1 Variable Speed Drive of Single Phase Induction Motor Using Frequency Control Method Mr. Aung Zaw Latt Department of Electrical Power Engineering Technological University (Myitkyina) Myitkyina, Myanmar Dr. Ni Ni Win Department of Electrical Power Engineering Mandalay Technological university Mandalay, Myanmar Phone: , Fax: Presented by Jason Wright ECGR 6185, Adv. Embedded Systems March 20, 2013

Agenda  Motivation  Induction Machine Operation: Speed Control  Traditional Variable Frequency Drives  A Simpler Approach for Single Phase Motors  Functional Block Diagram  Frequency Control  H-Bridge Inverter  Timing  Output Waveforms  Performance  Conclusion  References 2

Motivation: Induction Machine Operation: Speed Control 3 By far most popular type of motor used by industry Governed by the following Equation:

Motivation: Traditional Variable Frequency Drives 4 Costly (VFD > Motor) Complex Can be large More common for three phase motors DC inverters require high switching frequencies and more switching elements Can have smoother output

Simple Inverter Circuit 5 Three Phase Voltage Source Inverter (VSI):

Motivation: A Simpler Approach for Single Phase Motors Mr. Latt proposes using an H-bridge and a simple digital (ON or OFF) output signal to simulate AC with a DC source. The output voltage is a modified square wave, but given the motor windings’ inherent low-pass filtering, the current waveform approximates a sinusoid. This approach offers several advantages: 6

Functional Block Diagram 7 Block Diagram for the Speed Control of Single-Phase Induction Motor Using Inverter

Frequency Control 8 SG3525A PWM Controller Built-in oscillator Adjust PWM frequency with a potentiometer or other variable resistance Has two outputs to drive two transistors The two transistors then drive the H- Bridge Inverter IRF 840 Power MOSFET:

H-Bridge Inverter 9 1.T1-T4 ON: Applies positive voltage (Vs) to the load. 2.T2-T3 ON: Applies negative voltage (-Vs) across the load. 3.T1-T3 ON: Applies zero volts across the load. 4.T2-T4 ON: Applies zero volts across the load. There are 4 valid operative modes:

Timing Diagram 10

Waveform Comparison 11 Sinusoidal PWM (SPWM) with carrier signal: Six-Step Drive Waveform: Trapezoidal Waveform from Latt’s Variable Speed Drive:

Performance 12 No load: Under Load: Table of Results:

Conclusion AC asynchronous motor speed could be controlled by varying the pulse width frequency with a variable resistor. The crude waveform does a decent job at providing a sinusoidal current with the help of the low- pass filtering provided by the motor windings. Using a simple inverter consisting of only 4 power MOSFETs reduced drive cost: 13 PartQuantityUnit CostTotal Cost SG3525A, PWM Chip IRF 840, Power MOSFET GBPC3508-E4/51, 800V rectifier12.84 PDB12-F BF, Pot C 124 Transistor MJE Transistor , 12V DC Regulator OVERALL COST:$7.66

References Latt, Aung Zaw, and Ni Ni Win, Ph.D. "Variable Speed Drive of Single Phase Induction Motor Using Frequency Control Method." IEEE Xplore. N.p., 20 Apr Web. 10 Mar (datasheet for SG3525A) Photos: –Latt, Aung Zaw, and Ni Ni Win, Ph.D. "Variable Speed Drive of Single Phase Induction Motor Using Frequency Control Method." IEEE Xplore. N.p., 20 Apr Web. 10 Mar – – – – (datasheet for SG3525A) – – 14