A Novel Digital Firing Scheme for Soft Starting of Three-Phase Induction Motors

Abstract — In this paper a novel, simple and reliable digital firing scheme has been introduced for soft starting of three-phase induction motor. The switching signals are obtained from parallel port of PC computer for controlling the output voltage of three-phase ac chopper. The new proposed scheme depends on increasing the stator voltage gradually without increasing the stator current than reference value. The ac chopper used with this strategy is having six bidirectional switches. The new strategy can be used with any PC computer with any processor speed and for all the starting conditions of three-phase induction motor. The soft switching technique can be used also in speed control of induction motor after starting period. Simulation of the system is carried out by PSIM computer program. The simulation results show stable operation for different loading conditions. The simulation results have been compared with the experimental results from laboratory prototype. The experimental results are very near to simulation results. I