LCLC Resonant Converter Modelling in Synchronous Reference Frame

Resonant converters with LC, LLC, LCLC tank circuits are used in various industrial applications. Due to the sinusoidal behavior of the resonant tank current and the voltage, the conventional state space averaging technique fails to model the resonant converters. Several models are developed for LC, LLC resonant converters to capture the small signal model of the resonant converters. These models involve rigorous mathematical analysis and computations. In this work, a d-q-based small signal model in a synchronous reference frame for an LCLC resonant converter having a series branch (L-s, C-s) and a parallel branch (L-p, C-p connected in series) has been derived using the first harmonic approximation (FHA) circuit. The model is verified in simulation and hardware verification is carried out using the Texas Instruments Software Frequency Response Analyzer tool (SFRA) in the TMS320F28379D microcontroller on a LCLC converter prototype with rated power of 500 W.