Research On V2G-faced OBC Post-stage Bidirectional Resonant DC/DC Converter

In China’s 14 th Five-Year Plan,new energy vehicles have entered a significant stage of transition from the cultivation period to the development period and have been included in the charging infrastructure of the national new infrastructure key industry.Due to the increasing demand for new energy electric vehicles(EVs),research on on-board charging equipment has gradually become a boom.The proposed vehicle-to-grid(V2G)technology of EVs enables the vehicles with V2 G function to output energy to the grid as a kind of distributed energy,so as to take part in the dispatching of the grid and perform the function of peak clipping and valley filling.This requires that the on-board charging equipment of EVs can realize the two-way flow of energy and have a wide range of working voltage.To solve this problem,an LC-LLC resonant bidirectional DC converter is proposed in this paper to satisfy the charging and discharging requirements of V2 G electric vehicle power battery.Firstly,the different topologies and control modes of the existing bi-directional isolated DC/DC converters are reviewed.Starting from the idea of improving the resonant network topology,a novel bi-directional LC-LLC resonant converter is proposed by introducing auxiliary capacitor and auxiliary inductor series branch in the existing bi-directional LLC resonant network.The working principle of the converter in forward/reverse operation is analyzed in detail.In the forward operation,the auxiliary branch does not participate in resonance,and the converter is based on LLC resonance principle.A hybrid bridge modulation strategy is adopted to widen the voltage output range and improve the soft switching characteristics.Fundamental Harmonic Approximation is used to analyze the output characteristics of the forward operation,and the gain curve of the half-bridge/full-bridge combination is obtained.In the reverse operation,the auxiliary inductor and capacitor participate in the construction of a new resonant network structure,and the increase of notch points makes the reverse voltage gain greater than 1,thus improving the application range of the bidirectional DC converter to the battery load voltage change.Secondly,in order to optimize the performance of the converter,the influence of resonant network parameters on the gain is analyzed,and then the resonant frequency matching is carried out to determine the gain range of the converter.According to the analysis results and combined with the performance indexes,the parameter design of the bi-directional LC-LLC resonant converter is completed.Finally,an experimental platform of 1.8k W bidirectional DC power conversion is built,the software and hardware design program of bidirectional LC-LLC resonant converter is given,and the following experimental data are obtained on the experimental prototype: In the forward operation,the converter operates in the constant current charging output state and achieves the output voltage of 150～450V on the resistive load.The gain range is0.75～1.35 in the full bridge mode and 0.45～0.75 in the half bridge mode.Therefore,the gain range is 0.45～1.35 in the forward operation.In the reverse operation,the input voltage varies in the range of 250～450V,and the maximum reverse voltage gain is 1.33 when the converter keeps the output bus voltage constant at 400 V.The Zero-Voltage Switching of the inverter switch and Zero-Current Switching of the rectifier are realized when the converter is running in both the forward and reverse directions.In the forward/reverse working efficiency curve,the peak efficiency is 94.7% when the converter is charged and 94.6% when it is discharged.