A Dynamic Time-Domain Based Accurate Small Signal Model for LLC Converter

Abstract

LLC resonant converter has been widely adopted in switching power supply due to its high power density and high efficiency characteristics. However, because the switching frequency is close to the resonant frequency, it is difficult to derive the small signal model accurately. In this paper, an accurate small signal model for LLC converter is derived based on the dynamic time-domain model. The LLC converter dynamic time-domain model is developed by modeling three different stages, stage ending conditions, and the judgements of next stage. Combing with the basic concept of small signal modeling, the accurate control-to-output transfer function bode diagram can be derived, which is more accurate than the traditional extended describing function (EDF) method. Simulation results under various conditions are presented to verify the accuracy of the proposed small signal model. The small signal analysis results from the developed model are consistent with the commercial simulation software.