Analysis of Rectifier-Side Parasitic Capacitance Effects and Voltage Gain Modeling of LLC Resonant Converters in Wide Gain Range Applications

To address the significant discrepancy between theoretically predicted and experimentally measured output voltages caused by the junction capacitance effect of rectifier-side diodes in LLC resonant converters when operating away from the resonant point, an accurate voltage gain model is proposed. First, the junction capacitance is referred to the primary side, and an equivalent topology is established. Then, time-domain analysis is performed based on the above-resonance operating modes, and the output voltage expression is derived by combining the steady-state boundary conditions. Finally, a 1 kW experimental prototype is built for verification. The results show that the proposed model can accurately predict the output voltage and effectively reflect the influence of rectifier-side parasitic capacitance on the voltage gain, providing a theoretical basis for the precise design of LLC resonant converters.