Interleaved Bidirectional Chopper With Auxiliary Converters for DC Electric Railways

This article presents an interleaved bidirectional chopper with auxiliary converters for onboard energy storage systems that is capable of achieving a significant reduction in the mass and volume of the current-smoothing inductors. The proposed chopper consists of multiple interleaved subconverters, where each subconverter consists of a bidirectional chopper cell, a current-smoothing inductor at the low-voltage side, and an auxiliary converter that is formed by the cascade connection of multiple full-bridge cells. Each auxiliary converter is connected in series with its respective inductor to suppress the ac voltage component that produces ripple current in the inductor of each subconverter; hence, a smaller inductor can be used to meet the ripple current requirement when compared with the conventional bidirectional chopper. In addition, auxiliary converters can be used as dc-circuit breakers to protect the low-voltage side against faults in the power devices of the bidirectional chopper cells. This article discusses the operating principles and control method of the proposed chopper, followed by experiments using a downscaled experimental model.