A Control Strategy and Design Method for Interleaved LLC Converters Operating at Variable Switching Frequency

LLC converters face challenges in high-current applications, where the high conduction loss limits the maximum load capacity and reduces efficiency. Interleaving technique can be used to solve this problem, but the component tolerances of the resonant tanks will cause severe load sharing problem. The SCC-LLC converter was proposed to solve the load sharing problem. However, due to its constant switching frequency operation, it has some limitations over complete line and load variation compared to conventional LLC converters. In this paper, a new control strategy is proposed for the SCC-LLC converter, which enables variable switching frequency operation; thus, it provides uncompromised performance while achieving interleaved operation. Analyses and a design method are provided, and a 600-W two-phase interleaved SCC-LLC prototype is built to verify the feasibility.