A Bidirectional Isolated DC-to-DC Converter with Hybrid Control of Pulse Width Modulation and Pulse Frequency Modulation

This paper proposes a modified bidirectional isolated DC/DC converter with hybrid control, which can be applied to bidirectional power transfer between energy storage systems and DC microgrids. Batteries are usually applied to energy storage systems. The battery lifespan may be shortened if the converter has large current ripple during the battery charging process. The proposed topology consists of a CLLC converter and an interleaved buck converter. The first stage is an isolated full bridge CLLC converter, and the second stage is an interleaved buck converter with hybrid control of pulse width modulation (PWM) and pulse frequency modulation (PFM). Additionally, the proposed topology achieves zero voltage switching (ZVS) for all switches and reduces the output current ripple. The operational principles of bidirectional power flow in both directions are described in detail. Finally, a 1.5 kW experimental prototype, rated with a high side voltage of 380 V and low side voltage range of 40-58 V, was constructed and tested to investigate the system performance. The measured highest efficiency for the proposed converter is 90% in charging mode, and 94% in discharging mode.