A variable speed controller using pulse-width modulation for AC induction motors

There are three ways to vary the speed of a motor. These are varying its amplitude, voltage or current, or its frequency. Among them, variations of the voltage and current are popularly used. However, an accidental excess of amplitude can cause big damages to the motor. When frequency is used to vary the speed of a motor, it is assumed that it will be less prone to breakdowns since an excess amount of frequency would only correspond to a small proportional change in voltage. The frequency of a certain sine wave can be varied by means of a pulse modulation called Pulse-Width Modulation. In a PWM, the width output pulses are determined by the trigger pulses applied. By varying the clock which determines the time of the trigger pulses, the frequency is also varied. The photo type is composed of a digital control panel from which the speed of the motor is continuously varied having a ratio of 1 is to 10. A PWM generator is also included to produced the varied pulses coming from a signal source and a clock. An inverter will also be used to simulate a sine wave. An AC induction motor and a power supply are also included