Small Signal Analysis for LLC Resonant Converter

− In this paper, small signal characteristic of a LLC resonant converter is analyzed. LLC resonant converter was been reported in many papers recently because of its simple structure, high efficiency and high switching frequency capability. In order to make practical use of this topology, understanding its small signal characteristic is essential to design the control loop. For PWM converter, state space average method is well established and verified. For resonant converter, because of the different ways of operation, state space average model cannot give satisfactory result. In this paper, simulation method is used to derive the small signal model of resonant converter. With this method, Series Resonant Converter and LLC resonant converter were been analyzed. Finally, a prototype of LLC resonant converter was built and tested to verify the results get from previous analysis.