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Freescale Semiconductor, Inc.
Sensorless Brushless Motor Using MC68HC908MR32 Embedded Motion Control Development System
Berringer Bill Lucas Motorola Microcontroller Division Austin, Texas Leos Chalupa Libor Prokop Roznov System Application Laboratory Roznov, Czech Republic
Overview
Motorola's MC68HC908MR32 (MR32) microcontroller (MCU) specifically designed motor control applications. MR32 suitable induction motors well brushless (BLDC) motors. pulse-width modulator motor control (PWMMC) module configured control brushless (BLDC) motors using several different strategies. BLDC motors being designed into many applications that require fractional horsepower, highly efficient, variable speed motors. Brushless motors have several advantages over other motor types. instance: Because BLDC motors have brushes wear out, they have longer life greater reliability than normal brushed motors. BLDC motors offer performance similar motors with high starting torque high no-load speed.
Motorola, Inc., 2000
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Freescale Semiconductor, Inc. Application Note
BLDC motors typically have higher efficiency than induction switched reluctance motors. permanent magnets used rotor means that less energy wasted rotor losses.
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BLDC motors require electronic control. Some BLDC motors Hall effect sensors provide absolute position sensing. This results more wires higher cost. Sensorless control eliminates need Hall effect sensors, using back-EMF (electromotive force) motor estimate rotor position. Sensorless control essential low-cost variable speed applications such fans pumps. Refrigerator conditioning compressors also require sensorless control when using BLDC motors. Using Hall effect sensors inside compressor practical because environment suitable number electrical connections would problematic. Also, compressors difficult start perhaps most demanding sensorless BLDC application. motor must achieve high torque first rotation overcome piston compression.
MC68HC908MR32 Features
MR32 member low-cost, high-performance M68HC08 (HC08) Family 8-bit microcontrollers, designed specifically midrange motor control applications. Motorola HC08 Family MCUs enhanced, fully upward object code compatible architecture that evolved from M68HC05 (HC05) Family. HC08 Family performance extension HC05 Family low-cost MCUs. MCUs family enhanced M68HC08 central processor unit (CPU08) that includes addressing modes, many instructions, performance improvements existing instructions that result from introduction instruction pipelining. MCUs HC08 Family available with variety package types, input/output (I/O) modules, various memory sizes types.
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Application Note MC68HC908MR32 Features
MR32 motor control features include: High-performance M68HC08 (CPU08) architecture Fully upward-compatible object code with M68HC05 Family 8-MHz internal frequency Kbytes on-chip FLASH memory FLASH data security bytes on-chip random-access memory (RAM) 12-bit, 6-channel pulse-width modulator motor control (PWMMC) module Serial peripheral interface module (SPI) Serial communications interface module (SCI) 16-bit, 4-channel timer interface module (TIMA) 16-bit, 2-channel timer interface module (TIMB) Clock generator module (CGM) Digitally filtered low-voltage inhibit (LVI) 10-bit, 10-channel analog-to-digital converter (ADC) Optional computer operating properly (COP) reset Low-voltage detection with optional reset Fault detection with optional disabling Low-power design (fully static with wait mode) Master reset (RST) power-on reset (POR) 64-pin plastic quad flat pack package (QFP)
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Freescale Semiconductor, Inc. Application Note
Some features CPU08 include: Enhanced M68HC05 programming model Extensive loop control functions addressing modes (eight more than HC05) 16-bit index register stack pointer Memory-to-memory data transfers Fast multiply instruction Fast 16/8 divide instruction Optimization controller applications Improved language support
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This application note does discuss great detail each modules resident MR32. Figure shows block diagram MR32. detailed description MR32, refer 68HC908MR32, 68HC908MR16 Technical Data: Advance Information, Motorola document order number MC68HC908MR32/D. MR32's PWMMC module makes device excellent choice embedded motor control system. review PWMMC module features included here.
10-CH 10-BIT
TIMA 4-CH TIMB 2-CH PWM1 PWM2 PWM3 PWM4 PWM5 PWM6
CPU08
FLASH BYTES PWMMC
POLARITY SIGNALS
FAULT INPUTS
Figure MC68HC908MR32 Block Diagram
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Application Note MC68HC908MR32 Pulse-Width Modulator
MC68HC908MR32 Pulse-Width Modulator
pulse-width modulator (PWMMC) module resident MR32 specifically designed provide pulse-width modulated outputs drive power stage connected servo, brushless 3-phase motor system. PWMMC module partitioned configured several ways, depending specific control motor application. Figure shows block diagram PWMMC referenced throughout this explanation generator.
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Features MR32's PWMMC include: Three complementary pairs independent signals Complementary mode features include: Dead-time insertion Separate top/bottom pulse-width correction current sensing programmable software bits Edge-aligned signals center-aligned signals signal polarity 20-mA current sink capability outputs Manual output control through software Programmable fault protection
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Freescale Semiconductor, Inc. Application Note
PRESCALER GENERATORS UP/DOWN COUNTER PRESCALER CONTROL MODE SELECT DEADTIME INSERTION DIRECT OUTPUT CONTROL DISTORTION CORRECTION RELOAD INTERRUPT INTERRUPTS OUTPUT
FAULT PROTECTION
PWM1 PWM2
COMPARATORS
FAULT PARTITIONING
POLARITY CONTROL
PWM3 PWM4
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DOUBLE BUFFERED REGISTERS
FAULT MODE SELECT
HIGH CURRENT DRIVERS
PWM5 PWM6
MOTOR CURRENT POLARITIES
SYSTEM FAULTS
Figure PWMMC Module Block Diagram outputs generator configured individual pulse-width modulated signals where each output controlled independent output. Another option configure output pairs, with outputs complementary that driving complementary bottom transistors power stage becomes easy task. outputs capable sinking That drive capability allows direct drive optocouplers without need additional drivers. prevent erroneous signals being output from PWMMC module while loading values, bulk registers double buffered output inhibited until control register (LDOK) set, indicating output values.
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Application Note MC68HC908MR32 Pulse-Width Modulator
Fault Protection
Conditions arise external drive circuitry, requiring that signals become inactive immediately. These conditions include overcurrent, overvoltage, overtemperature, other error conditions. four fault input pins MR32's PWMMC module configured react number different ways, upon detection fault. Each fault input interrupt vector. fault conditions, output generator forced known inactive state. number fault control recovery options available systems architect. some cases, desirable selectively disable PWM(s) solely with software. Manual automatic recovery mechanisms available that allow certain acceptable fault situations occur, such starting motor using fault input limit maximum startup current. fault inputs partitioned MR32 used control multiple motors. fault inputs used brushless motor control software. Hardware overvoltage overcurrent faults these same fault pins. Both these faults configured turn power transistors jump error-handling routine. Another possible fault inputs provide cycle-by-cycle current limit. This type hardware current limit especially useful brushless switched reluctance motors. requirement isolation, hardware cycle-by-cycle current limit implemented power board. addition, software developed this application note uses software current controller during startup.
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Output Alignment
Depending system design, there choice between edge- center-aligned signals that output from MR32's PWMMC module. counter uses value timer modulus register determine maximum count. center-aligned mode, 12-bit up/down counter used create period. resolution center-aligned mode clock periods. highest resolution processor speed MHz. edge-aligned mode, 12-bit up-only counter used create period. Therefore, resolution edge-aligned mode clock highest resolution is125 processor speed MHz.
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Freescale Semiconductor, Inc. Application Note
BLDC motors might edge-aligned center-aligned signals depending application requirements. Most applications, that only require variable speed operation, independent edge-aligned signals. This provides highest resolution. application requires servo-positioning, dynamic braking, dynamic reversal, recommended that complementary center-aligned signals used. sensorless control method implemented this application note uses independent center-aligned signals minimize effect sampling noise.
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Load Operations
When generating sine waves motor, interrupt routine typically used step through sine table memory, scale that sine value, output result from generator. rate which sine table scanned derived from interrupt from generator. PWMMC module programmed provide interrupt rate every one, two, four, eight reload cycles.
Direct Output Control
some cases, user desire bypass generator directly control outputs. mechanism exists disconnect generator from outputs directly control outputs. When this mode used, generator continues run; however, output disabled, overridden direct output. PWMOUT register also used BLDC motor control selectively disable channels. This method permits single 8-bit pattern control BLDC motor commutation.
Dead-Time Insertion Dead-time Compensation
When generator used complementary mode, PWMMC module provides dead-time insertion. This provides short delay time between turning power transistor turning lower transistor phase leg. Dead-time essential safe switching low-power losses. Dead-time specified dead-time writeonce register. This 8-bit value specifies number clock cycles dead-time.
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Application Note Brushless Motor Control Algorithm
During dead-time, current might either positive negative. voltage motor phase will depend direction motor current. This leads distortion from desired voltage waveform. MR32 provides three current sense inputs which used deadtime compensation. Dead-time compensation provides smooth sine wave currents induction motors even low-speed operation. Most BLDC motors require complementary PWMs, dead-time insertion, dead-time compensation. software presented here does these features. only BLDC applications that might require these features high-performance BLDC servomotors, sine wave excited BLDC motors, brushless synchronous motors. These types motors account less than percent BLDC motor drives today, might find applications electric vehicles, electric power steering, robotics near future.
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Brushless Motor Control Algorithm
Many different control algorithms have been used provide sensorless control BLDC motors. Most hard disk drive controllers linear control (integrated circuit) provide sensorless control spindle drive. Typically, motor voltage controlled using power transistor operating linear voltage regulator. This practical when driving higher-power motors. High-power motors must control require microcontroller provide starting control functions. control algorithm must provide three things: voltage which controls motor speed Mechanism commutate motor Some method estimate rotor position using back-EMF (electromotive force) motor
Pulse-width modulation used apply variable voltage motor windings. effective voltage proportional duty cycle. When properly commutated, torque-speed characteristics BLDC motor identical motor. variable voltage used control speed motor available torque.
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Freescale Semiconductor, Inc. Application Note
commutation power transistors energizes appropriate windings stator provide optimum torque generation depending rotor position. conventional motor, this task performed brushes commutator. BLDC motor, must know position rotor commutate appropriate time. When rotor turning, acts generator. moving magnets induce voltage into stator windings. This voltage always present when motor turning. applied voltage must greater than this induced voltage provide torque-generating current. effect, motor pushing back with voltage. induced voltage called back-EMF. stands electromotive force, physics term voltage. BLDC motor drive circuits designed that three phases always open, with both upper lower transistors state. open phase used sense back-EMF motor. This provides useful information position rotor.
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Commutation
3-phase brushless motor power transistors arranged 3-phase bridge (see Figure power transistors switched according predefined commutation pattern. Several different patterns used BLDC motors. sensorless control, phase must always open. motor three windings, typically configuration. center point floating. open phase voltage relative center point. center point affected voltage applied other phases. Many BLDC motor drives modulate only bottom transistors. This causes center point shift upward voltage actively coupled open phase. This commutation pattern, therefore, suitable sensorless BLDC motors using PWM. delta winding electrically equivalent connection behaves similar fashion relative virtual center point.
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Application Note Brushless Motor Control Algorithm
LINE BLDC MOTOR BACK-EMF SIGNALS
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Figure BLDC Motor System sensorless control algorithm developed MR32 uses symmetrical commutation pattern (see Table signal always applied diagonally opposite transistors. This keeps center point center supply voltage. active windings balance that voltage coupled directly open winding. There still some noise winding mismatch capacitive coupling which filtered easily.
Table BLDC Motor Commutation
Bottom
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Freescale Semiconductor, Inc. Application Note
This commutation pattern requires only single signal. Identical signals applied transistors. software uses trick force unused channels state. unused channels disabled setting most significant (bit value register. This also corresponds sign 16-bit signed integer. PWMMC module designed that number equal less than will force channel off. This feature useful induction motors provides saturation data values outside normal operating range. Alternatively, unused channels could disabled writing value register. This commutation pattern also could accomplished using single with hardware multiplexer. However, this only acceptable strategy BLDC motors. Applications which require servo-positioning regenerative braking might require PWMs with dead-time. Large motors greater than 750W might require three PWMs minimize torque ripple. MR32 PWMMC module flexible enough used with most BLDC strategies.
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Back-EMF zerocrossing
back-EMF three motor phases measured using resistive divider. voltage also measured using identical divider circuit. Three comparators used provide zero-crossing signal each phase. Each phase voltage compared one-half voltage. comparators also have some filtering minimize effect noise zero-crossing signal. microcontroller command commutation knows exactly which channel open time. multiplexer used combine three zero-crossing signals into single combined zerocrossing signal open phase. microcontroller provides three signals used select open phase. single input capture function then used measure zero-crossing time. Each motor phase significant inductance. After motor commutated, winding inductance will force open phase voltage diode drop above voltage below ground. This results prominent notch start open phase voltage. This notch must ignored software.
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Application Note Brushless Motor Control Algorithm
Under normal running conditions, back-EMF zero-crossing ideally should located right center commutation period. When good zero-crossing detected, time measured from last commutation, doubled, added last commutation time. Thus, commutation period twice zero-crossing time zerocrossing right center period. Unfortunately, just measuring zero-crossing doubling does provide robust control BLDC motor. Sometimes zero-crossing does occur when expected. Sometimes zero-crossing happens early missed. inductive notch, noise, changing motor dynamics contribute occasional errors. more robust system requires predicting when commutate motor. prediction should based known motor speed. predicted commutation time used calculate time window zero-crossing signal. This time window used evaluate validity back-EMF voltage zero-crossing. zero-crossing occurs within valid window, zero-crossing used calculate commutation normally. zero-crossing does occur when expected, motor commutated using predicted commutation time. first order prediction based last period. This works fine only zero-crossing missed. predicted time improved providing correction based zero-crossing early late. software uses different correction equations predict next commutation time depending validity zero-crossing.
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Freescale Semiconductor, Inc. Application Note
Startup Operation When motor stationary, there back-EMF motor position unknown. motor position might possible commutation states. special procedure required start motor. software uses different control method starting acquisition than normal running mode. There course, also stop mode. motor control modes operation illustrated Figure
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BEGIN
ALIGN
ACQUISITION (ACCELERATE)
STOP
Figure BLDC Simplified Startup Algorithm rotor BLDC motor aligned setting commutation known state applying small voltage align motor. large voltage were applied motor, current might easily exceed ratings power transistors. voltage small, motor will align. current mode controller been implemented software provide maximum alignment torque. alignment mode fixed duration although this value modified according different applications.
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Application Note Software
most applications, acceptable motor turns slightly either direction before starting. piston compressor applications, desired align piston dead center. This will provide full revolution acceleration. starting position usually important centrifugal pump application. Some applications such disk drives require different algorithm prevent counter-rotation. Following alignment stage, motor accelerated according predefined acceleration curve. acceleration curve preset provide desired performance application. software uses simple S-shaped acceleration profile. During this phase, back-EMF zero-crossing evaluated according predicted commutation time. correction factors modified during acceleration phase. goal provide fast acquisition rotor position achieve lock. Once positive lock achieved, software uses normal running algorithm correction factors.
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Software
software provides modes operation: Manual mode PC-Master mode
Manual PCMaster Modes
manual mode provides start/stop operation using switches potentiometer used vary speed motor. Start/Stop switch MR32 control board provides both start stop functions. Once started, potentiometer provides speed control over full range motor. When potentiometer turned way, full voltage will applied motor motor will maximum speed. speed control turned down low, motor will lose synchronization stop. error will indicated with blinking LED. motor restarted turning potentiometer toggling start/stop switch
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Freescale Semiconductor, Inc. Application Note
software checks PC-Master mode startup. start/stop switch must stop position power-up. PC-Master Communication Software intended used developing motor control software. required actions motor control software manipulated operator when using PC-Master software. PC-Master software executes that connected isolated RS-232 serial port control board. PC-Master software executing uses Microsoft Internet Explorer user interface small program resident MR32 that communicates with PC-Master software parse commands, return status information process control information from latest information regarding PC-Master software, refer Motorola, Semiconductor Products Sector, Motor Control page: latest application note software, refer following links:
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Program Flow State Diagram
software uses both linear process flow interrupt service routines which occur variable time intervals. This makes development, debugging, documentation more complex than most software. program flow main function largely linear procedural shown flowchart form Figure First (phase-locked loop), ports, (analog-to-digital converter), timers initialized. After initialization, interrupts enabled. interrupt service routines PWMMC module output compare function might occur time after enabling interrupts. Next, start function called, which controls motor operation during startup phase. Once startup complete, start function will return main loop function will called. function controls motor operation during normal running mode.
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Application Note Software
RESET
INITIALIZE (CONFIG PORTS, PLL, ADC, TIMER.)
ENABLE INTERUPTS
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INITIALIZE VARIABLES (SPEED CONTROL, CHECK VOLTAGE, CALIBRATE CURRENT)
START
SW3=ON?
Figure Main Program Flowchart
program flow made more complex addition error handling capabilities. complete state diagram including error handling capabilities shown Figure commutation error might occur during acquisition running state. overvoltage gross overcurrent fault might occur time. fault occurs, outputs will disabled. Turning switch again will cause software restart from beginning.
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Freescale Semiconductor, Inc. Application Note
INITIALIZE
STAND-BY
SWITCH=ON
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STOP
ERROR FAULT
ALIGN
SWITCH=OFF
ERROR
ERROR TIME>ALIGN TIME
RUNNING
ACQUISITION
LOCKED=TRUE
Figure Main Program State Diagram Interrupt Service Routines Many motor control functions synchronized PWMMC interrupt. During PWMMC interrupt service routine, back-EMF signals analyzed. back-EMF sampling performed center center-aligned signal. This helps minimize noise back-EMF signal which coupled from active phases. single output compare function used schedule output commutation. Once motor been commutated, flag provide handshaking with procedural start functions.
Modify System Parameters
Most motor-specific constants defined file called const_cust.h. Some constants which might need changed startup current (Align_Curr), startup commutation period (St1_T2P), ramp constant (C_rmp). variables stored also modified using PC-Master software.
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Application Note System Hardware
System Hardware
system used sensorless brushless motors consists three boards: MR32 control board Optoisolation board 3-phase ac/BLDC high-voltage power board (power board)
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Each these boards comes complete with user's manual. Refer respective user's manual detailed description each board. This application note includes information overall system, basic description each board, highlights some circuitry used brushless motors. These modular development tools were developed provide motor control solutions many different kinds motors. different boards common, unified, 40-pin connector. This thirdgeneration connector provides interface signals sensorless BLDC motor control well sensorless vector control induction motors. Precautions These boards intended used laboratory suitcase demonstrations. When used laboratory, most users will want connect host system. should always earth grounded safety precaution. battery-powered notebook often used laboratory provides additional measure safety robustness. application, high-voltage BLCD motor operates from rectified power line. This presents safety issues developers.
WARNING:
high-voltage motor control boards should used only qualified engineers technicians with experience highvoltage power systems. motor control system described this application note capable operating dangerous voltages capable supplying high amounts power rotating machines. high-voltage board should powered down before changing probe connections. Wearing safety glasses, avoiding ties jewelry, using shields also advisable.
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Freescale Semiconductor, Inc. Application Note
Common practices (electrostatic discharge) protection present potential safety hazards when working with high-voltage circuits. Some precautions are: power board should placed wood plastic table. conductive table conductive mat. grounded chairs. Beware grounded floors wear rubber shoes. general, eliminate provisions from high-voltage work area.
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recommended laboratory setup shown Figure Recommendations laboratory setup include: isolation transformer should used power board. This essential when taking measurements actual voltages currents. variac used vary line voltage. isolation transformer should properly fused particular load. power circuit should allowed float with respect earth ground. digital oscilloscope should normally earth grounded. Portable oscilloscopes digital multimeters provide additional measure safety.
TARGET HEAD CABLE HOST MR32 CONTROL BOARD OPTOISOLATION BOARD POWER BOARD EMULATOR
POWER ISOLATION TRANSFORMER VARIAC
MOTOR
Figure Laboratory Setup
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Application Note System Hardware
available, high-voltage supply also used power power board. supply connected directly input rectifier power board. polarity supply does matter. While expensive, supply provides better protection against overcurrent faults. Make sure supply provides isolated output voltage. isolation board allows connected directly MR32 control board. This necessary when connecting target head adapter cable from emulator MR32 control board. isolation board provides safe isolation 40-pin connector signals.
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software code should developed debugged using emulator connected MR32 control board. This done using just MR32 control board. power board disconnected powered Once software been tested using MR32 board, then tested with motor using laboratory setup shown Figure After developer satisfied with performance software, FLASH MR32 programmed. FLASH device inserted into daughter board connected MR32 control board place target head cable. isolation board intended development purposes. More costeffective solutions available providing isolation user application. isolation board necessarily more complex need support many motor types. Many low-power applications will require optical isolation final system. Non-isolated systems must provide safe insulation mechanical means, enclosing whole system plastic housing providing safe, insulated user controls.
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Freescale Semiconductor, Inc. Application Note
MR32 Control Board MC68HC908MR32 control board designed hardware software design 3-phase brushless switched reluctance motor drive applications. control board does contain MR32 MCU. control board designed connected directly MR32 emulation module (EM) board, which part Motorola Modular Evaluation System (MMEVS) Motorola Modular Development System (MMDS). daughter board designed house MR32 plugs into control board place emulator cable. With daughter board plugged into control board, standalone operation system possible. Since this application note intended with brushless motor, only circuitry resident MR32 control board pertaining 3-phase brushless motor discussed. Applications control board with other types motors covered additional application notes. Figure shows complete block diagram control board. Control board features include: motor control outputs with indicators Speed control potentiometer Optoisolated half-duplex RS-232 interface Start/Stop forward/reverse switches Hall effect inputs brushless motor control Back-EMF inputs brushless motor control Tachometer input configuration jumpers 2-position (dual in-line package) switch user option control Emulator/Daughter board connector Processor reset switch system fault inputs Nine analog inputs Three software-controlled LEDs On-board regulated power supply Motor input/output (I/O) interface 40-pin ribbon cable
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Application Note System Hardware
TERMINAL
OPTO-ISOLATED FORWARD/REVERSE RS-232 SWITCH START/STOP SWITCH EMULATOR/ PROCESSOR CONNECTOR CONFIG JUMPERS
SPEED RESET SWITCH OPTION SWITCHES
TACH INPUT HALL EFFECT INPUTS
POWER 12-15
REGULATED POWER SUPPLY
STATUS LEDS
LEDS 40-PIN CONNECTOR
OPTO/POWER DRIVER CONNECTOR OVERCURRENT/ OVERVOLTAGE INPUTS BACK-EMF CURRENT/TEMP INPUTS SENSE INPUTS MISC. OUTPUTS(6) CONTROL
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Figure MR32 Control Board Block Diagram Fault Control system fault inputs control board designed protect power board. faults system overvoltage system overcurrent. input signals these fault comparators originate from signals power board. optoisolation board used system, these signals optocoupled transparently passed control board analog signal. comparator circuits provide digital signals MR32's fault fault inputs, respectively. These faults, should both occur, will force generator into known inactive state, protecting power board outputs. Figure schematic circuit used both fault inputs. potentiometer, connected inverting input comparator, sets threshold. When input from power board optoisolation board exceeds comparator threshold (voltage inverting input comparator), respective fault input MR32 driven logic triggering fault input generator. Adjusting point potentiometer allows user vary acceptable system current voltage thresholds fault generation. Approximately hysteresis included circuit with noise immunity.
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Freescale Semiconductor, Inc. Application Note
I_sense_DCB/V_sense_DCB
+5V_D
+5V_A_ref
OVERVOLTAGE LM339D
GNDA
I_DCB_ref/V_DCB_ref
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Figure Fault Generation Circuit Isolated Serial Port MR32 features asynchronous serial port that used standard RS-232 interface. MR32 used smart motor controller with user commands feedback communicated over single serial link. isolated serial port been implemented MR32 control board demonstrate this function low-cost system. circuit Figure schematic half-duplex optoisolated RS-232 interface used MR32 control board. RS-232 specification states signal levels range from volts volts. mark defined RS-232 specification signal that ranges from volts volts. space defined signal that ranges from volts volts. left half circuit provides signal inversion level shifting serial port. This section uses clever diode circuit provide voltage levels needed returning right half circuit provides signal inversion level shifting from MR32's serial port. RS-232 line driver, such MC1488, serves same purpose without optoisolation function.
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Application Note System Hardware
ISOLATION BARRIER +5V_D
SFH6106
+5V_D
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(+12 Vdc)
SFH6106
Figure Optoisolated RS-232 Circuit Back-EMF Multiplexer MR32 control board contains multiplexer back-EMF signals. three zero-crossing signals originate from power board discussed later. These zero-crossing signals passed through optoisolation board, when isolation required. microcontroller software command motor commutation. always knows what motor phase open. This information used select proper zero-crossing signal each commutation state. three multiplexer signals connected output port pins MR32. multiplexer signals changed each time motor commutated. three zero-crossing signals from phases routed into back-EMF selection logic shown Figure back-EMF selection logic designed combine three zero-crossing signals into single signal that into input capture timer channel. three open collector NAND gates shown Figure wire ORed such that these outputs changing logic will provide interrupt MR32's timer channel system software uses MUXA, MUXB, MUXC inputs NAND gates enable particular phase have ability interrupt processor.
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Freescale Semiconductor, Inc. Application Note
+5V_D
Zero_cross_A
+5V_D MC74HC03AD
Zero_cross_B BEMF_z_c
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MC74HC03AD
MC74HC03AD
Zero_cross_C
MUX_A MUX_B MUX_C
MC74HC03AD
Figure Zero Cross Back Circuit Optoisolation Board function optoisolation board provide galvanic isolation barrier between control board's I/O, both analog digital, high-voltage system power board's I/O. These isolated signals, from optoisolation board, connected 40-pin connectors. assignments both connectors same. Signal flow through optoisolation board, both directions, one-to-one relation source. more detailed description optoisolation board, refer Motorola's Embedded Motion Control Series Optoisolation Board User's Manual, Motorola document order number MEMCOBUM/D. Figure shows block diagram optoisolation board.
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Application Note System Hardware
BACK-EMF (ANALOG)
ZERO-CROSS (DIGITAL)
SERIAL BOARD CONTROL INHIBIT BREAK CONTROL AUX. PHASE CURRENT SENSE TEMP. SENSE CURRENT VOLTAGE
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SIGNALS CONTROL BOARD
SIGNALS POWER BOARD
PWM(6) POWER 12-15 CONVERTER
Figure Optoisolation Board Block Diagram Gate drive signals, from control board power board, passed from controller power board through high-speed digital optocouplers. Analog feedback signals from power board control board passed through HCNR201 high-linearity analog optocouplers. Ground signals between control board power board separated optocouplers' galvanic isolation barrier. Power requirements control board's circuitry satisfied with single external 12-Vdc power supply, connected optoisolation board control board through 40-pin ribbon cable. Excitation power board side circuitry supplied optoisolation board from power board. addition usual motor control signals, MC68HC705JJ7 serves serial link, which allows control board's software identify configuration optoisolation board power board.
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Freescale Semiconductor, Inc. Application Note 3-Phase ac/BLDC High-Voltage Power Board
more detailed description MR32 power board, refer Motorola's Embedded Motion Control Series 3-Phase BLDC HighVoltage Power Stage User's Manual, Motorola document order number MEMC3PBLDCPSUM/D. function power board provide high-power drive circuitry various types motors. power board suitable driving wide variety induction brushless motors. different board available switched reluctance motors. power board consists separate modules. printed circuit board contains IGBT (insulated gate bipolar transceiver) gate drive circuits, analog signal conditioning, low-voltage power supplies, power factor control circuitry, some large passive power components. This board also MC68HC705JJ7 microcontroller used board configuration identification. block diagram power board shown Figure
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POWER INPUT
SWITCH MODE POWER SUPPLY
CONTROL BRAKE
SIGNALS TO/FROM CONTROL BOARD
IGBT POWER MODULE GATE DRIVERS PHASE CURRENT PHASE VOLTAGE CURRENT VOLTAGE MONITOR BOARD BLOCK ZERO CROSS BACK-EMF SENSE MOTOR
Figure Power Board Block Diagram
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Application Note 3-Phase ac/BLDC High-Voltage Power Board
power electronics which need dissipate heat mounted separate power substrate. This substrate includes power IGBTs, brake IGBT, power factor corrector field effect transistor (MOSFET) temperature sensing diodes. Figure shows complete block diagram power module. Power board features are: 1-phase bridge rectifier Power factor switch diode brake IGBT brake current limiting resistors 3-phase bridge inverter (six IGBTs) Individual phase current sensing shunt resistors with Kelvin connections Power substrate temperature sensing diodes IGBT gate drivers Current temperature signal conditioning 3-phase back-EMF voltage sensing zero cross detection circuitry Board identification processor (MC68HC705JJ7) Low-voltage on-board power supplies Cooling fans
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Freescale Semiconductor, Inc. Application Note
(OFF-BOARD) LINE MOTOR
(OFF-BOARD)
R6-9
Freescale Semiconductor, Inc.
TEMP SENSE DIODES
Figure Power Module Simplified Schematic Power Electronics power module provides single-phase rectifier, optional boost converter, brake circuit, 3-phase inverter. single-phase rectifier permits power board operate directly line. isolation transformer recommended during development. power board also operate high-voltage supply. optional boost converter used power factor correction. power factor correction circuit used brushless motor software, circuitry should bypassed using jumpers described power board user's manual. power board initially configured with power factor correction circuitry bypassed. 3-phase inverter uses IGBTs with integrated free-wheeling diodes. IGBTs preferred power device high-voltage motor control. Power MOSFETs used low-voltage motor control some very low-power high-voltage applications.
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Application Note 3-Phase ac/BLDC High-Voltage Power Board
Current Sensing
Freescale Semiconductor, Inc.
Phase currents measured sensing voltage drop across sensing shunt resistors, located power module. Figure schematic diagram design analog signal conditioning circuit. output voltage amplifier proportional sensed currents. input circuit Figure derived across 0.075- shunt resistor connected series with particular current being measured. input signal amplifier multiplied times then output amplifier shifted 1.65-volt reference. final output circuit ±1.65 volts with input current 2.93 amps passing through 0.075- shunt resistor.
75.0 10.0 I_sense_A2 10.0 +3.3V_A
I_sense_A1
I_sense_A MC33502D
75.0 1.65
LM285M GNDA GNDA
33.2
Figure Current Analog Signal Conditioning Circuit
NOTE:
Excessive current destroy power transistors power board. Including overcurrent protection circuitry design wise choice, absolute necessity. Figure schematic overcurrent detection circuit. input signal this circuit 0.075- resistor, placed series with amplified same type circuit shown Figure output this circuit shown Figure drives shut down input gate drivers.
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Freescale Semiconductor, Inc. Application Note
I_sense_DCB
+15V_D
+3.3V_A OVERCURRENT THRESHOLD= 3.23
Shut_Down_Open_C. LM393
GNDA
Freescale Semiconductor, Inc.
Figure Overcurrent Detection Circuit Schematic Brake Circuit Under certain operating conditions, motor generator, delivering high voltage back into through inverter's power switches and/or power switch source-drain recovery diodes. That very undesirable condition damage power transistors other components inverter. excess energy must dissipated, otherwise voltage will rise above safe limit. power module contains IGBT current limiting resistors, which placed across brake dissipate excess energy. When using brake, careful exceed power dissipation brake transistor current limit resistors. Provisions made power board user install additional brake resistor across composed R6-R9, allowing additional brake current imposed system. Again, careful exceed ratings IGBT brake transistor when additional brake resistor installed system. Typically, system software will pulse-width modulate brake dissipate excess voltage until brought down acceptable level. Under certain operating conditions, motor generator, delivering high voltage back into through inverter's power switches and/or power switch source-drain recovery diodes. This damage power transistors other components inverter.
CAUTION:
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Application Note 3-Phase ac/BLDC High-Voltage Power Board
Sensing
Freescale Semiconductor, Inc.
system software must monitor number analog parameters when motor running. Those parameters include system voltage three individual phase voltages. four cases, high voltage divided down level within measurable range MR32's analog-to-digital converter (A/D). Figure schematic voltage divider used monitoring voltage. signal labeled V_sense_DCB_5 divided down voltage that microcontroller either directly optoisolator board, utilized system. signal labeled V_sense_DCB_half_15 used reference individual phase zero cross detection circuits.
DCB_Cap_pos 6.81 V_sense_DCB_half_15
V_sense_DCB_5 6.81
Figure Voltage Sensing Circuit Back-EMF Comparators similar fashion sensing circuit shown Figure individual phase voltages divided down match input level A/D. Figure shows schematic voltage divider individual phase monitoring circuit. There additional circuits voltage monitoring zero cross detection phases This technique allows sensing back-EMF from motor. individual phase voltage signals separate inputs microcontroller either directly optoisolator board, utilized system. signal shown labeled BEMF_sense_A (BEMF_sense_B BEMF_sense_C, depending particular phase signal).
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Freescale Semiconductor, Inc. Application Note
additional function circuit shown Figure detect zerocrossing phases Note that inverting input comparator reference from divider (V_sense_DCB_half_15). Using divider reference, when phases phase voltages reach percent signal, corresponding phase zero cross point, output comparator will transition from logic logic That transition used distortion correction information IS1-IS3 inputs generator input zero cross window logic zero cross interrupt generation.
Phase_A
Freescale Semiconductor, Inc.
+5V_D
Zero_cros_A LM339D
22.0 BEMF_sense_A 6.80 GNDA
GNDA V_sense_DCB_half_15
GNDA
Figure Back-EMF Zero Cross Detection Schematic
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Application Note Conclusion
power factor correction circuitry used this software. Power factor correction control (PFC) circuitry provides control switch handles necessary feedback provide sinusoidal power line current. capability enabled disabled changing jumper configuration power module. jumper found proximity capacitor. power board shipped with power factor correction circuitry disabled. Refer Motorola's Embedded Motion Control Series 3-Phase BLDC High-Voltage Power Stage User's Manual, Motorola document order number MEMC3PBLDCPSUM/D, information reconfigure power factor correction circuitry.
Freescale Semiconductor, Inc.
Conclusion
This application note describes software hardware solution sensorless brushless motors. software algorithm provides starting variable speed control variety applications. hardware based modular development system circuits have been highlighted. embedded motion control development system further used tailor software create software particular BLDC motor application. This development system provides support many different kinds brushless motors well other motor types. MC68HC908MR32 well suited kinds brushless motor applications. rich peripherals features PWMMC module expressly designed motor control.
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Freescale Semiconductor, Inc. Application Note
Freescale Semiconductor, Inc.
Motorola reserves right make changes without further notice products herein. Motorola makes warranty, representation guarantee regarding suitability products particular purpose, does Motorola assume liability arising application product circuit, specifically disclaims liability, including without limitation consequential incidental damages. "Typical" parameters which provided Motorola data sheets and/or specifications vary different applications actual performance vary over time. operating parameters, including "Typicals" must validated each customer application customer's technical experts. Motorola does convey license under patent rights rights others. Motorola products designed, intended, authorized components systems intended surgical implant into body, other applications intended support sustain life, other application which failure Motorola product could create situation where personal injury death occur. Should Buyer purchase Motorola products such unintended unauthorized application, Buyer shall indemnify hold Motorola officers, employees, subsidiaries, affiliates, distributors harmless against claims, costs, damages, expenses, reasonable attorney fees arising directly indirectly, claim personal injury death associated with such unintended unauthorized use, even such claim alleges that Motorola negligent regarding design manufacture part. Motorola registered trademarks Motorola, Inc. Motorola, Inc. Equal Opportunity/Affirmative Action Employer.
reach
USA/EUROPE/Locations Listed: Motorola Literature Distribution; P.O. 5405, Denver, Colorado 80217. 1-303-675-2140 1-800-441-2447 JAPAN: Motorola Japan Ltd.; SPS, Technical Information Center, 3-20-1, Minami-Azabu, Minato-ku, Tokyo 106-8573 Japan. 81-3-3440-3569 ASIA/PACIFIC: Motorola Semiconductors H.K. Ltd.; Silicon Harbour Centre, King Street, Industrial Estate, N.T., Hong Kong. 852-26668334 Technical Information Center: 1-800-521-6274 HOME PAGE:
Motorola, Inc., 2000
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