DEVELOPMENT AND PERFORMANCE OF MICROPROCESSOR BASED STARTING SCHEME OF LOAD COMMUTATED INVERTER FED CAGE INDUCTION MOTOR DRIVE

Abstract

The dissertation deals with the design, performance analysis and experimental studies of microprocessor based starting schemes for load commutated inverter (LCI) fed cage induction motor. Since the LCI fed cage induction motor can not be started due to the lack of sufficient induced voltage available at the motor terminals for commutation of thyristors of LCI at standstill and at lower speeds, therefore, some alternative arrangment is required to start the drive. Some of the schemes are developed and tested experimentally for the starting of LCI fed three phase cage induction motor. In these schemes, a variable frequency three phase supply for the three phase cage induction motor is obtained by dc link converters connected through link inductor. Commutation of load commutated inverter thyristors is achieved by (i) discontinuous link current and (ii) using force commutation circuit in dc link. For starting the drive, the frequency of the inverter output connected to the motor, is controlled by the triggering frequency of the inverter thyristors through software of microprocessor based system.