A Small-Signal Modeling Method for LLC Resonant Converter Based on Time-Domain Correction

LLC resonant converters possess excellent soft-switching characteristics and are extensively applied in the dc-dc converter field. To achieve closed-loop control of the LLC resonant converter, it is crucial to establish an accurate small-signal model. Traditional modeling methods suffer from the problems of decreasing accuracy away from the resonant frequency or high model complexity in practical applications. This article proposes a small-signal modeling method for an LLC resonant converter based on time-domain correction, which provides practical analytical small-signal models below, at, and above the resonant frequency. The proposed method strikes a balance between accuracy and complexity. Equivalent models of components and the average equivalent circuit of the LLC converter are established using simplified time-domain analysis to describe the average characteristics of the LLC converter. Small-signal perturbations are applied to the average equivalent circuit to derive an analytical second-order average small-signal model that can guide closed-loop regulator design and stability analysis of the LLC converter. Finally, the correctness of the proposed small-signal modeling method is verified through PLECS ac sweep simulations and experiments.