Home

PMSM Vector Control with Quadrature Encoder on Kinetis

1. Space vector modulation PWM registers update with the calculated duty cycle 4 7 4 3 PORTC interrupt Handling user buttons on the K40 tower board is performed in the ISR associated with the PORTC interrupt generated whenever one of the buttons is pressed At the beginning of the ISR simple logic is executed to evaluate what button is pressed and the interrupt flag is cleared Because there are only two user buttons in the application the assigned functions are RUN and STOP there is limited control possibility rotation only in one direction Pressing the RUN button causes the speed to increase in 10 steps Pressing the STOP button causes the speed to decrease in 10 steps and also a fault acknowledgment More about the application control via the user buttons in the chapter Application control Using the FreeMASTER control interface allows for enhanced control and diagnostic See details in the same chapter PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 39 Program flow 4 7 5 Project file structure The total number of source files c in the project is 36 and there are an additional 86 header h files in the project tree Therefore only the key project files will be described in more detail and the rest will be described in groups The main project folder is divided into three directories build Contains configuration files for th
2. Nominal Current phase 5 20A Nominal Torque 0 30 Nm Motor Model Parameters Stator Winding Resistance line to line 0 576 Ohm Stator Winding Inductance d axis 0 468 mH Stator Winding Inductance q axis 0 618 mH Number of Pole Pairs 3 Position Sensor Specification Manufacturer name INDUcoder Type ES 28 6 1024 05 D R Pulse Count per revolution 1024 Output 5 V 10 TTL PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 20 Freescale Semiconductor Inc Chapter 4 Software Design 4 1 Software design The application software was designed using the compiler AR Embedded Workbench for ARM v 6 21 4 2 Fractional numbers representation In the development of the vector control algorithm software libraries were used a Set of the General Maths and Motor Control Functions for the Cortex M4 Core Most of the mathematical calculations were performed with the numbers represented in Q1 15 or Q1 31 signed fractional format so all physical quantities were scaled to the lt 1 1 interval For more on the fractional format and variables scaling see DRM105 3 4 3 Application overview The application is real time interrupt driven with the background infinite loop handling the application states Initialization Run Fault and FreeMASTER communication polling There are two periodic interrupt service routines where the control process is executed Their timing is given by the requirements of the vector
3. The interface to the programmer is only via freemaster_cfg h file src Common Contains specific header files associated with the software libraries 4 7 6 Memory usage The following table summarizes chip memory usage Memory Total Available on the Kinetis Used by the Application MK40X256VMD100 Program Flash application code 256 000 20 994 Data Flash application constants 2 106 Data RAM application variables 64 000 1 662 PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 41 Program flow PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 42 Freescale Semiconductor Inc Chapter 5 Application Setup and Operation 5 1 Application set up and operation The application can be operated via the user s buttons on the K40 tower module or via the FreeMASTER interface The set up procedure of the FreeMASTER software on the PC as well as the application operation is described in the User s Manual 13 PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 43 Application set up and operation PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 44 Freescale Semiconductor Inc Chapter 6 Measurement Results 6 1 CPU load and the execution time The CPU load is influenced mainly by the execution of the ADC1 ISR in which the calculation of
4. The next step is to redefine the vector pointer in the vectors h file from the default ISR to the function that contains the code to be executed after an interrupt is generated Replace define VECTOR_084 default_isr with define VECTOR_084 PIT CHO ISR_Handler and add at the end of the file extern void PIT _CHO_ISR_ Handler void because the ISR is defined in the other file main c in this case PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 30 Freescale Semiconductor Inc SSS ee ee Chapter 4 Software Design Next set up the ARM core NVIC register Each interrupt vector must be independently enabled or disabled by setting the corresponding bit in the complementary pair of registers the Interrupt Set Enable Register NVIC_ISERx or the Interrupt Clear Enable Register NVIC_ICERx NVIC_ISERO contains the enable bits for IRQ numbers 0 through 31 NVIC_ISER1 contains the enable bits for IRQ 32 through 63 and so on To enable the PIT channel 0 interrupt interrupt number 68 it is necessary to write 0x00000010 b10000 to the NVIC_ISER2 register It is an advisable approach to clear any pending interrupt before it is enabled This is usually not necessary to do right after the reset when the MCU initialization is performed but during the program execution when a certain interrupt is disabled and later re enabled again If an interrupt flag has been set before the interrupt was enabl
5. and subdirectories in the src mcu_Init folder common and cpu Folders containing CPU initialization routines cpu vectors h An important file with definition of the peripherals interrupt service routines assigned to the interrupt vectors In this file you can add the definition of an ISR for an additional peripheral interrupt drivers Files in the subdirectories contain generic source and header files for UART and watchdog configuration as well as the CPU clock settings routines PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 40 Freescale Semiconductor Inc Chapter 4 Software Design peripherals Contains important files for static configuration of the peripherals used in the application FlexTimers ADC PDB SPI PIT platforms tower h Contains the Kinetis Tower card definitions CPU speed and UART parameters Files in the src twrk40x256 folder MK40X256VMD100 h Header file containing macro definitions of all the MCU registers and register bits Files in the src MC_Lib folder Cortex_M4 a Software library containing motor control general math and filter algorithms Other files in the folder and subfolders are associated header files each one for a particular function of the library Other subdirectories in the src folder s src FreeMASTER Contains all source files of the FreeMASTER application it is not necessary to access it or change anything inside
6. and the interrupts are enabled This particular state function is executed only once and transitions to the Calibration state e APP_CALIBRATION Calibration of the offset on the ADC channels for all three phase currents is performed The values are stored in the ADC offset registers The offset value represents the zero current and is automatically subtracted from the sampled value during the motor run so there is already a positive or negative value of the current available in the ADC result register e APP_ALIGNMENT The rotor is aligned to a known position by applying only the d portion of d q current system e APP_STOP The application is fully initialized and is awaiting the start of the motor run either by pressing the Start button or setting the state variable from the FreeMASTER software The PWM output pads are still disabled The Stop state can also be entered from the Run state e APP_RUN The voltage is applied to the motor and the speed of the motor is regulated according to the required speed profile e APP_FAULT The application waits for the fault removal and fault acknowledgment 4 7 3 2 Transitions definition e AppInitToCalib In this subroutine all application variables are initialized to their default values e AppCalibToAlign Enables the PWM output pads assigns the default ADC channels to the ADC modules and enables the ADC interrupt so that the vector control algorithm can be performed during the rotor alignment
7. half bridge and the turning on of the complementary transistor due to limited switching speed of the transistors FOC Field Oriented Control FTM FlexTimer module A timer module on the Kinetis K40 MCU that serves for generating of the 6 channel PWM GPIO General purpose input output IAR The name of the company producing compilers for different platforms and MCU manufacturers including ARM IDE Integrated Development Environment O0 Input output interfaces between a computer system and the external world A CPU reads an input to sense the level of an external signal and writes to an output to change the level of an external signal ISR Interrupt Service Routine A fragment of code a function that is executed when interrupts from the core or from the peripheral modules are generated LED Light emitting diode K40 Freescale Kinetis MK40 ARM Cortex M4 32 bit microcontroller MTPA Maximum Torque per Amp Algorithm A special algorithm used in vector control of AC motors Thanks to this algorithm the efficiency and the power of the motor is increased by using the reluctance torque of the motor MSB Most Significant Bit NVIC Nested Vector Interrupt Controller An integral part of the ARMv7 core responsible for the interrupts processing PDB Programmable Delay Block PI controller Proportional integral controller Table continues on the next page PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 50 Freescale Semic
8. of each peripheral module Table 4 1 shows an overview of the Kinetis K40 peripheral modules used by the application the number of modules and module channels reflect a 144 pin package Table 4 1 Kinetis K40 peripherals overview Kinetis K40 peripherals Used in the application Purpose Group Module Number of modules or channels Analog ADC 2 modules both 23 3 channels on DC bus voltage and channels single ended motor phase currents ADCO and 3 differential pairs sensing 2 channels on ADC1 Comparators 3 DAC 2 Communications SPI 3 1 MOSFET driver configuration UART 6 1 FreeMASTER communication CAN 2 USB 1 12C 2 SDHC 1 12S 1 Table continues on the next page PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 22 Freescale Semiconductor Inc Chapter 4 Software Design Table 4 1 Kinetis K40 peripherals overview continued Timers FlexTimer 8 ch 6 ch Generation 6 ch PWM for motor control 2ch 2ch Quadrature encoder signals decoding 2ch PIT 4 1 1 ms time base for speed calculation PDB 2 ch for ADC triggering 2 DC bus voltage and phase current sampling initiation 2 ch for DAC triggering LPT 1 CMT 1 RTC 1 4 4 1 FlexTimer0 configuration for generating a 6 channel PWM The FlexTimer Module FTM is a two to eight channel timer that su
9. of voltage that is currently available on the DC bus This approach together with use of an anti windup strategy in the algorithm of the PI regulator gives higher stability to the drive system during load variations rather than using only the circle limitation of the output voltage vector The integrator inside the regulator algorithm stops when the power limitation occurs due to a step increase of the load or a DC bus voltage drop The figure below is a block diagram of the fast current control loop including the computation of the current controller limitations PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 15 Control theory Fast control loop Inv Park From speed regulator z DC Bus Voltage e sses _ Phase Currents Measured To speed Speed regulator Figure 3 4 Block diagram of the fast control loop The equations 3 1 and 3 2 show the mathematical expression of the controllers limitation Eqn 3 1 U Ua tim Eqn 3 2 2 Upc 2 Ug Lim U d Where Ug Lim Uq_Lim are the limitations of the d and q current PI regulators respectively Upcp is the actual value of the DC bus voltage Ug is the output of the d current PI controller The parameters of the PI current regulators were tuned using the Ziegler Nichols method After the motor alignment in the d axis the rotor has stopped and according to the step response the parameters of the d cu
10. process e AppAlignToStop PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 36 Freescale Semiconductor Inc Ey y Chapter 4 Software Design After the rotor alignment the quadrature decoder counter FTM1 counter is cleared and all variables are set to their default values The PWM output pads are disabled e AppStopToRun The PWM output pads are enabled and the variables are again set to default values except for the speed and position related calculation just in case there was an attempt to run the motor in the stop state Toggling the user s LEDs on the K40 tower board signals the change of state e AppRunToStop If the speed is non zero the application waits till the motor stops by forcing the required speed to zero If the motor is in standstill the PWM output pads are disabled Toggling the user s LEDs on the K40 tower board signals the change of state e AppRunToFault The PWM output pads are disabled The user s LEDs on the K40 tower board are toggled to signal the change of the state See the triggering events in Section 5 e AppStopToFault In the Stop state measurement of the DC Bus voltage is performed and the value is compared against the overvoltage threshold The application can enter the Fault state from the Stop state in the case of an overvoltage error e AppFaultToStop Performing the reset and re initialization of the MC33937 MOSFET driver after a fault was acknowledged 4 7 4 Interrupt
11. the fast current control loop of the PMSM vector control is performed The complete ADC1 ISR requires 1628 machine cycles It is executed periodically with the same frequency as the PWM reload event when the values of the duty cycles are updated In this application the fast control loop is executed once per 63 us which corresponds to 16 kHz of the PWM frequency At 100 MHz on the Kinetis K40 device it consumes roughly 35 of CPU performance 6 2 Measurement results using FreeMASTER 6 2 1 3 phase current reconstruction Figure 6 2 is the measurement of the 3 phase motor currents The values are captured using the FreeMASTER recorder PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 45 Measurement results using FreeMASTER SAUNI e j n Current Phase A Current Phase B Current Phase C svmSector 0 50 S 0 25 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Figure 6 1 Motor phase currents and SVM sector 6 2 2 Speed controller The PI speed controller is executed in the PIT CHO ISR once per 1 ms The parameters of the regulator were tuned to obtain a sharp step response without overshoot The following figure shows the speed profile the required and measured speeds At first the motor is set to run at a nominal speed of 3000 rpm in a clockwise direction then reversed to a counter clockwise direction 3000 rpm PMSM Vector Control with Quadrature Encoder on Kinet
12. there has to be a certain software workaround performed in the PIT interrupt service routine to allow generation of the next interrupt 1 Disable the interrupt first by clearing the TIE bit while the TEN bit remained unchanged PIT TCTRLO 0x01 2 Clear the interrupt flag PIT _TFLGO 0x01 3 Enable the PIT interrupt again PIT TCTRLO 0x03 4 4 7 SPI configuration The SPI interface is used in the application for communication between the intelligent MOSFET driver MC33937 and the K40 MCU The MC33937 driver is placed on the Tower low voltage power module and serves for driving the high side and low side MOSFET transistors of the 3 phase inverter In the application the initialization of the MC33937 has to be performed mainly in setting the dead time During the motor run there is also periodic checking of the status register of the driver in the PIT interrupt to provide information on the latched faults The MC33937 driver requires precise timing of the SPI signals The default MCU setting is not possible to use The exact timing of the SPI signals is listed in 8 PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 29 Enabling the interrupts on the core level 4 4 8 SCI UART configuration The SCI is used in the application for the communication between the master system and the embedded application A master system is the notebook or the PC where the FreeMASTER s
13. 4 7 3 Application state machine A simple application state machine handles the switching between the application states and application state transitions This is executed in the infinite background loop in the program main The following figure gives an overview of the program flow through the application states and transitions Initialization AppInitToCalib APP INIT Calibration AppCalibToAlign APP_CALIBRATION qed AppAlignToSto APP ALIGNMENT PP g pU Stop _AppStopToRun 0 AppStopToR APP STOP a tata AA Run APP RUN AppStopToFault AppRunToFault AppRunToStop Fault APP FAULT AppFaultToStop Figure 4 4 Application state machine diagram The application states represent a steady state This means that usually the application is waiting on some trigger or condition to change the state The particular function is called each time the program makes one pass of the infinite background loop The application state transitions contain instructions that are executed only once when the application state is changed Typically the settings in the peripheral registers are performed only once and it is not necessary to repeat them PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 35 Program flow 4 7 3 1 States definition e APP_INIT The default state after the MCU reset The peripherals are configured the MOSFET driver MC33937 is initialized
14. ITTRIGEN MASK Finally the output pins of the MCU have to be configured to bring the signals out of the chip The assignment of signals to output pins is set in the Pin Control Register while the available signals are listed in the Signal Multiplexing chapter of 1 and are package dependent PORTC_PCR1 PORT _PCR_MUX 4 FTMO CHO PORTC_PCR2 PORT _PCR_MUX 4 FTMO CH1 PORTC_PCR3 PORT _PCR_MUX 4 FTMO CH2 PORTC_PCR4 PORT _PCR_MUX 4 FTMO CH3 PORTD PCR4 PORT PCR _MUX 4 FTMO CH4 PORTD PCR5 PORT _PCR_MUX 4 FTMO CH5 The port settings implemented in the application code of course reflect the hardware solution built on the Tower system modules PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 24 Freescale Semiconductor Inc SSS Chapter 4 Software Design 4 4 2 FlexTimer1 configuration for position detection using a quadrature encoder FlexTimer is used in the application to decode the quadrature encoder signals A detailed procedure on configuring the FTM for this operation as well as the principle of position and speed detection using a quadrature encoder is described in the application note titled Configuring the FlexTimer for Position and Speed Measurement with an Encoder document number AN4381 7 4 4 3 ADC and PDB module configurations The on chip ADC module is used to sample feedback signals motor phase current and DC bus voltage that are necessary to successfull
15. PMSM Vector Control with Quadrature Encoder on Kinetis Document Number DRM128 Rev 0 1 2012 V N o freescale PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc Contents Section Number Title Page Chapter 1 Introduction 1 1 Introdtctioi ceara nana ATE E E ERER EA EIEEE EREI A E igo ER EARE AAEREN i Chapter 2 System Specification eA a a N E E E E E E E E EE EEE AE A E E 9 Chapter 3 System Design 3 1 Comrol teoryen ariran E N AAR R ANRE AA EA AREAN ANEIRIN ataxsdaratiansmarpadeaaasatitiadeusenaaenignsases 11 3 1 1 3phase permanent magnet synchronous MOOK vias csscisemsivoransssavessvtcxnvmenvsiearaterisaversawiniavexapedvibawecneouanwioenveseqnerenes 11 SLA ECE ta RITES TWO airia E Muay etiean Glades 11 Sel Vector contol impleret osnan nae e a E EEEE E AE EAA NEEE EES 13 LLa Prenen cgtollers Doit iSe a a setat id epearecniauaueets 15 IA BLAU ABS gisele sins Sake ick ad xp A E aA Gass sOoanicitas E Sasha E A RE E AD A 17 So Horiwac Be lpr and INT AL IR sce pce secs id tsuneo sabi gas E aia ini onescide a sind a 17 Chapter 4 Software Design Al Sotware ISG UL scotia ccd vs ae ea ews a beak ech Wan tala alc ces Bees a mas ouuaSy Suess nea baa A A TRR 21 A2 Prac Hiei mmtibersteptes ntatiHi oaie N A E AR R E ERENS 21 dT APPIE On ONN E e a a EA E A A saxtitigunss 21 44 Kinets KAO peripheral madules cenit Porat ih snsnsvi ikoan iana Ar A aa aa k Eiei ua 22 4 4 1 FlexTimer0 conf
16. ay vary over time All operating parameters including Typicals must be validated for each customer application by customer s technical experts Freescale Semiconductor does not convey any license under its patent rights nor the rights of others Freescale Semiconductor products are not designed intended or authorized for use as components in systems intended for surgical implant into the body or other applications intended to support or sustain life or for any other application in which failure of the Freescale Semiconductor product could create a situation where personal injury or death may occur Should Buyer purchase or use Freescale Semiconductor products for any such unintended or unauthorized application Buyer shall indemnify Freescale Semiconductor and its officers employees subsidiaries affiliates and distributors harmless against all claims costs damages and expenses and reasonable attorney fees arising out of directly or indirectly any claim of personal injury or death associated with such unintended or unauthorized use even if such claims alleges that Freescale Semiconductor was negligent regarding the design or manufacture of the part RoHS compliant and or Pb free versions of Freescale products have the functionality and electrical characteristics as their non RoHS complaint and or non Pb free counterparts For further information see http www freescale com or contact your Freescale sales representative For informa
17. cal sensor is a significant portion of the cost of the whole drive Rotor quadrature axis Rotor direct axis Rotor with permanent magnets Stator Pi winding Figure 3 1 Synchronous machine and the main principle of the vector control As mentioned the required torque is proportional to the q portion of the orthogonal d q currents system The d portion reflects the generation of the rotor magnetic flux Because there are permanent magnets mounted on the PMSM rotor this current is usually kept at a zero level unless the field weakening is performed to accelerate the motor above the nominal speed or while performing the MTPA algorithm In such cases the required d current possesses a negative value Therefore the control process regulation is focused on maintaining the desired values of the d and q currents Because the d q system is referenced to the rotor the measured stator currents have to be transformed from the 3 phase a b c stationary frame into the 2 phase d q rotary frame before they enter the regulator block At first the Clarke transformation is calculated which transforms the quantities from the 3 phase to 2 phase systems Because the space vector is defined in the plane 2D it is sufficient to describe it in the 2 axis alpha beta coordinate system Consequently the result of the transformation into the 2 phase PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 12 Freescale Semiconducto
18. control algorithm The control process is composed of two control loops Execution of the fast current control loop is performed in the ADC1 interrupt service routine which is executed after the values of the sampled DC bus voltage and motor phase currents are put into the ADC result registers The sampling instance is precisely defined by the hardware trigger of FlexTimer0 that is configured to generate six PWM signals of frequency 16 kHz PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 21 a Kinetis K40 peripheral modules configuration The PITO interrupt service routine is triggered every one millisecond In this ISR the speed is calculated as a position derivation and the speed controller slow speed control loop is calculated The individual processes of the control routines are described in the following sections 4 4 Kinetis K40 peripheral modules configuration In this section peripherals configuration procedures used are described or referenced On all Kinetis family devices it is necessary to enable the system clock for the module before any access to the peripheral registers is performed The modules are enabled by writing 1 to the particular bit in the System Clock Gate Control Register Any write or read attempt to the peripheral register before enabling the clock for a particular peripheral module will yield a hard fault Refer to 1 for a detailed description
19. e AR compiler as well as the compiler s output executable and object files If the ILAR Embedded Workbench for ARM is installed on your computer double clicking the workspace file TWRK40X256_PMSM_FOC eww located in the directory build iar would launch the IAR IDE gui Contains the FreeMASTER configuration file Kinetis_FOC_demo pmp and supporting files control page in HTML format and the binary file with addresses of the variables src Contains the project source and header files and its contents will be described in the following text Files in the root of the src folder main c contains Application control interrupt routines fast and slow control loops as well as the background infinite loop with the application state machine main h Header file of the main application file containing the macros and structures related to the application control and constant definitions related to the application state machine enc c and enc h Contain the position and speed calculation from quadrature encoder signals freemaster_cfg h Configuration file for the FreeMASTER interface PMSMFOC_appconfig h Contains constants definition for the application control processes parameters of the motor and regulators and the constants for other vector control related algorithms The regulators parameters can easily be calculated using the K40_PMSM_Encoder_config xls file but the system parameters have to be identified Files
20. ed the interrupt controller may generate an unhandled exception fault if the interrupt flag has not been cleared before NVICICPR2 NVICISER2 0x00000010 clear pending interrupts first 0x00000010 enable the PIT CHO interrupt NOTE The ARM document 9 indicates that the registers have an underscore between NVIC and ISER NVIC_ISER1 However in the current header files used in the application the NVIC register names do not have the underscore NVICISER1 or NVICICPR1 NVIC interrupts are prioritized by updating an 8 bit field within the 32 bit NVIC_IPRx registers Thanks to macros contained in the Kinetis K40 header file used in the project setting the priority of the interrupt has been simplified The number of the interrupt is used as one of the parameters of the NVIC_IP macro The assigned value then determines the priority the higher the number the higher the priority of the interrupt If the interrupt priority is not specified the lower the number of the interrupt vector the higher priority the interrupt has by default On the Kinetis family there are 16 levels of interrupt priority implemented However the priority is set in the four MSBs of the 8 bit field NVIC_IP 68 OxFO set the highest priority for PIT ch 0 interrupt The next step is to enable the interrupts globally by clearing a 1 bit special purpose mask register PRIMASK The PRIMASK is cleared to 0 by the execution of the instruction CPSIEi In the ap
21. ent is used to control the rotor magnetizing flux The quadrature axis current corresponds to the motor torque The current PI controllers outputs are summed with the corresponding d and q axis components of the decoupling stator voltage Thus the desired space vector for the PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 13 OO Control theory stator voltage is obtained and then applied to the motor The fast control loop executes all the necessary tasks to achieve an independent control of the stator current components These include e Three phase current reconstruction e Forward Clarke transformation e Forward and backward Park transformations e Rotor magnetizing flux position evaluation e DC bus voltage ripple elimination e Space vector modulation SVM The slow control loop executes the speed controller field weakening control and lower priority control tasks The PI speed controller output sets a reference for the torque producing quadrature axis component of the stator current iq_ref and the flux producing current id_ref To achieve the goal of the PM synchronous motor control the algorithm uses feedback signals The essential feedback signals are three phase stator current and stator voltage For correct operation the presented control structure requires a speed feedback on the motor shaft 5 Kinetis K40 Inv Park Trans PWM Output Speed reference t
22. hazardous state described above The required and actual speed has to have the same orientation otherwise the fault is triggered and the motor is disconnected from the voltage Then the speed PI controller is calculated The step change in the required speed is ramp limited prior to the regulation error being computed As mentioned the output of the speed regulator is the required q axis component of the current that is directly proportional to the required torque needed for motor acceleration or for overcoming all drive frictions while maintaining a constant speed In the PIT channel 0 ISR there is also a periodic check on the status register of the MOSFET driver MC33937 via the SPI interface When any fault is latched by the driver the application is forced into the fault state and the user can check the source of the fault via the FreeMASTER control interface For more details see the User s Manual 13 Table 4 2 summarizes the software routines executed in the PIT CHO ISR Table 4 2 Software routines executed in the PIT CHO ISR Speed calculation PIT CHO ISR Speed filtering moving average Motor phase disconnection detection Ramp limitation of the required speed Speed PI controller calculation MOSFET driver status register check 4 7 4 2 ADC1 interrupt This interrupt request is triggered when the conversion of channel A of the ADC1 module is completed At the moment of the interrupt generati
23. he microcontroller the MCU is in debug mode This does not depend on the running code containing breakpoints or not The PWM signals generated by the FlexTimer0 are directly connected to the MOSFET driver Due to safety reasons the input signals for the top transistors on the MOSFET driver used on the Tower low voltage power stage have inversed polarity Therefore it is also necessary to set the right polarity of the PWM signals FTMO POL FTM POL POLO MASK FTM_ POL POL2 MASK FTM_ POL POL4 MASK The duty cycle is changed by changing the value of the FlexTimer Value registers These registers are double buffered meaning that their values are updated not only by writing the number but it is necessary to confirm the change by setting the Load Enable LDOK bit This ensures that all values are updated at the same instance FTMO PWMLOAD FTM PWMLOAD LDOK MASK It is necessary to write the LDOK bit every time the value registers are changed so not only at the stage of loading them with initial values but with every update after the duty cycle value is computed in the vector control algorithm As mentioned in section 4 3 4 in this application hardware triggering of the A D converter is employed The Initialization Trigger signal from the FlexTimer is used as the primary triggering signal which is fed into the Programmable Delay Block that services the timing of the AD conversion initiation FTMO EXTTRIG FTM EXTTRIG IN
24. ibes the design of a 3 phase permanent magnet synchronous motor PMSM vector control drive with quadrature encoder as a position and a speed sensor The application runs on the Kinetis K40 ARM Cortex M4 microcontroller The document briefly describes the theory of the PMSM vector control and the hardware solution used It is focused more on the application implementation on the Kinetis K40 microcontroller Although the paper describes implementation on the Kinetis K40 the application can successfully run on any of the microcontrollers from the Kinetis family Application features e Vector control of a permanent magnet synchronous motor using the quadrature encoder as a position sensor e Targeted at the Tower rapid prototyping system K40 tower board Tower 3 phase low voltage power stage e Vector control with a speed closed loop e Rotation in both directions e Application speed ranges from 0 to 100 of nominal speed no field weakening e Operation via user buttons on the Kinetis K40 tower board or via FreemMASTER software Solution Benefits Kinetis is a mixed signal MCU family based on the new ARM Cortex M4 core and the most scalable portfolio of mixed signal ARM Cortex M4 MCUs in the industry Five performance options are available from 50 to 150 MHz with flash memory ranging from 32 KB to 1 MB and high RAM to flash ratios throughout Common peripherals memory maps and packages both within and across the MCU families allow for easy m
25. igration to PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 7 Introduction greater or less memory and functionality A vector control algorithm demonstrated in this application enables PM Synchronous Motor control with excellent dynamic performance PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 8 Freescale Semiconductor Inc Chapter 2 System Specification 2 1 System specification The system solution is designed to drive a 3 phase PM synchronous motor The application meets the following performance specification e Application is targeted at the MK40x256 Kinetis ARM Cortex M4 microcontroller e Freescale s Tower rapid prototyping system is used as the hardware platform e The control technique incorporates e Vector control of a three phase PM synchronous motor with quadrature encoder e Closed loop speed control e Bi directional rotation e Close loop current control e Flux and torque independent control e Starting up with alignment e Field weakening is not implemented oReconstruction of three phase motor currents from two measured values e 63 Us sampling period on the MK40 with the FreeMASTER recorder e Works with the FreeMASTER software interface for application control and monitoring e Required speed setting start stop status motor current system status faults acknowledgment e Includes FreeMASTER software speed scope observes actual and desi
26. iguration for generating a 6 channel PWM cccccceseseceescesseeseeeseeseeseeacensecsecnnecaeenaeeneeeaeesees 2a 4 4 2 FlexTimer1 configuration for position detection using a quadrature encoder eesseeeeeeseeeeesrererrerererrsrerrerersees 24 AAS ADC and PDE module confi ourahonS ossiani araa ease dbaadesnasubascuenesumeedoesesonassiasconaubadusaccatie 23 44 4 ADC conversion timing currents and voltage Sampling x 0csccccscceseue aiescneenxensne oteasnncdzanskeeocaneneoodennnndanancatinenotinies 29 A CEDE N SE a reine te egwlanagp cat ocassehniamactapieciesafaaiapeediatonintah e ciesatanl autubissenantanmapislauaneeuaeiamants 26 BAS Ponodie mntemupt AUS EERE gurah asrida anane a b 28 E SEEE A E n E E A E A E E E E A A A T 29 PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 3 Section Number Title Page AAS SCHUAR TD coeurs a a Oa E A E E 29 a Brabling ihe interrepis on ihe Core lere Lencioni aaraa a E AEE E E a EEE 30 w Wee vies TE R TONN Enaria ra A E R S 32 4 6 1 E A T E E O E A E E A E E A E Ete 32 AG 2 FreeMASTER commmnication I Ese gids aie teatcsied ge accereeendgenaianbvoctelasedubtedaldacakaileunddesetquentdacdeaecantelantiereds 32 A03 FeeMASTER recorder and SCOPE ceirean A a TEE E R A AS 33 LF TOn O ea a tue cagumetinleiesgusgbadeicacubsapuecuntaliade 33 Abi BPA AML Smic ea R A A eines 33 ee PLAC UML DC ee ION cad slats acd dass an accuse an condoaat aids sosdetsiam
27. is Rev 0 1 2012 46 Freescale Semiconductor Inc Chapter 6 Measurement Results a e Required Speed gt 7 a l Actual Speed 0 0 2 5 5 0 7 5 10 0 12 5 15 0 17 5 20 0 22 5 Time sec Figure 6 2 Speed profile PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 47 Measurement results using FreeMASTER PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 48 Freescale Semiconductor Inc Chapter 7 References 7 1 References 1 K40 Sub Family Reference Manual Freescale Semiconductor 2011 2 JAR C C Development Guide Compiling and Linking for Advanced RISC Machines Ltd s ARM Cores IAR Systems AB 2011 3 Designer reference manual titled PM Sinusoidal Motor Vector Control with Quadrature Encoder document DRM105 Devices Supported MCF51AC256 Freescale Semiconductor 2008 4 User reference manual Set of General Math and Motor Control Functions for Cortex M4 Core document number MCLIBCORETXM4UG Freescale Semiconductor 2011 5 Matus Plachy Anders Lundgren Lotta Frimanson Designing advanced DSP applications on the Kinetis Cortex M4 MCU Embedded World 2011 Conference and Exhibition 6 Application note titled Using FlexTimer in ACIM PMSM Motor Control Applications document number AN3729 Freescale Semiconductor 2008 7 Application note titled Configuring FlexTimer for Position and Speed Measurement with Encoder documen
28. ku Tokyo 153 0064 Japan 0120 191014 or 81 3 5437 9125 support japan freescale com Asia Pacific Freescale Semiconductor China Ltd Exchange Building 23F No 118 Jianguo Road Chaoyang District Beijing 100022 China 86 10 5879 8000 support asia freescale com For Literature Requests Only Freescale Semiconductor Literature Distribution Center 1 800 441 2447 or 1 303 675 2140 Fax 1 303 675 2150 LDCForFreescaleSemiconductor hibbertgroup com Document Number DRM128 Rev 0 1 2012 Information in this document is provided solely to enable system and software implementers to use Freescale Semiconductors products There are no express or implied copyright licenses granted hereunder to design or fabricate any integrated circuits or integrated circuits based on the information in this document Freescale Semiconductor reserves the right to make changes without further notice to any products herein Freescale Semiconductor makes no warranty representation or guarantee regarding the suitability of its products for any particular purpose nor does Freescale Semiconductor assume any liability arising out of the application or use of any product or circuit and specifically disclaims any liability including without limitation consequential or incidental damages Typical parameters that may be provided in Freescale Semiconductor data sheets and or specifications can and do vary in different applications and actual performance m
29. lacieimiae 34 Aba Appicanon suie MacMini N 33 ATAT States dentea AN E A S ARA 36 ATIA Tronsri ns deiOh a A E EEE S 36 ATA TEN E aaran ea aa AAE A A EA EA R EA I EDT aN AMOUR nae 37 cere ME e E ROT En 10 nee E E E E E A e7 aE R BE a A E A EEA E A E AAE E A NATE NA A ET 38 krka PORN mE caa a AEE a idee aboasasbaiceert a 39 ATS o A a a E E A an E E E AE E E N E E A E cane E 40 AT Memory Ma Eea E R 41 Chapter 5 Application Setup and Operation Bol Applicaton setup and OPSLATLON dees cacsseasccucscavcznesisacan ennienni oae a EaR A SAR R E 43 Chapter 6 Measurement Results Gl CPU loadond the cretion Nao cs a Lied a A E bua deaeasgasasbncusancasancannees 45 6 2 Measurement results usine Free MASTER joc uica cos srecsoncenccdasspaeccsncaussnoateuovaluoceiseriedwut dee AA E e aAa SE 45 Gol SSMS GUE Nl econ O cicurmpesesedunsevenndsquaciMonipeuadutandociniasauccntehaned 45 De a A E A E E E E E E I T 46 Chapter 7 References AE E E E E E E E E A E E E O E A E 49 PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 4 Freescale Semiconductor Inc a Section Number Title Page FD Acronyms ani AORTA ON Soara nS Na E AA A ERE 50 PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 5 PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc Chapter 1 Introduction 1 1 Introduction This design reference manual descr
30. low transient phenomena such as the speed profile during motor acceleration 4 7 Program flow 4 7 1 Application structure Figure 4 3 is the application software structure PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 33 Program flow PIT CHO overflow ims done Speed calculation Speed PI controller Faults evaluation ADC1 conversion complete 63 ps done Position calculation Fast control loop Critical Faults evaluation FreeMASTER Recorder FreeMASTER poll App State machine PORTC IRQ asynchronous done Manual application control Figure 4 3 Application structure The software structure consists of the application main routine which enters after the CPU reset Here the CPU and peripherals initialize the Application State Machine is serviced and the interrupts generated periodically where the motor control algorithms are executed 4 7 2 Application background loop The endless application background loop contains only two lines calls to two functions The FreeMASTER communication polling function rmstr_po1l The application state machine appstatemachine appState The main application control tasks are executed in the interrupt service routines that interrupt the background loop PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 34 Freescale Semiconductor Inc Chapter 4 Software Design
31. ly as for the FTMO module The values in the channel delay registers are set to generate triggers to start sampling the DC bus voltage and the motor phase AD conversions The PDB module on the K40 MCU allows 15 for different input trigger sources They are listed in the chapter Chip configuration in the section PDB Configuration in 1 Similarly in FTMO the LDOK bit has to be set to acknowledge the changes in the modulo and the delay registers PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 25 Kinetis K40 peripheral modules configuration 4 4 4 ADC conversion timing currents and voltage sampling The FlexTimer0 is configured to trigger an internal hardware signal when its counter is reset after overflow to the initialization value This signal is fed into the Programmable Delay Block PDB that consequently triggers the AD conversion of the voltage and currents with a predefined delay On the Kinetis K40 MCU two ADC modules are implemented Each ADC module associates to one channel of the PDB module Each ADC module has two result registers two channels and they correspond to two programmable pre trigger delays of the PDB channels It is possible to perform four AD conversions without requesting an interrupt respecting that the DMA is not used for data transfer In this application only three conversions need to be triggered without CPU intervention two motor phase current
32. o Iq_req 2 Q9 PI controller Clarke DC Bus Voltage Udcb Measured Phase Currents a Ib speed D E SA l Encoder signals slow control loop fast control loop Figure 3 3 Simplified block diagram of PMSM vector control PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 14 Freescale Semiconductor Inc E Chapter 3 System Design In Figure 3 3 the algorithm of the PMSM vector control is represented as a chain of functions Outputs of one function serve as inputs to the other functions Each body of the functions contain mathematical equations not involving the peripherals To speed up the development of any motor control applications these motor control functions together with some commonly used mathematic algorithms such as trigonometric functions controllers or limitations and digital filters were placed into one set and create the Motor Control Library The motor control libraries are available for some Freescale MCU platforms optimized for each platform to maximize the use of available core features The functions were tested and are well documented Therefore building the motor control application is much simpler for the developer 3 1 3 1 Pl current controllers limitations As mentioned earlier for a better motor dynamic performance the vector control algorithm is enhanced to a dynamic limitation of the d and q current PI controller outputs The main reason is to require only the amount
33. oftware is installed to control the application and visualization of its state On the Kinetis K40 there are six UART modules implemented Due to the hardware solution based on the Tower modules the UART3 is used The communication speed is set to 56000 Bd and in fact it is limited by the USB to Serial Cable used The module configuration is performed in the FreeMASTER software driver included in the project 4 5 Enabling the interrupts on the core level The interrupt request enabled on the peripheral module has to be enabled also on the core level otherwise the interrupt request will not be generated The process is not straightforward and the necessary information is spread over several documents To help the user to enable any interrupt while enhancing the application to other features the process of setting up the PIT interrupt is described in this section as an example The interrupt request on the module level is enabled by writing 1 to the TIE bit of the Timer Control Register PIT TCTRLO PIT _TCTRL TIE MASK It is necessary to find the number of the interrupt and the IRQ vector Both values can be found in the K40 Sub Family Reference Manual 1 in the section 3 2 2 3 Interrupt channel assignments For the PIT channel 1 interrupt the interrupt vector is 84 and the interrupt number is 68 This is always 16 less than the vector number because the first 16 interrupt vectors are ARM core system handler exception vectors
34. on there are sampled values of physical quantities ready in the Result Registers A of the ADCO DC bus voltage Result Register B of the ADCO motor phase current 1 and Result Register A of the ADC1 module motor phase current 2 The interrupt is always enabled only for one module otherwise there would be two interrupt requests generated at the same time this is because the triggers for motor phase currents are generated in the same instance In the PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 38 Freescale Semiconductor Inc EE y Chapter 4 Software Design ADC1 ISR there is the fast current control loop of the PMSM vector control executed Besides the control algorithm computation there are also other supporting routines executed an overview is summarized in the following table Table 4 3 Software routines executed in the ADC1 ISR Reading the ADC result registers 2 based on the actual SVM sector calculation of the third current ADC1 ISR Software overcurrent and overvoltage detection Calculation of the rotor position from the encoder signals Clarke transformation Sin Fast control loop Cos Park transformation D current controller output limitation calculation D current PI controller Q current controller output limitation calculation included SQRT Q current PI controller Inverse Park transformation Elimination of DC bus voltage ripple
35. onductor Inc Chapter 7 Reference Table 7 1 Acronyms and abbreviated terms continued sS tem ng PIT Periodic Interrupt Timer PMSM PM Synchronous Motor permanent magnet synchronous motor PWM Pulse Width Modulation RPM Revolutions Per Minute SCl Serial Communication Interface see also UART SPI Serial Peripheral Interface UART Universal Asynchronous Receiver Transmitter An MCU peripheral module allowing asynchronous serial communication between the MCU and other systems PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc Acronyms and Abbreviations PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 52 Freescale Semiconductor Inc How to Reach Us Home Page www freescale com Web Support http www freescale com support USA Europe or Locations Not Listed Freescale Semiconductor Technical Information Center EL516 2100 East Elliot Road Tempe Arizona 85284 1 800 521 6274 or 1 480 768 2130 www freescale com support Europe Middle East and Africa Freescale Halbleiter Deutschland GmbH Technical Information Center Schatzbogen 7 81829 Muenchen Germany 44 1296 380 456 English 46 8 52200080 English 49 89 92103 559 German 33 1 69 35 48 48 French www freescale com support Japan Freescale Semiconductor Japan Ltd Headquarters ARCO Tower 15F 1 8 1 Shimo Meguro Meguro
36. ort the index signal this can be left disconnected Table 3 2 Motor and encoder connectors on the TWR MC LV3PH a A Motor connector J5 1 Motor phase A 2 Motor phase B 3 Motor phase C Encoder connector J8 1 5V DC 2 GND 3 Encoder phase A 4 Encoder phase B 5 Encoder index PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 19 Hardware CAUTION For Revision B of the TWR MC LV3PH Do not plug any other cables into the Tower system except for the power supply cable and serial communication cable Do not connect any USB cable to the Tower system while the power is applied to the power stage module TWR MC LV3PH The demo system can be powered only via the Tower Low Voltage Power Stage Connecting a USB cable to the Tower Elevator Module can cause damage to the Kinetis K40 See Errata for the revision B of the TWR MC LV3PH on how to correctly operate the board The motor used in the reference design is a standard production industrial 3 phase PM synchronous motor with an incremental encoder mounted on the shaft The motor and the sensor have the following specifications Table 3 3 Specification of the motor and incremental sensor Manufacturer name TG Drives Motor Specification Type TGT2 0032 30 24 TOPS1KX 1M Nominal Voltage line to line 18V Nominal Speed 3000 rpm
37. ortant for motor control applications A detailed users guide of FreeMASTER with useful hints for developing a motor control application can be found in the application note titled Real Time Development of MC Applications using the PC Master Software Visualization Tool document AN1948 11 4 6 2 FreeMASTER communication driver On the MCU side the FreeMASTER software driver is included in the project file structure It is a set of files supporting real time data capture Scope Recorder and handling the communication protocol There are some functions that are unique for each MCU family therefore FreeMASTER is issued for each MCU family separately In the freemaster_cfg h file the user can perform settings related to the communication and to the data buffer In the file are defined macros for conditional and parameter compilation The FreeMASTER driver does not perform any initialization or configuration of the SCI module it uses to communicate PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 32 Freescale Semiconductor Inc _ gt gt E E gt EI gt E gt b E E H gt L E gt 9EE AD LCLCLCLCLC LWDyE R7 R R _ E Chapter 4 Software Design The communication between the MCU and the PC side can be performed with help of the interrupt or via periodic calling of the polling function For a motor control application the polling mode is preferred B
38. oth the communication and protocol decoding are handled in the application background loop The polling mode requires a periodic call of the FMSTR_Poll function in the application main 4 6 3 FreeMASTER recorder and scope The recorder is also a part of the FreeMASTER software which is able to sample the application variables at a specified sample rate The samples are stored in a buffer and read by the PC via an RS 232 serial port The sampled data can be displayed in a graph or the data can be stored The recorder behaves as an on chip oscilloscope with trigger pre trigger capabilities The size of the recorder buffer and the FreeMASTER recorder time base can be defined in the freemaster_cfg h configuration file The recorder routine must be called periodically from the loop from where you want to take the samples The following line must be added to the loop code Freemaster recorder FMSTR_ Recorder In this application the FreeMASTER recorder is called from the ADC1 interrupt which creates a 63 Us time base for the recorder function Buffered data is transferred to the PC side after the trigger condition is met The FreeMASTER Scope is a similar visualization tool to the Recorder but the data from the embedded side is downloaded in real time The sampling rate is limited by the speed of the communication protocol and also influenced by the number of displayed variables It is usually used for waveforms visualization of s
39. plication this is defined as the macro define EnableInterrupts asm CPSIE i PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 31 a FreeMASTER software Finally the interrupt service routine has to be defined p1r_cxo_tsr_Handier and inside the body of the function the source of the interrupt must be cleared to leave the interrupt service routine For the PIT channel 0 interrupt this means that the interrupt flag is cleared by writing 1 to the TIF bit of the Timer Flag Register PIT _TFLGO PIT _TFLG TIF MASK 4 6 FreeMASTER software 4 6 1 Introduction The FreeMASTER software was designed to provide a debugging diagnostic and demonstrational tool for the development of algorithms and applications Moreover it is useful for tuning the application for different power stages and motors because almost all of the application parameters can be changed via the FreeMASTER interface This consists of a component running on a PC and another part running on the target controller Nowadays different communication interfaces are supported RS 232 USB Ethernet OSBDM and the work on improvements and support for new families of microcontrollers is still in progress In the application the RS232 interface is used because it represents minimal communication overhead that has to be handled by the MCU and requires no interrupts working in polling mode which is imp
40. pports input capture output compare and the generation of PWM signals to control an electric motor and power management applications The FTM time reference is a 16 bit counter that can be used as an unsigned or signed counter On the Kinetis K40 there are three instances of FTM One FTM has 8 channels the other two FTMs have 2 channels The procedure of the FlexTimer configuration for generating a center aligned PWM with dead time insertion is described in the application note titled Using FlexTimer in ACIM PMSM Motor Control Applications document AN3729 6 Because the referenced application note supports an earlier version 1 0 of the FlexTimer implemented on the ColdFire V1 and with respect to the hardware used TWR MC LV3PH there are a few differences in the configuration as described below e At first it is necessary to enable the system clock for the FlexTimer module in the Clock Gating Control Register SIM_SCGC6 SIM _SCGC6_FTMO MASK e It is necessary to disable the write protection of some registers before they can be updated FTMO_MODE FTM_MODE_WPDIS MASK e Then it is advisable to enable the internal FlexTimer counter to run in the debug mode PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 23 Kinetis K40 peripheral modules configuration FTMO_CONF FTM CONF _BDMMODE 3 While the HW debugging interface Link Multilink is connected to t
41. r Inc Chapter 3 System Design synchronous frame Park transformation is two DC values the d q currents It is much easier to regulate two DC variables than two variables changing in time The following picture shows the transformation sequencing 3 Phase Stationary Rotating to to to Phase C 2 Phase Rotating Stationary Phase B 3 Phase l l 2 Phase From measurement AC I Stationary Reference Frame l Rotating Reference Frame l Stationary Reference Frame l l Figure 3 2 Transformation sequencing 3 1 3 Vector control implementation There is an enhancement to the vector control algorithm implemented in the application described in the designer reference manual PM Sinusoidal Motor Vector Control with Quadrature Encoder document DRM105 3 The limitations of the PI current controllers are calculated in real time based on the available DC bus voltage Figure 3 3 is a simplified block diagram of the vector control algorithm The aim of this control is to regulate the motor speed at a predefined level The speed command value is set by a high level control The algorithm is executed in two control loops The fast inner control loop is executed within a hundred usec period The slow outer control loop is executed within a period of an msec The fast control loop executes two independent current control loops They are the direct and quadrature axis current isd isq PI controllers The direct axis curr
42. r board Serial board Low voltage power stage Figure 3 5 Hardware built on the modules of the Tower system It is recommended to place the MCU board on the top of the Tower system this way the user s buttons are easily accessible It is necessary to configure the Tower 3 phase low voltage power stage The jumper settings are listed in the following table and the jumper positions are highlighted in Figure 3 6 See also the user s manual 12 for more details for example hardware overcurrent threshold setting of the Tower low voltage power stage Table 3 1 Jumper settings of TWR MC LV3PH board ap ting at J2 VDDA Source Select 1 2 Internal analog power supply J3 VSSA Source Select 1 2 Internal analog power supply J10 AN6 Signal Select 1 2 Phase C current signal J11 AN5 Signal Select 1 2 Phase B current signal J12 AN2 Signal Select 1 2 Phase A current signal PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc Chapter 3 System Design Motor connector NX Power supply connector 2 A fe AL ti fao po fos eo ve 35 ba Encoder JEE connector Y Jumpers J2 J3 Jumpers J10 J11 J12 Figure 3 6 Jumpers and connectors positions on the TWR MC LV3PH Table 3 2 shows the signal assignment of the motor and encoder connectors of the TWR MC LV3PH Because the FlexTimer module on the Kinetis K40 does not supp
43. red speeds e Includes FreeMASTER software high speed recorder reconstructed motor currents voltages e Application includes overcurrent protection different faults latched by the MOSFET driver and a motor phase disconnection e User buttons for manual control PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 9 System specification PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 10 Freescale Semiconductor Inc Chapter 3 System Design 3 1 Control theory 3 1 1 3 phase permanent magnet synchronous motor The construction of the PM synchronous motor and its mathematical description using a space model can be found in the designer reference manual PM Sinusoidal Motor Vector Control with Quadrature Encoder document DRM105 3 3 1 2 Introduction to vector control The permanent magnet synchronous motor features high efficiency high torque capability high power density and durability are good for using the PMSM in motion control applications The key idea for the vector control algorithm of the AC motors was to achieve an AC motor torque speed characteristic similar to that of the separately excited DC motor In the DC motor the maximum torque is generated automatically by the mechanical switch called the commutator The commutator feeds current only to that coil whose position is orthogonal to the direction of the magnetic flux generated by the s
44. ree currents can be sampled the currents are sampled when the bottom transistors are turned on The pulse width is sufficient to stabilize the current and to perform the acquistion of the signal value by the AD converter At 30 the pulse is too short so the current of Phase A cannot be sampled PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 28 Freescale Semiconductor Inc Ey Chapter 4 Software Design 4 4 6 Periodic interrupt timer configuration The PIT serves to generate a 1 ms time base for the slow speed control loop There is one PIT module with four channels implemented on the K40 MCU The timer module has an internal 32 bit counter clocked from the system clock It possesses no prescalers The number of the value registers reflects the number of channels The timer generates a trigger at periodic intervals when enabled It loads its start value as specified in the LDVAL register then counts down until it reaches 0 It then loads its respective start value again Each time the timer reaches 0 it will generate a trigger pulse and set the interrupt flag The initialization is short and is performed in four steps e Enabling the clock for the module in the particular System Clock Gating Control Register e Enabling the internal module timer in the PIT Module Control Register e Writing the load value into the LDVAL Register e Enabling the interrupt Due to a bug on the chip mask 0M33Z see Errata 14
45. rrent PI regulator were tuned The same parameters were used also for the q current PI regulator because of the difference in values of the motor inductances Ld Lq is not significant PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 16 Freescale Semiconductor Inc EES Chapter 3 System Design 3 2 Hardware The hardware solution of the PMSM Vector Control with Encoder on Kinetis is built on the Freescale s Tower rapid prototyping system It consists of the following modules e Tower elevator modules TWR ELEV e Kinetis K40 tower module TWR K40X256 e 3 phase low voltage power module TWR MC LV3PH e Tower Serial Module TWR SER All modules of the Tower system are available to order via the Freescale web page or from distributors The user can easily build the hardware platform for which the application is targeted 3 2 1 Hardware set up and configuration Building the system using the modules of the Tower system is not difficult The peripheral modules and the MCU module are plugged into the elevator connectors while the white stripe on the side of the module boards determines the orientation to the Functional elevator the elevator with the mini USB connector power supplies and the switch see the following Figure 3 5 PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 17 Hardware Functional Dummy Elevator Elevator Kinetis K40 Towe
46. s The application requires the minimum number of interrupts because the MCU has the possibility of hardware triggering the AD conversion and the FlexTimer is able to effectively decode quadrature encoder signals 4 7 4 1 PIT channel 0 interrupt In this interrupt service routine the speed control loop is executed and the interrupt also serves as a precise 1 ms time base for speed computing Because the speed is calculated as a derivation of the position the precision of the time base is critical for obtaining the speed values Therefore the interrupt has the highest priority The speed calculation is described in the application note titled Configuring the FlexTimer for Position and Speed Measurement with an Encoder document AN4381 7 PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 37 Program flow After the speed calculation there is detection of the disconnected motor phase The loss of the voltage on one motor phase results in the generation of a rotating magnetic field in the opposite direction than that of the required speed The PI speed regulator generates each time a higher value of iq torque producing current because the regulation error between the measured and required speed increases during acceleration The motor reaches quickly the maximum speed in the opposite direction This behavior is unwanted and needs to be managed by software The detection is based on the
47. s and the DC Bus voltage The following time diagram shows the modules interconnection and the ADC interrupt generation FTMOVAL1 4 5 y6 5 f f FTMO counter FTMOVALO ORAS CaM te rA NEEESE ee ENE RTE EEN a FTMO Init trig PWM top channel PWM bottom channel PDBO CHO pet eae es ane DC Bus voltage gt ADCO RA i PDBO CH1 ere aia See e Phase current 1 gt ADCO RB PDB1 CHO A a ae a Phase current 2 gt ADC1 RA ADC1 ISR ADC1 ISR ADC1 ISR Interrupt AD channel conversion Result Register updated Figure 4 1 ADC conversion timing PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 26 Freescale Semiconductor Inc EyEEEEEEEE en Chapter 4 Software Design 4 4 5 Current measurement Closely related to the ADC conversion trigger timing is the assignment of the ADC channels to the measured analog signals For computation of the fast current control loop of the FOC it is necessary to know the values of all three motor phase currents Because there are only two ADC modules it is possible to sample only two analog quantities in one instance Assuming the motor represents a symmetrical 3 phase system the sum of all three instantaneous phase currents is zero Eqn 4 1 Because the phase currents are measured at the moment the bottom transistor
48. s are conducting in the case of high duty cycle ratios current value is in the maximum area of the sine curve the time when the current can be measured is too short The bottom transistor must be switched on at least for a critical pulse width to get a stabilized current shunt resistor voltage drop The selection of the channels is done based on the section where the space vector of the stator current is generated This assignment is performed at the end of the ADC1 interrupt service routine Therefore it is enough to sample only two phase currents while the third is easily calculated according to eq 4 2 Eqn 4 2 Sector 1 6 i45 z ic Sector 2 3 4a7ic Sector 4 5 ic ip7t The following figure explains in two cases case I at 60 case II at 30 why the calculation of the third current is necessary PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 27 Kinetis K40 peripheral modules configuration gt O O O P O o gt Phase A Phase B Phase C 2 2 Q S oO gt _ ge O o N Sector 1 Sector 2 Sector 3 Sector 4 Sector 5 Seco 6 PWM period PWM reload if PhaseA PhaseB 1 I 1 1 1 1 1 I I I I I I 1 I Phase C gt i I I 1 I I I I I 1 1 1 1 I 1 1 Critical pulse width ADCsampling point Figure 4 2 Current sensing At 60 all th
49. t number AN4381 Freescale Semiconductor 2011 8 Advanced information documet titled Three Phase Field Effect Transistor Pre driver document number MC33937 Freescale Semiconductor 2009 9 Reference Manual titled ARM v7 M Architecture ARM Limited 2010 10 Data sheet titled K40 Sub Family Data Sheet document number K40P144M100SF2 Freescale Semiconductor 2011 11 Application note titled Real Time Development of MC Applications using the PC Master Software Visualization Tool document numberAN1948 Freescale Semiconductor 2005 PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 49 Acronyms and Abbreviations 12 User s manual TWR MC LV3PH Freescale Semiconductor 2011 13 Demo set up guide PMSM Vector Control with Encoder on Kinetis Freescale Semiconductor 2011 14 Mask Set Errata for Mask 0M33Z Freescale Semiconductor 2011 7 2 Acronyms and Abbreviations Table 7 1 Acronyms and abbreviated terms a e AC Alternating current ADC Analog to digital converter BDM Background Debug Mode DC Direct current DMA Direct Memory Access Controller An MCU module capable of performing complex data transfers with minimal intervention from a host processor DSC Digital Signal Controller DT Dead time A short time that must be inserted between the turning off of one transistor in the inverter
50. tator permanent magnets or excitation coils The PMSM has the inverse construction the excitation is on the rotor and the motor has no commutator It is possible to control these two components independently and to reach the required performance thanks to the decomposition of the stator current into a magnetic field generating part and a torque generating part To keep the constant desired torque the magnetic field generated by the stator coils has to follow the rotor at the same synchronous speed Therefore to successfully perform the vector control the rotor shaft position must be known and is one of the key variables in the vector control algorithm For this purpose either the mechanical position sensors are used encoders resolvers and so on or the position of the shaft is calculated estimated from the motor phase currents and voltage This is then called sensorless control Using the mechanical position sensors bring several benefits The position is known over the entire speed range with the same precision there is no PMSM Vector Control with Quadrature Encoder on Kinetis Rev 0 1 2012 Freescale Semiconductor Inc 11 Control theory need to compute highly mathematically intensive algorithms that estimate the rotor shaft position So vector control with a position sensor can be implemented on less powerful microcontrollers The performance of the MCU can also be used for other tasks On the other hand the cost of the mechani
51. tion on Freescale s Environmental Products program go to http www freescale com epp Freescale and the Freescale logo are trademarks of Freescale Semiconductor Inc All other product or service names are the property of their respective owners 2012 Freescale Semiconductor Inc ey freescale K
52. y perform the vector control algorithm The Programmable Delay Block closely cooperates with the ADC and serves for hardware triggering of the sampling It is required to perform a self calibrating procedure of the ADC module before it is used in the application to obtain a specified accuracy The calibration process also requires a programmer s intervention to generate the plus side and minus side gain calibration results and store them in the ADC plus side gain and minus side gain registers after the calibration function completes The calibration has to be performed for both ADC modules After calibration the ADC modules are configured to a 12 bit accuracy The input clock of the ADC module is limited to 18 MHz according to the Kinetis K40 Datasheet 10 The CPU frequency is set to 100 MHz therefore by using an available prescaler value the input clock to the ADC module is set to 12 5 MHz That setting yields a conversion time of 2 2 us Finally the hardware trigger has to be enabled in the Status and Control Register 2 The Programmable Delay Block PDB provides controllable delays from either an internal or an external trigger or a programmable interval tick to the ADCs hardware trigger inputs so a precise timing between ADC conversions is achieved The PDB module has an internal counter that overflows on a modulo value Because the input trigger comes periodically from the FTMO the input clock source and the modulo value is set identical

PMSM Vector Control with Quadrature Encoder on Kinetis

Contents

Download Pdf Manuals

Related Search

Related Contents