Variable speed induction motor drive with a chopper in the rotor circuit

Abstract

This project deals with a variable speed three phase slip-ring induction motor drive using static rotor resistance control, by means of a parallel thyristor chopper. System analysis involved the development of de and ac circuit models. By determining the parameters of the equivalent circuit of the motor, it was possible to use these models for system design. A suitable thristor chopper was selected and designed, together with the necessary control circuitry. Steady state results indicated the validity of the analysis. A range of speed control of 30% below synchronous speed was obtained. A closed loop system based on PI control, comprising a speed loop and a current loop was designed, to improve the dynamic characteristics. A total system model was developed and closed loop operation simulated to effect controller tuning. Observation of the speed response of the system to a step input indicated the close relationship between simulated and practical results.