High-efficiency Operation of a Bidirectional Non-isolated DC-DC Converter Based on Flying-capacitor Converters

This paper presents the operating principles and control method of a bidirectional non-isolated dc-dc converter based on the flying-capacitor converter intended for high-efficiency operation. It consists of a main converter, an auxiliary converter, and an inductor, where the auxiliary converter is formed by the cascade connection of a single chopper cell and two bridge cells. The chopper cell generates a voltage with the same switching frequency as the main converter, and achieves the zero-current switching (ZCS). The bridge cells act as an active power filter, where the low switching losses can be achieved owing to the lower dc-capacitor voltages. Consequently, the proposed circuit can reduce the losses of the auxiliary converter. The operating principles and the control methods are verified using a 150-V, 500-W down-scaled model. Moreover, the losses and efficiency evaluations of the previous and proposed circuits based on an actual dc-dc converter system with the rated power of 100 kW are analytically calculated and compared with each other.