A Hybrid String-Inverter/Rectifier Soft-Switched Bidirectional DC/DC Converter

In this article, a new bidirectional dc/dc converter topology based on a hybrid string-inverter/rectifier structure with an isolated CLLC resonant circuit is presented for energy storage applications. In this topology, a novel inverter/rectifier leg is presented that enables this circuit to operate in rectifying mode with much lower voltage ripple compared to the standard four-switch string rectifier circuit with the same capacitive filter. Compared to the dual-active-bridge circuit structure, the proposed inverter/rectifier leg is able to reduce the number of high-voltage switches required. A CLLC resonant circuit is employed to step-up/down the dc voltage levels. The operating principles of the proposed converter are discussed in this article. Silicon Carbide switches are used in both legs of the proposed converter, with zero-voltage switching turn-on and zero-current switching (ZCS) turn-off realized for all switches, whereas ZCS turn-on and off are achieved for all diodes. Simulation and experimental results are provided on a 1-kW, 100-kHz, 400-V/700-V converter system to highlight the merits of the proposed converter. Experimental results demonstrated that an efficiency of close to 97% is achieved in the proposed converter in both boost mode and buck mode at the full-load condition.