A GaN Variable-Frequency Series Resonant Dual-Active-Bridge Bidirectional AC-DC Converter for Battery Energy Storage System

This paper proposes a novel single stage GaN AC-DC converter suitable for low voltage battery to grid application based on an improved Series Resonant Dual-Active-Bridge (SR-DAB) topology. The converter consists of an GaN AC switch-based half-bridge on the grid side and a center-tap secondary side with active clamp to interfaced with a 12.8V battery. Dual-phase-shift (DPS) and variable-frequency (VF) control are used to expand the zero-voltage switching (ZVS) range and to ensure power factor correction (PFC). Compared to the conventional Dual-Active-Bridge (DAB) topology, the SR-DAB can reduce the Root-Mean-Square (RMS) current flowing through the resonant tank as well as the turn-off current, thus improving the efficiency. Experimental results are presented for a 240Vac,rms to 12Vdc, 140–350 kHz prototype to highlight the very high efficiency and high power density.