Feedback Speed Control

Embedded Systems Interfacing

Overview Background Task 1 MATLAB® Step Response Root Locus Task 2 Scaled Coefficients Task 3 Proportional-Integral Speed Control Task 4 Step Response for:

Critically Damped Over Damped Under Damped

PWM/Motor Speed Labs

ADC

+5 VDC

PWM

+12 VDC+5 VDC

PIC24FJ128

TD62003AP

LM2907

V(speed)

Open-Loop Load-Speed Characteristics

Speed

Load

Block Diagram

_k(z-b)___

z(z-1) B_ (s+A)

-

+ R(z)

Y(z) U(s) E(z) ADC

Y(s) DAC

U(z)

InternalTo

feedback.cPIC24FJ128

Darlington Driver,Motor and

Freq-to-Volt

PID Controller Time-Domain

Laplace-Domain of PI Controller

dt

tedKdtteKteKtu DIP

s

KsK

sE

sU

KKK

Kss

KK

sE

sU

IP

PID

DI

P

0 and 0 ,0

PID

Stability Control Ratio

Critically Damped

I

I

KBsAs

KB

sR

sC

2

B

AK

KBA

cab

I

I

4

014

04

2

2

2

Control Algorithm

Tnene

Knunu

nTTnnene

Knunu

I

I

2

))()1(()()1(

12

))()1(()()1(

Task 1 – Step Response Analysis Within MATLAB®

Define A and B Define transfer

Function Use step()

Task 2 – PID Gains

Condition K1 = 1024k K2 = bK1

Under Damped

Critical Damped

Over Damped

Unstable

Task 3 Within main( ) Initialization

RD0 Timer 3 ADC Interrupts and Timer 3 Interrupt PWM ADC PMP then LCD LCD text on screen

Task 3 Within main( ) Endless Loop

Wait for for semaphore == 1 Clear semaphore Calculate new output value using

difference equation Write to PWM Update out(k+1), in(k+1), and in(k+2) Display Speed

Task 3 Within Timer 3 ISR Clear Interrupt flag Start sampling

Task 3 Within ADC ISR Get new speed reading and clear DONE Set semaphore Check for one-hundred passes (100 x

50ms = 5 s) If 100 passes then

Toggle RD0 Calculate new reference = Step*D0 + Offset Reset pass count

Else Increment pass count

Clear ADC interrupt flag

Task 3 Download to project

folder feedback.c peripherals.a (library

archive) peripherals.h

Create project and add all three files

Add linker script Create heap

Open-Loop Load-Speed Characteristics

Speed

Load

Closed Loop

Open Loop

Task 4 Use Internal Reference Use MPLAB’s Data Monitor and

Control Interface to Adjust K1 and K2 Capture Image on MSO and repeat for

Critically Damped Over Damped Under Damped

Data Monitor and Control Interface

DMCI Configuration

Right Click

DMCI Use Press Save after

Dynamic Data Control is configured

Press Halt Adjust Sliders

Use Mouse Up arrow and

Down arrow Press Start