A 1 MW GTO thyristor DC chopper with snubber passive energy recovery, for an electric locomotive

The paper describes the analysis, design and implementation of a 1 MVA, 1500 V, air cooled GTO thyristor DC chopper used to control the 700 V, 850 A DC motor of an electric locomotive. Because of air cooling and volume constraints, in order to reduce losses, interleaved chopper GTOs are used, each with independent turn-on and turn-off snubber passive energy recovery. The locomotive drive design is complicated by the need for battery backup, hence an intermediate 814 V (under charge) DC rail.