Simplified Time Domain Analysis of the LLC Resonant Converter

Abstract

Modern LLC resonant converters have a high efficiency. This allows neglecting the active resistance of the transformer windings, which has been discussed in some known publications. This paper deals with a simplified method for taking into account a magnetizing branch when using a T-shaped equivalent circuit of a two-winding transformer to analyze LLC resonant converter at the time interval of its linearity. As a result, the authors' previous neat description of the LLC resonant converter over its linearity interval by three linear differential equations is reduced to two first-order equations, which may simplify the calculations greatly. In this paper, the equation for determining the initial value of the state vector of LLC resonant converter at the interval of its linearity in the steady-state mode has been solved. The result relationships have afforded grounds for computer modeling of processes in the linearity interval using the parameters taken from the data for the commercial LLC resonant converter developed by the EKRA Research and Production Enterprise, Ltd. (Cheboksary). The modeling of LLC resonant converter using the exact and simplified equations has practically shown their exact match.