Speed Control of a Single Phase Induction Motor Using Step-down Cycloconverter

Abstract

Induction motor is a constant speed machine when operated from the mains. However it is necessary to vary the speed of the motor in some applications. The speed of a motor basically depends on the supply frequency and number of poles. While the frequency can easily be changed without changing the entire structure of the motor, the same cannot be said for the number of poles. This paper examines the use of cycloconverters to vary the speed of single phase induction motors. Cycloconverters work on changing the supply frequency to vary the speed of the motor. With the aid of three push buttons connected to the microcontroller and the program written on it, the speed of the motor was varied in three steps, at F, F/2 & F/3. The microcontroller sends the gating pulse through an optocoupler to trigger the thyristors in a dual bridge providing the alternating signal needed to drive the motor. As the frequency decreases, the speed of the motor also decreases. The cycloconverter was used on a single phase induction motor and the result shows that it can vary the speed of an induction motor.