Interleaved Bidirectional Chopper With Auxiliary Converters for Battery Energy Storage Systems

A battery energy storage system that is placed inside a dc electric railway vehicle is equipped with a bidirectional chopper that has heavy and bulky inductors for current smoothing. High-voltage-side and low-voltage-side current smoothing inductors are responsible for most of the chopper volume and mass. This paper presents an interleaved bidirectional chopper with auxiliary converters for on-board battery energy storage systems that is capable of achieving a significant reduction in the mass and volume of the current-smoothing inductors. The proposed circuit consists of multiple interleaved sub-converters, where each sub-converter consists of a bidirectional chopper cell, a current-smoothing inductor at the low-voltage side, and an auxiliary converter that is formed by a 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 current ripple in the inductor of each sub-converter; hence a much smaller inductor can be used to meet the current ripple 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. Furthermore, interleaving the sub-converters reduces filtering requirements for the high-voltage-side current and reduces the current-ripple factor of the low-voltage-side current. This paper discusses the operating principles and the control method of the proposed chopper, followed by experiments performed on a 150-V, 3-kW downscaled experimental model.