A synchronous rectification control method of bidirectional full-bridge LLC resonant converter with SIC MOSFETs

Abstract

Bidirectional LLC resonant converters have the advantages of ZVS and ZCS characteristics, high switching frequency, high transmission efficiency, wide voltage gain range, bidirectional power flow characteristics and etc which are widely used in intelligent micro-grid, new energy power generation, electric vehicles, uninterruptible power supply system(UPS) and other fields. Meanwhile, with the development of silicon carbide(SiC) as the third-generation semiconductor material, the power density and efficiency of LLC resonant converters have been greatly improved. This paper proposes a new synchronous rectification control method suitable for the SiC bidirectional full-bridge LLC resonant converters. Whether the SiC LLC converter works in the boost or buck mode, all of SiC MOSFETs can realize ZVS and ZCS through the zero-crossing detection module.The strategy proposed in this paper can effectively reduce the effect of circulating power of SiC converter, improve the output voltage gain of the converter, and further realize the bidirectional flow of energy. This paper analyses the principle of the control strategy in detail, establishes the equivalent model of the fundamental wave, analyses its voltage gain characteristics and soft switching characteristics, and completes the derivation of the corresponding formulas. Finally, the proposed control strategy is verified by PSIM simulation.