This article presents a novel single-stage series resonant dual-active-bridge (SR-DAB) for grid-con- nected bidirectional ac–dc energy storage applications. The single-phase SR-DAB is connected to the grid with an unfolding bridge on the ac side. Three SR-DABs are utilized to connect to a three-phase grid. A control scheme that combines dual-phase shifts and variable frequency is proposed to achieve zero voltage switching and power factor correction over a wide range of ac and dc voltages and loads. A series of comparisons in terms of inductor root mean square current, turn-off current of all transistors are conducted at different loads to prove the advantage of the proposed converter over the traditional dual-active-bridge-based ac/dc converter. A GaN-based hardware prototype connecting the 480Y/240/208$\Delta$ three-phase grid to a 48-V battery was developed with a peak efficiency of 97.2%.