Abstract：A modeling method based on fractional calculus was proposed to analyze the working mode of half

bridge LLC resonant converters and the influence of the "parameter drift" of the resonant capacitor on the working

mode of the converters. Then，based on the Oustaloup's filtering algorithm，a simulation model of a half bridge

LLC resonant converters was built to verify the theoretical analysis results，which considers the fractional-order

parameter characteristics of the resonant capacitor. A 240 W test prototype was built up，and the results indicate that the proposed fractional-order equivalent model can more accurately characterize the parameter drift influence of the resonant capacitor on the operating characteristics of LLC resonant converters compared to traditional integer-order models. Therefore，the proposed fractional-order modeling method can provide an accurate and effective theoretical basis for the optimization design of LLC resonant converters.

      Key words：fractional calculus；LLC resonant converter；Oustaloup's filtering algorithm；resonant capacitor