MENOUFIYA UNIVERSITY FACULTY OF ENGINEERING- SHEBIN EL- KOM DEPARTMENT OF ELECTRICAL ENGINEERING

Abstract

A-C ch::>ppers or ac voltage controller have been widely used to obtain variable a-c voltage from a fixed a-c source. A-C choppers are widely used in applications such as industrial heating, lighting control, soft starting of induction motors, speed controllers fans and pumps. Many of these are conventional phase-controlled a-c voltage controllers usmg thyristors, which have the advantages of simplicity of the control circuit and large power capability. However, these have the. inherent drawbacks that power factor decreases when the firing angle increases and that, Since the content ofthe line current harmonics is relatively large. The size of the passive filter circuit becomes bulky. These drawbacks can be overcome by using PWM a-c chopper.

This chopper offers several advantages such as sinusoidal input current with unity power factor, fast dynamics, and significant reduction in filter size. Some ofPWM a-c chopper that has been used is symmetrical angle control, asymmetrical angle control and high-frequency time ratio control. The developments achieved in the field of power electronics made it possible to improve the performance of electrical. system utilities.