Design of a Control Workstation for Controller Algorithm Testing

Aaron Mahaffey

Dave Tastsides

Dr. Dempsey

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Project Summary and Objective Hardware Controller Application

DC Motor Model Power Amplifier F/V Converter Modeling Summer Circuit Hardware Controller Design Experimental Results

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Software Controller Application Level Shifting Circuit BSP/Core Functions User Interface Command Signal Sampling Period Summer F/V Converter Digital Controller Digital Controller Results

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Demonstration Work Final Parts List Future Project Work

Project Summary

Design of a control workstation to test control algorithms for a Pittman DC motor

Provide insight to classical and digital control system theory through practical applications

First apply control system with all hardware components, then implement as much as possible into software

Project Summary

Quansar Consulting currently develops control workstations for $5,000

Each station requires a PC with an internal A/D and D/A converter

Goal is to develop a system at a much lower cost of $400 based on the 8051 development board

System Block Diagram

Motor Model

Gp(s) = 1949166 _

s2 + 920s + 114133

Poles at s= -148 and s= -772 rad/sec DC Gain of 17.08

Power Amplifier

Discrete Component Design Internal Controller for Stability

Passive Lag Network Internal Feedback Loop Open Loop Crossover Distortion ±27.5 Volt Output Range

Power Amplifier

Power Amplifier Model

Closed Loop Gain = 11 Results from Matlab after observing open

loop frequency response in PSpice:o Time Constant = 10 uso Pole = 628000 rad/sec

G(s) = 11 _ s/628000 + 1

F/V Converter Modeling

Desire Output of 2.5 V for Maximum RPM of 762o 762 RPM Corresponds to 38.4 kHzo Desired Gain = 2.5/38400 = .0000652

Experimentally Measured Results:o Time Delay = 5 mso Pole at 388 rad/sec

F/V Converter Modeling

G(s) = .0000652*e-.005s

s/388 + 1

Summer Circuit

Produces Error Signal from Difference of Command and Feedback Signals

Design using LF412 Operational Amplifier and precision resistors.

Experimental Transfer Function Vo = .9945V1 - .9895V2

Hardware System Controller

Motor Tracking System Motor shaft velocity follows analog

command signal All subsystems designed with hardware Drive up to 762 RPM in positive direction Command signal of 0 - 2.5 volts Controller Phase Margin of 60º Steady State Error of zero (integrator)

Hardware Controller Design

PI Controller Proportional Gain

Locates necessary crossover frequency to meet 60º phase margin specification

Obtained using Frequency Domain Design Integrator

Drives Steady State Error to zero

Hardware Controller Design

Design for crossover frequency and adjust gain to get correct PM

Final Frequency Design Results from Matlab:o K = 37.6o PM = 59.6ºo wc = 34 rad/seco Overshoot = 7.06 %

Experimental Results

Experimental Results

Experimental Overshoot = 33 % Why such a large deviation? D/A phase lag

o Sampling Period (T) = 2 mso Phase lag = -wcT = -3.5 º

Motor and F/V time delayo Added time delay = 6.1 mso Phase lag = -wcTd = -11 º

Experimental Results

Experimental Gain = 40o Could account for -5º phase lag

New phase margin = 40.5º New expected overshoot = 26 % New deviation = 7 %

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Software Controller Application Level Shifting Circuit BSP/Core Functions User Interface Command Signal Sampling Period Summer F/V Converter Digital PI Controller Digital Controller Results

Level Shifting Circuit

In all applications, a signal is sent from the EMAC D/A Converter

D/A Converter Output is 0-5 Volts Desired Signal is ±2.5 Volts for

Bidirectional Drive in Software Application

D/A Converter Output must be shifted by -2.5 Volts

Board Support Package (BSP)

Supports all Devices on Board Timer 0 Timer 2 D/A converter A/D converter Keypad LCD

Core

Contains Functions Common in all Applications Summer Conversion routines RPM measurement F/V calculation

User Interface

Communicates with User Ask for sampling period Ask for Proportional Gain Ask if Integration Desired Ask for step magnitude (+ or -) Verify all entries Display current motor RPM

Command Signal

Command Signal Magnitude and sign provided by user

interface routine Value entered is level shifted Value is written to the D/A:

0 – 2.5 Volts -> Negative 2.5 – 5 Volts -> Positive

Support for step inputs only

Sampling Period

Sampling Period Entered by user in terms of microseconds Value is converted to a timer reload value Timer 0 is setup with calculated reload

value All sample driven functions are called

from Timer 0 interrupt service routine

Summer

Summer Subtracts value of F/V converter

feedback signal from command signal Software version allows for bidirectional

error signal by determining motor direction from encoder signals

Called at sampling rate by Timer 0 interrupt service routine

F/V Converter

Timer 2 initialized to auto reload on negative encoder transition and capture on positive transition

Capture value in timer 2 registers holds cycles per encoder pulse width

RPM and F/V output calculated from measured pulse width

Continuously measures pulse width, but calculation occurs once every sampling rate

Digital P/PI Controller

Proportional gain entered by user in 1/255 increments

User chooses between P or PI control Integrator mapped in software as:

Z _

Z - 1

Digital Controller Model

Zero-OrderHold

z

1

Unit DelayStep1/628000s+1

11

Power amp

1

K

s +920s+1141332

1949166

Gp

1/5.9

GearRatio

z

z-1

Gc

.0005655

F/V GainExecution Time

81.5

Encoder Gain

1/51.2

D/A Gain

Digital Controller Results

For Simulated K = 1 Overshoot = 15.15% tp ≈ 55 ms

For Experimental K = 1 Overshoot = 16.4% tp ≈ 60 ms

For Simulated/Experimental K = 0.2 No overshoot

For Simulated/Experimental K = 5 Unstable

Digital Controller Results (K=1)

Digital Controller Results (K=0.2)

Digital Controller Results (K=5)

Demonstration Work

Model wheel loader demonstrates effectiveness of controller

DC generator shaft connected to controlled motor shaft provides voltage to power wheel loader motor

Moving bucket arm creates a variable load on the generator

Demonstration Work

Controller maintains constant motor velocity

DC generator maintains constant voltage

Bucket arm velocity remains constant for moderately varying loads

Demonstration Work

Separate EMAC controls bucket arm movement

Two different operation modes Auto - bucket arm moves up and down

continuously one second at a time Manual - pressing and holding buttons

on keypad moves bucket arm

Final Parts List

Pittman DC Motor 2 x GM9236C534-R2

EMAC x 2 Operational Amplifiers

2 x LF412 Transistors

2 x TIP30 4 x TIP31

Final Parts List

Diodes 2 x 1N5617

D Flip-Flop 7474

Future Project Work

Implement more complex controllers Multiple poles and zeroes

Add provisions for ramp or impulse commands

Use control workstation to test other devices and types of control Different plants and position control

Design of a Control Workstation for Controller Algorithm Testing

Questions?