11081 DIF - amoBBSd1.amobbs.com/bbs_upload782111/files_10/ourdev_287709.pdf · 11081 DIF Slide 2 Class objective OWhen ... 11081 DIF Slide 37 PWM Drive Position Sense Signal Conditioning

© 2007 Microchip Technology Incorporated. All Rights Reserved. 11081 DIF Slide 1

11081 DIFIntelligent Motor Control:

A Fan Application


Class objectiveWhen you finish this class you will:− Describe how PIC® microcontrollers can

be used to control and monitor brushless DC fans

− Discuss different control loop techniques and their associated tradeoffs

− Provide information on fully utilizing the available microcontroller peripherals


Agenda

Brushless motor basics (hardware background)

Interpreting inputs

Generating outputs

Control software


Brushless MotorBasics


Inside The FanFan

Windings

Magnetic Core

Hall-Effect Position Sensor

Permanent Ring

Magnet


Two PhaseSupply Voltage

Current Always Flows in the Same

Direction


Two Phase

N

N

S

S

N

N

S

S

Hall DeviceDetects Pole

Change


Two Phase

N N

S

SHall Device

Detects PoleChange

N NSS


Single PhaseSupply Voltage


Single Phase

N

N

S

S

N

N

S

S

NS N S


Single Phase

N N

S

SS

S

N

N

SN S N


What Are Intelligent Fans?


Why Use Intelligent Fans?Allow the fan to control its own speed

Incorporate other safety features

Can compensate for dynamic load conditions

Desire non-audible control loop


Intelligent Fan Block Diagram

Controller

Position Sense

Signal Conditioning

Voltage Regulator

Speed Input

Signal Conditioning

Speed Feedback

PWM Drives for Coils

Current Sense


Introducing…PIC12F615 PIC12HV615

PIC16F616 PIC16HV616

Program Memory

Data Memory

Comparators

ECCP PWM

Package

Timers

1024 words

64 bytes

Single

Half-bridge

8 pin

2 8-bit / 1 16-bit

2048 words

128 bytes

Dual

Full-Bridge

14 pin

2 8-bit / 1 16-bit


Position SensePosition Sense

Signal Conditioning

Voltage Regulator

Speed Input

Signal Conditioning

Speed Feedback


Current Sense

Controller


Hall Element

Power

Power

Output Output

Symmetrical deviceUn-buffered outputUsed with a current sourceOutput voltage


Hall-Element Schematic

CxINx+

1k

Supply Voltage

CxINx-


Hall Element

time

Voltage

Comp.Output

No Hysteresis

Comp.Output

Hysteresis


Hall Sensor

Digital deviceSeveral output types:− Logic level / open collector− Latching / non-latchingIntegrated power supplyIntegrated signal conditioning


Hall Sensor Diagram

+-

+V Output

Ground


Hall Device Mounting

Above Board On Board


Position Sense Resources

Hall element: Requires a comparator (CxINx- pin and CxINx+ pin)

Digital hall sensor: Any available interrupt-on-change pin


Voltage RegulatorPosition Sense

Signal Conditioning

Voltage Regulator

Speed Input

Signal Conditioning

Speed Feedback


Current Sense

Controller


Integrated Shunt RegulatorCan operate from almost any voltage

Supply regulated voltage to other components

Much cheaper than other types of regulators

CPU

+12V

PIC MCU


Considerations

More difficult to accommodate…− Wide input voltage ranges (i.e. 12V –

96V)− Wide required current ranges (4mA –

50mA)

Some cases are impossible to accommodate without additional effort


Shunt Regulator Resources

External resistor

Need to choose a microcontroller with the HV option

Application note AN1035


Speed InputPosition Sense

Signal Conditioning

Voltage Regulator

Speed Input

Signal Conditioning

Speed Feedback


Current Sense

Controller

Speed Input

Signal Conditioning


Speed Input Choices

Commanded speed PWM− kHz range (Intel and AMD specs use

25kHz)

Analog− RC filtered PWM− Thermistor


Timer1 Gate

Timer1 will increment when gate is active

Timer1Clock Source

Timer1Counter

Gate source can be an I/O or a comparator output

Timer 1 Gate


Timer1 Gate

Timer1 will increment when gate is active

Timer1Clock Source

Timer1Counter

Timer1 Gate can be active-high or active-low

PWM Input


Duty Cycle Measurement

Measurement period = (low + high)Duty cycle = high / (low + high)Math is performed as unsigned 24-bit by 16-bit division

Measure Low Measure High


Considerations…

Measurement period needs to be much larger than period of signal− Higher input PWM frequency means less

time to measure

Possible to approximate:− Measurement Period = (Low + High)

Timer1 can not overflow


Slow PWM Inputs

Possible to measure directly using interrupt-on-change pins

Need to account for the extremes: 0% and 100%


Analog Speed Choices

Why use analog filtered PWM?− PWM frequency range too wide for

direct measurement− Incoming PWM at a lower voltageTemperature control using a thermistorDirect analog input control


Speed Input Resources

Digital measurement: need a microcontroller with Timer1 Gate (use the T1G pin)

Analog measurement: any available ADC channel


PWM DrivePosition Sense

Signal Conditioning

Voltage Regulator

Speed Input

Signal Conditioning

Speed Feedback


Current Sense

Controller

Speed Input

Signal Conditioning


Full Bridge ForwardSupply Voltage

H

L

H

LH

L

H

L

P1B

P1A

P1D

P1C


Full Bridge ReverseSupply Voltage

H

L

H

LH

L

H

L

P1B

P1A

P1D

P1C


Two Phase DriveSupply Voltage

P1B P1DH

L

H

L


Other ECCP Pins

Enhanced Capture Compare PWM (ECCP)

P1A, P1C− Free tachometer output− Pin can be configured as an input


Using Single PWM Output

Pin steering− Steer a single PWM output to

multiple pinsNeed to ensure idle pin is in idle state

VDDP1A(1)P1B(1)GP3

VSSP1BGP1P1A

PIC12HV615


Extending PWM Resolution

Software dithering:

Based off of TMR2 interrupts (can use the post-scaler)

Dither Offset + Accumulator

OverflowFlag


Dithering Considerations

System needs to act in a low-pass manner

Dither frequency may be audible

Resource intensive


PWM Drive Resources

Timer2 used as the ECCP time base

ECCP in full-bridge mode, or a CCP with pin steering


PWM DrivePosition Sense

Signal Conditioning

Voltage Regulator

Speed Input

Signal Conditioning

Speed Feedback


Current Sense

Controller

Speed Input

Signal Conditioning


Speed Feedback

Tachometer signal− Generated using the ECCP module− Toggling an output pin

Alarm output− Generated if the fan speed is too low

for too long


Alarm Signal

Commanded Speed +

Scaling Factor

Threshold

Clear Counter

YesIncrement Counter

Counter Maxed?

No

No

Alarm!Yes

Current Speed >

Threshold

ExitRoutine


Speed Feedback Resources

Any available I/O pin


Current SensePosition Sense

Signal Conditioning

Voltage Regulator

Speed Input

Signal Conditioning

Speed Feedback


Current Sense

Controller

Speed Input

Signal Conditioning


Current Sense

Protect fan / host from drawing too much current

Hardware feature – no software required

Cycle-by-cycle


Current Limiting

+ 0.6 VoltReference

ShutdownEvent


Current Limiting

Current

PWM

0.6 Volt


Current Sense Resources

Inverting input of available comparator (can use the internal reference)

ECCP with auto-shutdown capability


Actual Speed MonitoringPosition Sense

Signal Conditioning

Voltage Regulator

Speed Input

Signal Conditioning

Speed Feedback


Current Sense

Controller

Speed Input

Signal Conditioning


Measuring Actual Speed

Can measure hall period

Need output from 0 to 255 corresponding to minimum and maximum speed


How to Monitor Actual Speed

y = 76117x-0.9977

R2 = 0.9998

0

50

100

150

200

250

300

0 200 400 600 800 1000 1200 1400Hall Period (in counts)

Rou

tine

Out

put


Speed Monitoring Equation

From Excel:

Better written as:

Constant:

9977.076117 −⋅ period

176117 −⋅ period

(Full Scale Value) Rotations 60 seconds(MaxRPM) (Tcount) (# Hall Periods) minute


Division NecessaryPerform division as unsigned 24-bit by 16-bit division, use lower byte out of output

periodoutput 76117

=

Three byte result:00 00 (0 – 255)


Consideration…

What if fan spins above the “maximum” speed?

Fan will attempt to speed up

periodoutput 76117

=

Three byte result:00 01 (small)


Resources Required

Time base− Possible to use Timer0 or Timer2

Reuse same division routine from duty cycle measurement


Control SoftwarePosition Sense

Signal Conditioning

Voltage Regulator

Speed Input

Signal Conditioning

Speed Feedback


Current Sense

Controller

Speed Input

Signal Conditioning


Fan SoftwareHardware

initializationSet point

measurement

Measure actual speed

Controlroutine

Set new duty cycle

TimingControl


Control Routine

PID Controller− Existing routines− MASTERs class

Limitations− Single set of control parameters


Control Routine

Integral Controller− Multiple control constants− Inherently stable to “DC” input

commands

Limitations− Slow response time


Multiple Control Constants

Control ConstantSpeed << set point

Speed close to set point

Speed >> set point

Large KI

Normal KI

Small KI

Condition


Transient Response

0

500

1,000

1,500

2,000

2,500

3,000

0 100 200 300 400 500

Sample

RPM


Demonstration


Quantifyingthe Results


Closed Loop Response

0500

1000150020002500300035004000

0.0% 20.0% 40.0% 60.0% 80.0% 100.0%Duty Cycle

RPM

Specification Limits


Transient Response

-500

0

500

1000

1500

2000

2500

3000

3500

0 100 200 300 400 500 600

Sample

RPM


PotentialPin-out Configurations


PIC12F615 – Hall Element

4-Wire Input

1234

0.1uF

100

+12

P1A

PIC12HV615

VddP1A-2GP4T1G

VssCIN+CIN-P1A

+12+5

10k10k

10k

2.2uF

100

100

+12

1.2k

+5

P1A

P1A-2

470

P1A-2 Hall Element

2.2uF

+5

1k


PIC12F615 – Hall Sensor

10k

0.1uF

+12

Hall Sensor

100

100

PIC12HV615

VddP1A-2GP4T1G

VssCIN+CIN-P1A

+5

10k

2

100

2.2uF

470

10k

P1A-2P1A

+5

2.2uF

P1A-2

+12

1k

+5

4-Wire Input

1234

+12

P1A


PIC16F616

2.2uF

+5

100

1004-Wire Input

1234

10k

1.2kPIC16F616

VddRA5T1G/AN3RA3P1AP1BP1C

VssC1IN+

C12IN0-RA2RC0

C12IN1-P1D

P1B100

+5

2

1k

+12

Hall Element

10k

+12

P1D

P1D

10k

2.2uF

P1B

0.1uF

+12

+5470


Intelligent Fan Overview

Controller is built directly into the fan

Closed loop control with good audible properties

Additional safety features


Summary

Brushless motor basics (hardware background)

Interpreting inputs

Generating outputs

Control software


ReferencesApplication Note:− AN1035 – Designing with HV

Microcontrollers


TrademarksThe Microchip name and logo, the Microchip logo, Accuron, dsPIC,

KeeLoq, KeeLoq logo, microID, MPLAB, PIC, PICmicro, PICSTART, PRO MATE, rfPIC and SmartShunt are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.

AmpLab, FilterLab, Linear Active Thermistor, Migratable Memory, MXDEV, MXLAB, SEEVAL, SmartSensor and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A.

Analog-for-the-Digital Age, Application Maestro, CodeGuard, dsPICDEM, dsPICDEM.net, dsPICworks, ECAN, ECONOMONITOR, FanSense, FlexROM, fuzzyLAB, In-Circuit Serial Programming, ICSP, ICEPIC, Mindi, MiWi, MPASM, MPLAB Certified logo, MPLIB, MPLINK, PICkit, PICDEM, PICDEM.net, PICLAB, PICtail, PowerCal, PowerInfo, PowerMate, PowerTool, REAL ICE, rfLAB, Select Mode, Smart Serial, SmartTel, Total Endurance, UNI/O, WiperLock and ZENA are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.

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Documents

11081 DIF - amoBBSd1.amobbs.com/bbs_upload782111/files_10/ourdev_287709.pdf · 11081 DIF Slide 2 Class objective OWhen ... 11081 DIF Slide 37 PWM Drive Position Sense Signal Conditioning