A Novel Low-Loss Modulation Strategy for High-Power Bidirectional Buck + Boost Converters

A novel, low-loss, constant-frequency, zero-voltage-switching (ZVS) modulation strategy for bidirectional, cascaded, buck-boost DC-DC converters, used in hybrid electrical vehicles or fuel cell vehicles (FCVs), is presented and its benefits over state-of-the-art converters and soft-switching solutions are discussed in a comparative evaluation. To obtain ZVS with the proposed modulation strategy, the buck+boost inductance is selected and the switches are gated in a way that the inductor current has a negative offset current at the beginning and the end of each pulse period. This allows the MOSFET switches to turn on when the antiparallel body diode is conducting. As the novel modulation strategy is a software-only solution, there are no additional expenses for the active or passive components compared to conventional modulation implementations. Furthermore, an analytical and simulation investigation predicts an excellent efficiency over the complete operating range and a higher power density for a nonisolated multiphase converter equipped with the low-loss modulation. Experimental measurements performed with 12 kW, 17.4 kW/L prototypes in stand-alone and multiphase configuration verify the low-loss operation over a wide output power range and a maximum efficiency of 98.3% is achieved.