Design of a Control Workstation for Controller Algorithm Testing Aaron Mahaffey Dave Tastsides Dr. Dempsey

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

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

Presentation Preview 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) = _ s s 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 us o Pole = rad/sec G(s) = 11 _ s/

F/V Converter Modeling Desire Output of 2.5 V for Maximum RPM of 762 o 762 RPM Corresponds to 38.4 kHz o Desired Gain = 2.5/38400 = Experimentally Measured Results: o Time Delay = 5 ms o Pole at 388 rad/sec

F/V Converter Modeling G(s) = *e -.005s s/

Summer Circuit Produces Error Signal from Difference of Command and Feedback Signals Design using LF412 Operational Amplifier and precision resistors. Experimental Transfer Function  V o =.9945V V 2

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 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 = 37.6 o PM = 59.6º o wc = 34 rad/sec o Overshoot = 7.06 %

Experimental Results

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

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

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

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  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  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  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

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?