A Phase-Shift Modulation Strategy for a Bidirectional CLLC Resonant Converter

A novel phase-shift modulation strategy is applied to a bidirectional CLLC resonant converter (RC). Different from the well-known pulse-frequency modulation strategy, the switching frequency of the CLLC RC is constant, which is beneficial for optimal design and control of the converter. Theoretical analysis proves that voltage gain is independent on load and resonant tank. As a result, topology is optimized with ensuring symmetry of converter. Simulation model is built in Simulink and a 1kW prototype is made. Simulation and experimental results verify the voltage transfer ratio. Dynamic response with load stepping up and down is stable and rapid. In addition, soft-switching of all the power switches can be achieved to reduce switching losses and improve efficiency. Detailed operation principles and characteristics of the modulation strategy are analyzed and verified with experimental results.