccncconononaoncnnonnnannnanononnnos 68 Figu
18. B FPU Field Point Unit LIMIT This would appear as the current output is limited during a fault due to an excessive voltage drop over the CSB LTspice Design simulation tools for electrical circuits MPPT Maximum power point tracking PV Photovoltaic RESLab Renewable Energy Systems Test Centre Symbols HV y The DC input voltage to the PV array simulator This voltage is supplied from the DC genset HVoyr The DC output voltage of the PV array simulator This voltage supplies the DUT Ip Current across the diode Ipn Current derived from solar radiance Isc The short circuit current of the IV curve that is simulated by the PV array simulator Vescs The current source control signal This is the signal that is fed through the CSBs Voc The open circuit voltage of the IV curve that is simulated by the PV array simulator Chapter One Introduction This project studies the capability of a PV array simulator that was developed by Prof Haberlin and his staff at the Berne University of Applied Sciences in Burgdorf Switzerland The simulator has a power rating of 25kW an open circuit voltage of up to 750V as well as a short circuit current of up to 40A In addition there are eight different IV curve options with different fill factors available for selection The development of the simulator was initiated for the testings of PV applications such as inverters or MPPT charge controllers T
19. ENG460 ENGINEERING THESIS FINAL REPORT PV Array Simulator Performance Evaluation Joshua Yong Ern CHAN 2011 A report submitted to the School of Engineering and Energy Murdoch University in partial fulfilment of the requirements for the degree of Bachelor of Engineering D A wy Murdoch UNIVERSITY Declaration declare that this thesis is my own account of research and contains as its main content work which has not previously been submitted for a degree at any tertiary institution Joshua Chan 18 11 2011 Academic Supervisor endorsement pro forma This is to be signed by your academic supervisor and attached to each report submitted for the thesis am satisfied with the progress of this thesis project and that the attached report is an accurate reflection of the work undertaken Signed Date Abstract This dissertation evaluates the performance of a 25kW PV Array Simulator based on a design from Prof Heinrich Haberlin and his staff from the PV laboratory of the Berne University of Applied Sciences in Burgdorf Switzerland The simulator was set up and is operated by ResLab based at Murdoch University The device has a power rating of 25kW an open circuit voltage of up to 750V and a short circuit current of up to 40A The design and concept of the simulator replicates the operations of an actual PV array Incorporated in its controls are eight IV curves of different fill factors that wer
20. ach of them has ten current source circuits IQ750s connected in series a9 3 lies Sa ci cany ODE a a Fei Eai a ai ai rece ws y AN A A ho Ga We dl d r a mos s E Figure 17 Current Source Blocks 35 Once this has been done the user sets the correct number of CSBs selects the curve as well as the short circuit current Isc in DEFINE mode of the Labview programme The Labview user interface is shown in Figure 18 As the output from the DC generator V would initially be equal to the simulator input Vout without any adjustments the desired open circuit voltage Voc Vou must be fine tuned by adjusting the Rvoc while in TUNE mode These operations are documented in detail in Section 3 1 Research Institute for Sustainable Energy Figure 18 Labview user interface In order to capture the curves a DUT was needed to set the voltage ranges to be applied across the diode strings In this test an IV curve tracer was utilised and connected at the output of the simulator A dedicated software comes with the tracer and operating instructions were obtained from the DS 100C I V CURVE TRACER User Manual 17 The IV curve tracer obtains the curve by receiving the output from the PV simulator HVoyr and varying the impedance of the output from zero to infinity which is done by connecting it to a capacitor As the capacitor charges the operating range of the simulator s out
21. ally located at the bottom of the PV array simulator For the FPUs to interact with the dedicated computer through Labview it must be connected via a communication cable The FPUs include a communication module as well as six other analog and digital modules Details of their functions are stated in the table below 5 14 Table 1 Field Point Units and their functions 1 FPU No Functions FPO Communication module FP1 amp FP2 Monitors the heatsink temperature of the CSBs as well as the temperature inside the cabinet of the PV simulator The corresponding temperatures are displayed under Temperatures in the Labview programme FP3 amp FP4 Monitors the CSB control circuit and detects any FAULT or LIMIT The shutdown and diode selection status are being sensed as well A status display is made available in the Labview programme for each CSB FP5 Monitors the simulator s output current as well as its input and output voltage These are respectively displayed as Tout Vin and Vout on the Labview interface FP6 Allows the user to select the IV curve output of the PV simulator via the Labview programme The user has to toggle the Rygc which would then adjust the gain to produce Voc This Field Point Unit controls the state of the simulator as well eg Run Tune Stop 15 2 4 Diode Strings PCB The diode strings which are used for the IV curve production are situated on a PCB Looking at Figur
22. amps an accurate representation of the curve through a physical test was not feasible The calculation in Excel can be obtained from Appendix E 61 4 4 Duplicating physical tests in LTspice 4 4 1 Single diode test Simulation software LTspice was also utilised as an additional method to observe the IV characteristics of the diodes Results led to the understanding on how diodes operate and also served as a testing platform before any of the physical tests were conducted The figures below compare curves attained in the simulation software against the results of the physical tests Physical test And SPICE simulation of 1N4148 SPICE T 3 wa a 1 Physical test 0 1 0 2 0 3 Volts V Figure 38 Physical test And SPICE simulation of 1N4148 diode Figure 38 compares the physical and simulated results of the IV curve attained from a forward biased 1N4148 diode There is a very slight variance between the two results with a 0 05V difference between the two conduction voltage LTspice functions by drawing information on the parameters of the diode and simulating the IV curve As there was only 0 1uA difference between the two curves SPICE and Physical test it can be inferred that the 1N4148 model created by LTspice is reasonably accurate Screenshots of LTspice can be obtained from Appendix D 62 Physical test And SPICE simulation of BZX79C6V8 SPICE T 2 uv e lt Physical te
23. and the principle of operation In addition the Labview control software would also be discussed The university also arranged for Andrew Ruscoe who was involved with the development of the RESLab simulator to conduct a brief introductory session on the operation of the PV simulator The aim of this session was to demonstrate the principle of operation of the simulator as well as the basic functions of the simulator Clear documentation of the findings for the future use of students and academic staff Objective 2 Operation of the PV Array Simulator and Comparison of results under different test conditions With theoretical knowledge gained from the familiarization the next objective was to learn how to operate the PV simulator within the safety ratings acquired from the technical manuals This includes the generation and recording of IV curves An evaluation of the operation under different test conditions on the array Selection of different options of measurement after consultation with the supervisor The simulator requires power input from a DC genset that is connected to a field power supply The study covers the familiarization and includes the documenting of the maintenance procedure of the power generating device Additional equipment involves the IV curve tracer which is utilised to set the IV curves Likewise a familiarization must be conducted prior to the use of the IV curve tracer Classification of the IV curves produced by t
24. as proven through these tests as well as documentations from past tests that the simulator was very stable even when it was made to operate at its threshold limit As the varying fill factors were obtained by the different configuration of diode strings a study was focused on developing a basis or pattern associated with the formation of different classifications of diodes in series The diode strings found in the simulator were replicated and reverse engineered Acknowledgements would like to sincerely acknowledge and thank the following Murdoch staff Associate Professor Graeme R Cole my supervisor for his continuous guidance and inspiration Dr Martina Calais my associate supervisor for her constructive feedback and assistance Andrew Ruscoe who took the time to help me with the familiarization of the simulator Will Stirling and Jeff Laava for the constant technical support And my family and friends who have supported and encouraged me throughout my degree Contents Declaration A aiii i Academic Supervisor endorsement pro forMa ccccononoooonconnnononononnnnnnncnnonannnnnonnnnnnnonannonnnnnnnnnnnnnnnos ii ADS bid AA A A A A ada ii A AS suveahasedeedeveadevuae codaededs qu duatuchaaetessdu evathles iaaa iv LiStOf FIGULES a Ate ds din cd Ad hee ls ole Leia DA ds A li taal Ad vii Listo Tes ir cates viii ACTO MS cr A A A A A e A A A E ix SYVIMBOINS 250 Ach Secale dr ds de MA de co Lo A de rd ix Chapter One Introducido 1
25. atical operation subtracting of I y can take place to generate an IV curve 1 2 2 4 Diode string MUX There are 8 diode strings available for selection in the Labview interface Each string produces an IV curve of a certain fill factor In the Tune mode of the software programme when the user selects a diode string a multiplexer is employed to connect the desired diode string anode The cathodes of the diodes are common 1 12 In addition a 1N962 Zener diode with a reverse breakdown voltage of 11V is placed parallel to the diode strings as shown in Figure 5 The purpose of this diode is to ensure that an IV curve would still be generated even without the diode strings A test that was done to verify the IV curve of this diode is documented in Section 4 1 2 1 D26 1N 962 1 1V Figure 5 1N962 zener diode between anode and cathode of selected diode string 1 13 2 3 Supervisory amp Operational Control 2 3 1 Labview Control Software This control is the final level of control and contains the Labview software that manipulates and monitors the system In addition the Labview software allows the user to fine tune Voc Isc as well as the selection of the IV curve To achieve this the Supervisory amp Operational Control utilises Field Point Units for communication between the system as well as a monitoring platform 2 3 2 Field Point Units The National Instruments Field Point Unit is physic
26. ation of the simulator was conducted as the second task of the thesis During the operation the different IV curve options of the simulator were produced and captured Each curve was Classified under the three main cell technologies Monocrystalline Polycrystalline and Amorphous Performance of the simulator was also analysed to observe any discrepancies in the test results when different test conditions were inflicted on it These findings are presented and analysed in Chapter Three It was realised that the varying fill factors in each IV curve option were due to the configuration of diode strings within the PV Array Simulator Therefore an array of tests and reverse engineering was conducted on the strings to find out if there is a basis or pattern that is associated with the fill factors LTspice was also utilised as part of the study to compare physical test results against simulated ones The final results obtained from the diode strings were inserted into a mathematical equation acquired from the Main Control to confirm that the correct understanding was established Chapter Four presents the outcomes of the study This thesis also discusses the possibilities of improving the current IV curve production functions by introducing a digital IV curve circuit As this has already been looked into during the development of the simulator 1 several modifications have already been made on the control PCB Therefore the next step would be to implem
27. blue the forward biased diodes in red and the links are in black IR means that the diode is installed reversed or against the polarity The normal operating function of a zener diode is in its reverse region and therefore is commonly installed reversed Table 2 Layout of diode strings IR IR IR Curve 1 EN BZX79C2V7 BZX79C2V7 BZX79C2VW7 BZX79C2V7 BZX85C3V9 1N4148 LINK LINK LINK Curve 2 umez cave BZX79C3V0O BZX79C3V0 BZX79C3V0O 1N4148 1N4148 BZX79C3V3 LINK LINK LINK IR IR IR IR Curve 3 BZX85C4V3 BZX85C5V1 BZX85C3V9 BZX79C2V7 LINK I Curve 4 cunea BZX79C6V8 BZX85C3V9 1N4148 1N4148 1N4002 LINK LINK LINK LINK LINK IR IR IR Curve 5 cures BZX85C6V2 BZX79C3V3 LINK LINK LINK LINK LINK IR IR Curve 6 BZX79C8V2 BZX79C3VO LINK LINK LINK IR IR Curve 7 BZX79C7V5 BZX79C3V0 Orange LED LINK LINK LINK LINK LINK IR IR Curve 8 unes fan BZX79C3V0 LINK 1N4002 LINK LINK LINK LINK LINK LINK 17 The breakdown voltages of the Zener diodes can be identified by looking at the last three figures of the serial number For example a BZX79C2V7 and BZX79C3V0 diode would break down at 2 7V and 3 0V respectively Apart from the orange LED that has a forward voltage drop of 2V the forward biased diodes all have a voltage drop of 0 7V while the links do not contribute to any drops The total voltage drops for each curve is calculated and displayed in the table below 7 8 9 10 11 Table 3 Diode strings voltage dr
28. e 6 it can be seen noticeably that there are 8 strings of diodes in series Each string represents a curve that would be produced by the PV array simulator Two of the strings had only Zener diodes connected while the other six strings had forward biased diodes in the combination 1 At the end of each string metal links are installed to keep the current loop to the minimum length This is done for the purpose of keeping the induced noise of the circuit to the minimum From String 1 Curve1 in Figure 6 it can be observed that the first 6 diodes are installed in reverse as opposed to the overlay as they are supposed to be reverse biased during operation while the last diode is installed forward biased 1 The PCB is interchangeable and other versions of the board can be created by soldering different combinations of diodes With different combinations 8 new curves can be created for testing 1 Further improvements have been made in terms of the production of the generation of curves and a digital IV curve has now been realised However the only available documentations are in the German language and therefore limited information can be obtained from it until a translated copy is obtained 1 6 16 Installed Reversed Metal links Installed Forward Figure 6 Diode strings PCB 2 4 1 Diode Strings Configuration The diodes that were configured in the 8 strings are identified in Table 2 Zener diodes are marked in
29. e A HU a ata 16 2 4 1 Diode Strings Configuration c ccccccccccssssscecececessessaecececeseeseensaeeeeeesssesseaeeeeseesees 17 2 5 Mathematical analysis of Main Control cccccsccccecesessssssceeeeecesseseaeseceescessessaeaeeeescesees 19 2 5 1 First contribution to lisina is 19 2 5 2 Second Contribution to rsisi a a 20 23523 Final PO UC tue dl qt ai dd 23 2 6 Familiarization and Service of the DC genset ccccccconononocnnonononanonononnnnncononnnnnnnnnnnnnanonanns 24 2 6 1 Operating the DC genset ie ai a a s a a ia ia naa 25 A E O 28 Chapter Three Operation of the PV array simulator ccccononocooncnncnnnanononnnnnoncnnnnnnnnnnnnnnncnnonnnns 32 3 1 Modes ot Operation aeea r oicec vss vansvecs oihee a Ee EEEE a aa ENO AKE iE 32 3 2 Producing And Recording of IV CUIVES ccsssssscceceeessesssaececeeesesseaeaeeeeeceseeeaaeaeeeesensees 34 3 2 1 Acquired IV curves from the PV simulator occcccononoooonnnnnnnnanonannnnnnncnnonannnnnononnnos 37 3 2 2 Classification of the IV curve options to various cell technologies oooocccco o 39 3 3 Investigation of repeatability of tests under different conditions cocccooccnccncnnnannns 40 323510 Time Drie TOS ui dia td 40 3 3 2 gt TEMPEFAtU res Td E SE 41 3 3 3 Further Anal iS iii ias 42 Chapter Four Analysis of the IV curve productiON occccconnnooooncnnononanononnnnnononnnnnnnnnnnnnnncanonnnns 45 4 1 Confirming the
30. e configured to portray different cell technologies The development of such a test device was initiated when PV applications such as inverters required a device that could repeatedly produce consistent testing conditions as well as a platform that could perform precise MPPT measurements First the study goes into understanding the control options of the simulator in terms of its IV curve production abilities The initial familiarization stage was conducted with technical manuals and a brief session with Andrew Ruscoe who was involved in the development of the simulator Through that and further research it was comprehended that the Main Control which is the control responsible for all IV curve generations is designed electronically to follow the single diode model circuit of the PV array A mathematical aspect has been included in the thesis to confirm the operation of Main Control Designers of the simulator expanded on this theory by utilising individual sets of diode strings with different configurations which developed certain fill factors when a voltage is applied Operation of the PV Array Simulator commenced after the understanding of the controls was established The eight IV curves of varying fill factors were captured and observed As part of the study the curves were classified against the three most common cell technologies The performance of the simulator was evaluated using different test conditions to observe its stability It w
31. ee E E ta eee ee 76 List of Figures Figure 1 Circuitota Solarica llos ticas tt baca a tdi 4 Figure 2 System Control layo Utens sasori niiit iiri iiaa aeai aa aa iia ees 9 Figure 3 Circuit diagram of the 1Q750 cccsssccccecessesensececececessesssaeseeeescessesaaeseeeesseesesssaeeeeess 10 Figure 4 M in Control layout cocida at Bina eas 11 Figure 5 1N962 zener diode between anode and cathode of selected diode string 13 Figure 6 Diode strings PEB ia id edad iad 17 Figure 7 Circuitry depicting first contribution to l oooooocccncnccanononoonnoncnnnanonononnnoncnnonannnnnnnnnnnos 20 Figure 8 Circuitry depicting second contribution to l cccccinonoononcnnnnnnanononnnnnoncnnnnanannnoncnnnos 22 Figure 9 The Field Power Supply Left and the DC GENSET FIELD SUPPLY output Right 25 Figure 10 PV Simulator Input DC Genset Output Panel ooooccccccnnoccnoncncnonanononanonanonnnanorananonns 26 Figure 11 DC Genset AC circuit breaker Left and DC Genset DC circuit breaker Right 27 Figure 12 2 DC BeNSet lit a a tad 29 Figure 13 AC motor Left and DC genset Right grease outletS oooncccccnonocccnnononcnnnonananoos 30 Figure 14 Voltage measurement Of a capacitor cccononococcccnnnnnonononnnnnnncnnnnnnnannnncnnconnnnnnnnnonnnnnos 31 Figure 15 States of the PV SiMUlatO Tita cdas 32 Figure 16 Physical connection during the Setup cccononocoocnnnonononononnnnnoncnn
32. ent and commission the new circuit 1 1 Background 1 1 1 Initiative of the PV Array Simulator The Photovoltaic industry is growing rapidly with a great amount of research and development dedicated to the technology With consumers gaining interest in solar power and with more of it being introduced into the grid a greater demand is placed on the quality of the system It is a known fact that the efficiency of a particular system does not rely on the solar panel technology alone In fact it is reliant on inverters to perform conversion from DC to AC as well as to acquire the maximum possible power from the panel An apparatus was therefore needed to test inverters for their performance under different test conditions 2 1 1 2 The 25kW PV Array Simulator With a power rating of up to 25kW an open circuit voltage up to 750 Volts and a short circuit current of up to 40 Amps the PV array simulator offers up to eight different IV curves and allows the testing of a wide range of grid connected inverters or similar applications in a controlled setting 3 The simulator uses a control PCB which utilises National Instruments Field Point Units to communicate with a Labview programme to simulate solar panels of different types and power ratings Initially operation of the PV array simulator was conducted by members of RISE and Murdoch University However since RISE has vacated the premises the building as well as several test equipm
33. ent were left behind for the use of the University All the equipment have been transferred to the School of Engineering and Energy in Murdoch University 1 2 Concept of Design 1 2 1 Fundamentals of the solar cell The solar cell is essentially a semiconductor diode that is exposed to light Both cell and diode are made of the same material silicon and have similar structure and properties therefore the one diode model circuit below represents the fundamentals of how solar cells generate electricity 1 4 The equivalent circuit of the solar cell shown in Figure 1 is comprehensive enough to understand the theory of its operation The current source which is in parallel with the diode simulates the light generated or photo current Ipn Ip represents the current through the diode I is the resultant output current V is the terminal voltage 4 Lon V Figure 1 Circuit of a solar cell Kirchhoff s current law depicts the resultant output current of the solar cell by the equation I lpn Ip 1 A cell technology is characterized by its IV curve and therefore a set current and voltage are the two factors that differentiate one technology from the other The Isc is the largest possible current that occurs during a short circuit while the V is the largest possible voltage during an open circuit The diode quality factor which portrays how close the diode is following the ideal diode equation is also an additional
34. ere acquired and classified under the three most common cell technologies An investigation of the repeatability of test results under different test conditions was also conducted to evaluate the performance of the simulator Through tests and documentations of past tests the simulator was shown to be very stable and did not seem to change its properties even when exposed to different test conditions The properties of the IV curves were dependent on the configured diodes strings that were installed in the simulator It was concluded that the configuration of the strings were formed through experimentation procedures A further improvement would be to employ the use of digital IV curve generation for proposed future works with regards to the PV Array Simulator 67 Appendices Appendix A Replicating the amplification control Aims and Objectives To observe the outputs of the AD826 Dual Operational Amplifier Equipment 2 X DC Power Supply 1 X Protek DMM 1 X 33kQ Resistor amp 1 X 1kQ Resistor Breadboard Leads Diode string 1 X AD826 Dual Operational Amplifier Set up Figure 40 Connection diagram of the AD826 amp set up circuit 68 Procedure The steps are as follows Assemble the diode physical test circuit Connect a 1kO resistor in series with the diode strings This resistance ensures that some leakage currents would be passed through from the strings A 33 kO resistor is connected to terminal
35. factor that is responsible for the representation of a certain cell 4 1 2 2 How the PV array simulator simulates a PV array To simulate a PV array the characteristic of the cell technology was explored For the PV array simulator a DC generator is used to supply power The desired amount of current source breakers this is activated via breakers among ten current sources is first adjusted based on the anticipated that the user wants to set The precise J is then selected through the labview interface To produce V the input of the DC genset is fed through several control circuits which then generates the simulator s output voltage This output voltage can be fine tuned via the labview interface and is fed into the device under test DUT The DUT adjusts the operating voltage and likewise a voltage that is proportional to it is fed into the diode strings The simulator offers up to eight different diode strings which means that different IV characteristics can be simulated with the desired V and Isc 1 1 3 Objectives Objective 1 Familiarization with the PV Array Simulator and its control options in terms of l V curves produced This objective involves the familiarization of the PV simulator in terms of its set up operation and its control option in terms of IV curves produced and includes familiarization with the available documentation and technical manuals Detailed analysis of the system controls to underst
36. g of their operational behaviour The diodes were differentiated by forward or reverse biased and have to be installed correctly to produce the correct results The figures below depict the setup for the test It can be seen in Figure 30 that the diode is forward biased because the polarity of the DC power source allows for electrons to flow within the diode In a forward biased configuration the positive end of the diode is the anode while the negative end is the cathode Figure 31 displays the diode installed opposed to the polarity of the DC power source and therefore works reversed biased Included in the circuit are an ammeter and resistor connected in series as well as a voltmeter connected in parallel to the diode DC power source ZV Voltmeter Ammeter Resistor V Ground Figure 30 Connection for the forward biased diode DC power source WZ Voltmeter EEE Ammeter Resistor E A V Ground Figure 31 Connection for the reverse biased diode 52 To capture the IV characteristics of the diode a DC voltage sweep was achieved by manually adjusting the voltage of a DC power source from OV to 10V The current was kept at 1004A and this was achieved by adjusting the correct resistance for each test The resistance was toggled according to two main parameters of the diode which are respectively the voltage current Vz Ip for forward biased diodes as well as the voltage current Vp Ip for rever
37. ge of 750V Power generators generate power based on the occurrence of electromagnetic induction Firstly current is fed into the field coil of the generator creating a magnetic field When a conductor moves through the magnetic field an electric current is generated An armature which compromises of coil windings on an iron core acts as the conductor within the electric generator When the armature is rotated the coils pass through the magnetic field generating current With each repeated passes through the field an AC current is produced as the magnetic flux change through the coils changes at a sinusoidal rate Therefore to produce DC outputs split rings are used to force current to flow in only one direction and in the event rectify the voltage output 13 14 A generator does not work independently and requires a prime mover for the rotating of the armature In this case a three phase induction AC motor is employed for that purpose The whole set up which consists of the AC motor and DC generator is referred to as a genset In this section details of the operation and servicing of the DC genset that was done in conjunction to the requirements of the project are documented However this documentation is not an instruction manual but rather a summary of what was done in the course of the project There are associated manuals in regards to the operation and maintenance and they are located in the equipment cabinet of RISE 15 2
38. he PV array simulator to various cell technologies Objective 3 Analysing the operation of the IV curve production of the PV Array Simulator The initial objective set asked for a comparison between the IV curve results generated from the PV simulator against the IV curves of physical arrays However through subsequent analysis of the simulator it was realised that there was no basis to compare results produced by the simulator against outputs from physical cells the simulator s main function is to generate IV curves of varying fill factors and does not offer additional possibilities to realistically simulate a particular panel Therefore with the discretion of Associate Professor Graeme Cole the focus was shifted to the study of the operation of the diode strings installed in the simulator Determination of an operating range for the tests by replicating certain components of the controls Tests to observe the behavioural aspects of individual diodes as well as selected diode strings The application of the simulation software LTspice and comparison of simulated results and test results Chapter Two Familiarisation with PV array Simulator Familiarization of the PV array Simulator was prepared with the available documentation manuals as well as a visit from Andrew Ruscoe who was involved in the development of the RESLab PV array simulator Prior to his visit the PV Simulator Software Specification Description 1 was utilised t
39. hese tests were initially conducted on physical PV arrays However there were issues associated with these types of tests Firstly outputs from an actual PV array are dependent on environmental conditions Shadings temperature differences and different irradiance levels affect the performance of the cell Therefore consistent repeated readings cannot be measured In addition as inverters were improving rapidly in terms of their efficiency more precise MPPT measurements were needed With RESLab s 25kW PV array simulator an efficient and steadier platform was realised for all testings of PV applications The tests or studies can also be conducted in a controlled environment which makes it possible for consistent repeated outputs Chapter One of the thesis explains the concept behind the design of the simulator 1 To evaluate the simulator three main tasks were formulated and discussed in the thesis The first task involves the familiarization of the controls of the simulator and an understanding of how the IV curve production is achieved This is crucial for the smooth operation of the simulator A mathematical analysis was conducted to understand the Main Control This information as well as the other controls and components associated with the curve production abilities of the simulator is presented in Chapter Two This chapter also discusses the simulator s Labview control software and the familiarization with the DC genset The oper
40. hip between the initial input V and VD the voltage across the diodes VD e R6 oan V 7 X x x R5 R3 R4 R5 7 In addition V5 sets the voltage across the diodes and the diode current flows through R7 The signal is fed into the negative terminal of an operational amplifier 21 6 V contribution II is calculated as the inversion of the diode current across R2 This generates a voltage component for the simulator and is displayed as the equation below Vp V contribution II R2 x Is enraVr 1 8 An additional factor n number of diodes is included in this diode equation as there is more than one diode in each string I is the diode s saturation current or scale current this is typically 1 x 1071 Vp is the voltage across the diode q is the quality factor of the diode usually 1 or 2 for silicon diodes Vy is the thermal voltage approximately 25mV at 20 C 12 7 The current across the diode string in terms of the number of CSBs operated can then be calculated from the equation below Vp ID V6 M a Ig enaV 1 9 x V6 m x T RS RS sle 9 V6 is the product of buffering of V contribution II and for this calculation they are considered to be equal Figure 8 Circuitry depicting second contribution to 22 2 5 3 Final Product The PV array simulator simulates the currents by working with proportional voltages The simulator is contro
41. ines the structure of the main control When the simulator feeds a positive voltage Vout back into the simulator the output that is generated becomes negative with reference to ground This negative output is first fed into the Voltage divider amp filter This ensures that the voltage range is compliant with the controls for the next stage The output is then passed through to the Op Amp amp Digital POT where the fine tuning process of the voltage output which is adjusted through the Labview interface is achieved by the control of a digitally selectable gain In addition the operational amplifier in this stage inverts the negative voltage input into a positive one This positive voltage Vy y is fed into the selected diode string and a resulting current I4y is generated The final stage of this control subtracts Lay from a continuously drawn current representing the user s input array short circuit current Loc This inverses the signal from the previous stage and thus display a PV array s IV curve These stages are explained in detail in the following paragraphs 1 Array short Latched diode string selection H Selected ene string Diode oe 7 E DS Me De NA reset Me FPUs aling and changing ground reference divider Filter HVoure Vour ze Protection Figure 4 Main Control layout 1 11 2 2 1 Voltage divider amp filter The output v
42. ing greasing the DC genset is then operated without a load Running the genset ensures that the grease is evenly distributed With the grease cartridge marked AC 30 full pumps are applied to each of the outlets on the AC motor Likewise the grease cartridge marked DC is used to pump 10 full pumps on each of the outlets of the DC generator 16 With both AC motor and DC generator lubricated the DC genset is left to run for an additional hour This is done to allow for the expulsion of excess old grease from the bearings With that done the AC motor s grease outlet is closed and the DC genset shut down The appropriate box was then checked off in the DC Genset Maintenance Schedule 16 30 Checking the voltages of the capacitor bank There are two parallel strings of two 500V 9200uF capacitors connected to the output of the DC genset In an ideal situation two capacitors in series would equally share the output voltage However over prolonged periods the capacitor might degrade and display different leakage currents This would cause voltage imbalance and will cause a failure in the operation of the DC genset Therefore it is paramount that the voltage across each capacitor is checked annually to verify that it is still operating in the correct voltage range 16 The four capacitors are located behind the DC Genset panel As the panel had been designed not to operate with their doors open a pair of plier was used to manua
43. iode strings are operating in very small leakage voltages currents The steps are as follows For individual diode test select a diode at Table 7 For diode string test select a string at Table 2 from main report Insert diode in breadboard The circuit layout for this test can be seen in Figure 43 The diode should be installed according to its conducting direction as it can be seen from the two figures Connect an ammeter in series with the power source as shown in Figure 43 Connect a voltmeter in parallel with the individual diode diode strings The ammeter measures the current in the circuit while the voltmeter measures the voltage across the individual diode diode strings A resistor must also be connected to adjust the correct current flow in the circuit Once set up is completed calculate the proposed voltage drop across the resistor This can be done by subtracting the forward voltage drop from the maximum input voltage of 10V With the proposed voltage drop across the resistor acquired adjust the resistor to allow 100uA to flow in the circuit Measurements can now be taken Toggle the input power from OV 10V in increments of 1V Take the current reading and voltage reading at each increment Record the data and insert into excel Generate IV curve 73 Appendix D Screenshots of LTspice simulation w normaldiode raw econ on dc V1 011m D3 1N4148 10 a rr T Seca or eee atte e
44. itched on therefore 3 x 10 30 stages Therefore the final equation is 33 Vp I 30x x 0 0836 33 x 1071 x cwaxors 220 19 The only factor that changes is Vp which is the voltage applied across the diode strings 60 Calculated IV curve of String 1 4 0005001 4 0005 4 0005 4 0004999 T 4 0004999 amp 4 0004998 2 4 0004998 4 0004997 4 0004997 4 0004996 4 0004996 0 2 4 6 8 Volts V 3 7620001 3 762 3 7619999 3 7619998 A 3 7619997 3 7619996 3 7619995 3 7619994 10 Calculated IV curve of String 4 Calculated IV curve of String 3 3 7620001 3 762 3 762 3 7619999 T 3 7619999 amp 3 7619998 3 7619998 3 7619997 3 7619997 3 7619996 3 7619996 0 2 4 6 8 10 12 Volts V 6 8 10 12 Volts V Figure 37 Calculated IV curve of the diode strings When the above method of calculation was applied to the three diode strings acquired from the test the IV curve recorded displayed the essence of a PV array s IV curve which can be seen in Figure 37 This confirmed the accuracy of the calculations and the understanding of Main Control These three IV curves however were not similar to the actual curves provided by the PV simulator This is because the PV simulator draws approximately 200 300 data points to form an IV curve compared to only 10 data points acquired by the physical test With the constraint of so minimal data points and with working ranges in micro
45. itors the operation of the simulator The details of each control are documented in the following sections 1 HVvin CB3 CB12 Supervisory and Operational Control cts CSB1 CSB10 6 te RAR A FPUs o o o o o o o o o HVout Br CONi TE 0 On Vout pe PC HVin HVout Z ON ASA y AS A A Figure 2 System Control layout 1 2 1 Current Control The Current Control is the lowest level of control in the System Control Its main function is to ensure that the correct current which is defined by the current source control signal Vescs is passed through to the current source blocks CSB 1 2 1 1 Current Source blocks CSB Within the simulator are 10 CSBs which are arranged in parallel Each CSB produces 4A and consists of ten 0 4A current source PCBs that are mounted on a heatsink For the implementation of the current control these current sources are arranged linearly and each contains an operational amplifier and transistor A dedicated control PCB CSB Control Circuit controls each individual CSB 1 2 1 2 IQ 750 CSB Current Source Circuit There are ten Q750s current source circuits within each CSB A circuit diagram of the Q750 in Figure 3 displays a voltage follower operational amplifier followed by a transistor at its output The current source control signal Vescs is fed into the input of
46. lled by V1 voltage that is proportional to Isc Ipn and V feed back from the DUT and applied across the diode string These two signals pass through an operational amplifier where V is subtracted from V1 This is in accordance to the PV array circuit diagram where I Lon Ip 10 The theory explains that the resultant output current of the PV array is the subtraction of the diode current from the generated current Detailed documentation regarding the operation of PV arrays is included in Section 1 2 2 The simulator translates these currents into voltages so that it can be fed into the controls of the circuitry An equivalent equation is compiled V2 V contribution I V contribution II R2 Vp AR era a 14 V2 is a voltage that is proportional to the output current of each 1Q750 Therefore in the equation above it can be seen that the voltage applied across the diode strings the DUT sets the voltage range influences the value of the output current in the desired way 23 2 6 Familiarization and Service of the DC genset The PV Array Simulator requires a high DC input for simulating solar panels in operation A large variation of voltages is required and the only equipment that can provide a high enough output in the university is the DC genset situated at RISE It can produce a maximum current of 88A and a DC voltage of 800V which powers the PV Array Simulator so that it has a maximum current of 40A and volta
47. lly turn on the DC circuit breaker This is extremely hazardous as the capacitors will be charged and therefore can only be done by qualified personnel 16 With the DC genset running without a load the field power supply was adjusted to 500V field supply voltage A voltmeter with a 1000V probe was used to measure the voltages across each capacitor In Figure 14 the measurement of a capacitor displays 253V across one of the capacitor This capacitor falls under the correct voltage range of between 220V to 280V Any capacitor falling out of the range would have to be replaced with the same model number 16 Figure 14 Voltage measurement of a capacitor 31 Chapter Three Operation of the PV array simulator 3 1 Modes of Operation To efficiently control the simulator s operation four modes are programmed and can be controlled via the Labview software The four modes are STOP RUN DEFINE and TUNE When the Labview programme is initially started up the System Status would be flashing if Labview is connected correctly and the FPUs are operating the operating mode is STOP In this mode the PV simulator is on standby and does not produce any output In DEFINE mode the user selects the number of CSBs corresponding to the ones set physically at the PV simulator The IV curve is also selected in this mode As the corresponding output voltage Voc would only be approximated TUNE mode is used to adjust it to the desired voltage Thi
48. nanonononnnnnnnnnnnnnannnnnnnnos 34 Figure 17 Current Source Blocks vomita A ados 35 Figure 18 Labview user interface ooooccccconononooncnnnnncnnnnonnnnnnnnnnnnnnnonnnnnnnnnnnnnnnn nn nnnnnnnnnnannnnnnnnnnnos 36 Figure 19 IV curve tracer used for the test oooo ccccccconononaonnnnnnnnnnnananoncnncononannnononnnncnnnnannnonononnnos 37 Figure 20 IV curves acquired from the PV simulator occcccononooncncnnnnnnanonannnnnnnnnnnnannnonononnnos 38 Figure 21 Time Drift Test for Curve 4 cccconononocnnnnonocinonenonnnononnnnnnnononnnnnnnnnnnnnnnnnnnnnnnnnnnnnonnnnnnnnos 40 Figure 22 Temperature Test for Curve 4coccconocococanonoconononononononnnnnonononnnnnnnnnnnnnnnnnnnnncnnnnnnnonnnnnnnnos 41 Figure 23 IV curve Of Test2 cccccessssscececessessnnececececeseesesaeaeeeeecesseeaaeseeeescussesaaaeseeeessesseaaaeeeeess 44 Figure 24 Zoom ins of current ripple ccoconocoonnnnncnononononnnnnonnnananononnnoncnnonnnnnnnonnnnnnnnnnnnannnnnnnnos 44 Figure 25 Zoom ins Of power ripple ccoconoccononnnncnonononnnnononnnanonononnnnncnnnnnnnnnnonnnnnnnnnnnnnnnnnnnnnos 44 Figure 26 Circuit depicting the limited voltage applied on the diode strings cocoococcncono 47 Figure 27 Circuit of the amplifying test cooonocoocccncnccononononnnononnnnnnnonnononnnnnnnnnnonnnnnnncnnnnnnnnnnnnnnnnos 48 Figure 28 Circuit of diode strings in the teSt occcononocococnnonnnonononnnnnoncnnnnnnnnnnnnnnncnnnnnnnnnnnnnnnnos 4
49. nd the AC motor Checking the voltages of the capacitor bank 28 Checking of the DC genset air filer The air filter is located at the front side of the DC generator set Access was achieved by the removal of the lower 2 and the loosening of the top 2 bolts of the lid which was covering the filter From Figure 12 it shows that the filter was stained black but it was explained by Wayne Clarke that it was normal An obstruction test done later showed that the filter was still in a satisfactory state as adequate air flow was felt while the generator was running With the check done the appropriate box was checked off in the DC Genset Maintenance Schedule 16 Figure 12 DC genset air filter Lubrication of the DC generator and the AC motor The DC generator and the AC motor require annual lubrication with their respective grease Two separate grease guns with cartridges marked DC and AC respectively are located ina plastic container inside the engine room In addition two spare cartridges are also available 16 There are two grease outlets each in the DC generator and the AC motor From Figure 12 the locations of the outlets are shown circled in red The AC motor s grease outlets require opening and this can be done by lifting two levers located at the bottom of the outlets No opening of outlets is required for the DC generator 16 29 Figure 13 AC motor Left and DC genset Right grease outlets Dur
50. o understand the controls that were needed to operate the simulator It is understood that the System Control acts as a control platform for the simulator Within the System Control are three different controls They are respectively the Current Control Main Control and Supervisory 8 Operational Control Their positions within the System Control are displayed in Figure 2 below 1 The Labview programme PVSimulator v7 which is the user interface was located on the RISE network drive and was uploaded to a computer nearest to the simulator for ease of use A configuration was also done to adjust for the correct settings so that the Field Point Units would be able to communicate with the computer 1 The overall operation of the simulator involves the initial application of HV DC input voltage to the PV array Simulator through the CSBs A 50V voltage drop occurs across the CSBs and the resultant voltage HVoyr DC output voltage of the PV array Simulator is fed into the DUT The DUT determines the PV array Simulator voltage that is adjusted before being fed back to a selected diode string in Main Control In addition the Main Control generates a user defined short circuit current and subtracts the diode current from it A current source control signal Vescs is then generated also from Main Control and passed through to the current source blocks which is ensured by Current Control The Supervisory amp Operational Control controls and mon
51. oltage from the simulator HVoyr can be varied over a very large range and therefore needs to be adjusted to fit into the correct range that the controls are utilising To achieve this HVoyr is passed through a voltage divider where a proportional signal Voy is generated The dividing ratio of the voltage divider is automatically referenced against the Viy which is the voltage proportional to the DC genset s input HV y 1 2 2 2 Op amp amp digital pot For this stage a 10k digital potentiometer is used to vary the gain of the operational amplifier in the control The gain is adjusted by toggling of resistance displayed as Ryoc in the labview programme which fine tunes the input Voyy to the desired Vgc value This is done while the PV array Simulator is operating in open circuit and the gain is adjusted to obtain Vgc In addition the signal is inverted from a negative to a positive value in preparation for the next stage 1 2 2 3 Array short circuit current The Isc is the simulated array short circuit current that is being supplied via the FPUs for the simulator It is first generated as a current where it is converted into a proportional voltage so that it can be an input signal to the control The signal is then fed into an isolation amplifier for isolation scaling and inversion This creates another voltage that is proportional to the original Isc and is continuously drawn into the next operational amplifier so that a mathem
52. oltage would only be an output of 13 5V 1 5V less than voltage at the rails Furthermore a Zener diode circled in red with a breakdown voltage of 11V is placed between the anode input and cathode output of the diode strings This signifies that the voltage range would be approximately 11V at the output As there were several strings that have a total breakdown voltage of more than 11V it was inferred that the curve production was occurring before the knee of the string s IV curve 1 21 D26 1N 962 1 IV EJ AD826AN Figure 26 Circuit depicting the limited voltage applied on the diode strings 1 47 Therefore to understand what the circuit was actually doing a part of the simulator s control was replicated as seen in Figure 27 The test was set up to study the output of the U21B operational amplifier in Figure 26 As it was known that the maximum voltage across the diode strings was 11V the voltage was varied from 0 11V in the test Figure 27 Circuit of the amplifying test Curve 1 One of the curves produced by the PV array Simulator which had a total breakdown voltage of 18 1V was tested in this setup It was realised that no significant voltage change was observed at the output of the operational amplifier when the voltage across the diode string was varied from OV to 11V At this point it still was not clear why there was no reading coming out of the operational amplifier However the output result
53. one by wiring the input of the PV Array Simulator to the appropriate sockets The DC genset to PV simulator the left switch in Figure 10 circuit breaker is turned on to complete the connection It was noted that the panel was designed to only allow one switch to turn on at one time for safety reasons The right switch in Figure 10 is OTHER DC SOURCE to PV SIMULATOR For safety the circuitry has been designed to only allow one switch to be turned on at one time 15 Figure 10 PV Simulator Input DC Genset Output Panel 26 After the field power supply is correctly connected to the DC genset the DC genset s AC circuit breaker and DC circuit breaker on the left and right of the DC Generator Panel as shown in Figure 11 are switched on The emergency stop button is rotated anti clockwise to ensure it is not engaged With this done the green start button is pressed to start the DC genset It can be observed that the DC genset s voltmeter above the DC circuit breaker increases slightly This is normal as the DC genset is expected to run at 4V without a field 15 Another check is made a breeze is felt to ensure that the ventilation fan on the roof is activated upon starting the DC genset Figure 11 DC Genset AC circuit breaker Left and DC Genset DC circuit breaker Right 27 With the field power supply Figure 9 turned on and connected to the running DC genset the supply voltage is increased by turning
54. op String No Diode string voltage drop 1 2 7V x 5 3 9V 0 7 18 1V 2 3 0V x 4 0 7 x 2 3 3V 16 7V 3 4 3V 5 1V 3 9V 2 7V 16V 4 6 8V 3 9V 0 7 x 3 12 8V 5 4 3V 6 2V 3 3V 13 8V 6 8 2V 3 0V 11 2V 7 7 5V 3 0V 2V 12 5V 8 7 5V 3 0V 0 7V 11 2V 18 2 5 Mathematical analysis of Main Control The following section probes deeper into the understanding of a portion of Main Control To achieve this the schematics associated with the control were analysed and studied in detail Design of the control was based on manipulating two set of currents which are associated with the theory of the one diode model of a solar array theory is documented in Section 1 2 2 The control does this by drawing continuously a user defined voltage which is proportional to Isc Ipn and subtracting l4y the current through the diode strings this current is also represented by a proportional voltage Through these circuits the current and voltage were generated for the IV characteristics of the curve Figure 7 and 8 displays the circuitry of the operation 1 2 5 1 First contribution to I Figure 7 displays how the first contribution to the resultant current is achieved This first contribution acts as the Isc Ipn and is set by the user through the labview programme The circuitry is separated into four parts and is numbered in Figure 7 below An actual copy of Main Con
55. operating range of the diode Strings ococcooocccncnccanononnnncnnnnnnnnnnannnnonnnos 47 4 1 1 Replicating the amplification COnNtrol cccononooconnnnnnnnonononnnnnnnnnonanonononnnnnncnnano nacos 47 4 1 2 Measurement of Voltage and Current across the diode strings PCB 00006 49 4 2 Diode physical test E E E E E AEE 51 4 2 1 Individual diode Sasae eneee aiai ais 52 4 2 2 Diode Strii bs 57 4 3 Mathematical confirmation of the controls of the PV simulator sses 59 4 4 Duplicating physical tests in LTSPIC cccccononocoononnnnnnonononnnnnononnnnnnnononnnoncnnnnnnnnnnonnnnnos 62 AAT Single diod test ninenin ne a a ida 62 4 4 2 Diode String teSt cccccsssscecececsssesseaeeeeecsceeseseeaeeeeeesseesesaeaeeeeeeeseeesaaaeeeeeeessessaaeas 64 F ture Work amenena da oceania seca te cog datas acne ca cadena e td 65 CONCUSSION iia dd iaa 67 APpendiCe Snoer e aa a a a a ae Faas eI Ra anae 68 Appendix A Replicating the amplification control ocococononcononcnnnnnonananononcnncnnnnnnnnnnnnnnnnos 68 Appendix B Measurement of Voltage and Current across the diode strings PCB 70 Appendix C Individual diode and diode strings IV curve characteristics test 0 ccceees 72 Appendix D Screenshots of LTspice simulation ccccccceceseesscseceeeeecessessaaeceeeeesessesnsaeeeeess 74 Appendix E The CD Contents hreinir iiaiai ae aaa aaiae aar a aiki 75 vi BIDlOBTADOY e
56. put is recorded starting at Isc and finishing at Voc Information regarding the IV curve tracer DS 100C is available electronically in Appendix E 36 DS 100C PHOTOVOLTAIC l V CURVE TRACER Figure 19 IV curve tracer used for the test 3 2 1 Acquired IV curves from the PV simulator Table 4 Simulator output of the 8 IV curves Curve No Power W Isc A Voc V Ipeax A Voeax V Fill Factor 1 325 3 3 763 101 228 3 595 90 496 85 4 2 343 5 3 754 113 537 3 546 96 875 80 6 3 347 7 3 763 104 474 3 693 94 155 88 4 4 265 9 3 736 107 120 3 344 79 500 66 4 5 339 7 3 760 100 515 3 699 91 847 89 9 6 278 5 3 754 109 221 3 326 83 741 67 9 7 312 2 3 754 112 130 3 519 88 713 74 2 8 272 2 3 754 111 342 3 299 82 521 65 1 Eight IV curves of varying fill factors were captured using the IV curve tracer The adjusted V and I output from the simulator was respectively 100V and 4A for the test Table 4 displays the outputs from the PV array simulator It can be seen that eight varying fill factors were produced Each curve is specifically designed to generate a fill factor that depicts a certain cell technology Figure 20 depicts the eight different curves that were obtained 37 IV curve of Curve 1 05 20 40 60 80 100 120 Volts V IV curve of Curve 3 20 IV curve of Curve 2 40 60 80 100 120 Volts V IV curve of Curve 4 0 20
57. re 41 Voltmeter connection ICadS cccccccccecessesssseseceeecessesnsaeeeceeseessesuaeseeeessessesssaeeeeess 70 Figure 42 Ammeter connection leads cccsscccccecessessnseceeececesseseaesecececesseeaaeaeeseseessesaaeeeeess 70 Figure 43 Connection for forward biased diode Left Connection for reverse biased diode Right E 73 Figure 44 LTspice simulation Of 1N4148 di0de coconcooocccncncconononncnnononncnnnnonnoncnncnnnnnonannnnnnnnos 74 Figure 45 LTspice simulation of BZX C6V8 Zener diode ccccononocoonccnnnnnanononnnncnnnnnonananononcnnnos 74 List of Tables Table 1 Field Point Units and their functiONS cooconoccccnononcconononnconononccononono cocoa nono nnnn nc cc nnan ocn 15 Table 2 Layout of diode StriNgS oooococccncnononononnnnnnnnnonanononnnnnnnnnnnnnonnnnnnnnnnnnnnnnnnonnnnnnnnnnnnnnnanannnos 17 Table 3 Diode strings voltage OrOP occccconononocnnononononononnnnnnnnnnnnnnnnnnnnnnnnnnonnnnnononnnncnnnnnnnnonanannnos 18 Table 4 Simulator output of the 8 IV CUIVES ooccccccnonononoonnnnnnnnanonononnnononnnnnnnonnnnnnnnonnnnnnnnnnnnnnnos 37 Table 5 Classification of the IV curve options to various cell technologies ccoconcccocnnnnnons 39 Table 6 Results of Temperature TEST n e a A a adana aine 43 Table 7 Individual dodes rnrn r r E E EA UEA A ENS 72 viii Acronyms CSB Current Source Block FAULT This depicts an over heating or fuse failure condition of the CS
58. region it would be damaged On the other hand Zener diodes are made specifically to operate in their breakdown region A Zener diode acquires its properties from a heavily doped P N semiconductor junction When a forward voltage is applied the Zener diode functions like a normal forward biased diode and conducts at 0 7V On the contrary if a reverse voltage is applied the Zener diode allows conduction to occur by operating in its reverse region 20 The diode has an I V characteristic and it is explained by the Shockley diode equation VD Ip Is eWr 1 12 where I is the diode s saturation current or scale current this is typically 1 x 107 2A Vp is the voltage across the diode q is the quality factor of the diode usually between 1 and 2 for silicon diodes Vy is the thermal voltage approximately 25mV at 20 C 12 45 The first few stages of the Main Control are essential as the input from the simulator needs to be adjusted to fit into an appropriate operating range However the simulator s ability to generate IV curves of varying fill factor lies in the output coming from the diode strings Since the fill factors are determined by the set of diodes the purpose for the study is to realise how the IV curves are physically produced by the different configuration of diodes installed in the PV simulator When that is achieved an additional incentive would be to learn if there is a way to create a curve of a desired fill fac
59. res ees qs oiy 0 E i 0 6Y O7 08y 0 9 1 0 Figure 44 LTspice simulation of 1N4148 diode Y zenerdiode raw Lo J 0 3 D1 de V1 0 10 1m Bzx79 C6v8 gt va R1 1k 10 lt 7 Rser 0 gt Figure 45 LTspice simulation of BZX C6V8 Zener diode 74 Appendix E The CD Contents e Temperature Test Excel sheet e Time Drift Test Excel sheet e DS 100C specifications e Main Control calculation performed by Dr Martina Calais e Excel sheet of Individual Diode Test e Excel sheet of 8 IV curves IV curves of Diode String Test Curve Inversion IV curve of 11V Zener diode 75 Bibliography 1 Ruscoe Andrew PV Simulator Technical Manual s l RESLab 2006 2 Haeberlin H Bogna L Gfeller D Schaerf P Zwahlen U Development of a fully Automated PV Array Simulator of 100kW Online Cited 15 August 2011 http www pvtest ch fileadmin user_upload lab1 pv publikationen PV array simulator 100kW 2 mit K_F_geschuetzt pdf 3 Ruscoe Andrew PV Simulator Operating Instructions s l RESLab 2006 4 E M G Rodrigues R Melicio V M F Mendes J P S Catalao Simulation of a Solar Cell considering Single Diode Equivalent Circuit Model Online Cited 15 September 2011 http www icrepq com icrepq 11 339 rodrigues pdf 5 Ruscoe Andrew PV Simulator Software Specification Description s l RESLab 2006 6 P Schmid and D Zbinden Der Solargenerator Simulator Burgdorf Switzerland s n 2000 7
60. rol uses voltages as signals a voltage that is proportional to the Is is generated As the Icc of String 4 was measured to be 3 763A actual value measured from the simulator after the selection of 4A the voltage signal V1 can be calculated by the equation the equations can be obtained from Section 4 3 V2 Rs xm I 13 Where RS 220 1 m 30 3 CSBs were switched on therefore 3 x 10 30 stages ls 3 763A reading from the PV simulator Rearranging the equation gives V2 I1 3 763A aan 2 76V 14 x F x ay se m 30 14 As V2 V1 33V1 15 Where R2 33k4 1 R1 1k 1 Vas ee 5536 16 NS 16 59 The voltage signal V1 is then inserted into the equation below where the product current I still in the form of a voltage is calculated V2 V contribution I V contribution II R2 Vp p Vit 82 x ds ema r 1 17 Where n 4 There are 5 diodes in string 4 V1 0 0836 I 1 x 1071 Vp Voltage across the diode strings q 1 for silicon diodes Vr 25mV at 20 C When inserted into the equation the final current in terms of a voltage is attained However as the aim was to display the IV curve in the correct settings the final current output is obtained by converting the voltage signal V2 to current J The relationship between the voltage signal V2 and I is depicted by the equation 3 1 18 x Rs a 18 Where RS 220 1 m 30 3 CSBs were sw
61. s is achieved by adjusting an operational amplifier with an electronic gain With all these parameters set RUN mode is selected and the PV simulator begins to output an IV curve according to the voltage operating range set by the DUT It must be noted that these procedure is not in order RUN mode is used multiple times to observe Voc after the adjustment The correct procedure to operate the simulator would be to select STOP after DEFINE and TUNE has been adjusted before going on to RUN This enables the simulator to accurately output the desired values STOP TUNE RUN Figure 15 States of the PV simulator The modes of the PV simulator are depicted in Figure 15 Each mode is programmed to perform a certain task and details of their operation are discussed in the paragraphs below STOP MODE The DUT is disconnected thus cutting off the feedback input Main supply coming through the current source outputs are also ramped down to zero From this point the user can select either RUN or DEFINE Selecting RUN would operate the simulator on the defined current settings while selecting DEFINE gives the user the option to set or modify the settings DEFINE MODE In this mode the user can set the correct number of CSBs under Define Parameters in the Labview programme This must be set correctly as it tells the control how many m stages are being applied In this mode the user can also choose from eight different IV curves SAVE
62. sed biased diodes Vr and Vp are then respectively subtracted from the maximum voltage of 10V to calculate the voltage drop across the resistor Therefore to control the operating current of the circuit to 10014 the resistor can be adjusted accordingly Ip and Ip depicts the diode s normal operating current and it must be noted that currents higher than the permissible working range should not be applied However as the maximum operating current in the circuit was a mere 100A this was not a concern The methods and procedure of the test is included in Appendix C 53 Forward biased diode IV curve of 1N4148 100 8388 50 Amps uA 30 20 10 o 0 1 0 2 03 0 4 05 0 6 Volts V Figure 32 IV curve of 1N4148 diode Figure 32 displays the IV curve of a 1N4148 forward biased diode Like all normal forward biased silicon diodes the 1N4148 starts conducting close to 0 7V It can be observed from the steep inclination of the curve that as soon as the voltage reaches the forward voltage drop of the diode the voltage would remain constant irregardless of the current applied 1N4148s are mainly used as signal diodes As signals require only small voltages to operate the 1N4148 diode with a forward voltage drop of 0 7V is well suited for such operations 10 54 Reverse biased diode IV curve of BZX79C6V8 Amps uA
63. st 4 Volts V Figure 39 Physical test And SPICE simulation of BZX79C6V8 diode Figure 39 compares the simulation and physical tests of the BZX79C6V8 Zener diode in the reverse biased mode By looking at the curve acquired by the LTspice simulation it can be observed that conduction occurs at the 6 8V mark On the other hand the physical test demonstrates that in actual operation diodes do not conduct precisely at their breakdown voltages Similar to the previous comparison the results from LTspice is very close to the acquired measurement data from the physical test It can therefore be learnt that LTspice is a useful tool to observe the behaviour of diodes if a physical test was not possible Screenshots of LTspice can be obtained from Appendix D 63 4 4 2 Diode string test LTspice was not able to produce reasonable results when the physical test was replicated This was because for all of the diode strings the input voltage was lower than the total breakdown voltage of the diodes in series This led the simulation software to believe that as the breakdown voltages were not met the strings would not conduct and allow any current to pass through In addition LTspice does not take leakage currents into consideration as it is often neglected in real life applications Therefore with the simulator representing no current passing through there was no possibility of generating any output 64 Future Work It was concl
64. teristics are inserted In addition different conditions such as shading different temperature levels and different irradiance level can be simulated This will further improve the testability of the ranges of PV applications There were recommendations discussed in A Stability Discussion for Main Control located at Appendix P PV Simulator Technical Manual that two options be utilised for the IV curve generation 1 They are the A D converter EPROM EEPROM 65 The A D converter is a circuit that converts analog data into digital information Therefore in the case of the PV simulator a programmed signal can be passed through to the A D converter circuit where a digital output would be produced EPROM or EEPROM means Erasable Programmable Read Only Memory and Electronically Erasable Programmable Read Only Memory respectively They both serve as programmable memory devices that are programmed electronically and yet can be erased and re used The difference between the two is that the former erases its data under UV light while the latter can erase its data electronically Benefits of the EPROM EEPROM are that the user would be able to programme and re programme the selection of IV curves freely 22 Both options ease the tedious process of sampling by the configuration of diode strings to produce a certain IV curve characteristics They should therefore be further analysed in future developments regarding the PV array simulator This
65. the operating current the potentiometer was used to adjust the resistance for each individual string Figure 35 Experimental setup for diode strings 57 IV curve of String 1 IV curve of String 3 so 45 4s 40 40 35 35 30 3 fas E 20 g 20 lt s 45 10 10 5 5 o o o 2 4 6 8 10 12 o 2 4 6 8 10 12 Volts v Volts V IV curve of String 4 16 14 12 310 E Z 8 lt 6 4 2 o o 2 Ss 6 8 10 12 Volts V Figure 36 IV curves of diode strings Three strings from the test were selected based on their varying curve characteristics Looking at the IV curves of String 1 String 3 and String 4 of the diode strings in Figure 36 it can be confirmed that the curves were being produced by currents of very small magnitudes Both String 1 and String 3 were generated in the 5044 range which was half of the operating range of the individual diode test The test demonstrates that the designers of the simulator is utilising small currents to generate IV curves 58 4 3 Mathematical confirmation of the controls of the PV simulator The Main Control explains that the IV curve production was achieved by subtracting the current across the diode string from the applied short circuit current these currents are all represented by voltages in the controls of the simulator Calculations based on formulas provided in Section 4 3 was used to demonstrate how the IV curve of String 4 was used to produce an IV curve mathematically As the cont
66. the voltage follower operational amplifier A transistor at the output acts as a current controlled switch Voltage across RS shown in the circuit controls the current output of the simulator For each CSB used a multiple of ten stages are engaged 1 gt M stages in parallel Z js Vs Figure 3 Circuit diagram of the 1Q750 1 2 1 3 CSB Control Circuit The CSB Control Circuit controls the ten Q750s on each CSB by relaying the V input into each of them Throughout the operation the Q750s communicate by sending feedback of their statuses to the circuit Besides that the control circuit also monitors the over temperature switch as well as the voltage drop across the CSB In the event of a fault across any of the Q750s over temperature or if the voltage drop across the CSB is beyond the normal range the circuit would perform a control measure by limiting the input Veses which would reduce the output current The circuit would also send a FAULT or LIMIT signal to the supervisory control 1 2 2 Main Control Main Control of the simulator represents the second level of control and consists of several stages that collaborate to generate the IV characteristics output of the PV array simulator It does so by monitoring the output voltage of the simulator and adjusting the current source control signal V to be at the correct range to produce the desired IV curve 1 10 Figure 4 outl
67. three stages with varying temperatures Firstly a test was done at ambient temperature and depicted the simulator under normal operating condition For the second test the simulator was intentionally heated up by being made to operate on large resistors for a specified duration When the heatsink temperature reached 55 degrees shut down temperature is 60 degrees the IV curve was recorded The simulator was then allowed to operate till shut down occurred and another test was performed at 60 degrees 19 42 Results of the three tests are as follows 19 Table 6 Results of Temperature Test Test No Temperature C Voc V Impp A Vinpp V Pnpp kW 1 Ambient 757 29 11 502 622 97 7 165 2 55 757 29 11 534 622 24 7 117 3 60 757 32 11 527 622 86 7 180 From Table 6 it can be observed once again that the temperature did not seem to affect the output of the simulator There was also zoom ins of the curves that were taken for the Test 2 when the simulator was operating at 55 degrees Figure 23 displays the I V and P V curve of Test 2 Figure 24 displays the zoom ins of the current ripple and it could be observed that the ripple was in the order of 5mA maximum Figure 25 displays power ripple and it is within SW at maximum Zoom ins of the curves of the other two temperatures were not included in the document but it was mentioned that the magnitude of the ripples were consistent with Test 2 55 degrees
68. tor As the documentations provided very little information on this aspect of the operation a study was conducted to confirm the operating range of the diode strings in operation Once this was achieved the IV characteristic of a single diode as well as the diode string are explored The study was conducted in the following order Confirm the operating range of the diode strings Observe IV curve of an individual diode Observe IV curve of a diode string 46 4 1 Confirming the operating range of the diode strings Identifying the range was of utmost importance because diodes behave differently when exposed to different voltages and currents However there was little or no basis regarding the operating range of the diode strings in any of the available documents Therefore to obtain more information regarding this aspect of the operation two tests were conducted prior to the physical testing of the diodes as an attempt to confirm the range 4 1 1 Replicating the amplification control An attempt was made to amplify the voltage across the diode strings as it was believed that very small voltages were used in the controls The implementation behind this consideration was due to two main reasons Firstly the amplifier bottom operational amplifier in Figure 26 used in the schematic was an AD826AN High Speed Low Power Operational Amplifier The operational amplifier has an operational voltage of 15V which means that the maximum v
69. trol calculations performed by Dr Martina Calais is available electronically in the Appendix 1 Firstly a positive voltage that has been adjusted to be proportional to the set sc is fed into stage 1 shown in Figure 7 2 This output voltage is fed into the negative terminal of an operational amplifier between Step 2 and Step 3 3 The operational amplifier inverts and amplifies the input The operation is portrayed by the simple equation below ontribution I R2 L V1 2 V x V 26 en R1 R1 2 As it can be seen in Equation 2 the product V gt contribution I is simply a proportional voltage of the initial input V1 19 4 This stage depicts the final output current of the addition of V contribution I and V contribution II details of contribution Il are documented in the following section For every CSB that is being utilised ten Q750s are employed Each Q750 is calculated as a m stage and is multiplied in accordance to the number of CSBs selected The equation for the operation is shown in Equation 3 R2 V1 I k 3 m x m x x m MRa gi RS At this stage the output current is obtained by dividing the resultant voltage with resistor RS Depending on the CSBs utilised 1CSB 10 Q750s 10 m stages a multiplication factor is acquired The output current depends on how many CSBs are utilised mM stages in parallel V contribution I 2 3 Floating ground
70. ts V 10 Figure 21 Time Drift Test for Curve 4 40 3 3 2 Temperature Test Similar to most electronic equipment the performance of the simulator might have the tendency to degrade in higher operating temperatures Therefore it was paramount that the curves produced were observed over different temperatures It was suggested by Andrew that the heating system in the lab be utilised to increase the ambient temperature As the highest temperature that the heater could attain was 30 degrees the test was structured for measurements to be taken 3 times with intervals of 30 minutes Two thermocouple wires included with the IV curve tracer were used to measure the ambient temperature The three ambient temperatures recorded were 23 8 degrees 26 8 degrees 28 4 degrees It could be seen again that although the temperature varied by approximately 5 degrees from the first and last test the IV curve output from the simulator was not affected Figure 22 shows Curve 4 over the three temperatures It can be derived from the test that the superior stability of the simulator allows the output to be unaffected even when temperature condition changes l V Curve Comparison for Curve 4 23 8 degrees 26 8 degrees 28 4 degrees 0 20 40 60 80 100 120 Volts V Figure 22 Temperature Test for Curve 4 41 3 3 3 Further Analysis The time drift and temperature tests did not s
71. ual diodes that formed the diode strings were tested and compared alongside to observe the basis of their operation This was done also to observe if the diodes operated according to their stated ranges After substantial research and confirmation of the previous two tests the physical diode tests was conducted employing an input voltage of 10V and a limited maximum current of 100A The operating range for the test was decided after consulting the diploma thesis Der Solargenerator Simulator 6 this thesis can be obtained in the Projekt AUS file in RISE which was completed by students affiliated to the Berne University of Applied Sciences that was involved in the development of the PV simulator The basis of such a small magnitude was because diodes change their properties when they heat up Therefore to attain the accuracy of the test controlled voltages as well as minimal currents were used to ensure that the temperature was controlled The second test involved the testing of three selected diode strings These strings were configured to replicate the diode strings which were used in the PV simulator 6 51 4 2 1 Individual diodes The test was previously conducted with Protek 506 digital multimeters However they proved to be unfit for accurate measurement of micro amps and therefore a higher precision multimeter was employed for the test Individual diodes found in the diode strings of the simulator were tested to aid in the understandin
72. uded that the simulator is very useful and can be utilised for the testing of inverters However the limitation of the simulator s usage lies in the choices of IV curve options This limits the versatility of the usability of the simulator because it confines the user to only eight different options of fill factors Such a restriction sets a constraint for the simulator Therefore further improvements must be made in the current IV curve generation function During the development of the simulator another form of curve generation was realised This curve generation was in the form of a digital IV curve generation It was implemented by two students undertaking a diploma thesis Der Solargenerator Simulator 6 this thesis can be obtained from the folder marked Projekt AUS situated at RISE which was written in German Due to the language constraints details of how the implementation worked could not be attained However there are a few benefits that can be derived from such a technology The benefits of having a digital IV curve generation are tremendous The user will be able to simulate any kind of cell technology This can be done by either conducting an initial physical test to capture the behaviour of the particular cell or by researching to obtain the characteristics of the panel that needs to be simulated As the digital IV curve generation is programmable predictable and accurate results can be obtained as long as the correct cell charac
73. uggest any changes to the curves when the simulator was placed under different conditions It was thus decided that the simulator would have to be stressed as without any loads involved the machine would not significantly heat up It was noted as well through discussions with the supervisor that the ambient temperature should not be the determining parameter Instead the internal components of the machine monitored by FPUs should have been the varying factors Initially there was an attempt to utilise two load banks that were situated at RISE However through analysis and calculations of the ratings it was realised these did not provide a large enough load to be taken into consideration An initiative was also made to obtain permission to connect the PV simulator to a grid connected inverted The operation of inverters however exposes the user to dangerous voltages There was not a suitable candidate that could facilitate the test during the time frame of the project the attempt was abolished However a documentation regarding an acceptance test was obtained through further research The test demonstrates the stability of the PV simulator in different conditions by using big resistors as loads A temperature test was performed at the Burgdorf PV laboratory at the Berne University of Applied Sciences during the presence of Dr Martina Calais She has approved of the documentation of the test in this thesis 19 19 The test was conducted in
74. ulator while it is in operation High voltages are exposed at this point Utilise the IV curve tracer to conduct a DC sweep While the sweep is being conducted observe the voltmeter and ammeter for any readings 71 Appendix C Individual diode and diode strings IV curve characteristics test Aims and Objectives Capture and understand IV curves of individual diodes through a practical setup Configure the 8 strings of diodes and measure their IV curves Equipment DC Power Supply 2 X Protek DMM for individual diodes 2 X UT803 high precision DMM for diode strings Variable Resistor Breadboard Leads Range of diodes Set up Table 7 Individual diodes Direction Diode No Forward Biased 1N4148 1N4002 Orange LED Reverse Biased BZX79C2V7 BZX79C3V0 BZX79C3V3 BZX79C6V8 BZX79C8V2 BZX79C7V5 BZX85C3V9 BZX85C4V3 BZX85C5V1 BZX85C6V2 72 DC power source DC power source _ ZW Voltmeter o Y Voltmeter Ammeter Ammeter Resistor Resistor V Ground V Ground Figure 43 Connection for forward biased diode Left Connection for reverse biased diode Right Procedure The procedure of tests for the individual diode test and the diode string are identical Equipment wise the individual diode test utilises the Protek DMM while the diode strings utilises the UT803 high precision DMM The reason for the difference of measurement devices is that the d
75. whilst the tracer was conducting the DC sweep The first test was conducted with the connection between the input voltage and the seven other strings of the diodes broken Results for each curve selection through the labview interface displayed an identical curve same fill factor By the reading of the schematic it shows that the signal has went through the diode strings and passed through the zener diode between the D_An and D_Cat Information of this diode is included in the previous test Therefore it has been confirmed that the diode strings share a common cathode and the breaking of the connection between the signal and diodes caused an open circuit IV curve with broken connection 0 20 40 60 80 100 120 Volts V Figure 29 IV curve with broken connection Figure 29 displays the IV curve when the diode strings were broken The IV curve has a fill factor of approximately 96 and is generated consistently with each curve number selected when there is an open circuit in the PCB For the second test the broken connection for the strings were restored This time the eight curves were generated as per normal with their respective fill factors However the voltage and current readings were displayed as noises the current measured was less than 100uA The test procedure is discussed in detail in Appendix B 50 4 2 Diode physical test The Diode physical test was separated into two tests In the first test individ

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