Snubber circuits for traction drives

This paper gives an overview of snubber circuits used in railway traction inverter drives. Discussion is primarily restricted to GTO Voltage Source Inverter (VSI) propulsion equipment. Future trends, including the design targets for IGBT propulsion inverters are described at the end of the paper. The turn-on and turn-off snubber circuits are designed to limit the GTO dI/dt and dV/dt to around 200A/μs and 500V/μs typically. The stray inductance in the turn-off snubber loop is a critical design parameter. With a maximum permitted value of around 150 nH, this means that correct layout of the inverter leg circuitry is a crucial design requirement