Comparison of Modeling Approaches for LLC Resonant Converter Based on Extended Describing Function

Resonant Converter has surpassed traditional PWM DC-DC converters for their power dense and efficient operation. Along with the rapid growth of the resonant converters, accurate modeling and control is essential. In resonant converters, the conventional averaged modeling method is ineffective because the switching frequency components cannot be disregarded, as in PWM converters. The most suited modeling approach used in resonant converters based on Fundamental Harmonic Approximation (FHA), is the Extended Describing Function (EDF) method. In this paper, comparison of those modeling approaches for LLC resonant converter (LLC-RC) is validated through suitable experimental results. Results from simulations have also revealed the potential existence of Right Half Plane (RHP) zero. The validity and the limitation of the models are also elaborated with a 1kW digitally controlled LLC-RC laboratory prototype. Furthermore, a comparison of different controllers that are appropriate for the model is discussed and supported by relevant experimental results.