Analysis and Simulation of a Bidirectional CLLC Resonant Converter

Carbon Neutrality by 2050 is the goal of the European Green Deal. From the Smart Grids point of view, in which BEVs (Battery Electrical Vehicles) participate in the stabilization of the network through the V2G (vehicle-to-grid) configuration, the development and the installation of bidirectional chargers therefore becomes a necessity. The state of the art sees the emerging birth of CLLC resonant converters, characterized by greater efficiency compared to previous bidirectional DAB (Dual Active Bridge) and unidirectional LLC resonant converters. The research and development work conducted at the company Prima Electro had the objective of using the results obtained as a first evaluation tool for the possible creation of CLLC resonant converters. Using the FHA (First-Harmonic-Approximation) concept known from the literature, an analytical study has been conducted on a converter simplified model to obtain the formulas describing its frequency behaviour. The expression of the voltage gain depending on the operating frequency and defining the buck or boost operation mode has been obtained first. Then, the inductive and capacitive behaviour was studied as a function of frequency to ensure Soft Switching operation. To conclude the analytical procedures the expression of the delay for controlling the rectifier bridge switches was found to guarantee the SR (Synchronous Rectification) and to limit the losses. Finally, simulations were conducted on Plecs to verify the validity of the analytical models, to evaluate the error made with the assumptions, and as a tool to map the operating regions of the converter. Furthermore, component stresses were evaluated, as an evaluation tool for future design work.