Improved soft starter with thyristor chopper

An improved soft starter with thyristor chopper is presented. Different time varying functions for firing angle have been developed to speed up an induction motor with a chosen constant torque, without current and torque peaks. The firing angle functions influence the building up of the main flux, in order to avoid the normal transient problems. Simulation of the transients based on the analytical solutions of the machine differential equations for all modes of operation has been provided. The beneficial effect of the suggested switching functions in smoothing the transient flux, currents and torque is illustrated. Application of the switching functions has been performed with actual laboratory tests