Driving of a 3-phase BLDC Motor by 120
Contents
1. how we commutate the motor the speed it rotates at is a function of the motor current which we set by controlling the phase voltage as outlined in section 3 2 1 F Transistor Active sep We Sp Un aep Sr m F 6 Z Figure 3 6 Typical Commutation sequence 3 3 Measuring Speed There are a few basic methods for measuring the mechanical speed in a rotating motor The simplest is to use a tachometer attached to the rotor that outputs a given number of pulses for a single rotation In essence we will use the Hall Sensors as a tachometer of sorts Although not attached to the rotor they do give a fixed number of pulses for a single rotation i e a direct relationship to rotor speed We will feed the Hall sensors into an interrupt pin of the R8C and detect both edges to double the number of speed measurements in a given rotation This number will be Number of Hall sensors number of edges the number of pole pairs in the motor measurement points For the demo motor which has 5 poles this will be 3 2 5 30 measurements per rotation If we measure the time between each interrupt using a fixed processor clock and timer we can then derive the speed Speed clock period number of counts We have in effect created an input capture timer using three inputs The code uses Timer RB as a 16 bit down counter It does this by reading both the pre scaler and the Timer RB register during the interrupt service routine The 16 bi2. damages incurred as a result of errors or omissions in the information included in this document 6 When using or otherwise relying on the information in this document you should evaluate the information in light of the total system before deciding about the applicability of such information to the intended application Renesas makes no representations warranties or guaranties regarding the suitability of its products for any particular application and specifically disclaims any liability arising out of the application and use of the information in this document or Renesas products 7 With the exception of products specified by Renesas as suitable for automobile applications Renesas products are not designed manufactured or tested for applications or otherwise in systems the failure or malfunction of which may cause a direct threat to human life or create a risk of human injury or which require especially high quality and reliability such as safety systems or equipment or systems for transportation and traffic healthcare combustion control aerospace and aeronautics nuclear power or undersea communication transmission If you are considering the use of our products for such purposes please contact a Renesas sales office beforehand Renesas shall have no liability for damages arising out of the uses set forth above 8 Notwithstanding the preceding paragraph you should not use Renesas products for the purposes listed below 1 artificial life
3. NO snatesarneticeonunrsrdarenoscecntentasundiacetoasDiiacwiauniemekiaieomunesaiarnnniiean 3 5 1 The 6 step state machine and COMMUTATION cccceeeeeeeeeeeeeeeeeeeeesaeeseeeeeeees 3 5 2 lal Signature PO SUWAG wescrcotcs accede tendstabadsaetacsententeaeeeseateeddetenschtetaecdadeteeenentenceeeet 50 0 Molor TES UN esere E E E AO POLO O oana aa a E E eee ee Os OO aN O E e E R E NS E N E AT A A A A E E A E E TA C ACOS o E E E E E REU05B0074 0101 Rev 1 01 December 2008 TEET N 2 aero e a 3 Page 1 of 14 R8C 25 Group Six Step Trapezoidal Control using HALL Sensors CENESAS 1 0 Abstract This Application Note shows the implementation of 3 phase BLDC motor drive by 120 degree trapezoidal wave commutation The method shown utilizes the HALL sensors in the motor to determine the motors rotor position effect commutation and provide speed measurement This example applies to MCUs in the R8C 24 Group 2 0 Conditions The explanation of this issue is applied to the following condition Applicable MCU R8C 24 Group such as R8C 25 device R5F21256 MCU operational frequency 20 MHz Memory size ROM 32 KB RAM 1 KB Peripherals Timer RD for PWM motor drive Timer RB for speed measurement 3 0 Introduction The R8C Family has a number of peripherals suitable for motor inverter drive applications In this application note we will take a look at the R8C 24 Group specifically the R8C 25 driving a 3 phase BLDC motor usi
4. To our customers Old Company Name in Catalogs and Other Documents On April 1 2010 NEC Electronics Corporation merged with Renesas Technology Corporation and Renesas Electronics Corporation took over all the business of both companies Therefore although the old company name remains in this document it is a valid Renesas Electronics document We appreciate your understanding Renesas Electronics website http www renesas com April 1 2010 Renesas Electronics Corporation Issued by Renesas Electronics Corporation http Awww renesas com Send any inquiries to hitp www renesas com inquiry CENESAS 8 10 11 12 Notice All information included in this document is current as of the date this document is issued Such information however is subject to change without any prior notice Before purchasing or using any Renesas Electronics products listed herein please confirm the latest product information with a Renesas Electronics sales office Also please pay regular and careful attention to additional and different information to be disclosed by Renesas Electronics such as that disclosed through our website Renesas Electronics does not assume any liability for infringement of patents copyrights or other intellectual property rights of third parties by or arising from the use of Renesas Electronics products or technical information described in this document No license express implied or otherwise is granted
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6. c overview let s discuss the quick testing method we did and some insight into how this was implemented in software 3 5 1 The 6 step state machine and Commutation So we first had to implement a simple finite state machine so we could commutate the motor and know which windings to drive We chose to do simple enumerations of the steps and start the numbering at 0 so we can use STEP1 though STEP6 as look up variable into tables Since we were making this portable we included some steps underflow and align required for open loop operation but that is for another app note For now we can just understand we will use STEP1 through STEP6 NO_STEP is used to force no commutation drive in open loop SO you can see from the code piece in Figure 3 10 we have typedef enum defined the steps in such a manner as to provide a direction STEP_UNDERFLOW 1 look up into the drive tables i e STEP1 through STEP6 lea equal 0 through 5 respectively In addition we have defined STEP3 an Underflow value to detect when our open loop STEP4 commutation should move from STEP1 to STEP6 ieee Tr ALIGN_ STEP Now that these values are set up in this manner we can use NO STEP them to directly look up the proper pins to drive in the look up STEP_STATE table See figure 3 11 FIGURE 3 10 STEP Enumerations REU05B0074 0101 Rev 1 01 December 2008 Page 8 of 14 R8C 25 Group Six Step Trapezoidal Control using HALL Sensors CENESAS p
7. cise the reader can validate the rest of the states to confirm the drive matches the drive given in the previously given tables Tek JL Acq Complete M Pos 2 560ms TRIGGER i i I I I I I Type li i i TWIN WELLE TTT NA A A N eese ATA Source i i i T CH4 I I I I I I I I I I I I I aiid Te er l l l l I pil I al i ial I E i i i ae Mode Narnal Pe LU Coupling EEEH CHI Suiv CH Aivi M500us CHIZ 140mA CH3 20v 1 1 1 20 Aug 07 13003 130 120Hz l o 4 ee ee ee ee a ee A a ai a A A Qa Lu Lu Lu Lu Lu Lu Lu a U N a N V U Figure 3 15 Motor Winding on Commutating Motor REU05B0074 0101 Rev 1 01 December 2008 Page 11 of 14 R8C 25 Group Six Step Trapezoidal Control using HALL Sensors CENESAS 4 0 Reference YMCRPR8C25 Kit User Manual Application Notes REJ05B0845 0100 Rev 1 00 Timer RD in Complementary PWM Mode REJ05B0486 0100 Rev 1 00 Solutions for Three Phase Motor Control Programming REU05B0073 0100 Rev 1 00 Six Step Trapezoidal Control of a BLDC Motor Using Back EMF Hardware Manual R8C 24 group R8C 25 Group Hardware Manual Rev 1 0 YMCRPR8C25 Motor Control Demo Kit Use the latest version on the home page http www renesas com Renesas Technology Corporation Semiconductor Home Page http www renesas com Technical Contact Details Global csc renesas com Inquiries http Awww renesas com inquiry 5 0 Programming Code The example program was w
8. e control and malfunction prevention appropriate treatment for aging degradation or any other applicable measures Among others since the evaluation of microcomputer software alone is very difficult please evaluate the safety of the final products or system manufactured by you 11 In case Renesas products listed in this document are detached from the products to which the Renesas products are attached or affixed the risk of accident such as swallowing by infants and small children is very high You should implement safety measures so that Renesas products may not be easily detached from your products Renesas shall have no liability for damages arising out of such detachment 12 This document may not be reproduced or duplicated in any form in whole or in part without prior written approval from Renesas 13 Please contact a Renesas sales office if you have any questions regarding the information contained in this document Renesas semiconductor products or if you have any other inquiries 2008 Renesas Technology Corp All rights reserved REU05B0074 0101 Rev 1 01 December 2008 Page 14 of 14
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10. ev 1 01 December 2008 Page 7 of 14 R8C 25 Group Six Step Trapezoidal Control using HALL Sensors CENESAS So now we have a current reference representing how we should drive the motor so we need to get that into the correct domain so we can drive the motor with voltage This means we need to go from Current to Volts Ohm s law to get an absolute motor voltage After this we need to bring that into our Bus Voltage domain for example we might need 12V on the motor and we have 24V on the Bus Finally the ratio is converted to an absolute count for the PWM timer This transition is shown in a few lines of pseudo code below Voltage PWM Current_Reference Motor_Impedance Current to Absolute Motor Voltage Counts Voltage PWM VBus_Inverse ratio of Motor Voltage to Bus Voltage PWM_Counts Counts PWM_MAxX finally actual PWM counts to load in timer The reader should download the source code as listed in section 5 for complete details and actual code implementation NOTE This sample project for driving BLDC motors is not optimized rather it is written for clarity an example purposes Many of the calculations can be rolled into a single calculation For example a single multiply in the soeed loop can encompass both the P Gain and the Motor Impedance so you get a number back from the speed control function that can be converted to PWM counts directly 3 5 Implementation and Testing So now that we ve given you a basi
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12. ignature Note that the state changes every 60 for one electrical cycle We can then read these on GPIO pins of the R8C and decode them into a 60 rotor position The number of electrical cycles in one mechanical rotation is based on the number of pole pairs magnetic poles in the motor For the figure given this is 1 pole pair the motor in the YMCRPR8C25 demo kit has 5 pole pairs Hall IC Signals H1 H2 and H3 are Hall IC 0 60 120 180 240 300 360 Figure 3 4 Hall Mounting Figure 3 5 Typical HALL Signature REU05B0074 0101 Rev 1 01 December 2008 Page 4 of 14 R8C 25 Group Six Step Trapezoidal Control using HALL Sensors CENESAS 3 2 3 Commutating So now we can control the voltage we know where the rotor is so let s put them together A motor manufacturer s data sheet will typically tell you when you see this HALL signature drive these phase windings Figure 3 6 shows a typical commutation sequence For this motor when we see the HALL signature for STEP1 we drive Up and Vy The rotor will move because the torque being caused by the magnetic fields in the stator coils are being applied at the correct angle to the magnets on the rotor and they will attempt to align When we see the Hall signature change state to indicate Step 2 we switch the drive from Up and Vx to Up and Wy and the rotor will continue to move This will continue for the entire cycle until we are back at Step one and the process repeats This is
13. ill connect the microcontroller to the power inverter stage to control the gates of the IGBTs In effect the PWM duty cycle controls the voltage at the motors terminal There are various modulation methods used in today s inverter drives Typically modulation techiques are Upper modulation Lower Modulation rotating Modulation or Balanced Modulation For this application note we will be showing Upper modulation only Figure 3 3 shows the basic upper modulation waveforms Note that in this method only the P or upper IGBTs are modulated REU05B0074 0101 Rev 1 01 December 2008 Page 3 of 14 R8C 25 Group Six Step Trapezoidal Control using HALL Sensors FIGURE 3 3 Upper Modulation Active low Drive NOTE Timer RD in the R8C Family can do any of the modulation techniques and is not limited to single sided modulation techniques This would include sinusoidal modulation for other motor types such as 3 phase induction 3 2 2 Rotor Position Now we have control over the voltage on the windings and indirectly the current through the use of a PWM timer but we must present these signals in the appropriate sequence to properly commutate the motor In order to do this we must know the rotor position We will do this with the Hall sensors which sense the position of the rotor They can do this because they are positioned relative to each motor phase winding in the stator coils see figure Figure 3 Figure 3 5 shows a typical HALL cell s
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15. late Step Response 7 V v Y Vv wr D v s Turvy 10 19 28 37 46 55 64 73 82 91 100 109 118 127 136 145 154 163 172 181 190 199 Time Figure 3 8 Loop Response P Gain and I Gain So now back to our implementation So the pseudo code would look like this Error or r calculate the speed error Current_ Reference P Gain Error calculate our current reference Current_Reference Current_Reference Current_Integral add in the integral Current_Integral Current_Integral Error l Gain accumulate the error as Integral The key to this implementation is the fact that the speed loop corrections are applied synchronously to the PWM frequency at some fixed rate that is a sub frequency of the carrier So although the speed measurements are asynchronous in nature i e we don t know when a Hall interrupt will come in we apply the correction at a give frequency Also an important point to remember there are multiple ways to implement these control loops The way we show it here is very simple in software but it does require the Integral portion for the loop to converge on the correct speed If integral gain is set to 0 this loop will tend to bang back and forth trying to correct the speed but never actually hitting the correct soeed How fast it does this is based on the having the correct P Gain and l Gain in the software too in depth to explore in this application note REU05B0074 0101 R
16. ng the 120 trapezoidal method also referred to as 6 step The 6 step method is one of the simplest method for driving 3 phase BLDC motors and in the past was done using discrete logic gates but with the more powerful peripherals available in today s microcontrollers such as the R8C Family we can provide more functionality better energy usage and higher safety level when driving motors In this application note we will show 6 step commutation using HALL Sensors speed measurement using TimerRB Current measurement using A D and a basic Proportional Integral PI Speed loop This application note is intended to be a primer in 6 step commutation and using the R8C peripherals to drive a three phase BLDC motor It is not intended to provide in depth theoretical motor training 3 1 Basic 3 phase Inverter Topology 3 1 1 General Inverter Topology Figure 3 1 shows the basic Inverter topology for driving 3 phase motors In the case of this application note the control electronics would be the R8C 25 It is important to note that it requires 6 outputs to drive the inverter section Timer RD in the R8C family is perfectly suited for this task and supports dead time to prevent shoot through current on the IGBTs LINE INPUT INPUT RECTIFIER DC BUS OUTPUT INVERTER CAP CONVERTER INVERTER Figure 3 1 Basic Converter Inverter Connections REU05B0074 0101 Rev 1 01 December 2008 Page 2 of 14 R8C 25 Group Six Step Trapezoidal C
17. ontrol using HALL Sensors CENESAS 3 1 2 R8C 25 Specific Inverter Topology Figure 3 2 shows the specific architecture of the YMCRPR8C25 Demo board used to develop this Application Note Note the additional functions over the basic inverter motor drive topology We can use A D channels to monitor the Bus voltage for droop motor current for excessive current or to implement torque control We can use the R8C timer set to measure speed and implement a speed control loop rather than just the simple open loop control R8C 25 Inverter Phase E gt Current DC e Vbus cn a yutput buffer cut off input Monitor C Over current oopa J Hal Signals a pE To host Figure 3 2 Block Diagram R8C 25 Motor Control 3 2 Basics of Trapezoidal Commutation 6 step The 6 step method is one of the simplest methods for driving 3 phase BLDC motors Itis also know as 120 Degree trapezoidal since it drives each winding for 120 degrees of the electrical rotation and leaves the winding un driven for 60 degrees Note although the drive method is simple this lack of drive for 60 degrees also results in higher torque ripple in the end application The system designer must decide if this is acceptable or other drive methods should be considered 3 2 1 Controlling Phase Voltage The basic voltage control for the three windings of the motor is performed using Phase Width Modulation PWM In section 3 1 we showed how we w
18. r in this case software that scales the error by gain and computes voltage required to correct the speed Very similar to controls you see in hardware One important point to note we can control the voltage of the motor through PWM Since torque in a motor is related to current and not voltage the output of the ASR calculations is a current reference for the given error We will need some calculations to convert current to voltage REU05B0074 0101 Rev 1 01 December 2008 Page 6 of 14 R8C 25 Group Six Step Trapezoidal Control using HALL Sensors CENESAS So a quick review of Proportional Gain and Integral Gain is in order now The most basic type of control loop is Proportional where the correction provided is simply a factor of how much difference there is between the commanded and actual values The more error the more correction This type is usually stable but allows some error to exist so it is not good for highest accuracy Step Response 120 10 19 28 37 46 55 64 73 82 91 100 109 118 127 136 145 154 163 172 181 190 199 Time Figure 3 8 Loop Response P Gain Only By using an integrator in the loop adding the accumulated error over time we can eliminate long term error that the Proportional loop allowed This improves the basic accuracy But these systems can also become unstable and oscillate around the set point Some damping in the system like friction or resistance does reduce the tendency to oscil
19. ragma rom high_side_step_ table pragma rom low_side_step_ table const UIl08 high_side_step_table 8 const Ul08 low_side_step_table 8 UP_ON Step 1 Up Active modulated VN_ON Step 1 UP_ON Step 2 Up Active modulated WN_ON Step 2 VP_ON Step 3 Vp Active modulated WN_ON Step 3 VP_ON Step 4 Vp Active modulated UN_ON Step 4 WP_ON Step 5 Wp Active modulated UN_ON Step 5 WP_ON Step 6 Wp Active modulated VN_ON Step 6 UP_ON Align Up Active modulated ALIGN_MASK Align 0 NO Step 0 NO Step j FIGURE 3 11 Pin Drive Look up tables So you can see when using these tables if when we see STEP1 on the HALL Cells we will drive UP_ON on the high side and VN_ON on the low side All we need to do is construct these tables properly for a given motor and connections and it will commutate properly In order to test these we do not hook them up to the motor or power stage bad things happen when motor software has bugs Rather we hook a signal generator into one of the Hall inputs on the microcontroller to simulate a spinning motor We then look at our commutation using scopes and analyzers Figure 3 12 shows the actual PWM signals from the processor during our 6 step commutation ae jedi STEP1 STEP2 STEP3 STEP4 STEP5 STEP6 STEP1 Figure 3 12 Logic analyzer capture of 6 step PWM signals Active low NOTE STEP1 signal is I O port set in software to signal
20. re was taken from an electrically driven motor but the Hall signals would look the same if you were spinning it by hand You can observe the un driven times of the phase current This is one thing that produces torque ripple in 6 step motor drive So electrically they look like we would expect so how does our Hall look up table function For this we need to capture the values in software As our STEP machine was commutating from the Hall sensors the software tracked where it thought it was and where the Hall sensor told us it was It captured this in an array named test_data NOTE Since we used enumerations for the steps the watch window is able to decode and display in basically an easy to read English language rather than us trying to decode a 0x05 for example REU05B0074 0101 Rev 1 01 December 2008 Page 10 of 14 R8C 25 Group Six Step Trapezoidal Control using HALL Sensors CENESAS 3 5 3 Motor Testing At this point would feel somewhat safe in hooking up my motor to my power stage and trying to run the motor My first attempts would probably be with fixed duty cycles on the PWM so as not to worry about un tuned PI loop but it should run So finally let s look at the Motor phase voltages of a properly commutating BLDC motor You can clearly see the commutation states as shown in figure 3 15 In Step1 we drive Up and Vy in Step 2 we switch the drive from Up and Vy to Up and Wy and so on As an exer
21. ritten to run on the Renesas R8C 25 Motor Control Platform YMCRPR8C25 but could be modified to implement motor control in a user application The program is written in C Renesas M16C Standard tool chain V5 43 Code may be downloaded from the Application Section of the Renesas Website Filename an_reu05b0074_r8c_apl zip Use the latest version on the home page http www renesas com 6 0 Glossary The following terms acronyms and or abbreviations appear in this app note 6 1 Acronyms BLDC Brushless DC Motor IGBT Insulated Gate Bipolar Transistor PWM Pulse Width Modulation REU05B0074 0101 Rev 1 01 December 2008 Page 12 of 14 CENESAS APPLICATION NOTE Revision Record Description Rev Date Page Summary 1 00 Feb 05 08 First edition issued 1 01 Dec 08 08 14 Updated references All trademarks and registered trademarks are the property of their respective owners REU05B0074 0101 Rev 1 01 December 2008 Page 13 of 14 R8C Family Six Step Trapezoidal Control using HALL Sensors CENESAS Notes regarding these materials 1 This document is provided for reference purposes only so that Renesas customers may select the appropriate Renesas products for their use Renesas neither makes warranties or representations with respect to the accuracy or completeness of the information contained in this document nor grants any license to any intellectual property rights or any other rights of Renesas or any third party wi
22. s products or if you have any other inquiries Note 1 Renesas Electronics as used in this document means Renesas Electronics Corporation and also includes its majority owned subsidiaries Note 2 Renesas Electronics product s means any product developed or manufactured by or for Renesas Electronics RENESAS OO arruicarionnore R8C 25 Group Driving of a 3 phase BLDC Motor by 120 Degree Trapezoidal Wave Commutation using HALL Sensors Table of Contents wO ADSI meen ee en ne E ee eee 20 COO O i a 30 MUOU UOM R E a ck otecees 3 1 Basic 3 phase Inverter Topology cccccssececesseeecceeseeeceeseeeceaseecseseeeesaseeessaneessnaaeees 3 1 1 General Inverter TOPOlOQGY ccccccccceeeceseeseececeeeeseeeeeeeeeeeeeesaaeeeeeeeeeesseaeeeeeeeees 3 1 2 R8C 25 Specific Inverter TOPOlOGY cccccccccesssseeeeceeeeeeeeeeeeeeeseesseeaeeeeeeeeeeeaaas 3 2 Basics of Trapezoidal Commutation 6 StED cece eeceeeeeeeeeeeseeeeeeeeesaaeeeeeeeeeeeeeneaeees 3 2 1 Controlling Phase Voltage sssrin inaano naaa EE E 3 22 PROOF Ie O SILOM aee E E E 323 COMTMUTAUNO ices aeisesiea dae de cesanactcetsacediect clo palsediinesend E a ai 3205 WICASUPIMNG SD ECC cts iesccetoccssseseetasenncetscedneadacedesciasogeestasaensetasedetensedeenegeeseessats odenesesebeaatess 3 4 Basics of PI Speed LOOP cccccccsssseeecccesseeeccceeesececcceeuseeeescueuseeeesseaueeeessaaeeeeessaaseeess SiOz IMPIEMENlATIONFANG TSI
23. state is STEP1 So looking at these signals we have a pretty good idea that our motor will spin if driven by this code assuming our Hall Sensor Signature look up table is correct REU05B0074 0101 Rev 1 01 December 2008 Page 9 of 14 R8C 25 Group Six Step Trapezoidal Control using HALL Sensors CENESAS 3 5 2 Hall Signature Testing So we still do not need to hook up the motor windings To reiterate bad things happen when motor software has bugs We just hook up the Hall sensor to our inputs and capture the Hall signals with a scope and the software Tek elle Acq Complete M Pos 40 00 us TRIGGER oa Type U Phase Current slope Falling Mode Mormal Hall A Hall B Coupling a oi Hi So0y tHe E M Lims CHI 3004 Hall C CHS 5 00 CH4 1 004 2o Noy OF 09 54 106 499Hz Figure 3 13 Hall Sensor signature and Phase Current You can see from this figure that the HALL pattern is not directly correlated to a STEP number however the software needs to know where the rotor is For this we construct a revesre look up table that translates pragma rom HallTable const HALL_TBL_ENTRY HallTable NO_STEP O 0 NO_STEP STEP2 THETA_60DEG 1 STEP2 STEP4 THETA_180DEG 2 STEP4 STEP3 THETA _120DEG 3 STEP3 STEP6 THETA 300DEG 4 STEP6 STEP1 THETA _ODEG 5 STEP1 STEP5 THETA 240DEG 6 STEP5 NO_STEP 0O 7 NO_STEP FIGURE 3 14 HALL Reverse look up Table NOTE This scope pictu
24. support devices or systems 2 surgical implantations 3 healthcare intervention e g excision administration of medication etc 4 any other purposes that pose a direct threat to human life Renesas shall have no liability for damages arising out of the uses set forth in the above and purchasers who elect to use Renesas products in any of the foregoing applications shall indemnify and hold harmless Renesas Technology Corp its affiliated companies and their officers directors and employees against any and all damages arising out of such applications 9 You should use the products described herein within the range specified by Renesas especially with respect to the maximum rating operating supply voltage range movement power voltage range heat radiation characteristics installation and other product characteristics Renesas shall have no liability for malfunctions or damages arising out of the use of Renesas products beyond such specified ranges 10 Although Renesas endeavors to improve the quality and reliability of its products IC products have specific characteristics such as the occurrence of failure at a certain rate and malfunctions under certain use conditions Please be sure to implement safety measures to guard against the possibility of physical injury and injury or damage caused by fire in the event of the failure of a Renesas product such as safety design for hardware and software including but not limited to redundancy fir
25. th respect to the information in this document 2 Renesas shall have no liability for damages or infringement of any intellectual property or other rights arising out of the use of any information in this document including but not limited to product data diagrams charts programs algorithms and application circuit examples 3 You should not use the products or the technology described in this document for the purpose of military applications such as the development of weapons of mass destruction or for the purpose of any other military use When exporting the products or technology described herein you should follow the applicable export control laws and regulations and procedures required by such laws and regulations 4 All information included in this document such as product data diagrams charts programs algorithms and application circuit examples is current as of the date this document is issued Such information however is subject to change without any prior notice Before purchasing or using any Renesas products listed in this document please confirm the latest product information with a Renesas sales office Also please pay regular and careful attention to additional and different information to be disclosed by Renesas such as that disclosed through our website http www renesas com 5 Renesas has used reasonable care in compiling the information included in this document but Renesas assumes no liability whatsoever for any
26. ts are kept coherent by stopping the timer to prevent a pre scaler underflow in between the read of the pre scaler and the read of the timer The value is assembled in a structure accessible as 2 BYTEs or aWORD The timer and pre scaler are then reloaded with the normal reload value OxFF and OxFF Since the upper level code that converts counts to RPM uses positive numbers the value is inverted by subtracting it from the timer RB starting count of 65 535 Oxffff and this value is returned REU05B0074 0101 Rev 1 01 December 2008 Page 5 of 14 R8C 25 Group Six Step Trapezoidal Control using HALL Sensors CENESAS In applications that may require very high accuracy the return value may be adjusted by the number of counts required to stop read and re start Timer RB This value may be derived empirically or determined by evaluating the code using the cycle accurate simulator in the tool chain So let s look at an example Assume we are using a 2 5MHz clock for timer RB and we get a count of 2500 2500 counts 2 5M counts second 1 millisecond Since this represents 60 electrical degrees or 1 30 of a revolution we can then calculate out 30 1mS 30MmS per revolution or 33 33 Revs per second 60 seconds minute 2000 RPM In addition to measuring speed the Timer RB underflow can be used to detect slow or stalled motor NOTE Due to asymmetry in the output of the Hall sensors it is highly recommended that speed measurements be a
27. veraged or filtered Since the speed loop is typically running at some lower rate than the PWM this is typically not a problem In addition if the averaging is a power of 2 2 4 8 etc the averaging then becomes just a shift which is easily performed by the R8C 3 4 Basics of PI Speed Loop SO now we can commutate to move the motor measure its speed and vary the phase voltage to control its soeed how do we keep the speed accurate under varying loads For this we will incorporate a basic PI speed loop a feedback system quick run Control Systems 101 rears its ugly head Figure 3 7 Speed Loop ee shows our basic PI speed loop i Voltage to Ww PWM Count Timer RD Conversion GPIO Counter Timer RB Rotating speed Micro Computer ASR Auto Speed Regulator PI Controller Although it is actually telling us position we only use that information for commutation Not part of control loop but shown for clarity Or Commanded speed in Radians per second Or Measured speed in Radians per second Hall Sensor position tach Figure 3 7 Basic PI Speed loop Remember from your basic control systems a typical loop consists of a feedback element in this case the Hall sensor and timer RB feeding back speed b error detection typically summing junction in this case single line of code that compares commanded speed against measured speed to calculate error c Gain stage amplifie
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