Enhanced Small-Signal Model for Charge-Controlled LLC Resonant Converters Using Time-Domain Analysis

The conventional models employ fundamental harmonic approximation for charge-controlled LLC resonant converter. However, when the switching frequency deviates from the resonant frequency, significant distortion occurs in the state variables, leading to degraded accuracy in the models. To address this issue, this brief proposes a novel small-signal modeling approach based on time-domain analysis. The proposed method first derives the simplified time-domain operating constraints for the converter. The simplified constraints relieve the computation burden and reduce the number of intermediate variables, making it more suitable for small-signal modeling. Next, the relationships between small-signal variables are derived from these constraints. Finally, a complete mathematical model of the charge-controlled LLC resonant converter is constructed. Experimental validation is performed on a 200V/1kW LLC resonant converter prototype. Both simulation and experimental results confirm the superior accuracy of the proposed model.