DIGITAL COMPUTER TRANSIENT MODEL OF THREE-PHASE GTO THYRISTOR INVERTER FEEDING AN INDUCTION MOTOR

Although the autosequentially commutated cOtrent source inverter (ASCI) is widely used with the induction motor for speed control, it is limited for high power and high frequency induction motor drives, mainly due to the commutation capacitors in the inverter circuit. For its advantages over the conventional inverters, the Gate Turn off (GTO) thyristor inver-ters has attracted attention in recent years. The computer model of the current source GTO thyristor inverter feeding an induction motor is simulilted. The developed digital computer program has three subprograms, each of them has a special function but linking them together provides the output variables. The main subprogram contains the input data and the logic concerned with the operation of the six GTO thyristors, six diodes, three-phase bridge. The second subprogram deals with the specification of the differential equations according to the conducting states of the GTO's and diodes of the inverter circuit determined in the main subrogram. In the third subprogram, the set of differential equations is solved according to the fourth order Ringe-kutta method. The output results will be a main factor for the determination of the conducting state of each thyristor in the main subprogram. This operation will be repeated every time step. The computed results compared favorably with those obtained recently in practice.