A Multiobjective Optimization Method for the Resonance Parameters of an LLC Resonant Converter

ABSTRACT To address the inaccuracy of the fundamental harmonic approximation (FHA) method when the LLC resonant converter operates away from the resonant frequency, this paper proposes a design methodology that combines operating‐mode time domain analysis with a multiobjective optimization algorithm. First, the operating characteristics of different modes are analyzed, and the PO mode is identified as the optimal operating mode. Based on the characteristics of the PO mode, the corresponding time domain equations are derived. Subsequently, the mode boundaries, zero‐voltage‐switching (ZVS) conditions, and resonant capacitor voltage extrema are imposed as design constraints, while the resonant current root‐mean‐square (RMS) value and converter losses are selected as optimization objectives. A decomposition‐based multiobjective evolutionary algorithm combined with a radial basis function (RBF) surrogate model is then employed to approximate the Pareto front efficiently and obtain a set of nondominated optimal design solutions. Finally, a simulation model and a 400‐W/50‐V experimental prototype are developed to validate the proposed method. The results demonstrate that the designed converter achieves ZVS and high efficiency over the entire load range, confirming the effectiveness of the proposed design methodology.