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Speed Control of H-Bridge Controlled DC Motors

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serge samardzic

on 3 June 2013

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Transcript of Speed Control of H-Bridge Controlled DC Motors

Project by: Srdjan Samardzic Supervisor: Dr. PJ Radcliffe INTRODUCTION METHOD SIMULATION and HARDWARE SIMULATION RESULTS FUTURE WORK and CONCLUSION Speed Control of H-Bridge Controlled DC Motors Apply and test two methods of electronic speed measurement of DC motors PROPOSED SOLUTION HOW IS MOTOR SPEED MEASURED? Motor speed measurement is usually done with the use of shaft encoders. However, shaft encoders have disadvantages Some motors and systems have limited or no space for shaft encoders Using:
Motor Back-EMF
Motor current
Shaft encoder Motor current Motor back-EMF VDC can be defined as, Bi-directional H-Bridge built using discrete components
Open-USB-IO board as main system controller
Various DC motors for testing PROPOSED HARDWARE With the help of resistor Rs in series with the motor, we can measure motor current MOTOR SPEED MEASUREMENT IS VITAL FOR PRECISE MOTOR CONTROL IMPLEMENTATION Motor control failure QUESTIONS? SYSTEM BLOCK DIAGRAM PROPOSED SOFTWARE Graphical User Interface for displaying and recording results
Inbuilt motor control loop ELECTRONIC SPEED MEASUREMENT Using PWM to modulate input voltage VDC will allow for measurement of back-EMF So since back-EMF is proportional to motor speed, where k is a constant Motor speed can be defined as, Motor current can be defined as, So, using formulas from back-EMF strategy, We can solve to find motor speed, Motor speed can be defined as, Which is better? VS VS VS Shaft encoder Back-EMF Current MOTOR CONTROL Closed-loop motor control will be used in this project
Using the Open-USB-IO, closed-loop control will be implemented as coding CLOSED-LOOP CONTROL ADVANTAGES PI or PID controller? Feedback for precision control
Eliminate/reduce output errors
Run systems precisely and efficiently that would otherwise be unstable BASICS OF CLOSED-LOOP CONTROL Block diagram of closed-loop system The output Y(s) is fed back to a summing point where it is compared against the input signal R(s), this gives us the error signal E(s)
The controller C(s) manipulates the error signal and outputs a control signal U(s) to the Plant G(s)
The feedback information is used to eliminate output errors in the system Selecting the right controller for the systems is crucial for precision, the choice will depend on steady-state characteristics of the system and specific motor characteristics. "LT Spice" SIMULATION SIMULATION CIRCUIT PWM and Gate-driver circuitry H-Bridge The power MOSFETs and gate-drivers are both accurate spice models of the purchased hardware
Spice models downloaded from supplier website 'International Rectifier' SIMULATION CHALLENGES Learning new software in limited time frame
Incorporating spice models into the software
Optimizing results and MOSFET/gate-driver selection
Implementing bootstrap technique, and calculating the required value of the bootstrap capacitor PROPOSED HARDWARE H-Bridge H-Bridge will be built using discrete components including, MOSFETs, gate-drivers and input capacitor bank DISCRETE COMPONENTS AND OUSB BOARD Metal Oxide-Semiconductor Field-Effect Transistor The MOSFETs within the H-Bridge will control speed and direction of the motor
'AUIRFB4410' N-channel MOSFET was chosen for this system due to its high frequency, voltage and current capabilities Gate-driver The 'IR2112' high and low side driver was chosen as the for its high voltage and frequency capabilities
Each gate-driver will control two MOSFETs
The gate-drivers will control the frequency and duty-cycle of the switching MOSFET Open-USB-IO Circuit diagram of the proposed H-Bridge including external blocks used for system control OUSB will be used main control unit for the system
Programing ATMEGA32 micro will be necessary for successful implementation of motor control loops MAIN PROBLEM ENCOUNTERED Motor voltage overshoot was the biggest problem encountered during simulation Shown above is the motor voltage overshoot that was encountered

Eliminating overshoot required a Snubber circuit across the motor Motor Voltage after Snubber circuit implementation shown above MOTOR VOLTAGE AND CURRENT, when input voltage = 40Vdc 10% Duty-cycle 50% Duty-cycle 90% Duty-cycle At 10% duty-cycle and 40Vdc input voltage, the expected average voltage is 4V.

The simulation result shows and average voltage of 3.63V At 50% duty-cycle and 40Vdc input voltage, the expected average voltage is 20V.

The simulation result shows and average voltage of 20.13V At 90% duty-cycle and 40Vdc input voltage, the expected average voltage is 36V.

The simulation result shows and average voltage of 35.76V Future Work Test H-Bridge using matrix-board
PCB design
H-Bridge assembly/test
Software write/test/debug for GUI
Write software for microprocessor
Acquire/mount/cage motors for testing
Test motors with speed strategies Conclusion Results very accurate
Hardware construction to commence soon
Research useful for in depth view of project
Speed measurement comparison promises to be interesting and informational
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