Novel small signal modeling and control of an LLC resonant converter

In this paper, a novel approach to determine the small signal model of an LLC resonant converter is presented. The proposed model uses analysis techniques from communications theory to determine the control-to-output transfer function required for the design of a digital compensation network. The model considers the effects of higher order harmonics and sideband frequencies generated by the variable switching frequency control method, as well as the effects of the LLC resonant tank and the output voltage rectifier. Experimental data from a prototype LLC resonant converter was obtained to verify the analytical results, and revealed that the proposed model is an accurate representation of the prototype converter dynamics. Simulation results demonstrated that a digital compensator design based on the proposed model was able to achieve output voltage regulation.