Linearization of LLC resonant converter model based on extended describing function concept

LLC resonant DC-DC converters are becoming increasingly popular due to their ability to work with zero voltage switching (ZVS) feature. The reduction in switching power losses, especially in high frequencies, greatly enhances the efficiency of these converters in comparison with conventional PWM boost converters. This paper presents theoretical details for modeling the LLC resonant converter, by which its characteristic and dynamic behavior can be analyzed. To obtain an accurate model, the extended describing function concept is used and the approximate nonlinear model derived. Then the derived model is linearized in vicinity of the steady state operating point and the state space matrices of the system are obtained. The accuracy and validity of the model is then verified using MATLAB/Simulink.