Due to their great efficiency, LLC resonant converters have found widespread application in various industries, including photovoltaics and electric vehicles. The secondary-side LLC converter was proposed as a solution to the engineering challenges associated with implementing the primary-side LLC resonant inductor in high-gain boost applications. However, due to its multimodal nature, accurately modeling the full frequency band to achieve optimal dynamic performance remains a complex task. Hence, it is crucial to utilize small signal modeling in order to achieve more accurate control. The extended describing function method is a modeling approach that offers greater accuracy for resonant converters. However, it typically focuses on the vicinity of the resonance point, neglecting states such as under-resonance and over-resonance. Consequently, this paper aims to perform small-signal modeling of the secondary LLC resonant circuit across the entire frequency range, resulting in a more accurate small-signal model. The validity of the derived model is confirmed by simulation and experimentation.
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