High-Efficiency Bidirectional LLC Resonant Converter with Primary Auxiliary Windings

In this paper, high-efficiency bidirectional LLC resonant converters with primary auxiliary windings in transformers of resonant circuits are proposed. Even though resonant capacitors are used on the primary and secondary sides, the proposed converter can operate, regardless of the direction of the power flow, with the high gain characteristics of the LLC resonant converter without the mutual coupling of resonant capacitors. The operation principles and gain characteristics of the proposed bidirectional DC-DC converters are described in detail. A 3.3 kW prototyped bidirectional LLC resonant converter for interfacing 750 V-DC buses was built and tested to verify the effectiveness and applicability of this proposed converter.