Analysis and Performance Characteristics of Three-Phase Thyrode AC Voltage Controllers

A generalized approach based upon numerical evaluation of the Fourier coefficients is used to evaluate the comprehensive performance of three-phase phase-controlled thyrode ac voltage controllers. Balanced resistive and inductive loads of different power factors are considered. Various electrical properties are computed and compared graphically for different circuit configurations. Though the branch-controlled delta connected load gives the highest distortion and power factors, it offers limited control of input power. The line-controlled star connected circuit offers full range of power control, a simple control scheme over a wider range of firing angle retardation and good distortion and power factors. For applications where even harmonics may he tolerated in the line currents, such a controller has superior performance characteristics compared to the conventionally used thyristor voltage controller of similar configuration.