High-Efficiency Bidirectional DC–DC Converter With Low Circulating Current and ZVS Characteristic Throughout a Full Range of Loads

A high-efficiency bidirectional dc-dc converter with low circulating current and zero-voltage switching (ZVS) characteristic throughout a full range of loads is proposed. In the proposed converter, an auxiliary circuit consisting of an inductor, two switches, and four diodes is utilized for achieving high efficiency regardless of the load. At medium and heavy loads, ZVS of main switches is achieved by appropriate energy stored in the auxiliary inductor. Since the energy stored in the auxiliary inductor varies in accordance with loads, the conduction loss can be minimized. At light load, ZVS of main switches can be achieved without the help of the auxiliary circuit. Therefore, the auxiliary circuit stays inactive so that conduction loss can be minimized. Consequently, the conduction loss which is associated with ZVS of main switches is minimized while ZVS of main switches is achieved throughout a full range of loads. The proposed converter shows high efficiency since the switching loss is significantly reduced due to ZVS operation of main switches without severe increase of the conduction loss. Compared with a conventional hard-switching bidirectional dc-dc converter, the efficiency is improved about 3.1% in boost mode (2.76% in buck mode) at full load. In order to verify the performance of the proposed converter, experimental results from a 200-W prototype are presented.