This article presents a 10-kW novel gallium-nitride (GaN)-based three-phase grid to 48-V battery energy storage system (BESS). The BESS utilizes a single-stage ac–dc dual-active-bridge (DAB) converter with dual-phase-shift (DPS) and variable-frequency (VF) control. 600- and 80-V GaN power transistors, as well as planar magnetics, are used to achieve 96.6% efficiency and 50-W/in$^3$ power density. The operation principle and power transfer characteristics are derived based on time-domain analysis of the DAB inductor current. VF and DPS are utilized to achieve power factor correction and zero-voltage switching simultaneously while minimizing the DAB rms current. An online calculation algorithm is presented with short execution time, which enables the closed-loop control of the BESS. Experimental results are presented to validate the novel control.