Variable Speed Drive of Single Phase Induction Motor Using Frequency Control Method

1. Variable Speed Drive of Single Phase InductionMotor Using Frequency Control Method • Mr. AungZawLatt • Department of Electrical Power Engineering • Technological University (Myitkyina) • Myitkyina, Myanmar • azlatt@gmail.com • Dr. Ni Ni Win • Department of Electrical Power Engineering • Mandalay Technological university • Mandalay, Myanmar • Phone: 095-02-88712, Fax: 095-02-88702 • Presented by Jason Wright • ECGR 6185, Adv. Embedded Systems • March 20, 2013

2. 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

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

4. Motivation: Traditional Variable Frequency Drives • 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

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

6. 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:

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

8. Frequency Control 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:

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

10. Timing Diagram

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

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

13. 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:

14. References • Latt, AungZaw, and Ni Ni Win, Ph.D. "Variable Speed Drive of Single Phase Induction Motor Using Frequency Control Method." IEEE Xplore. N.p., 20 Apr. 2009. Web. 10 Mar. 2013. • http://en.wikipedia.org/wiki/Induction_motor • http://ecee.colorado.edu/copec/book/slides/Ch4slide.pdf http://www.onsemi.com/pub_link/Collateral/SG3525A-D.PDF (datasheet for SG3525A) http://www.digikey.com/ • Photos: • Latt, AungZaw, and Ni Ni Win, Ph.D. "Variable Speed Drive of Single Phase Induction Motor Using Frequency Control Method." IEEE Xplore. N.p., 20 Apr. 2009. Web. 10 Mar. 2013. • http://www.mindconnection.com/library/electrical/motorslip.htm • http://ecee.colorado.edu/copec/book/slides/Ch4slide.pdf • http://www.iccfl.com/product_info.php?products_id=8191 • http://www.onsemi.com/pub_link/Collateral/SG3525A-D.PDF (datasheet for SG3525A) • http://www.iccfl.com/product_info.php?products_id=8191 • http://www.aliexpress.com/compare/compare-irf840-mosfet.html