A novel three-phase high-power soft-switched Dc-Dc converter for low-voltage fuel cell applications

Abstract—An efficient dc/dc converter is needed as the interface between a low-voltage fuel cell source and a high-voltage bus for inverter operation. In this paper, a three-phase transformer-isolated dc/dc converter utilizing phase-shift (PS) modulation is proposed. The converter must be able to boost the voltage signif-icantly and operate at current levels above 240 A on the source side. Key features of the proposed converter include reduced transformer turns ratio by a factor of two while maintaining the same output voltage, reduced size of passive components including output filter and input dc bus capacitor using three-phase inter-leaving, eliminated inductor current ripple at PS angles above 120◦, and achieved soft switching over a wide load range without auxiliary circuitry. The proposed converter has been analyzed, simulated, and implemented in hardware. An efficiency of above 96 % was achieved using the prototype unit. Experimental results were used to verify all designs and analyses. Index Terms—Converter, dc/dc converter, multiphase, phase shift, soft switching, zero-current switching (ZCS), zero-voltage switching (ZVS). I