A Small-Signal Modeling Method for Bidirectional CLLC Resonant Converter

The bidirectional capacitor-inductor-inductor-capacitor (CLLC) resonant converter featuring excellent soft-switching characteristic has been widely used in the fields of renewable energy sources, electric vehicles and energy storage systems. The fundamental harmonic approximation (FHA) has been proved an effective modeling method to CLLC resonant converter. However, the accuracy of model based on FHA is significantly reduced as the operating frequency moves from the resonant point. In this paper, a more accurate small-signal model is established and the reduced-order simplification is developed. Finally, the effectiveness and precision of the established model are verified by simulations. The simplified third-order model completely fits the simulation in low frequency range.