A 98.3% Efficient GaN Isolated Bidirectional DC-DC Converter for DC Microgrid Energy Storage System Applications

This paper presents a novel 400 to 12 V isolated bidirectional dc-dc converter based on a phase-shift-controlled-modified dual-active-bridge power stage. The proposed converter consists of a half-bridge and center tap with active clamp circuit, which has promising performance for low-voltage high-current applications. 650 V gallium-nitride high electron mobility transistors are used on the high voltage side to avoid issues encountered using Si superjunction MOSFETs in phase-shift-controlled-bidirectional power conversions. The operation principle and power transfer characteristic are obtained based on a time-domain analysis of the inductor current. Design methodology and criteria and converter's efficiency analysis are discussed. Both the analysis and experiments verify that the proposed converter is capable of achieving low power loss and high power density in soft-switching and hard-switching modes. Experimental results are presented for a 1-kW, 400 V-to-12 V dc-dc prototype converter operating at 100 kHz switching frequency. A power density of 30 W/in(3) and a peak efficiency of 98.3% in a wide input/output voltage range are achieved.