Tp Ftf2008 Motorctrl Part4

June, 2008

Hands-on Workshop: Motor Control Part 4 Brushless DC Motors Made EasyAZ114

Eduardo ViramontesApplications EngineerTM

Freescale Semiconductor Proprietary Information. Freescale and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. Freescale Semiconductor, Inc. 2008.

Agenda


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1

Motor Anatomy


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2

Motor AnatomyBrushed DC Rotor

Commutator

Stator

The

first electric motor was the Brushed DC Motor

Basic idea is to repel rotor from stator


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Motor Fundamentals

N

S


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Motor Fundamentals

N+ _

N

S+ _

S

V


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5

Motor Fundamentals

N+ _

N

S+ _

S

V


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6

Motor Fundamentals

S N S_ +

N_ +

V


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7

Motor Fundamentals

N N S+ _

S+ _

V


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8

Electric Motor Type Classification


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Electric Motor Type ClassificationELECTRIC MOTORS AC ASYNCHRONOUS SYNCHRONOUS DC VARIABLE RELUCTANCE

Induction

Sinusoidal

Brushless

SR

Stepper

Permanent Magnet Surface PM Interior PM Wound Field

Known as Universal DC motors or Brushed DC MotorsAC power Tools Washers, Dryers Garage Openers Blenders Vacuum Cleaners HVAC Toys


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Brushed DC Motors

Rotation due to electromagnetic force Continues rotation with multiple coils Undesirable effects due to friction and current reversing


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Induction

Sinusoidal

Brushless

Reluctance

SR

Stepper


Robots Traction Control Servo Systems Hard Drives Fans Sewing Machines Treadmills Industrial Machines


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Brushless DC (BLDC) MotorsThe confusion arises because a BLDC Motor does NOT directly operate off a DC voltage source

Reverse design of brushed motors:Magnet is on the rotor Inductors are on the stator

Benefits vs. BrushedNo mechanical commutator(higher speeds)

Better torque/inertia ration(higher acceleration)

Easier to cool(Higher specific outputs)


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Brushed and Brushless Motors ComparisonFeatureCommutation Maintenance Life Speed/Torque Speed range Building Cost Control Control Requirements

Brushed DC motorBrushed commutation Periodic maintenance is required Shorter Moderately Flat. Higher speeds produces higher friction and this reduces torque. Lower Mechanical limitations by the brushes Lower Simple A controller is required only when variable speed is desired

BLDC MotorElectronic commutation based on Hall position sensors Less required due to absence of brushless Longer Flat Higher No mechanical limitation Higher Permanent magnets Complex and expensive A controller is always required


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Induction

Sinusoidal

Brushless

Reluctance

SR

Stepper


Washing Machines Vacuum Cleaners Machine tools Food Processors Fans Small Appliances


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Switched ReluctanceBoth The

the rotor and stator have salient poles

stator winding is comprised of a set of coils, each wound to the stator


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Induction

Sinusoidal

Brushless

Reluctance

SR

Stepper


Cruise Control Air Vents Medical Scanners Gauges Office Equipment Printers Instrumentation


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Stepper MotorThese

motors turn as different voltages are applied to the different windingsField

rotates in one direction while rotor moves in opposite direction of fieldIn It

this example, field rotates 60while rotor only moves 30

takes four complete cycles of the control system to rotate motor through one cycle. This is because the Rotor has 4 poles


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Induction

Sinusoidal

Brushless

Reluctance

SR

Stepper

Permanent Magnet Surface PM Interior PM Wound Field Get name from sinusoidial windings


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Brushless DC Motor ControlBLDC

Motor versus PMSM Motor

Both motors have identical construction. The difference is in stator winding only. The BLDC has distributed stator winding in order to have trapezoidal Back-EMF. The PMSM motor has distributed stator winding in order to have sinusoidal Back-EMF.Phase B Phase B Phase C Phase C

Phase A Phase A

Trapezoidal Back-EMF voltage

Sinusoidal winding distributionSource: Hendershot J. R. Jr, Miller TJE: Design of brushless permanent-magnet motors


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Induction

Sinusoidal

Brushless

Reluctance

SR

Stepper


Large Appliances HVAC Blowers Fan Pumps Industrial Controls Lifts Inverters


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Induction MachinesInvented over a century ago by Nikola Tesla Stator same as BLDC Difference in rotor construction If properly controlled Provides constant torque Low torque ripple

No permanent magnets Think of it as a rotating transformer. Stator is the primary Rotor is the secondary Rotor current is induced from stator current


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AC Induction Motor SlipBasic Principle: The stator is a classic three-phase stator with the winding displaced by 120 The rotor is a squirrel cage rotor in which bars are shorted together at both ends of the rotor by cast aluminum end rings The rotor currents are induced by stator magnetic field.rotating Field ( s)

Indu ced

Torque

curr ent

r

The motor torque is generated by an interaction between the stator magnetic field and induced rotor magnetic fieldNO BRUSHES, NO PERMANENT MAGNETS


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Induction

Sinusoidal

Brushless

Reluctance

SR

Stepper

Permanent Magnet Surface PM Interior PM Wound Field Unpractical for large motors yet practical in small sizes


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ReluctanceIf

the rotating field of a motor is de-energized, it will still develop 10 or 15% of synchronous torque slots are cut into the conductor-less rotor of an induction motor, corresponding to the stator slots, a synchronous reluctance motor results like an induction motor but runs with a small amount of synchronous torque

If

Starts


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Freescale Roadmap for Motor Control

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BLDC In Depth: BLDC Motor ConfigurationsTM


27

Windings Electrical Connection - Star

AA C

+

A

-

B C

B

B

C

Star connection


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Windings Electrical Connection - Delta

C

A

A

C

+ -

A B B

B

C

Delta connection


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BLDC motor configuration4 pole pairsSN N

H3 B A H2 C B H1N N

C S A

S

H1 H2 H3 1 0 1


30

STM

BLDC motor configuration

3 pole pairs

H1

N

9 coils


31

N

S

H2

S

NSTM

H3

External Rotor Different Motor Configurations

1 pole pairs

2 pole pairsN

4 pole pairsSN N

H3H1 B A H2 C A B H3 S C

H3 B A H2 C B H1N N

A S H2 B

C N

C S A

H1

S

H1 H2 H3 1 0 1

H1 H2 H3 1 0 1

H1 H2 H3 1 0 1


32

S

S

N

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Internal Rotor Different Motor Configurations

1 pole pairH3 A

2 pole pairs

B H1

4 pole pairs

B H3

S

H2

N

H2

H2

NC A H3

N

C

H1 H2 H3 1 0 1

B

H1 H1 H2 H3 1 0 1

B

H1 H2 H3 1 0 1

B


33

NS S

N

N

C

A

C

AN

S

C

S

S

S

A

H1

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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

Phases voltage

Power Stage


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Brushless DC Motor ControlCommutation example Stator field is maintained 60 120relative to rotor field ,

Before commutation

After commutation


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Brushless DC Motor ControlSix

Step BLDC Motor Control contd1 2 R S 3 4 T c 5 61 1 0

Controller

b

a

Source: Eastern Air Devices, Inc. Brushless DC Motor Brochure


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Brushless DC Motor ControlSix

Step BLDC Motor Control contdHall a Hall b Hall c

PWM 1 PWM 3 PWM 5 PWM 2 PWM 4 PWM 60 60 120 180 240 300 360

Rotor Electrical Position (Degrees)


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Brushless DC Motor ControlExample

of commutation table


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Brushless DC Motor ControlSinusoidal

BLDC motor control

iSbAll three phases are powered by sinewave shifted by 120

iS

iSa iScWe are able to generate stator field to any position over 360


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Brushless DC Motor Control SummarySix

step control versus sinusoidal control

Six step control+ Simple PWM generation Ripple in the torque (stator flux jumps by 60 ) A little noise operation (due to ripple in the torque) + Simple sensor + +

Sinusoidal controlMore complex PWM generation (sinewave has to be generated) Smooth torque (stator flux rotates fluently) Very quiet Requires sensor with high resolution


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Sensor Example: Hall Effect SensorHall

effect sensor is a transducer that varies its output voltage in response to changes in magnetic field Hall sensors are used for proximity switching, positioning, speed detection and current sensing applications In this case, hall sensors are used in On/Off modeHall Sensor Everytime a magnetic field is sensed, a change in voltage can be detected Permanent Magnet


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Putting All Together


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Lab1


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How to Set Up the BoardsAC16 board

6.Jumper J13 APMOTOR board

7. 8LED array3

2

2. BDM1

3.BLDC Motor

1. PowerSupply (9V DC)

J13


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Create a New CodeWarrior Project1. Click on the Open Icon

2. Select the MC9S08AC16 MCU 4. Click next

3. Select P&E Multilink/Cyclone Pro


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Name Your CodeWarrior Project1. Set new name for your project

2. Select Project Path

3. Click next


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Add Additional Files

1. Select AC16DaugherCard.h

2. Add To Project Files

3. Click next


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Processor Expert

1. Click next


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C Options

1. Click next


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PC-Lint Options

1. Click Finish


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New Project Set Up

1. Click On Make


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Commutation Table & Knowing Position with Hall Effect sensors


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Necessity of Knowing the PositionTo

spin 3-phase BLDC motor:Detect position/commutation Read commutation table Mask and swap phases1 0 1 0 1 0

Signal sequence diagram for the hall sensors60 H1 H2 H3 120 180 240 300 360

It is important to know the rotor position in order to maintain the rotating magnetic field

Supplied motor voltage+A-B

_ +

B-C

_ +

C-A

_


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3-Phase InverterVb

Q1

Q2

Q3 A B C

With the 3-phase inverter, you can control which phases need to be fed in order to turn the motor

Q4

Q5

Q6

0v

Q1, Q2 and Q3 is where the current goes in the motor and Q4, Q5 and Q6 is where the current goes out of the motor


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Control of 3-Phase Inverter Determined on the Hall Sensor Position

AN S

B C

C B

A

B

BLDC Motor

C

A


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Control of 3-Phase Inverter Determined on the Hall Sensor PositionAN S

B C

C B

A

B

BLDC Motor

C

A

H1 1 1 1 0 0 0

H2 0 0 1 1 1 0

H3 1 0 0 0 1 1

Phase A +VDCB +VDCB NC -VDCB -VDCB NC

Phase B -VDCB NC +VDCB +VDCB NC -VDCB

Phase C NC -VDCB -VDCB NC +VDCB +VDCB


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Control of 3-Phase Inverter Determined on the Hall Sensor PositionAS

B C

C B

A

B

BLDC Motor

C

N

A

H1 1 1 1 0 0 0

H2 0 0 1 1 1 0

H3 1 0 0 0 1 1





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Control of 3-Phase Inverter Determined on the Hall Sensor PositionA B CN S

C A B

A

B

BLDC Motor

C

H1 1 1 1 0 0 0

H2 0 0 1 1 1 0

H3 1 0 0 0 1 1





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Control of 3-Phase Inverter Determined on the Hall Sensor PositionA B CN S

C B

A

B

BLDC Motor

C

A

H1 1 1 1 0 0 0

H2 0 0 1 1 1 0

H3 1 0 0 0 1 1





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Control of 3-Phase Inverter Determined on the Hall Sensor PositionA BS N

C B

A

B

BLDC Motor

C

C

A

H1 1 1 1 0 0 0

H2 0 0 1 1 1 0

H3 1 0 0 0 1 1





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Control of 3-Phase Inverter Determined on the Hall Sensor PositionA B C C BN SBLDC Motor

A

B

C

A

H1 1 1 1 0 0 0

H2 0 0 1 1 1 0

H3 1 0 0 0 1 1





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Lab 1Make a program that On/Off transistorsTO DO:Enable

moves the motor in the clockwise direction

Switch1 to enable commutations Enable 3-Phase Inverter LEDs will still reflect HALL Effect sensors Each time Switch1 is pressed, we will advance one step in the commutation table Commutation table will tell us which transistors to turn on When Switch1 is not pressed, turn OFF transistors


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Import Table Add Variables, Enable Switch1, Enable Inverterextern unsigned char table_rotate[8]; unsigned char value; unsigned char commutation; void main(void) { EnableInterrupts; /* enable interrupts */ /* include your code here */ ENABLESWITCH(1); ENABLELED(1); ENABLELED(2); ENABLELED(3); ENABLE3PHASEINVERTER(); for(;;) {


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Wait for Switch1 to be Pressedfor(;;) { __RESET_WATCHDOG(); /* feeds the dog */ LED1_PIN = HALL_1; LED2_PIN = HALL_2; LED3_PIN = HALL_3; if(!SW1_PIN) { }


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Once Pressed, Advance Counter, Commutatefor(;;) { __RESET_WATCHDOG(); /* feeds the dog */ LED1_PIN = HALL_1; LED2_PIN = HALL_2; LED3_PIN = HALL_3; if(!SW1_PIN) { value++; if(value>=7) value = 1; commutation = table_rotate[value]; if(commutation & Q1_MASK) Q1 = 1; if(commutation & Q4_MASK) Q4 = 1; if(commutation & Q2_MASK) Q2 = 1; if(commutation & Q5_MASK) Q5 = 1; if(commutation & Q3_MASK) Q3 = 1; if(commutation & Q6_MASK) Q6 = 1; }


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Wait for Switch to be Releasedif(commutation & Q3_MASK) Q3 = 1; if(commutation & Q6_MASK) Q6 = 1; while(!SW1_PIN) { __RESET_WATCHDOG(); LED1_PIN = HALL_1; LED2_PIN = HALL_2; LED3_PIN = HALL_3; } } IT IS IMPORTANT TO TURN OFF TRANSISTORS!

TURNOFFTRANSISTORS();


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Download and Run Code1. Click On Run

4. Click On Run

2. Click On Connect on the Debugger 3. Click On Yes To Reprogram the MCU


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Lab2


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Lab 2Make a program that On/Off transistors

move the motor in clockwise direction

TO DO: Enable Switch5 to enable commutations Check Hall Effect sensors to evaluate which commutation state motor is in When Hall Effect sensors changes state, transistors will commutate


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Add Variables, Enable Switch5unsigned char pasthallsensors; unsigned char hallsensors; void main(void) { EnableInterrupts; /* enable interrupts */ /* include your code here */ ENABLESWITCH(5); ENABLESWITCH(1); ENABLELED(1); ENABLELED(2); ENABLELED(3); ENABLE3PHASEINVERTER(); for(;;) {


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Wait for Switch5 to be Onfor(;;) { __RESET_WATCHDOG(); /* feeds the dog */ LED1_PIN = HALL_1; LED2_PIN = HALL_2; LED3_PIN = HALL_3; while(SW5_PIN) { } TURNOFFTRANSISTORS();


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Once On, Display and Check Hall Effect Sensorswhile(SW5_PIN) { __RESET_WATCHDOG(); /* feeds the dog */ LED1_PIN = HALL_1; LED2_PIN = HALL_2; LED3_PIN = HALL_3; hallsensors = 0; if(HALL_1) hallsensors |= 0x04; if(HALL_2) hallsensors |= 0x02; if(HALL_3) hallsensors |= 0x01; if(pasthallsensors != hallsensors) { /* Do something */ }

}


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Once On, Display and Check Hall Effect Sensorsif(pasthallhensors != hallsensors) { pasthallsensors = hallsensors; value++; if(value>=7) value = 1; commutation = table_rotate[value]; IT IS IMPORTANT TO TURNOFFTRANSISTORS(); TURN OFF if(commutation & Q1_MASK) Q1 = 1; TRANSISTORS! if(commutation if(commutation if(commutation if(commutation if(commutation } & & & & & Q4_MASK) Q2_MASK) Q5_MASK) Q3_MASK) Q6_MASK) Q4 Q2 Q5 Q3 Q6 = = = = = 1; 1; 1; 1; 1;


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Download and Run Code1. Click On Run

4. Click On Run

2. Click On Connect on the Debugger 3. Click On Yes To Reprogram the MCU


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Sensorless SensingSensors

are expensive and take up space Several techniques can be used to determine the motor position/speed without an external device These techniques are based on the electrical characteristics of motors, mainly on their inductance characteristics:

Based on BEMF Speed range from 5-10% up to 100% of nominal speedThe BEMF must be high enough

Based

on Motor Inductance SaliencySpeed range from standstill to about 20% of nominal speed


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BEMF-

-

BEMF is just an acronym for Back Electromagnetic Force Back electromagnetic force is a fancy term for the generator characteristics of a motor As has been shown not all phases of the motor are on at the same time BEMF voltage can be measured on the inactive phases of the motor The characteristics of the voltage curve generated by BEMF can tell the position/speed of the motor The method that will be exposed is the zero crossing method. When BEMF voltage equals zero, the motor is in a specific position By measuring the zero crosses against time, the speed of the motor can be determined


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BLDC Motor Back-EMF Shape

Phase A-B Voltage

Phase B-C Voltage

Phase C-A Voltage

Phase A

Phase B

Phase C

A CH40V

C

B


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Sensorless BLDC Motor Control with BEMF Zero-Crossing Detection

Appropriate Phase Comparator Output selected

Zero Crossing event detected


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Sensorless Commutation and BEMF0 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


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BLDC Central Point is Not Accessible3-phase

inverter and DC bus current measurementInverter Stage

Udcbus

RshuntHB1A

Idcbus

V0

B

HB2

BLDC MotorHB3C


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Zero Crossing Sensing ReferenceHB1V0

B

A

+ + C

V0

B

HB2

+ HB3 + C

+ HB3 + -

HB3

UDCB reference

GND reference

Virtual CP referenceUdcbus

BLDC

Motor central point is not accessible

Rshunt IdcbusBV0

HB2

HB1

A

C

HB3

B

BLDC Motor

V0

HB2

A

+ -

HB1 + -

Udcb + -

HB1

HB2

A


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Zero Crossing Sensing using ADCThe

principle is the same as the HW topology, but more flexibleGND referenceHB1 ADC1 ADC2 HB3C BV0

Virtual CP referenceHB1 ADC1 ADC2 ADC3 ADC4C

UDCB referenceHB1A BV0

V0

ADC2 ADC3 ADC4

B

HB2

HB2

HB2

ADC3

HB3

HB3

A

ADC1

Udcb

A


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Application DetailsADC

Measurement Back-EMF evaluation


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Back-EMF Detection Window

0

30

60

90

120

150

180

210

240

270

300

330

360

390 uVA uSa

- visible Back-EMF

detectable zero crossing


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Lab3


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Sensorless BLDC Motor Control using MC9S08ACAC microcontroller6 6 PWM 4 ADC inputs 3 Zero-cross detection circuit 3.3V Power supply3

ApplicationPH A,B,C 3-phase inverter DC current sensing3

Diagram

BLDC motor

APMOTOR board

3 outputs

Fault LED Direction LED Run/Stop status PB_A PB_B SW

9 Vdc

3 inputs

BDM

Freemaster on PC Read/set variables


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Sensorless BLDC Motor Control using MC9S08ACMC9S08AC

Peripheral Utilization

Timer 16 channels: PWM modulation for BLDC motor (complementary bipolar)

Timer 2Time base for commutation period measurement Channel 0: commutation Channel 1: timing of application

A/D ConverterDC bus current, phase voltages (zero-cross detection)


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PI ControlProportional

Control

Error multiplied by constant Deals with present behavior


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PI ControlIntegral

Control

Ads long-term precision Takes longer to settle, but provides better precision Deals with past behavior


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PI controller on AC MCU

These variables are used To tune the system

This is the control Algorithm inplemented In AC16 MCU for Motor control


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PWM and manual dead time insertionPWM

Generation

TIMER

set to center aligned mode (TPM1SC:CPWMS=1)Example:

PWM0: switching (duty cycle (50 - 100%) + dead time), negative polarity (TMP1CxSC:ELSnB =x,TMP1CxSC:ELSnA =1) PWM1: switching (duty cycle (50 - 100%) - dead time), positive polarity (TMP1CxSC:ELSnB =1,TMP1CxSC:ELSnA =0) PWM2: switching (duty cycle (50 - 100%) - dead time), positive polarity (TMP1CxSC:ELSnB =1,TMP1CxSC:ELSnA =0) PWM3: switching (duty cycle (50 - 100%) + dead time), negative polarity (TMP1CxSC:ELSnB =x,TMP1CxSC:ELSnA =1) PWM4: OFF PWM5: OFF


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Dead Time

Q1

Q1

Q4

Q4

a) Center aligned PWM, Q1 and Q4 change in the same instant, it can short circuit between Vb and GND

b) Center aligned PWM, Q1 and Q4 triggered with different PWM duty cycle avoiding that both transistors turn on at the same time.


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Measurement

DC bus current, Back-EMF voltage Single result register only 3.5 us conversion time ADC measurement has to be synchronized with PWM


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Measurement PWM -> ADC Synchronization

Overflow interrupt is used for PWM->ADC synchronization


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Measurement Back-EMF evaluation


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FlexTimer in the MCF51ACThis part pending because dev board was delivered on April 29Freescale Semiconductor Proprietary Information. Freescale and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. Freescale Semiconductor, Inc. 2008.TM

96

FlexTimer advantages

Supports up to 8 channels which can be synchronized in pairs for complementary signal generation. Dead time insertion supported by software. FTM can trigger ADC conversions automatically. Fault input supported by hardware (automatically turns of PWM pin outputs). Synchronized reloading of PWM duty cycle from several sources (ADC, analog comparator, software). Polarity for PWM output can be configured. Edge and center alligned PWM generation.


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Dead time insertion

Used to avoid to power devices to be turned on at the same time.

No CPU load generated to make dead time insertion. To configure simply enable dead time insertion bit and configure the number of timer counts of dead time, the rest is done by timer module.


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ADC Synchronization

Reduces CPU load by saving time needed to start conversions (to detect zero-crossings or instantaneous current. When doing back-EMF sensing measurements need to be made in certain timing windows. If measurements are always taken at the same times, control algorithm is more precise.

Timer Channel ISR t1 1 ADC conversion ADC Channel ISR t3 1 Process ADC data Manual start of ADC conversion t2

Timer Channel ISR Automatic start of ADC conversion t1 ADC conversion ADC Channel ISR t3 Process ADC data

Without hardware T = t1 + t2 + t3

trigger

With hardware trigger T = t1 + t3


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Related Session ResourcesSessions (Please limit to 3)Session IDAZ131 AZ121 AZ120

TitleMotor Control Part 1 Fundamentals and Freescale Solutions Motor Control Part 2 Solutions for Large Appliances and HVAC Motor Control Part 3 Solutions for Small Appliances and Health Care Applications

Demos (Please limit to 3)Pedestal ID312 214 706

Meet the FSL Experts (Please limit to 3)Title Time Location

Demo TitleLarge Appliance Demo 3-Phase PMSM Vector Control demo with Encoder Air Hockey Demonstration featuring the Flexis AC Products


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Documents

Tp Ftf2008 Motorctrl Part4