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Experimental verification of a bidirectional chopper for battery energy storage systems capable of reduction in size and weight of an inductor

A conventional medium-voltage large-capacity bidirectional chopper used in a battery energy storage system for dc electric railways is equipped with a heavy and bulky inductor for current smoothing. This paper presents a bidirectional chopper for the purpose of reducing the size and volume of an inductor, which is characterized by using an auxiliary converter in addition to the main converter. The auxiliary converter is formed by a cascade connection of multiple single-phase full-bridge converter cells. Applying the so-called “phase-shifted PWM” to each cell can reduce a voltage step across an inductor along with increasing the ripple frequency, resulting in a significant reduction in size and weight of the inductor. This paper discusses the operating principles and control method of the bidirectional chopper, followed by experiment using a 150-V, 2-kW down-scaled model and computer simulation using the “PSCAD” software package. It is shown that the inductance value can be reduced to less than 1/60 compared to the conventional chopper.