A gate-turn-off thyristor chopper for traction drives

The paper describes a chopper circuit using three gate-turn-off thyristors in which the need for regrouping contactors, to change from motoring to braking or from braking to motoring has been eliminated. As the braking and motoring components are independent they can be rated for their specific duty cycles. Not only do gate-turn-off thyristors permit a higher chopping frequency than achieved with choppers using conventional thyristors, but they also enable the circuit to be reconfigured during the chopping cycle. In this way, line-voltage changes and other disturbances can be dealt with more precisely, within the chopping cycle, rather than more slowly over a period of several cycles as is the case when conventional thyristors are used.