Research On Hybrid Controlled Bidirectional Full Bridge Three-Level LLC Resonant Converter

With the rapid development of electric vehicles,the development of vehicle to grid(V2G)system has attracted more and more attention.In V2 G system,electric vehicle as energy storage linking with bidirectional DC / DC converter can cut peak and fill valley,adjust power quality and grid frequency.In this paper,under the background of V2 G system,the research status of bidirectional DC/DC converter is analyzed,and the key technologies of LLC converter are studied.According to the characteristics of LLC resonant converter and the advantages of constant frequency control and variable frequency control,a hybrid control method is adopted.Under the condition of three optimal switching modes,the optimal switching mode suitable for full bridge three-level structure is selected.On this basis,the voltage gain of the converter is divided into three modes: high,medium and low.The principle and modes of all gain modes are studied.The first harmonic analysis is used to analyze the three gain modes of the converter.The correctness of hybrid control is verified.In addition,the soft switching characteristics of forward and reverse operation of the converter are analyzed.According to the characteristics of soft switch,some parameters of the converter are obtained.All gain modes and soft switch are verified by simulation.Aiming at the unbalance of neutral point potential caused by the difference of controller,drive and switch parameters,the neutral point voltage self-balance is realized by introducing flying capacitor into the topology.This paper analyzes the mode of full bridge three-level DC / DC converter with flying capacitor,realizes to provide additional current compensation branch for input voltage divider through flying capacitor,studies the factors influencing the steady-state error of neutral point voltage,deduces the expression of steady-state voltage difference,and verifies it by simulation.The experiment platform of bidirectional full bridge three-level LLC resonant converter based on DSP and FPGA controller is designed.The correctness and validity of the theory are verified by the experiment.There are 62 figures,3 tables and 75 references shown in this thesis.