A Wide Bandgap Device-Based Isolated Quasi-Switched-Capacitor DC/DC Converter

This paper proposes an isolated quasi-switched-capacitor (QSC) dc/dc converter to serve as an auxiliary power supply in electric and hybrid electric vehicles, managing a bidirectional power flow between the high-voltage (HV) battery and the low-voltage dc bus. A QSC dc/ac circuit with a 3:1 voltage step-down ratio is proposed to serve as the front-stage circuit of the converter. Based on it, an isolated QSC dc/dc converter is proposed with a synchronous-rectifier, current-doubler post-stage circuit. Compared with existing full-bridge, half-bridge, and three-level converters, the features of the proposed converter include: 1) the voltage stresses on HV-side switches are reduced to two-third of the HV-dc-bus voltage; 2) the voltage stress on transformer is reduced to one-third of the HV-dc-bus voltage; 3) the transformer turns ratio is reduced; 4) it has soft-switching capability and high efficiency; and 5) bidirectional power-flow and simple control can be implemented. The operation principles, soft-switching analysis, and simulation results are presented. Wide Bandgap devices are selected for the proposed converter to shrink the size of passive components, provide high efficiency, and decrease the cooling requirement. Guidelines are given to estimate the key circuit parameters, including the capacitance of the switched capacitors, the transformer dc-bias flux density, and the average currents of the post-stage inductors. Experiment results provided from a 1-kW prototype built with SiC MOSFETs on the HV-side validate the feasibility and superior performance of the proposed converter.