Synchronous Rectification Control Strategy for Bidirectional Full-bridge LLC Resonant Converter

Synchronous rectification (SR) control strategy for bidirectional full-bridge LLC resonant converter is proposed in this paper. The converter can operate either in boost or buck mode through controlling the switches in the converter. The boost mode operation of SR control is analysed in detail. All the input-side switches can realize zero-voltage-switching (ZVS), while the output side switches can achieve zero-current-switching (ZCS). On this basis, the circulating energy issue in boost mode operation under synchronous pulse frequency modulation (SPFM) control method can be solved by SR control thus the converter efficiency is improved. The principle of boost mode operation, voltage gain and soft-switching characteristics are analysed in detail. The feasibility of the proposed control strategy is verified by simulation and experimental results.