Research On Efficiency Optimization Of Electric Vehicle Wireless Power Transfer System

Compared with wired transmission by metal wires,magnetic coupled resonance wireless power transmission(MCR-WPT)as an emerging technology has unparalleled advantages of wired transmission.Traditional wires may produce negative effects of aging and leakage during use,and the complicated wire and interface types bring many inconveniences to people’s life,MCR-WPT technology is widely used because of its long transmission distance and high efficiency.In this paper,we study and analyze the three-coil electric vehicle wireless charging system,and conduct an argumentative optimization study on the transmission efficiency from the perspective of relay coil optimization.First,the two-coil and vertical relay-based U-type three-coil models are modeled and analyzed,and the system efficiency expressions are derived by considering cross-coupling.This provides a theoretical basis and research direction for the following system efficiency optimization.Next,according to the characteristics of two/three coils,this paper proposes the design of U-type relay triple coil switching system,which can be switched at the suitable distance point to realize the advantages of combining the triple coil and two coils,and achieve the optimal efficiency under the change of transmission distance.The system can be switched at a suitable distance point to achieve the optimal efficiency under the change of transmission spacing.Then the relative positions of transmitting and relaying coils and the parameters of relaying coils are designed and optimized,and the designed switching system avoids the efficiency concave point of its vertical relay structure.The transmission efficiency of its switching system is higher than that of even a single structure.Simulation analysis is performed under the present experimental parameters,and the simulation results show that the designed switching system improves the radio energy transmission efficiency by 58% at both closer and longer distances compared with the single two-coil or three-coil structure model;compared with the common three-coil structure,the maximum wireless power transmission efficiency of the system improves by 71%.Finally,considering the effects of load change and receiving coil displacement,the optimal capacitance compensation of efficiency based on vertical relay triple coil is proposed based on the determined triple coil switching model,and the expressions of system efficiency and optimal compensation capacitance of relay coil are derived by analytical method based on the circuit model of triple coil structure,and the effects of vertical and horizontal coil movement and load resistance on optimal compensation capacitance and transmission efficiency are analyzed in detail.The efficiency of the three coils is compared between the optimal compensation capacitor and no compensation capacitor,and the maximum efficiency can be increased by 16.27% after the optimal compensation of the capacitor when the vertical displacement occurs,and the difference between the efficiency before and after the compensation increases with the increase of the displacement distance when the horizontal displacement occurs,which proves that the optimal compensation of the capacitor can effectively resist the coil offset,and in addition,the overall efficiency is improved significantly after the compensation from the viewpoint of the load,and in the load change Within the range of 5-50Ω,the average improvement after compensation is 3.55% compared with that before compensation.By designing the relay coil compensation capacitor array,the optimal compensation capacitor is optimized for real-time compensation of changing mutual inductance when the system receives coil position movement or load changes to maximize system transmission efficiency.