Control and Experimental Verification of a Bidirectional Nonisolated DC-DC Converter Based on Switched-Capacitor Converters

This article presents a bidirectional nonisolated dc-dc converter based on switched-capacitor converters intended for electric railway system applications. It consists of plural main converters with two power devices per converter, plural auxiliary converters each of which is formed by cascaded chopper cells, and small-sized inductors for current control. The dc-dc converter can achieve zero-current switching (ZCS) for all power devices used in the main converters under arbitrary load conditions and an arbitrary voltage ratio of high-voltage-side voltage and low-voltage-side voltage. Consequently, square-wave currents can be removed from both the high- and low-voltage sides of the converter. The validity of the operating principles as well as the control methods proposed in this article is verified by experiments using a 200-V, 2-kW downscaled model.