This paper proposes a circuit structure of bidirectional dc–dc converter. This structure uses two switches, two capacitors, a 1:1 transformer, and a control circuit for pulse-frequency modulation. The windings of the transformer are connected in a series-aiding configuration to reduce current ripples and to increase power conversion efficiency . The capacitors and the leakage inductance of the transformer provide soft-switching conditions. When the proposed converter was designed to operate at a switching frequency of 110–240 kHz, input/output voltages of 100–400 V, and output power of 30–300 W, was ≥97% for and 93.5% at . Experimental results show that the proposed converter is suitable for use in photovoltaic power conversion systems and energy storage systems.