Semisynchronous Rectification Scheme for Hybrid Modulated LCC Resonant Converter With Wide Voltage Gain Range

Secondary-side phase-shift-control (SSPSC) is an effective method to widen the gain range of resonant converter with pulse frequency modulation (PFM). However, SSPSC not only induces a large circulating current through MOSFETs in secondary side semiactive bridge but also makes these MOSFETs operate under hard switching, thereby diminishing efficiency. To address these issues in this article, a semisynchronous rectification (S-SR) scheme is proposed, and it is realized on LCC resonant converter with SSPSC and PFM (SSPS-PFM LCC). This scheme will not conflict with SSPSC, can avoid circulating current flowing through body diodes of secondary side MOSFETs, and realize ZVS turn-on of these MOSFETs, thus improving efficiency. First, the concept of S-SR is proposed. Second, a time-domain state trajectory model of SSPS-PFM LCC is built. According to this model, the mathematical relation of S-SR conduction angle with switching frequency (SF) and secondary-side phase shift angle (SSPSA) is derived, and a simple calculation method of S-SR conduction angle is designed. This enables the realization of S-SR scheme with no additional sensors and almost no additional controller computational burden. Finally, a SSPS-PFM LCC prototype is built to verify the effectiveness of the proposed S-SR scheme.