3-Phase BLDC Sensorless Control using MCF51AG128
Contents
1. This constant defines the maximal required motor current torque during the run state define CURRENT SCALE A 2 CURRENT HW HALF RANGE MAX A This constant defines the current scaling during the run state 5 4 12 3 Voltage Fault Threshold Constants define FAULT OVERVOLTAGE THRESHOLD MV 30000 milliVolts 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 12 Freescale Semiconductor This constant defines the maximal DC bus voltage in mV Over this DC bus voltage and an overvoltage fault is generated define FAULT UNDERVOLTAGE THRESHOLD MV 10000 milliVolts This constant defines the minimal DC bus voltage in mV Under this DC bus voltage and an overvoltage fault is generated 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 13 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 14 Freescale Semiconductor Chapter 6 Sensorless BLDC Demo Operation 6 1 Application Control The BLDC motor control application can be controlled by the manual interface consisting of the desired direction switch and Up Down buttons Figure 6 1 or remotely by a PC The BLDC drive can operate in speed and torque operational modes 6 2 BLDC drive operational modes 6 2 1 Speed operational mode If the application is set to the speed operational mode the user can set the required speed manually or by the PC The DC bus current torque is2. IMM Group oer Roznov pod Radhostem pa freescal e z semiconducto Czech Republic g a BLDC Sensorless Application using options Comm MAP Files Pack Dir HTML Pages Demo Mode Communication C Plugin Module T Save settings to project fle IV Save settings to registry use it as default Communication state on startup and on project load Open port at startup Do not open port at startup C Store port state on exit apply it on startup T Store state to project file apply upon its load Desired Cancel velocity a stimulator Commutation Error Fa 2 DC Current Limiting velocity ramp Desired Velocity Value Unit Period a m So Gn 3 Not connected A Figure 6 2 FreeMASTER Communication Settings The FreeMASTER s control page offers a similar interface as the manual controls although it offers some other features such as the change of operational mode settings and displays some additional status information To start a remote operation run FreeMASTER and open the project file located at Freemaster AG128_ BLDC Sensorless pmp The remote operation is active when the START STOP switch is in the START position The motor speed can be set to any value within the range of 400 to 4000 rpm The DC bus current torque can be set to any 3 Phase BLDC Sensorless Control using MCF51AG12
3. e 005 o o Praseb rang s 00 o nG Phase Crating a me nose Dos Presoaren 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor Table 5 2 Commutation table for clockwise direction Vector Phase Voltage Number A B Cc Sensing Ho por mo noo Prese Breno Phase Araling DCB i NC isi 008 Doo no Preset rising Ho nG bos oee Phase Anang 0 cee bos nC Phase Crating The application constants are split into BLDCparameters h and LVpowerStage h File BLDCparameters h deals with main motor parameters like electrical and mechanical parameters of BLDC speed scale and particular states parameters alignment start up run and the main peripherals used for BLDC control File LVpowerStage h deals with the low voltage power stage pinout and fault threshold settings voltage and current scales As much as possible all constants are recounted from the floating point into the fix point values Throughout the whole code the floating point constants contain _REAL in their name 5 4 11 BLDC motor parameters BLDCparameters h 5 4 11 1 MCU settings parameters define CPU CLK 48000000 Hz This constant defines the value of CPU clock frequency which is set in the Device Initialization tool define TPM3 PRESCALER 32 This constant defines the value of TPM3 prescaler which is set in the Device Initialization tool define T
4. 4 3 Process Standstill Detection This process compares all six commutation periods If the difference between periods is higher than defined a standstill is detected It also detects incorrect commutation during start up or loss of synchronization between commutation sector and sensed Back EMF voltage At any error the motor is stopped and the start up sequence is repeated When the standstill detection is enabled then this process is executed every 5 ms in the isrVtpm3ch interrupt 5 4 4 Process Commutation This process updates the variable ucSector only The PWM update based on the new commutation sector is performed in the PWM Update process The commutation process is called on every new commutation event So the execution period depends on the motor speed 5 4 5 Process Manual Interface This process checks the state of the input pins where the CCW_DIR STOP CW _ DIR switch and UP DOWN buttons are connected If a change is detected the particular status bit is set These status bits are evaluated in the Application State Machine The process is executed every 5 ms in the isrVtpm3ch1 interrupt 5 4 6 Process Application State Machine The application state machine ASM consists of init stop alignment start up stabilization run and error states see Figure 5 3 After an MCU reset the ASM goes through the init state to the stop state As soon as the user turns the CCW DIR STOP CW DIR switch to the desired direction position the A
5. AA AA TETAY FO 6 1 6 2 BLDC drive operational modes a KAANAK LAKAS OR ERE ORS 6 1 6 2 1 Speed operational mode a a KAKANAN ANG 6 1 6 2 2 Torque operational mode Ku ice GG AA da dwa eK ew eee ee 6 1 6 3 Manual Remote Operation 0 eee nent ees 6 2 63 1 ANONG oe ABA okt ot soa KG WG ee ede eee eas sd odeneendadin 6 2 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 4 Freescale Semiconductor Chapter 1 Introduction 1 1 Introduction This design reference manual describes the design of a sensorless 3 phase Brushless DC BLDC motor drive based on Freescale s 32 bit MCF51AG128 control device BLDC motors are very popular in a wide application area The BLDC motor lacks a commutator and is therefore more reliable than the DC motor The BLDC motor also has advantages when compared to an AC induction motor Because it achieves a higher efficiency by generating the rotor magnetic flux with rotor magnets a BLDC motor is used in high end white goods such as refrigerators washing machines dishwashers high end pumps fans and in other appliances which require a high reliability and efficiency The concept of the application is a speed and torque closed loop BLDC drive using a sensorless BEMF zero crossing technique It serves as an example of a BLDC motor control design using a Freescale ColdFire V1 Family MCU This reference design includes basic motor theory system design concept hardware implementation and sof
6. Continued Term Meaning CCW_DIR Counter clockwise direction CDC driver USB communications device class COP Computer operating properly watchdog timer CW_DIR Clockwise direction DAC Digital to analog converter DC Direct current DMA Direct memory access module DRM Design reference manual DT Dead time a short time that must be inserted between the turning off of one transistor in the inverter half bridge and turning on of the complementary transistor due to the limited switching speed of the transistors FTM Flextimer module GPIO General purpose input output HSCMP High speed comparators module 1 0 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 LED Light emitting diode MCF51AG128 Freescale 32 bit ColdFire V1 family microcontroller MCU Microcontroller PDB Programmable delay block module PLL Phase locked loop a clock generator circuit in which a voltage controlled oscillator produces an oscillation that is synchronized to a reference signal PWM Pulse width modulation RPM Revolutions per minute SCI Serial communication interface module a module that supports asynchronous communication SPI Serial peripheral interface module 1 5 2 Glossary of Symbols Table 1 4 shows a glossary of
7. is in the desired CCW CW position the motor starts running with a minimal speed of 400 rpm or with a minimal DC bus current of 0 2A based on the operational mode To increase decrease the speed DC bus current torque use the UP DOWN buttons The speed increments continuously up to the maximal motor speed of 4000 rpm The DC bus current increments up to the maximal DC bus current of 2 A The default operational mode is speed mode The direction of rotation but not the operational mode can be changed only manually To change the operational mode use the FreeMASTER 6 3 1 1 Remote operation Remote operation can be provided by FreeMASTER software via the SCI to USB interface For correct FreeMASTER operation follow the given steps 1 Go to Project Options Comm and set communication via the Direct RS232 see Figure 6 2 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 2 Freescale Semiconductor 2 Select the COM port where the MC9S08JMxx CDC driver is connected see System Properties Device Manager Ports The communication speed is 9600 Bd 3 The next step is to toggle the communication button After that in bottom right corner should be RS232 COMxx 9600 which means the communication is established 4 Ifnot toggle STOP the communication and unplug plug the FreeMASTER USB cable Then toggle START the communication button Toggle the Refresh content communication Designed by Roznov csc Pg i Pa
8. non fed phase because of mutual inductances and mutual capacitor couplings between the motor windings Non fed phase branch voltage is then disturbed by PWM switching Figure 3 6 shows the effect on the non fed phase because of the mutual inductance 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 6 Freescale Semiconductor Figure 3 6 Effect of mutual inductance on Back EMF The non fed phase branch voltage is disturbed at the PWM switching edges Therefore the presented BLDC Motor Control application synchronizes the Back EMF zero crossing detection with the PWM The A D conversion of phase branch voltages is triggered at the end of a PWM pulse Then the voltage for Back EMF is sensed at those time moments when the non fed phase branch voltage is already stabilized The MCF51AGx is equipped with the Programmable Delay Block PDB synchronization of the FTM PWM and ADC modules Therefore several assumptions have to be considered during the ADC sampling implementation The first factor is the choice of PWM modulation From this point of view the complementary bipolar switching is the best choice This PWM switching can be implemented in such a way that the duty cycle is in the range of 50 to 100 at any time of motor operation With unipolar switching the duty cycle starts from 0 It means that there is limitation for ADC sampling at narrow pulses regardless of whether hardware synchronization is available or not In
9. selectable slew rate control on ports when used as inputs Master reset pin and power on reset POR Internal pull up on RESET and IRQ pins to reduce customer system cost up to 69 general purpose input output I O pins 48 64 and 80 pin low profile quad flat package LQFP and 64 pin quad flat package QFP The key peripherals for 3 phase BLDC motor control are the FTM PWM module sample synchronization PDB module and an A D converter The MCF51AG128 includes two 6 channel FTMs The 6 channel FTM1 module allows the generation of any PWM pattern for any 3 phase motor control The FTM main module features include FTM has a 16 bit counter It can be a free running counter or a counter with an initial and final value The counting can be up or up down A total of six channels Each channel may be input capture output compare or buffered edge centre aligned PWM Rising edge falling edge or any edge input capture trigger Set clear or toggle output compare action Selectable polarity on PWM outputs Dead time insertion is available for each complementary pair Clock source to the prescaler for each FTM is independently selectable as the bus clock fixed system clock or an external pin Prescaler divide by 1 2 4 8 16 32 64 or 128 Generation of triggers match trigger 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor e Software control of PWM outputs MASK func
10. software flow chart is given in Figure 5 1 Apart from the background loop the software incorporates the following three periodic and two event interrupts e FTM 1 Fault Interrupt Execution period event interrupt called in the case of overcurrent detection The routine handles DC bus overcurrent event e ADC End of Conversion Interrupt Execution period called once per 50 us The routine saves new DC bus voltage current and specific BEMF sample provides zero crossing detection e TPM 3 Ch0 Compare Interrupt Execution period event interrupt called every commutation The routine updates the commutation sector e TPM 3 Chl Compare Interrupt Execution period 5 ms The routine provides ramp generation speed torque PI controllers calculation standstill detection and manual interface handling UP DOWN buttons CCW_DIR STOP CW _DIR switch 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 1 Main background Loop Initialize e Peripheral initialization e Application variable initialization isrVtpm3ch1 isrVadc TPM3 Ch1 Compare ADC End of Conversion e Ramp generation e Saves first sample uDC iDC e Speed calculation e Saves second sample BEMF e Torque calculation e Zero crossing detection e Torque PI controller calculation e Speed PI controller calculation e Standstill detection e Manual interface handling isrVtpm3ch0 TPM3 Ch0 Compare e Updates new commutation secto
11. symbols used in this document Table 1 4 Glossary of Symbols Term Definition back EMF voltage current 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor Table 1 4 Glossary Continued of Symbols Term Definition n speed S switch u v voltage angular velocity 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 8 Freescale Semiconductor Chapter 2 Control Theory 2 1 Brushless DC Motor BLDC Motor The Brushless DC Motor BLDC Motor is a rotating electric machine with a 3 phase wound stator the rotor has surface mounted permanent magnets It is also referred to as an electronically commuted motor There are no brushes on the rotor and the commutation is performed electronically at certain rotor positions The stator is usually made from magnetic steel sheets A typical cross section of a BLDC Motor is shown in Figure 2 1 The stator phase windings are inserted in the slots distributed winding or it can be wound as one coil onto the magnetic pole Because the air gap magnetic field is produced by permanent magnets the rotor magnetic field is constant The magnetization of the permanent magnets and their displacement on the rotor is chosen so that the Back EMF the voltage induced into the stator winding due to rotor movement shape is trapezoidal This allows the DC voltage see Figure 2 2 with a rectangular shape to be used to
12. the Fault state stops the motor and waits for the fault reset over the Reset switch Beyond this the FreeMASTER interface enables monitoring and adjustment of all system variables 3 3 System Blocks Concept 3 3 1 PWM Voltage Generation for a Brushless DC Motor A 3 phase voltage system as described needs to be created to run the BLDC motor This is provided by a 3 phase power stage with 6 power switches IGBT s or MOSFET s controlled by the MCF51AG128 on chip FTM PWM module When generating PWM signals for the BLDC motor control application the Bottom and Top power switches of the non fed phase must be switched off See Figure 3 2 and Figure 3 3 For the BLDC motor control application PWM signals can be created in two ways Complementary PWM Mode and Independent PWM mode Thanks to the flexible MCF51AG128 FTM PWM module both these modes are available 3 3 1 1 Complementary PWM Mode In complementary PWM mode the top and bottom switches of a phase are operated complimentarily This mode has to be used if four quadrant drive operation is required This mode needs dead time insertion 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 3 between the top and bottom switches to avoid any phase short circuit The complementary switching can be implemented in both a bipolar or unipolar manner The unipolar switching leads to lower switching losses and current ripple However from a Back EMF point of
13. the motor related parameters A detailed motor specification is shown below Table 4 1 Main Electrical Parameters of the LINIX 45ZWN24 40 Motor Characteristic Symbol Typ Units Rated Voltage Vi 24 V Rated Speed V 4000 RPM Rated torque T 0 0924 Nm Rated power 40 W Terminal Resistance Ri 0 1 Q Continuous Current les 2 34 A Number of Pole Pairs PP 2 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor Chapter 5 Software Design 5 1 Introduction This section describes the design of the drive s software blocks The software description comprises these topics e Main Software Flow Chart e Data Flow 5 2 Main Software Flow Chart The main software flow chart incorporates the main routine background loop entered from reset and the interrupt states The Main routine includes the initialization of the microcontroller and the main loop After initialization the main routine enters an endless loop which executes the application state machine consisting of init stop alignment start up run and error states The transition between the states depends on state of the CCW_DIR STOP CW _DIR switch UP DOWN buttons and drive status In the case of remote control besides the motor speed torque the operational mode and the rotation direction can be set from FreeMASTER The main
14. this case a different sensing method has to be chosen where the Back EMF voltage is compared to zero instead of half DC bus voltage The right setting for the FTM PWM module is shown in figure Figure 3 7 The FTM PWM module is configured to run in complementary combined mode The PDB module has two times a lower clock so therefore PDBMOD is two times lower than FTMMOD The PDB can generate two triggers TriggerA and TriggerB The TriggerA is used for DC bus current or voltage measurement in the middle of a PWM On pulse The DC bus current measurement rotates every PWM period with DC bus voltage measurement The TriggerB is used for Back EMF sensing of the non fed phase The result of the conversions can be read on the Conversion Complete B interrupt Since the A D converter has two result registers the conversion of more channels can be serviced in the same interrupt The sampling process can seen in Figure 3 7 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 7 Phase A PWMO Phase A PWM1 PIMIMOD een a FTM PDB Counter a ne earn ee eee i eee PDBMOD eae a nme ie PDBDLYA ee oe a IER se PDBDLYB FTMICNTIN ee eee FTM1COV TriggerA TriggerB Read ADC i iDCB vDCB BEMF results sample sample Figure 3 7 FTM PWM to ADC Synchronization with PDB 3 3 3 Back EMF Zero Crossing Sensing The Back EMF Zero Crossing is detected by sensing the motors non fed phase branch vo
15. well E di Va 7 Vpcp 7 Rgl Li ey When we combine equations Eqn 2 1 and Eqn 2 2 the neutral voltage v is equal _ VpcB aT Eb g 2 2 The sum of the back EMF voltages is equal to zero in a balanced three phase system e tep te 0 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Eqn 2 1 Eqn 2 2 Eqn 2 3 Eqn 2 4 Freescale Semiconductor Incorporating equation into yields Eqn 2 5 _ Voces amp W9 ta The branch voltage v can be calculated Eqn 2 6 Ve Va es The branch voltage v can be calculated when considering the above equations and Eqn 2 7 v v ne DCB tio 7 BOB Be At the phase C BEMF zero crossing the branch voltage v is equal to the half of DC bus voltage Eqn 2 8 _ Voce Ye zc T9 The Figure 2 6 shows branch and motor phase winding voltages during a 0 360 electrical interval Shaded rectangles determine the time when the Back EMF voltage can be sensed during designated intervals Thus the Back EMF voltage is obtained and the zero crossing can be recognized uVA UA E Back EMF can be sensed Figure 2 6 Phase Voltage Waveforms For more detailed information about BEMF sensing see Section 1 5 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 6 Freescale Semiconductor Chapter 3 System Concept 3 1 System Specification The motor control system is designed to drive a 3 phase Brushless DC Motor BLDC Motor in a combined speed torq
16. 3 Phase BLDC Sensorless Control using MCF51AG128 Design Reference Manual Devices Supported MCF51AG128 MCF51AG96 Document Number DRM123 Rev 0 05 2011 How to Reach Us Home Page www freescale com E mail support freescale com USA Europe or Locations Not Listed Freescale Semiconductor Technical Information Center CH370 1300 N Alma School Road Chandler Arizona 85224 1 800 521 6274 or 1 480 768 2130 support freescale com 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 support freescale com Japan Freescale Semiconductor Japan Ltd Headquarters ARCO Tower 15F 1 8 1 Shimo Meguro Meguro 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 303 675 2140 Fax 303 675 2150 LDCForFreescaleSemiconductor hibbertgroup com Information in this document is provided solely to enable system and software implementers to use Freescale Semiconductor products There are no express or imp
17. 6 0 0625 0 5 Amp This constant defines the motor current torque during the start up sequence and required current torque in Torque mode For scaling see Section 5 4 12 2 define RUN TORQUE FRAC16 0 125 1 Amp This constant defines the maximum motor current torque at the zero crossing BEMF during the run sequence in Speed mode 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 11 define START CMT NUMBER 6 This constant defines the number of start up commutation periods see Section 3 3 5 2 define STABILIZATION CMT NUMBER 6 This constant defines the number of stabilization commutation periods see Section 3 3 5 3 5 4 12 Power stage parameters LVpowerStage h 5 4121 DC Bus Voltage Scaling The voltage scaling on the 3 phase Motor Control Drive stage can be calculated as Eqn 5 7 __Voltageyy 1000 _ Q09091v1y Voltagetscated VOLTAGE SCALE MV VOL 33v 0 1 define VOLTAGE SCALE MV 36300 milliVolts This constant defines the power stage voltage scale in millivolts For additional details about the voltage and current scale see Section 1 5 5 4 12 2 Current Torque Constants and Scaling The scaled fractional current range is 0 5 0 5 The current scaling can be calculated as follows Eqn 5 8 E Tray E 0 4125V A I ceea PAN pa AHE scaled CURRENT SCALE Aja 4 33V define CURRENT HW HALF RANGE MAX A 4 0 Amps
18. 8 Rev 0 Freescale Semiconductor 3 value within the range of 0 1 A to 2 A The direction of rotation can only be changed by the manual direction switch In addition to the remote control the Free MASTER displays some variables in the scope see Figure 6 3 The FreeMASTER defines a speed stimulator for an automatic demonstration of the sensorless BLDC demo To use the speed stimulator switch the direction switch to the desired rotation and then start the speed stimulator The speed will change according to a predefined ramp Actual Velocity Desired Velocity mf16SlopedVelocity 0 00 0 05 0 10 0 15 0 20 0 25 0 30 0 35 Time min 4 velocky tamo Desred Velocky mfl6dcb V mf16TorqueFiltered mf16dcb I wOuryCyde 0 0453106 nd 16TorqueReqared REZ COMIT speed OO Beeps furri Figure 6 3 Scope variables during enabled stimulator 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor
19. DC motor parameters BLDCparameters h e main MCU peripherals settings e BLDC motor parameters e alignment state e start state e run state The application header file LVpowerStage h includes the following application constants See Power stage parameters LVpowerStage h e AG128 daughter board pinout e current scale e voltage scale The application header file MCUinit h includes the following application constants e application state machine constants e user types definitions 1 4 Microcontroller Memory and Peripheral Usage Table 1 1 shows how much memory is needed to run the 3 phase BLDC sensorless drive without FreeMASTER using the MCF51AG128 microcontroller A significant part of the microcontroller memory is still available for other tasks Table 1 1 Memory Usage Available Memory MCF51AG128 used Flash 128 KB 8 3 KB RAM 16 KB 4000 The MCF51AG128 microcontroller offers many features that simplifies the drive design Table 1 2 describes the individual available blocks and its usage for the introduced system 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 5 Table 1 2 Modules Usage Module available on the MCF51AG128 Purpose Timer FTM1 6 channel PWM generation Timer TPM3 2 channel Commutation timer CHO Control loop timer CH1 1 5 SCI1 FreeMASTER interface SPI1 MC33927 interface ADC DCB
20. PM3CH1 CMP TIME REAL 5e 3 sec This constant defines the TPM3 channel 1 compare period which is set in the Device Initialization tool This period defines the combined speed torque PI controller loop period as well define PWM MODULO 2399 This constant defines the FTM1 timer modulo value for the PWM switching frequency 20kHz This constant should be the same as FTM MOD in the Device Initialization tool Eqn 5 1 6 FTM1 CLK jax 48x10 wins 2399 PWM_MODULO FTMI PRESCALER SWITCHING FREQ 120x102 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 9 5 4 11 2 Speed Constants and Scaling define VELOCITY SCALE 6000 RPM This constant defines the minimal required motor speed The motor speed scaling for motor LINIX 45ZWN24 40 can be calculated as Eqn 5 2 S 60 TPM3 CLK 6 VELOCIIYOCONST NUM_PHASES PP TPM3 PRESCALER TIKLO Eqn 5 3 VELOCITY_CONST_SCALED See 32768 Eqn 5 4 Sines _ VELOCITY_CONST Y RPM mfl6PeriodFiltered Eqn 5 5 ere ere _ Velocityrrpm _ VELOCITY_CONST_SCALED Y scaled VELOCITY SCALEfjppm mf16PeriodFiltered where TPM3 PRESCALER 32 TPM3 CLK 24 MHz NUM PHASES number of stator phases 3 for motor LINIX 45ZWN24 40 PP number of pole pairs 2 for motor LINIX 45ZWN24 40 define MAX SPEED REAL 4000 RPM This constant defines the maximal required motor speed define MIN SPEED REAL 400 RPM T
21. SM goes into the alignment state where the motor is aligned to a known position After a predefined time the ASM continues to the start up state At the start up state the six commutations are performed without any feedback The timings between the commutations are defined by START PERIOD and START ACCELERATION After the start up state the ASM goes into the stabilization state where the 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 4 Freescale Semiconductor measurements of the torque and speed are stabilized The stabilization state is optional an by default this state is disabled This state goes through the next six commutations where zero crossing is already employed After the stabilization state the ASM goes into the run state where the control loop is closed During the run state requests for new speeds and torques are accepted and maintained by the PI controllers If a standstill of the rotor is detected the ASM goes again into the alignment state and tries to execute a new start up sequence In the case of any fault the ASM goes into the error state and then into the stop state The ASM is executed in the background loop CPU RESET Stabilization Figure 5 3 Application State Machine 5 4 7 Process Speed and Torque PI Controller The general principle of the speed PI control loop is illustrated in Figure 5 4 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor Actual spe
22. ariable load inertia however a number less than three leads to an unreliable start up In other cases the six starting flux vectors one electrical revolution seem to be the optimal value Once the last flux vector has executed Back EMF voltage evaluation is enabled and the motor enters a sensorless mode 3 3 5 3 Stabilization The stabilization process immediately follows the start up sequence and is optional The purpose of this process is to stabilize the measured values As described in Section 3 3 4 the torque is calculated as the average value from the last six commutations Also the speed is calculated in the same manner Since during the start up sequence the periods are not too stable the speed and torque values can be incorrect Therefore the stabilization process is executed This process is for at least six additional periods where the motor is kept in an open loop During these additional periods the speed and torque values are stabilized and the control loop can be closed 3 3 5 4 Run As soon as the control loops are closed the motor enters the run state Here the motor keeps to the desired speed or torque according to the selected operational mode and user commands Besides controlling the desired quantity the motor is checked for a locked rotor This might happen when the motor is suddenly overloaded Standstill detection is performed as a comparison of the actual period with the average period If the difference is too
23. automatically set to the value of 1 A In this case the BLDC drive maintains the required speed until the maximal DC bus current torque is exceeded 6 2 2 Torque operational mode Similarly in torque operational mode the user can set the DC bus current torque of the BLDC motor The required value can be set by the UP DOWN buttons or remotely by the PC The speed limit is set to a maximal speed of 4000 rpm In this case the BLDC drive maintains the required DC bus current torque until the maximal BLDC motor speed is achieved The operational mode can be changed only when the motor is stopped direction CCW STOP CW switch is in the STOP position only The default setting is speed operational mode 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 1 6 3 Manual Remote Operation Te22 re Tab ppibiniinig 124 r 00384 IYO NU Gop rss NG BOM ii mi ye eou ff Car YAN a a N4 C10 gp LETE Che et D cer no EL D 2 gest Mc2e a e 2 AY CSC seu 4 j gt PWM Status REPPI Lupecion Up Down LEDs LEDs PUiion switch buttons SW4 SW3 Figure 6 1 Manual Interface 6 3 1 Manual Operation To run the BLDC motor switch the direction switch to the desired direction position STOP is the middle position If the direction switch is in the CW or CCW position when applying the power supply turn the switch to the STOP position before running the BLDC motor Once the direction switch
24. avior This means that the tuning of the speed controller is very difficult and the drive exhibits low torque at a discontinuous current Using unipolar switching is also not recommended due to problematic Back EMF voltage and current sensing at narrow pulses All of the figures Figure 3 2 Figure 3 5 show detail of one PWM period for the BLDC motor Phase A is connected to a positive DC bus voltage phase B is connected to a negative DC bus voltage Phase C is non fed and is not shown The duty cycle is 50 3 3 1 3 Conclusion The complementary bipolar switching is selected for the this sensorless BLDC drive due to easy implementation of the Back EMF voltage sensing method and the MCF51AG128 features point of view The details of the Back EMF voltage sensing method can be seen in the next chapter 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 5 ON Phase A PWMO OFF ON Phase A PWM1 OFF ON Phase B PWM2 OFF ON Phase B PWM3 OFF PWM period gt lt 4 Figure 3 4 Independent Bipolar Switching Patterns for a BLDC Motor ON Phase A PWMO OFF ON Phase A PWM1 ON Phase B PWM2 OFF ON Phase B PWM3 PWM period gt lt Figure 3 5 Independent Unipolar Switching Patterns for a BLDC Motor 3 3 2 ADC Sampling Mechanism The power stage PWM switching causes voltage spikes on the phase voltages These voltage spikes are generated on the
25. compared with half DC bus voltage in relation to 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 8 Freescale Semiconductor an expected positive or negative slope If zero crossing is recognized the new period and commutation event is calculated The zero crossing detection process can be seen in Figure 3 8 _ PWM Switching magng 80 100 of DCB Voltage BEMF Zero Crossing Phase Voltage 0 20 of DCB Voltage Freewheeling Figure 3 8 Zero crossing detection process 3 3 4 Current Torque Sensing Besides the speed control the drive can run in torque control mode In this mode the torque is limited to the desired value In BLDC motor theory it can be seen that the torque is proportional to the motor current In six step control the current amplitude varies during the commutation period To get a stable value as the actual motor torque the current is sampled at a zero crossing event The resultant value is calculated as the average value from the last six commutation periods So the acquired value can be used as the actual motor torque for the torque control loop This value can not be used for current control cycle by cycle Overcurrent limitation is performed by the MC33927 driver 3 3 5 Sensorless Commutation Control This section presents sensorless BLDC motor commutation with the Back EMF Zero Crossing technique In order to start and run the BLDC motor the control algorithm has to go th
26. create a rotational field with low torque ripples Stator Stator winding in slots Shaft Rotor Air gap Permanent magnets Figure 2 1 BLDC Motor Cross Section The motor can have more than just one pole pair per phase The pole pair per phase defines the ratio between the electrical revolution and the mechanical revolution For example the shown BLDC motor has three pole pairs per phase which represents the three electrical revolutions per one mechanical revolution The rectangular easy to create shape of the applied voltage ensures the simplicity of control and drive However the rotor position must be known at certain angles in order to align the applied voltage with the 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 1 Back EMF The alignment between Back EMF and commutation events is very important Under this condition the motor behaves as a DC motor and runs at the best working point Thus simplicity of control and performance makes the BLDC motor the best choice for low cost and high efficiency applications Voltage Phase B Electrical angle i i 30 60 902 120 150 180 2102 240 270 3002 330 0 30 Figure 2 2 Three Phase Voltage System for BLDC Motor Figure 2 3 shows the number of waveforms the magnetic flux linkage the phase Back EMF voltage and the phase to phase Back EMF voltage The mag
27. ductor products for any such unintended or unauthorized application Buyer shall indemnify and hold 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 claim alleges that Freescale Semiconductor was negligent regarding the design or manufacture of the part Wey Z freescale semiconductor Freescale and the Freescale logo are trademarks of Freescale Semiconductor Inc The ARM POWERED logo is a registered trademark of ARM Limited ARM7TDMI S is a trademark of ARM Limited Java and all other Java based marks are trademarks or registered trademarks of Sun Microsystems Inc in the U S and other countries The PowerPC name is a trademark of IBM Corp and is used under license The described product contains a PowerPC processor core The PowerPC name is a trademark of IBM Corp and used under license The described product is a PowerPC microprocessor The PowerPC name is a trademark of IBM Corp and is used under license The described product is a PowerPC microprocessor core The PowerPC name is a trademark of IBM Corp and is used under license All other product or service names are the property of their respective owners Freescale Semiconductor Inc 2011 All ri
28. ection Application State Machine Speed and Torque PI Controller appState a sede FreeMASTER wDu cle mf16DesiredVelocity mf16TorqueRequired ac Aa ka C Ramp ucControlMode Process Be A mf1 PWM Ms Update Figure 5 2 Data Flow Chart 5 4 Processes description The main processes of the Brushless DC motor sensorless drive application can also seen in Figure 5 2 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 3 5 4 1 Process Zero Crossing detection This process is called every 50 us in the isrVadc interrupt The process is called after the second A D conversion when a new sample of phase voltage BEMF is available This new sample is checked for appropriate voltage level and compared to the midpoint of the DC bus voltage Details of zero crossing detection are described in Section 3 3 3 If zero crossing is detected the new commutation period is calculated and saved for speed calculation Then the new commutation event is calculated and set to the timer TPM3 channel 0 as a new compare event 5 4 2 Process Torque and Speed Calculation Both torque and commutation periods are filtered to get suitable input values to the Torque and Speed PI controllers Both values are calculated as the averages from the last six commutation events Then the averaged commutation period is recalculated as the motor speed This process is executed every 5 ms in the isrVtpm3ch1 interrupt 5
29. ed Desired speed Speed gt Ramp gt p gt hi ta PI controller Lj Duty cycle Controlled System 9 Desired current lt Current gt PI controller Actual current Figure 5 4 Closed Loop Control System The speed and torque closed loop control is characterized by the feedback of the actual motor speed and torque This information is compared with the reference set point and the error signal is generated The magnitude and polarity of the error signal corresponds to the difference between the actual and desired speed torque Based on the speed torque error the PI controller generates the corrected motor voltage in order to compensate for the error The application allows operation in two operational modes speed and torque mode Independently of the operational mode both the speed and torque PI controllers are calculated The operational mode defines the required values of the speed and torque at start up only If the drive is running in the speed operational mode the required speed is set to the minimal speed and torque to the maximal allowed limit during start up Vice versa in the torque operational mode the required torque is set to the minimal torque and the required speed is set to the maximal allowed speed The lower value of the PI controllers is chosen as the duty cycle and is applied to the motor To avoid the saturation of the integral parts o
30. ether with a daughter board creates a single unit for developing BLDC PMSM motor control applications With one of the available daughter boards accommodating a selected microcontroller it provides a ready made software development platform for 3 phase motors Feedback signals that allow a variety of algorithms to control 3 phase PMSM and BLDC motors are provided A detailed description including the hardware specification of the 3 phase BLDC PMSM Low Voltage Motor Control Drive board is located in LYMCDBLDCPMSMUG available from Section 1 5 It contains the schematic of the board description of individual function blocks and bill of materials The board does not need any hardware modification or jumper setting before first usage Before first usage the user should pay attention to the correct USB SCI driver installation All about the driver installation is also included in the board user s manual BLDC motor BDM connector J1 connector Power supply connector J3 iiiimiiii gt FreeMASTER USB connector J10 Reset Direction button switch SW4 SW3 Figure 4 2 3 phase Motor Control Drive with MCF51AG128 Daughter Board View Hall sensors connector J6 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 2 Freescale Semiconductor 4 2 2 Motor LINIX 45ZWN24 40 The following motor is used by the BLDC Sensorless application Of course other motors can also be adapted to the application just by defining and changing
31. f the PI controllers these parts are limited If the speed PI controller output is applied to the output the torque PI controller integral part is limited by the speed PI controller integral part and vice versa This type of cross limitation allows running the drive under speed and torque limitations at the same time The speed torque PI controllers proportional and integral constants were set experimentally The PI controllers are executed every 5 ms in the isrVipm3ch1 interrupt 5 4 8 Process Ramp The ramp process slopes some quantities to ensure a smooth motor rotation The ramp process is used at run state to slope the required motor speed The process is executed every 5 ms in the isrVtpm3ch1 interrupt 5 4 9 Process FreeMASTER The FreeMASTER process is part of the application software FreeMASTER communication is implemented fully by the SCI interface FreeMASTER writes new values through the SCI interface into 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 6 Freescale Semiconductor data RAM where particular variables are located This operation is executed every time FreeMASTER FMSTR Poll and FMSTR_Recorder functions are executed 5 4 10 Process PWM Update This process generates the correct voltage pattern on the motor based on the actual PWM sector direction of rotation and required output voltage The process is called every 50 us in isrVtpm3ch0 The commutation table is derived from Back EMF voltage measured o
32. f these application source code main c LVpowerStage c MCUinit c and application header files BLDCparameters h LVpowerStage h a MCUinit h The application source file main c includes the following software routines e main This is the entry point following a Reset It calls the initialization routines and contains the application state machine The application source file MCUinit c includes the following software routines e ZCdetectBemf A B C Rising Falling The functions detect the BEMF zero crossing and set the appropriate commutation time e App The functions which start with App are the application state machine functions e isrVftmIfault_ovf This is the over current fault ISR e isrVtpm3ch0 This ISR serves the commutation event e isrVtpm3ch1 This calculates the speed torque control loop and updates the PWM duty cycle 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 4 Freescale Semiconductor e isrVadc This serves the ADC end of conversion ISR After a new BEMF sample it calls the BEMF detection functions The application source file LVpowerStage c includes the following software routines e DelayCPU This generates delay for the bootstraps charge e MC33927Config This configures the MC33927 pre driver e MC33927ChargeBootstraps This function serves the bootstrap capacitors charge The application header file BLDCparameters h includes the following application constants See BL
33. f16Torque R PhA mf16Torque F PhB mf16Torque R PhB mf16Torque F PhC mf16T1orque R PhC The commutation period is also filtered from variables wPeriodZC F PhA wPeriodZC R PhA wPeriodZC F PhB wPeriodZC R PhB wPeriodZC F PhC wPeriodZC R PhC and recalculated as the motor speed mf164ctualVelocity Both values input into the Speed and Torque PI Controllers as actual values The required values mf 6DesiredVelocity and mf16TorqueRequired are updated based on commands from the user The required speed is sloped mf16Sloped Velocity by a ramp 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 2 Freescale Semiconductor to avoid exceeding the max motor current The resultant Speed and Torque PI Controllers wDutyCycle together with the actual commutation sector ucSector and the required direction of rotation ucDirection define the duty cycle of every PWM channel The Application State Machine sets its state appState based on inputs from the Manual Interface Standstill detection FreeMASTER interface and another state variables not mentioned in the main data flow chart mf16Bemf A mf16Bemf B mf16Bemf C mf16dcb_V mf16dcb_ wPeriodZC F PhA mf16Torque_F_PhA wPeriodZC R PhA mf16Torque R PhA wPeriodZC F PhB mf16Torque F PhB wPeriodZC R PhB mf16Torque R PhB wPeriodZC F PhC mf16Torque F PhC wPeriodZC R PhC mf16Torque R PhC Standstill Detection Y ucStallError mf16ActualVelocity mf16TorqueFiltered ucDir
34. ghts reserved DRM123 Rev 0 05 2011 mk ck ck kh hk ORION 2 1 4 1 4 2 Chapter 1 Introduction POGUE OP PATA AA eee buds cet eee sees 1 1 Freescale MCF51AG128 Advantages and Features 1 2 SO ere LIGNE AA AA de heed PAP kes ieee h dee oe ee eb ees 1 4 Microcontroller Memory and Peripheral Usage 2002 2c eee eee eee 1 5 BELAT cd KPAG heeds Cae aed ead Oe AKA PAR 1 6 1 5 1 Acronyms and Abbreviations a a AA KE AG KAKA 1 6 1 52 O O NO AKA AG NYA KB BABE BLK ANGAS EN AD DES hpi 1 7 Chapter 2 Control Theory Brushless DC Motor BLDC NIDO 2a GG eee deen ee ee eee ee 2 1 Mathematical Description of a Brushless DC Motor AA 2 4 2 2 1 Power Stage Motor System Model a 2 4 api SB AA AA AAP APAN 2 4 Chapter 3 System Concept a ly Ba an APAPAP 3 1 Sensorless Drive Concept 6 3 bk RAGE PG DAPER COME LE HR OTA ON 3 2 O Blocks ING lana NAPAKA KAMA ee ge ELABAG DADA KAKA EREEREER 3 3 3 3 1 PWM Voltage Generation for a Brushless DC Motor 3 3 3 3 2 ADC Sampling Mechanism ccc220sc5cnee eee cust eled i deeneeecde een 3 6 3 3 3 Back EMF Zero Crossing Sensing cciceses eee hi sds ieee KAKA ARKA 3 8 3 3 4 Current Torque Sensing a sa KA KG ie dee eee es AKALA LIPS 3 9 3 3 5 Sensorless Commutation Control nassa aasa eie vi eedeu eee ee eee KAG 3 9 Chapter 4 Hardware Hardware Implementation 5 2a nak ww AGAPAN ARR ESKER SRR Ew RS 4 1 Component Descri
35. high for a predefined time a standstill or incorrect commutation is detected Also if the actual period does not correspond to the applied voltage on the motor the error is indicated In the case of a standstill or incorrect commutation the motor is stopped and the start up sequence is repeated 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 11 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 12 Freescale Semiconductor Chapter 4 Hardware 4 1 Hardware Implementation The BLDC sensorless application runs on Freescale s MCF51AG128 daughter board 3 phase BLDC PMSM Low Voltage Motor Control Drive board and a LINIX 45ZWN24 40 motor For more information see Section 1 5 Please note that although this reference design demonstrates the application using low voltage power stages it can be adapted to high voltage power stages and applications as well P amp E USB MULTILINK 7 BLDC Motor LINIX 45ZWN24 40 DOWN g 3 phase BLDC PMSM Low Voltage Motor Control Drive board Figure 4 1 Hardware Diagram with 3 phase BLDC Motor Control Drive board 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 4 2 Component Descriptions 4 2 1 3 phase Motor Control Drive with MCF51AG128 Daughter Board Freescale s 3 phase BLDC PMSM Low Voltage Motor Control Drive is a 12 24 V 50 V optional DC 4 A power stage that as a main board tog
36. his constant defines the minimal required motor speed 5 4 11 3 Alignment constants define ALIGNMENT TIME REAL 1 0 sec This value gives the alignment time 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 10 Freescale Semiconductor define ALIGNMENT CURRENT FRAC16 0 25 2 Amps This value defines the alignment current The alignment current is controlled by the PI controller 5 4 11 4 Start Up Constants define START PERIOD 28610 This value defines the first commutation period during start up The value is tuned experimentally The conversion to the time in seconds can be done as Eqn 5 6 TPM3_PRESCALER START PERIOD sec START PERIOD Teor where TPM3 PRESCALER 32 TPM3 CLK 24 MHz NOTE The first period is calculated as START PERIOD 2 The constant START PERIOD is used for calculating other periods during start up define START ACCELERATION FRAC16 0 8 This value defines other commutation periods during start up see Section 3 3 5 2 The value is calculated as a constant from the range 0 1 Example If the start acceleration constant is set at 0 8 and START PERIOD is set at 28610 then start up periods will be calculated as 14305 see note at START PERIOD 22888 18311 14648 11719 and 9375 define START SPEED REAL 400 RPM This constant defines the motor speed after the start up sequence define START TORQUE FRAC1
37. in circuit programmable flash memory with block protection and security options e 16 KB of on chip RAM e 4channel DMA with selectable peripheral sources e 1Event module for peripheral to peripheral triggering with no CPU intervention 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 2 Freescale Semiconductor 28 channel 12 bit ADC and PWM Hardware Triggering Two 6 channel 16 bit flexible timer PWM modules FTM with DMA request option dead time insertion is available for each complementary channel pair channels operate as pairs with equal outputs pairs with complimentary outputs or independent channels with independent outputs One 2 channel 16 bit timer pulse width modulator TPM modules Selectable input capture output compare and edge aligned PWM capability on each channel Each timer module may be configured for buffered centred PWM CPWM on all channels Two serial communications interface SCI modules two serial peripheral interfaces SPI and one 2C module 2 High Speed Analog Comparators HSCMP with integrated DAC External voltage monitor EVM allowing input level monitoring with selectable trigger point and interrupt generation ICS providing accurate low cost internal clock source Advanced Independently Clocked Watchdog for System Safety Software selectable pull ups on ports when used as input selection is on an individual port bit basis during output mode pull ups are disengaged Software
38. lied 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 and all 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 may 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 the failure of the Freescale Semiconductor product could create a situation where personal injury or death may occur Should Buyer purchase or use Freescale Semicon
39. ltage u in Section 2 2 2 and DC bus voltage ug utilizing the ADC Refer to Section 2 To get the right Back EMF voltage two assumptions have to be made e Top and bottom switches in diagonal are driven by the same PWM signal e No current is going through the non fed phase used to sense the Back EMF The first assumption is achieved by the FTM PWM module The FTM ADC synchronization at the end of PWM ON pulse is done by the PDB module The second condition can be detected directly from the sensed Back EMF voltage As soon as the phase is disconnected from the DC bus there is still current flowing through the freewheeling diode The conduction time depends on the momentary load of the motor In some circumstances the conduction time is so long that it disallows the detection of Back EMF voltage The conduction freewheeling diode connects the released phase to either positive or negative DC bus voltage The next two steps taken are done to detect current in the non fed phase 1 The first three samples after commutation are not considered for Back EMF voltage detection due to transient event The freewheeling delay can be changed in the reference design S W in FREEWHEEL DLY constant 2 The Back EMF samples within the range of 0 to 20 and 80 to 100 of the DC bus voltage are ignored As soon as the Back EMF voltage falls into the range of 20 to 80 of the DC bus voltage evaluation of zero crossing starts The Back EMF voltage samples are
40. n the idea of Back EMF sensing technique the basic circuit topology see Figure 2 4 is provided e e ee Sat Sst Set m A w A rq 7 Voce O an e oe Sab Seb Scp ae e o Rshunt B Figure 2 4 Power Stage and Motor Topology The motor drive model consists of a 3 phase power stage plus a Brushless DC motor The power for the system is provided by a voltage source Vpcp Six semiconductor switches S A B C tp controlled elsewhere allow the rectangular voltage waveforms see Figure 2 2 to be applied The semiconductor switches and diodes are considered as ideal switches 2 2 2 Back EMF Sensing The Back EMF sensing technique is based on the fact that only two phases of a Brushless DC motor are energized at a time see Figure 2 5 The third phase is a non fed phase that can be used to sense the Back EMF voltage Let us assume the situation when e The phase A bottom switch and the phase B top switch are switched on 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 4 Freescale Semiconductor e The phase C is non fed No current passes through this phase NG Rehunt Figure 2 5 Power Stage and Motor Topology for BEMF Sensing From the phase B we can derive the neutral voltage v vam RgitL Te From the phase A we can derive the neutral voltage v as
41. n the motor see Figure 5 5 Besides the proper commutation pattern the Back EMF sensing can be evaluated from Figure 5 5 For example if phase C is connected to positive DC bus voltage and phase B is connected to negative DC bus voltage the falling Back EMF voltage of phase A has to be evaluated for zero crossing The resultant commutation table includes sensing of the Back EMF voltage as can be seen in Table 5 1 for counter clockwise direction and in Table 5 2 for clockwise direction 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 7 LINIX 45ZWN24 40 BLDC motor Counter Clockwise direction Phase A white yellow motor picture Phase B blue cyan Phase C green violet A TOP A TOP C TOP C TOP B TOP B TOP Phase State C BOT B BOT B BOT A BOT A BOT C BOT B OFF C OFF A OFF B OFF C OFF A OFF Vector Number 5 0 1 2 3 4 Tek YAYA AN DALDAN ALVA HAA ALEAN ILADA AAN AAAA AAAA AAAA MAAN NO COND MAYA IA N N WAAN NIAN AABANAANAN NAA ANN HARADAAA BHD RU AANO EP UN NAN NN IN NAWA NN l AW MINA MAAN WNW WM NWA MAI HC W NAHAHANAP WWW WA AWWA WWW OAR YALA ALAS alia WA nan DY AOA CEP 5 UE e Ee E Z 10 0ms S 00MS s JF 80 0mY 10M points 20 Aug 2010 09 17 30 Figure 5 5 Motor Back EMF Measurement and evaluation Table 5 1 Commutation table for counter clockwise direction Vector Phase Voltage Number A B c Sensing O BO BA eee ee LE NG mar DE AA
42. netic flux linkage was measured by calculating the integration phase Back EMF voltage which was measured on the non fed motor terminals of the BLDC motor As can be seen the shape of the Back EMF is approximately trapezoidal and the amplitude is a function of the actual speed During speed reversal the amplitude is changed and its sign and the phase sequence change too The filled areas in the tops of the phase Back EMF voltage waveforms indicate the intervals where the particular phase power stage commutations are conducted As can be seen the power switches are cyclically commutated through the six steps The crossing points of the phase Back EMF voltages represent the natural commutation points In a normal operation the commutation is performed here Some control techniques lead the commutation by a defined angle in order to control the drive above the PWM voltage control 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 2 Freescale Semiconductor Phase Magnetic Flux Linkage PsiA PsiB Ch Psi_C Ph A Phase Back EMF A ef eK oo Ph pt bh uic Atop Bto Ctop Ph C Speed reversal Figure 2 3 BLDC Motor Back EMF and Magnetic Flux 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 2 2 Mathematical Description of a Brushless DC Motor 2 2 1 Power Stage Motor System Model In order to explai
43. op alignment start up run and error states After an MCU reset the ASM goes through the init state to the stop state The direction switch and Up Down buttons are continuously monitored over the GPIO interface As soon as the user turns the direction switch to the desired direction position the ASM goes into the alignment state where the motor is aligned to a known position After a predefined time the ASM continues to the start up state At the start up state the six commutations are performed without any feedback The timings among the commutations are defined by START PERIOD and START ACCELERATION start up constants After the start up state the ASM goes into the run state where zero crossing is employed and the control loop is closed During the run state requests for new speeds and torques are accepted and maintained by the PI controllers If a standstill of the rotor is detected the ASM goes again into the alignment state and tries to execute a new start up sequence In the case of any fault the ASM goes into the error state and then into the stop state The ZC detection process compares the actual BEMF voltage mf16Bemf_A B C with half of the DC bus voltage mf16dcb_V_ZC The appropriate phase voltage vector is chosen based on sector ucSector The ZC detection process defines the time difference between two consecutive BEMF zero crossings wActualPeriodZC The commutation time is given by the compare value of TPM3 module and is calcula
44. ptions a Ka KAG dens KANA KPA KW LAWA KIN NGABA EBEKAPARG 4 2 4 2 4 3 phase Motor Control Drive with MCF51AG128 Daughter Board 4 2 4 2 2 Motor LINIX 45ZWN24 40 2a WAN AGBAKA NAKA Hoe ORNs KAG GREEEAKG 4 3 Chapter 5 Software Design Ji cali PA esd sade ee AAP POPE PP oe APOS 5 1 Main Software AA AA 5 1 DA FON ee ee eer ee er ee er re ee er PRAAN 5 2 Processes description 0 2a dsc recive w deer derdesecbee enon ieee ivedacae ese es 5 3 5 4 1 Process Zero Crossing detection 02 c cee ee 5 4 5 4 2 Process Torque and Speed Calculation 0 cece eee eee 5 4 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 3 5 4 3 Process Standstill Detection naaa waaa ABAKA de ws eee enee ee ees 5 4 544 Process UNMIS vata tadkicepe Sed eeedbeaelal ge be badenesanaws 5 4 5 4 5 Process Manual Interface a dais RAR eed dd eawse ieee vane ens 5 4 5 4 6 Process Application State Machine 0 ccc eee eee eee 5 4 5 4 7 Process Speed and Torque PI Controller 0 5 5 See POE POND 62 28 5266 AK ALABANG KG ERADAN Ei KAG DRAED 5 6 54 9 Process FreeMASTER as vidiagacudarees BER KI Wa bn Sed rd idi be ce ees 5 6 5 4 10 Process PWM Update AP PP ttd O SPER DREN 5 7 5 4 11 BLDC motor parameters BLDCparameters h nonna naana aeea 5 9 5 4 12 Power stage parameters LVpowerStage h a 5 12 Chapter 6 Sensorless BLDC Demo Operation 6 1 Application Control APAN PAA
45. r e Updates PWM Application State Machine Init state Stop state Alignment state Start Up State Stabilization state Run state Error state isrVftm1fault_ovf FTM1 Fault interrupt INFINITE LOOP e Overcurrent handling Figure 5 1 Main Software Flow Chart 5 3 Data Flow The Brushless DC motor sensorless control drive control algorithm is described in the data flow charts shown in Figure 5 2 The variables mf16Bemf_A mf16Bemf_B mf16Bemf_C mfl6dcb_V and mf16dcb_I contain the results of A D conversion The Zero Crossing Detection process compares the phase voltage with half of the DC bus voltage mf76dcb V ZC The appropriate phase voltage is chosen based on ucSector containing the actual commutation sector The result of the Zero Crossing Detection process defines the time difference for the next commutation saved in TPM3COV TPM3COV is the compare value register of TPM3 In addition individual commutation periods are stored for every commutation in variables wPeriodZC_F_PhA wPeriodZC_R_PhA wPeriodZC_F_PhB wPeriodZC_R_PhB wPeriodZC_F_PhC wPeriodZC_R_PhC for further speed calculation In a similar manner in every zero crossing event the value of mf16dcb_I is copied to variables mf16Torque_F_PhA mf16Torque R PhA mf16Torque F PhB mf16Torque R PhB mf16Torque F PhC mf16T1orque R PhC The variable mf167orque Filtered is calculated as the average value of variables mf 6Torque F PhA m
46. rough the following processes e Alignment e Start Up e Stabilization e Run Firstly the rotor is aligned to a known position without the positional feedback When the rotor moves the Back EMF is induced on the non fed phase and sensorless position detection can be employed As a result the position is known and can be used to calculate the speed and process the commutation in the Run state 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 9 3 3 5 1 Alignment The main aim of Alignment is to align the rotor to a known position This known position is necessary to start rotation in the proper direction and to generate maximal torque during Start up During alignment all three phases are powered Phase A is connected to the positive DCB voltage and Phases B and C are connected to the negative DCB voltage The resultant rotor position gives the same condition for Start up regardless of rotational direction see Figure 3 9 The alignment time depends on the mechanical constant of the motor including load The time has to ensure the rotor steady state at the end of the Alignment process VCC Phase A Next flux vector eee ee mmm oe ee ee eB ee gt Ph B Phase C J Mage ad N i l an Ng vcc VCC Alignment flux vector Figure 3 9 Rotor Alignment 3 3 5 2 Start Up The Back EMF technique can be used when the rotor is moving The start up process ensures the initial rotor movement follo
47. ted as follows 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 2 Freescale Semiconductor Eqn 3 1 TPM3COV wTimeZC mfl6AdvanceAngle wActualPeriod At every control period all ZC rising and falling periods are averaged The sum of these averaged rising and falling periods is given by mf16PeriodFiltered The actual scaled speed mf16ActualVelocity is calculated as follows Eqn 3 2 VELOCITY CONST SCALED ea PN a mf16PeriodFiltered For more details about speed constants and scaling see Section 5 4 11 2 The actual current mf16TorqueFiltered is given by the average of the last six currents mf16Torque_R F_PhA B C at the ZC events Both values are input into the Speed and Current PI controllers as actual values The required values of the speed and the limitation current thresholds mf 6DesiredVelocity mf16TorqueRequired are updated based on commands from the user The required speed slope is limited by a ramp to avoid exceeding the maximal motor current The Speed and Current PI controllers outputs together with the actual commutation sector define the duty cycle wDutyCycle for the FTM PWM module The new duty cycle wDutyCycle is a lower output value from the Speed and Current PI controllers mf16DutyCycleSpeed mf16DutyCycleTorque The integral term of the PI controller with the lower duty cycle is assigned to the integral term of the second PI controller Once a fault condition occurs the application switches to
48. tion e Synchronized loading of write buffered FTM registers e Up to 4 fault inputs for global fault control e One interrupt per channel plus a terminal count interrupt for each TPM module e Testing of input captures for a stuck at zero and one conditions The A D converter has the following features e Linear successive approximation algorithm with the maximum 12 bits resolution e Output format in 12 10 or 8 bit right justified format e Selectable asynchronous hardware conversion trigger PDB RTC or iEvent0 output e Can be configured to take two samples with no software reconfiguration required based on hardware triggers during ping pong mode e Single back to back or continuous conversion automatic return to idle after single conversion e Conversion complete flag and interrupt or DMA request e Input voltage values may range from Vgsaq to Vppa e Up to 28 analog inputs e Configurable sample time and conversion speed power e Input clock selectable from up to four sources e Operation in wait or stop modes for lower noise operation e Asynchronous clock source for lower noise operation e Temperature sensor The A D converter is used for evaluation of Back EMF zero crossing detection without any external comparators and for sensing other analogue quantities which are necessary for BLDC motor control 1 3 Software Listing The code is written in C Freescale CodeWarrior for HCS08 and ColdFire V1 family The software consists o
49. tware design including the FreeMASTER software visualization tool 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor Br Figure 1 1 Sensorless 3 phase BLDC Motor Demo using an MCF51AG128 1 2 Freescale MCF51AG128 Advantages and Features The MCF51AG family expands the 32 bit ColdFire microcontroller portfolio by offering products with DMA and iEvent modules to handle data transaction and interrupt management thereby off loading CPU overhead and increasing overall performance It also includes functionality important for system safety and integrity such as an advanced independently clocked COP external Watchdog monitor and a cyclic redundancy check CRC engine providing CLK failure protection and memory content validation for applications covered by regulations such as IEC60730 The MCF51AGx family is designed to be very robust in a variety of environment with very good EMC performance This family is suitable for smart Appliance white goods and Industrial applications with a peripheral set which is aligned to the needs of advanced 3 phase motor control to improve the overall energy efficiency of the application For detailed information follow the MCF51AG128 Reference Manual by Freescale Semiconductor Inc 2010 available from www freescale com The MCF51AG128 incorporates the following specific features e ColdFire V1 core delivering a 50 MHz core speed and 25 MHz bus speed e 128 KB of on chip
50. ue closed loop The application meets the following performance specifications e Sensorless Brushless DC Motor Control by Back EMF zero crossing sensing e Targeted at the MCF51AGx platform e Running on a low voltage 24 V 3 phase Motor Control Drive board e Control technique incorporates Sensorless control with the combined speed torque closed loop Using an ADC for zero crossing sensing Rotation in both directions Full 4 quadrant operation Start from any motor position with rotor alignment Manual interface Direction switch Up Down push button control FreeMASTER software control interface motor run stop speed torque set up FreeMASTER software remote monitor MCU initialization is done by Device Initialization tool part of Processor Expert 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor 3 2 Sensorless Drive Concept The chosen system concept is shown below Figure 3 1 3 phase BLDC PMSM Low Voltage Motor Control Drive board DC bus voltage and current sensing 3 phase voltage source inverter Back EMF sensing ADC module PWM module Zero Crossing Period Evaluation Commutation Control Speed Up Current Controller Start Stop Speed Down Speed Controller FreeMASTER Figure 3 1 Drive Concept The basic state machine operation of the system is as follows The background loop executes the application state machine ASM consisting of init st
51. view the bipolar switching is a better choice since this allows having a duty cycle in the range of 50 to 100 This significantly simplifies the Back EMF voltage and current sensing commutation commutation commutation commutation commutation commutation commutation comm utation L l 120 60 I I l Sat A Off a TAN i A Se i l enn I l ienne s One n in eS Li nena ANAC LIL B Off C Off Figure 3 2 Complementary Bipolar Switching Patterns for a BLDC Motor 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor commutation commutation commutation commutation commutation commutation commutation commutation l ho i o i i e122 60 Se NAAN 1NA ning nl ed UE Se Dn Sey a e Lin ie Figure 3 3 Complementary Unipolar Switching Patterns for a BLDC Motor 3 3 1 2 Independent PWM Mode In Independent PWM mode the top and bottom switches of a phase are operated independently over a commutation period If a top switch performs a PWM the bottom switch is off and vice versa In this mode the drive can operate in two quadrants Again the bipolar and unipolar switching are available The use of independent bipolar switching has significant drawbacks The drive can work with discontinuous or continuos currents During the transition from discontinuous to continuous current the drive significantly changes its beh
52. voltage current and BEMF measurement PDB PWM FTM1 to ADC synchronization Bibliography 1 3 Phase BLDC PMSM Low Voltage Motor Control Drive User s Manual LVMCDBLDCPMSMUG Initial version by Freescale Semiconductor Inc 2009 2 MCF51AG128 Reference Manual by Freescale Semiconductor Inc 2010 3 Code Warrior Development Studio for Freescale Microcontrollers V6 2 by Freescale Se miconductor Inc 2008 4 MCF51 General Functions Library User s Manual MCF51_GFLIB Initial version by Freescale Se miconductor Inc 2009 5 MCF51 Motor Control Library User s Manual MCF51_MCLIB Initial version by Freescale Se miconductor Inc 2009 6 3 Phase BLDC Motor Sensorless Control using MC9SOSAW60 DRM086 by Freescale Se miconductor Inc 2005 7 3 Phase BLDC Motor Sensorless Control using MC9SOSMP16 DRM117 by Freescale Semiconductor Inc 2009 For a current list of documentation refer to www freescale com 1 5 1 Acronyms and Abbreviations Table 1 3 contains sample acronyms and abbreviations used in this document Table 1 3 Acronyms and Abbreviated Terms Term Meaning AC Alternating current ADC Analog to digital converter ASM Application state machine BDM Background debug mode BEMF Back electromotive force BLDC Brushless DC motor 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 Freescale Semiconductor Table 1 3 Acronyms and Abbreviated Terms
53. wed by Back EMF evaluation The start up process starts immediately after the alignment process The first flux vector applied on the motor is orthogonal to the alignment flux vector The right flux vector is chosen based on the required direction of rotation see Figure 3 9 The flux vector is applied for a period which is defined as a constant value during the drive tuning The next five flux vectors follow in order to create a rotational field The period timing of all six periods is given by the following equation Eqn 3 3 Turw START ACCELERATION Torgvious The constant START ACCELERATION has to be less than 1 and a value within range 0 7 to 1 gives an approximately constant acceleration The initial period START PERIOD constant has to be tuned based on load inertia Another way is to define a start up table with period timing 3 Phase BLDC Sensorless Control using MCF51AG128 Rev 0 10 Freescale Semiconductor The start up tuning is the heaviest task in the Back EMF sensorless technique The tuning difficulty depends on the load type On a passive load where the load torque starts at 0 Nm and grows with the motor speed it is quite easy A more difficult situation can be observed on drives which have non zero starting torque or a variable torque within one revolution such as compressors If load inertia is variable the number of starting flux vectors can be changed A number smaller than six brings about a more robust start up at v
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