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Variable Speed Drive of Single Phase InductionMotor Using Frequency Control Method

Presented by Jason WrightECGR 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

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Motivation: Induction Machine Operation: Speed Control

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• By far most popular type of motor used by industry

• Governed by the following Equation:

Motivation: Traditional Variable Frequency Drives

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• 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

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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:

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Functional Block Diagram

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

Frequency Control

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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

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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

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Waveform Comparison

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Sinusoidal PWM (SPWM) with carrier signal:

Six-Step Drive Waveform:

Trapezoidal Waveform from Latt’s Variable Speed Drive:

Performance

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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:

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Part Quantity Unit Cost Total Cost

SG3525A, PWM Chip 1 0.483 0.483

IRF 840, Power MOSFET 4 0.79223 3.16892

GBPC3508-E4/51, 800V rectifier 1 2.84 2.84

PDB12-F4151-104BF, Pot. 1 0.48 0.48

C 124 Transistor 1 0.02124 0.02124

MJE 12002 Transistor 1 0.47 0.47

7812, 12V DC Regulator 1 0.19375 0.19375

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. 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, 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. 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

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