Modeling and Simulation of LLC Resonant Converter in Grid-Forming Photovoltaic System

LLC resonant converters have a wide range of applications in industry. However, so far, there is no simple and accurate small signal equivalent circuit model available. This article proposes an equivalent circuit model for LLC resonant converters based on the modified and extended description function method. This model can effectively predict the characteristics of LLC resonant converters at switching frequencies below, close to, or above the resonant frequency. Finally, the effectiveness of the model was verified through simulation. As shown in the research results: the simple third-order equivalent circuit model for LLC resonant converters can effectively predict the dynamic characteristics of the beat frequency and better understand the small signal model and all transfer functions of the model can help engineers design control feedback correctly.