Design and Analysis of Cycloconverter to Run Split Phase Induction Motor Using PWM Control

Abstract

In this paper, novel design of a cycloconverter to run a split phase inductor motor to minimize the total harmonic distortion is proposed. The design of a cycloconverter involves two semiconductor switching devices, namely, IGBT and Thyristor for reducing the total harmonic distortion (THD). To realize this, a demand torque and rotor speed of a split phase induction motor is studied. The cycle duration of torque characteristics is divided into suitable number of time intervals (subdivision). These subdivisions of time intervals are in the form of frequencies and used to simplify the cycloconverter design. Change in the frequency at a particular subdivision results in the change in electromagnetic torque of the split phase induction motor. Proposed designs with IGBT and thyristor are compared for their performance with reference to cyclcoconverter designs without any switching devices and with varying firing angles and it is observed that the performance of the thyristor switched cycloconverter reduced the total harmonic distortion more than the IGBT controlled cycloconverter. Varying firing angles were generated using PWM techniques. In other words, split phase induction motor is used as a load for the cycloconverter. However, to drive varying mechanical loads for longer duty cycle, machine needs to minimize the transients which can be made possible with PWM techniques. The output voltage can also be accomplished without any external components for reducing total harmonic distortion (like switching devices). PWM is used to control the switching thereby minimizing the lower order harmonics while it turns on the device and eliminates the higher order harmonics when it turns off the switching device. This gives a reduction in the total harmonic distortion of upto 65.85% for IGBT switching while it reduces to 62.58% with Thyristor controlled switching.