Comparison among different analysis methodologies for LLC resonant converter

The LLC resonant converters have been widely used in many applications due to their features such as wide input voltage range, high efficiency, and high power density. Therefore, the analysis methodology for the LLC resonant converter is of great importance. Based on the existing literature, there are mainly four analysis methodologies: (i) fundamental harmonic analysis; (ii) frequency domain with time domain partial correction; (iii) frequency domain with time domain complete correction; (iv) time domain analysis or operation mode-based analysis. However, there is no systematic view and study on different LLC analysis methodologies. Therefore, the main purpose and contribution of this study are to make a comprehensive study and comparison of these analysis methodologies and to provide guidance on analysing and designing of the LLC resonant converter to the readers. In this study, the principles of these four analysis methodologies are introduced briefly. Then, by introducing gain error and peak gain frequency error as definitions, comprehensive comparison studies on these four different methodologies for different conditions are implemented. Recommended applications for each methodology are summarised; finally, an experimental prototype is built to verify the theoretical analysis, and a conclusion is drawn.