Bidirectional DC-DC converter with seriesconnected resonant tanks to realise soft switching

This study presents a new topology of a direct current (DC)-DC converter with series-connected LLC resonant tanks to realise zero voltage switching and quasi-zero current switching. Two LLC resonant tanks are connected in series on the lowvoltage side and complementarily implemented to balance the current in the transformers. Moreover, the transformers are connected in series to share the load voltage, thus, the size of each transformer can be reduced. A fully controlled H-bridge on the high-voltage side achieves bidirectional power transmission. The voltage stress on each power switch of the active H-bridge is equal to the output voltage, rather than twice the conventional centre tapped topology. Besides, a high-transformer ratio guarantees high-DC voltage gain, which allows power supply under high-voltage conditions. Furthermore, based on phase-shift control, the output voltage can be regulated smoothly and continuously, and surplus power on the output side is transferred back to the power source automatically. The proposed converter can be applied as power supply cells in vehicles or motor-controlled systems. Simulation with a 3000-W prototype and laboratory experiments with a 90-W prototype are carried out to verify the feasibility and efficiency of the proposed converter.