Bidirectional DC-DC Converter with High Voltage Conversion Ratio Based on Active-Clamped Flying Capacitor Unit

This paper proposes a novel topology for a bidirectional DC-DC converter applicable between a 48V DC bus and a single battery cell. With an active-clamped flying capacitor unit (FCU) as the core sub-module, the proposed topology can halve the voltage stress of the main switches and achieve doubling of the effective switching frequency, which greatly reduces the required inductance and improves the power density of the converter. A pre-charging circuit is integrated into the topology, which can complete the pre-charging process by virtue of its own circuit characteristics without additional control strategies. Only six power switches are required to achieve a high voltage conversion ratio of 15. By utilizing the opposite-phase characteristics of the currents through inductors L₁ and L₂, the output current ripple is significantly suppressed. The switches S₁ S₄ can realize zero-voltage switching (ZVS), and the topology has inherent fault tolerance capability. To verify the feasibility and superiority of the proposed topology, a 100 W prototype is built. Experimental results show that the prototype achieves excellent power conversion efficiency under the operating condition between 48V and 3.2V conversion.