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3-Phase Sensorless BLDC Motor Control Using MC9S08MP16

January 22 th , 2010. 3-Phase Sensorless BLDC Motor Control Using MC9S08MP16. Presentation. Libor Prokop System Application Engineer. Presentation Outline. BLDC Motor Control Generally Sensorless BLDC with BEMF Zero Crossing DRM117 Sensorless BLDC Motor Control Application.

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3-Phase Sensorless BLDC Motor Control Using MC9S08MP16

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  1. January 22th, 2010 3-Phase Sensorless BLDC Motor Control Using MC9S08MP16 Presentation Libor Prokop System Application Engineer

  2. Presentation Outline • BLDC Motor Control Generally • Sensorless BLDC with BEMF Zero Crossing • DRM117 Sensorless BLDC Motor Control Application

  3. BLDC Motor Control Generally 120o 60o A B C

  4. 0% 0% Phases voltage 6 - Step Commutation Diagram • Six Step BLDC Motor Control • Voltage applied on two phases only • It creates 6 flux vectors • Phases are power based on rotor position • The process is called Commutation A B C 1. 3. 5. 2. 4. 6. BLDC ØA ØC ØB

  5. 6 step (120 Degree) 3-phase BLDC Motor Control • Stator field is maintained 60° to 120° relative to rotor field • Therefore the rotor position must be estimated • Right After Commutation • Right Before Commutation

  6. Power Stage – Motor Topology 3-PHASE POWER STAGE B PWM1 PWM3 PWM5 S S S AT BT CT POWER C A SOURCE DC VOLTAGE PWM2 PWM4 PWM6 S S S 3-PHASE BLDC MOTOR AB BT CT MOSFET/IGBT DRIVERS PWM1 PWM2 PWM3 PWM4 PWM5 PWM6 Controller

  7. Quadrants of Operation Current (Torque) Second Quadrant First Quadrant negative speed-positive torque positive speed-positive torque “reverse-braking” “forward-accelerating” Generating Motoring I Voltage (Speed) II III IV Motoring Generating Fourth Quadrant Third Quadrant Positive speed - negative torque negative speed - negative torque “forward-braking” “reverse-accelerating”

  8. commutation commutation commutation commutation Bipolar BLDC Commutation (3 Complementary PWM pairs) • Allows energy recuperation • BOTTOM is opposite of TOP • Requires sophisticated PWM support commutation commutation commutation commutation 120o 60o A - Off A - Off SAt SBt SCt SAt A - Off A - Off SAb SAb SBb SCb B - Off B - Off SBt B - Off B - Off SBb C - Off C - Off C - Off SCt ØB 3phase Brushless DC motor C - Off C - Off C - Off SCb ØA ØC

  9. Bipolar BLDC Commutation (Complementary PWMs) Detail • BOTTOM is opposite of TOP Dead Time Dead Time Dead Time Dead Time Dead Time Dead Time A - Off SAt A - Off SAb B - Off SBt B - Off SBb C - Off B - Off SCt C - Off B - Off SCb Swap Dead Time Dead Time Dead Time Dead Time

  10. commutation commutation commutation commutation Unipolar BLDC Commutation (3 Complementary PWM pairs) • Allows energy recuperation • BOTTOM is opposite of TOP • Requires sophisticated PWM support commutation commutation commutation commutation 120o 60o A - Off A - Off SAt SAt SAt SCt SAb A - Off A - Off SAb SBb SCb B - Off B - Off SBt B - Off B - Off SBb C - Off C - Off C - Off SCt ØB 3phase Brushless DC motor C - Off C - Off C - Off SCb ØA ØC

  11. Sensorless BLDC with BEMF Zero Crossing

  12. Synchronous PM Motors • Stator Field needs to be close to orthogonal (90°) to rotor field to get maximal torque and energy efficiency: +Vp (PWM) La Running Direction Motor Torque S N Lc 90` Lb Stator Flux GND (PWM)

  13. A C H 4 0 V B C BLDC Motor Back-EMF Shape P h a s e A - B V o l t a g e P h a s e B - C V o l t a g e P h a s e C - A V o l t a g e P h a s e A P h a s e B P h a s e C

  14. A B C 1. 3. 5. 2. 4. 6. 0% BLDC ØA ØC ØB 0% BLDC Commutation Specifics • After the commutatation current transient: • Ic = 0 and so UC = BEMFC USc = UbackEMFc

  15. Sensorless BLDC Motor Control with BEMF Zero-Crossing Detection Appropriate Phase Comparator Output selected Zero Crossing event detected

  16. Sensorless Commutation and BEMF 0 60 120 180 240 300 360 Rotor Electrical Position (Degrees) Phase R Phase S Phase T Zero crossings PWM 1 PWM 3 PWM 5 PWM 2 PWM 4 PWM 6

  17. BLDC Central Point Is Not Accessible • 3-phase invertor and DC bus current measurement Inverter Stage Udcbus Not Accessible Rshunt Phase c BLDC Motor Phase b Idcbus Phase a

  18. - - - - + + + + - - - - + + + + PhC PhA PhB BLDC Motor Voltages at Bipolar Switching Phases Regeneration I 1 2 1 2 V -V Q2 Q1 Regeneration Q4 Q3 3 4 3 4 -I VDCB Motor Phase A Voltage VDCB/2 3 4 1 2 Motor Central Point Voltage V0 GND 1(4) Top Bottom in diagonal on 2(3) Top Bottom in (inverse) diagonal on

  19. - - + + - - + + PhC PhA PhB BLDC Motor Voltage at Unipolar Switching Phases 1 2 One cycle in Quadrant 1 1 Top Bottom in diagonal on 2 Two Bottoms on 3 4 One cycle in Quadrant 3 3 Top Bottom in diagonal on 4 Two Bottoms on (inverse current) Motor Phase Voltage VDCB VDCB/2 3 4 1 2 Gnd Motor Central Point Voltage U0

  20. Zero Crossing Sensing Reference HB1 + HB1 Udcb HB1 • BLDC Motor Central Point is not accessible A - + + HB2 0 A A - - B V HB2 HB2 + 0 0 B V B V - + + - - + HB3 HB3 C - + + HB3 C - - • ½ UDCB reference • GND reference • Virtual CP reference Udcbus Rshunt HB1 HB2 A BLDC Motor Idcbus 0 B V HB3 C

  21. Bipolar Commutation (Complementary PWMs) Detail • BOTTOM is opposite of TOP Top and Bottom in diagonal on Top and Bottom negative in diagonal on A - Off SAt A - Off SAb B - Off SBt B - Off SBb B - Off C - Off SCt C - Off B - Off SCb Dead Time Dead Time

  22. Unipolar Commutation (Complementary PWMs) Detail • BOTTOM is opposite of TOP Top and Bottom in diagonal on Two Bottoms on A - Off SAt A - Off SAb B - Off SBt B - Off SBb C - Off B - Off SCt C - Off B - Off SCb

  23. Zero Crossing Detection Measurement Window • BOTTOM is opposite of TOP Top and Bottom in diagonal on Two Bottoms on SAt SAb SBt SBb C - Off SCt C - Off SCb Zero-Crossing Sampling Window

  24. Back-EMF Zero Crossing Sensing Circuit • ½ UDCB reference Phase Selection According to PWM Sector Phase a Udcb Positive MUX A Phase b 0 V B Sampling Cout Phase c + - C Negative MUX Udcb/2 ZC Sampling Window Ud/2 Sampling Window Generator PWM Sync

  25. Back-EMF Detection Window CMT CMT ZC Zero Crossing Detected BLDC Commutation Zero Crossing Detection Process BLDC Commutation Current Recirculation

  26. BLDC Commutation with Back-EMF Zero Crossing Sensing

  27. Calculation of the Commutation Timing

  28. Sensorless Commutation - Forced PLL2nd algorithmimplemented on3-phase Sensorless BLDC Motor Control Using MC9S08MP16 Regulator Motor ZC Detector 3-phase Power Stage + -

  29. Sensorless Commutation Control States • Sensorless commutation needs three commutation states : • Alignment • Open-Loop Start • Sensorless Run • Alignment must be performed before every start. • Alignment duration and current is dependent on motor electrical and mechanical time constant. • Because after alignment, motor is not spinning, there is state a Open-Loop Start between Alignment and Running, in which no Zero Crosses are detected and commutation must be performed manually.

  30. Alignment Vector

  31. BLDC Motor Vectors at the Start-up • Starting ModeOpen Loop Ramp: • no feedback • Regular Running Mode– Close Loop: • Position estimation fedback q b q b supposed rotor position d d a a

  32. Open Loop Start Velocity Open Loop Commutation velocity Ramp Acceleration OL Velocity Desired Closed Loop Commutation velocity Ramp Acceleration CL Open Loop Start Alignment Run Velocity Threshold OLtoRun real speed time Alignment Period

  33. 3-ph BLDC Motor Idc Control BLDC Current Control and Limitation

  34. Speed Controller with Current Limitation • Current (torque) limitation provided with: • “slow current limitation control” - 2 ms sampling Current Limitation PI Controller Desired DC Bus Current Limit + - Actual DC Bus Current Speed PI Controller 1/T + Velocity Required To PWM Period Zero Crossing Filtered/Estimated - Velocity Actual

  35. + - Current Control/Limitation • Technique • SW current limitation with slow control loop • Issue: • Problematic current sensing during commutation transient Controller 3-ph BLDC Motor SW current control ADC Idc HW OVC

  36. Current Sampling at Back-EMF Zero-crossing • Commutation Transient: • Current not sensed during commutation transient Back-EMF Zero-crossing Phase Voltage Phase Current DC Bus Current Envelope DC Bus Shunt Current Current Sampling At Back-EMF Zero Crossing

  37. Freescale Reference Design DRM117 3-phase Sensorless BLDC Motor Control

  38. Freescale Applications for Sensorless BLDC Motor Control • DRM117: 3-phase Sensorless BLDC Motor Control using MC9S08MP16: • Uses MC9S08MP16 MCU device with 8-bit S08 core • Some peripheral of the MC9S08MP16 are similar with MCF51AG128 • FlexTimer module for 3-phase PWM • Application s/w written in C-language with some S08 assembler subroutines • Design Reference Manual DRM117 document • Modular h/w design: • 3-phase BLDC/PMSM Low Voltage Motor Control Drive board – 36V, 4A • The MC9S08MP16 daughter board module can be replaced with MCF51AG128 daughter board • Application demo available • New application - Released November 2009 • MCF51AG128 application can be based on existing DRM117

  39. Application Usage: Fans Compressors Pumps Industrial drives Appliances Application Features: Targeted at the MC9S08MP16 8-bit microcontroller Sensorless 3-phase trapezoidal BLDC motor control with six-step commutation (60, 120 degree control) Three sensorless synchronized commutation control algorithms incorporating One of unipolar or bipolar PWM commutation techniques possible Back-EMF zero crossing used to synchronize six-step commutation with rotor position Running on a Three-phase low voltage (24V) power board MC9S08MP16 daughter controller board FreeMASTER software control interface and monitor Main application components s/w - written in C-code using some library algorithms - available for the MC9S08MP16 h/w - based on Freescale universal motor control h/w modules documentation - DRM 3-Phase Sensorless BLDC Motor Control Using MC9S08MP16

  40. 3-Phase Sensorless BLDC Motor Control Using MC9S08MP16 Design Reference Manual Application Code Control page Demo Hardware

  41. SPI 3-Phase BLDC/PMSM Low-Voltage Motor Control Drive 3 Phase Inverter DC Bus Voltage & Current Sensing 24V DC Power Input 3 Phase BLDC Motor 3 Phase Voltages Over-current FAULT Vdcb, Idcb Vphasea,b,c PWM1..6 FTM HSCMP2 ZC Comparator FTM2 PWM 3pps Generator ADC Module Simmilar Peripheral to MCF51AG128 PDB2 ZC to PWM Synchronization FTM1 Timer Cmt (and) ZC PDB1 Synchronization ADC to PWM MC33927 driver Config. Zero Crossing Period & Position Recognition Commutation And PWM Control ADC Sensing Sensorless Commutation I/O Ports PWM Duty cycle GPIO Module Superior System Application Monitoring and Control Zero-crossing Period Application Control 1/T MTIM Time Base Desired speed Actual speed USB to COM Convertor - On Board Programming SCI Module Ramp Generation + Speed PI Controller Required speed Freemaster BDM Limitations DC Bus Current - Torque PI Controller MC9S08MP16 Required torque +

  42. S/W - Data Flow

  43. S/W - BLDC Control State Diagram

  44. S/W – Application Flow chart (1)

  45. S/W – Application Flow chart (2)

  46. Sensorless BLDC Motor Control Using MC9S08MP16 – HCS08 Core Load(slow speed control loop is not considered) Assumptions: Core speed 20MHz Motor Speed 4000rpm, 8 poles => 625us commutation period sensorless BLDC motor direct commutation using comparators PWM frequency – 20kHz Sensorless Run BLDC Direct Commutation Timer Cmt Commutation Timeout 25us (*) Timer Cmt Current dec Timeout 10us (*) Timer ZC Zero-Crossing Detected 20us (*) 100% 625us 55usec -> 10% (*) Ca 300us 12 bit Analog Variables Sensing and Filtering Service ADC service 14us ADC service 14us ADC service 14us ADC service 14us ADC service 14us ADC service 14us 100% 50us 55usec -> 30% (*) 50us (*) Sensorless BLDC Commutationusing HSCMP comparators occupiesaround 10%and ADC service occupies around 30% (*) of HCS08 8bit processor computational power at 4000rpm with 8-pole motor and 50kHz pwm.

  47. Thanks for Your Attention • Questions and answers • Contact: • Libor ProkopFreescale1.maje 100975661Roznov pod RadhostemCzech Republic • E-mail:Libor.Prokop@freescale.com • www.freescale.com/motorcontrol

  48. Back-up slides

  49. 3-ph BLDC Motor Idc Control BLDC Current Control and Limitation 2

  50. SW Current Control • Commutation Transient: • Current not sensed during commutation transient Phase Voltage Phase Current DC Bus Current Envelope Current Control Current Sampling Current Control DC Bus Shunt Current Tregulator

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