Research On Bidirectional Isolated Charging System Based On CLLLC Resonant Converter

Traditional fuel vehicles not only consume a lot of fossil energy,but also cause serious environmental pollution.Under this situation,the demand for new energy electric vehicles is increasing.For the huge electric vehicle group in the future,it has set off an upsurge of research on V2X(Vehicle to X,V2X)technology.Bidirectional AC/DC converter is the core device of this technology,on which the research have a profound and lasting impact.By comparing various bidirectional AC/DC converters,this thesis selects a two-stage isolated topology charging system.The front and rear stages are bidirectional totem pole converter and bidirectional CLLLC resonant converter respectively.They are connected through DC bus,which can realize energy exchange and functional decoupling.This thesis analyzes the working principle of the front stage and rear stage of the charging system.The mathematical model of the bidirectional totem pole converter and the transfer function of the current duty cycle are established by the small signal analysis method.The First Harmonic Approximation is used to simplify the bidirectional CLLLC resonant converter,and the equivalent circuit model and voltage gain expression are acquired.Then the influence of inductance coefficient and quality factor on voltage gain characteristics is analyzed,and the limiting conditions of resonant parameter design are clarified to ensure the realization of soft switching of switches.According to the design index of the charging system,the key components of the main circuit such as input inductance,DC bus capacitance and high-frequency transformer are designed and selected.In accordance with the calculated main parameters,the control program of the charging system is designed.The pre-converter adopts double a closed-loop control strategy.This scheme can ensure that the phase of the input voltage and the input current is basically the same,and can also keep the DC bus voltage stable.The parameters of the compensation controller are also designed.The rear converter adopts high-frequency soft start and frequency conversion control.The charging system can not only make the electric energy flow from the grid side to the battery side,but also ensure the reverse flow of energy to supply other electric equipment.In addition,it also has the functions of power factor correction and wide voltage output.By building a simulation platform,the working conditions of the charging system in the forward and reverse working modes are studied.The hardware circuit of the charging system is designed,and the software design process is explained.Finally,an experimental prototype with a power of 300 W is trial produced,and the simulation and test results verify the correctness of the theoretical analysis.