Design of a Control Workstation for Controller Algorithm Testing

1
Design of a Control Workstation for Controller
Algorithm Testing

• Aaron Mahaffey
• Dave Tastsides
• Dr. Dempsey

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Presentation Preview

• Project Summary and Objective
• Hardware Controller Application
• DC Motor Model
• Power Amplifier
• F/V Converter Modeling
• Summer Circuit
• Hardware Controller Design
• Experimental Results

3
Presentation Preview

• 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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Presentation Preview

• Demonstration Work
• Final Parts List
• Future Project Work

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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

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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

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System Block Diagram
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Motor Model

• Gp(s) 1949166 _
• s2 920s 114133
• Poles at s -148 and s -772 rad/sec
• DC Gain of 17.08

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Power Amplifier

• Discrete Component Design
• Internal Controller for Stability
• Passive Lag Network
• Internal Feedback Loop
• Open Loop Crossover Distortion
• 27.5 Volt Output Range

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Power Amplifier
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Power Amplifier Model

• Closed Loop Gain 11
• Results from Matlab after observing open loop
  frequency response in PSpice
• Time Constant 10 us
• Pole 628000 rad/sec
• G(s) 11 _
  s/628000 1

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F/V Converter Modeling

• Desire Output of 2.5 V for Maximum RPM of 762
• 762 RPM Corresponds to 38.4 kHz
• Desired Gain 2.5/38400 .0000652
• Experimentally Measured Results
• Time Delay 5 ms
• Pole at 388 rad/sec

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F/V Converter Modeling

• G(s) .0000652e-.005s
• s/388 1

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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

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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)

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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

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Hardware Controller Design

• Design for crossover frequency and adjust gain to
  get correct PM
• Final Frequency Design Results from Matlab
• K 37.6
• PM 59.6º
• wc 34 rad/sec
• Overshoot 7.06

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Experimental Results
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Experimental Results

• Experimental Overshoot 33
• Why such a large deviation?
• D/A phase lag
• Sampling Period (T) 2 ms
• Phase lag -wcT -3.5 º
• Motor and F/V time delay
• Added time delay 6.1 ms
• Phase lag -wcTd -11 º

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Experimental Results

• Experimental Gain 40
• Could account for -5º phase lag
• New phase margin 40.5º
• New expected overshoot 26
• New deviation 7

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Presentation Preview

• 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

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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

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Board Support Package (BSP)

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

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Core

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

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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

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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 -gt Negative
• 2.5 5 Volts -gt Positive
• Support for step inputs only

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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

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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

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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

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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

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Digital Controller Model
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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

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Digital Controller Results (K1)
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Digital Controller Results (K0.2)
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Digital Controller Results (K5)
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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

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Demonstration Work

• Controller maintains constant motor velocity
• DC generator maintains constant voltage
• Bucket arm velocity remains constant for
  moderately varying loads

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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

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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

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Final Parts List

• Diodes
• 2 x 1N5617
• D Flip-Flop
• 7474

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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

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Design of a Control Workstation for Controller
Algorithm Testing

• Questions?