Performance Improvement of Induction Motor Controlled by Thyristor Chopper on the Rotor Side

Abstract

In this paper, the performance characteristics of a variable-speed drive system with a wound rotor induction motor incorporating a 3-phase diode bridge rectifier - thyristor chopper with a modified commutation circuit system on the rotor side were studied. A DC equivalent circuit was used in the analysis of the motor-rectifier-chopper system and suitable equations have been derived for the determination of the system performance. The analytical results obtained are compared with those obtained experimentally to ascertain the validity of the system in practical applications. The results obtained indicate that a true variable speed drive system based on a thyristor chopper-controlled induction motor is successfully implemented. It is shown that the thyristor chopper control using the Hitachi commutation circuit permits the realization of a slip-ring induction motor as a variable speed and improved power factor. Also, the torque level obtained by the chopper control was found to be three times that obtained from conventional rotor resistance control at the same conditions.