When a new control strategy for LLC resonant converter will be designed,the traditional designing process requires manual setting and adjusting control parameters,and the closed-loop stability analysis involves the calculation of higher-order functions.In order to simplify the traditional designing process,this paper introduces the generalized state space averaging(GSSA)theory to model the LLC resonant converter system.The traditional impedance physical model is transformed into a mathematical model,and the GSSA closed-loop large-signal and small-signal models are derived. The transfer function matrix of the system is derived by GSSA model and the dynamic characteristics of the full-bridge LLC resonant converter are analyzed.The closed-loop PI control parameters are designed.Finally,the stability of the closed-loop system is judged by eigenvalue analysis method.GSSA theory and model combined with MATLAB simulation can directly solve the calculation of higher-order functions,quickly derive control parameters,and simplify the parameters adjustment and stability analysis in designing new control strategies.In order to verify the correctness of the modeling,a prototype of a400W full-bridge LLC resonant converter is built according to the parameters of the modeling derivation elements.Experiments are carried out under both no-load and fullload conditions.The experimental results show that the system responds quickly,which is consistent with the set output parameters,and the output voltage ripple is less than 1%and the maximum error is 0.4 V.The results of simulation and prototype experimental results demonstrate the effectiveness of the LLC resonant converter model based on GSSA.