Optimal Study Of Resonant Wireless Power Transfer Technology For Electric Vehicles

In recent years,with the intensification of global environmental pollution and the reduction of fossil energy,electric vehicle?EV?has quickly attracted the attention of many countries owing to their advantages of low-carbon and pollution-free.However,the traditional wired charging has many disadvantages in convenience and safety,which limit the development of EV.Compared to wired charging,wireless charging can be widely used because of its advantages such as high flexibility,high safety and strong adaptability.At present,there are two types of wireless charging for EV:induction and resonance.Inductive wireless charging is suitable for short transfer distance.Once air gap is increased,the system transfer efficiency is drastically reduced.Resonant wireless charging is suitable for high power fields such as EV due to its advantages of high transfer efficiency,long transfer distance,high transfer power,and small influence of magnetic field on people and the surrounding environment.Therefore,this paper mainly focuses on the simulation optimization of resonant wireless power transfer?WPT?technology for EV.Firstly,the two-coil series-series topology is analyzed by the equivalent circuit theory,and the three-dimensional diagrams of load voltage and transfer efficiency with frequency and coupling coefficient respectively is drawn,and the paper explains the frequency splitting phenomenon and critical coupling coefficient.In order to ensure the energy transfer efficiency,a frequency tracking control scheme is designed based on the principle of phase locked loop,to ensure that the system is always in resonance state.At the same time,the resonant WPT system model with frequency tracking control function is built in Matlab/Simulink.The simulation result shows that the inverter output voltage can well track the current phase in the primary loop,which verifies the correctness of the design.Secondly,the resonant wireless power transfer coil is analyzed and optimized.Equivalent circuit theory is used to obtain four factors that affect the system transfer efficiency:system resonant angle frequency,mutual inductance between the transmitting and receiving coils,coil equivalent series resistance,and load.Then,the commonly used planar circular charging coil is selected for optimization analysis.The coils can be optimized by increasing the number of coil turns,increasing the average radius of the coil,reducing the transfer distance and selecting the proper load without considering the influence of the coil equivalent series resistance,and the difference between the inner and outer diameters of the planar coil should be reduced as much as possible,so as to enhance the system transfer efficiency.However,the circular structure and the square chassis of the EV do not have a high degree of fit,resulting in a lower space utilization rate of the chassis of the vehicle.Therefore,the paper optimizes and analyzes planar square coils with high degree of fit with the vehicle chassis.The specific planar square structure can maximize the space utilization of the vehicle chassis and further increase the system transfer power.The system transfer efficiency can be optimized by selecting the optimal number of coil turns,selecting the optimal length of the coil side,reducing the transfer distance and selecting the proper load with considering the influence of the coil equivalent series resistance,and the approximate optimal relationship between the square coil side length d and the transfer distance D is also obtained,d=2D.At the same time,the COMSOL Multiphysics software is used to simulate and optimize the circular and square coils,and two magnetic field distribution diagrams of both transmitting and receiving coils during each resonance are obtained.Therefore,complete and intuitive optimization of coils design of the resonant wirelee power transfer system can be achieved,and thus high transfer efficiency of EV resonant wireless charging system can be realized.Finally,the coil structure with magnetizer and the coil horizontal misalignment are optimally study.In order to further improve the system transfer efficiency,the paper selects the coil structure for optimal simulation study.The effect of magnetizer is analyzed by the circuit theory,and the paper improves the design of three types of magnetizers:the circular type or the square type?including two structures respectively?and the lampshade type.The optimal simulation results show that the magnetizer helps to increase the magnetic flux of the hinge between the transmitting and receiving coils,and further improve the charging efficiency of the EV,The best structure of the magnetizer is the lampshade type,but the specific structure and the dimensions need to be considered in combination with the chassis structure of EV and economic cost.Moreover,the receiving coil on the chassis of the EV is often not fully aligned with the transmitting coil when the EV is being statically or dynamically charged,the horizontal misalignment of the charging coils occurs,and the system transfer power and efficiency drop sharply.The paper takes the plane circular coil and the planar square coil as the models for comparative simulation research.The simulation study shows that the system transfer efficiency is less affected when the horizontal misalignment of the transmitting and receiving coils occurs within a certain range?m<m₀?.Once the horizontal misalignment distance exceeds this range,the system transfer efficiency is significantly reduced.The specific value of m₀ can be determined by taking the horizontal misalignment of the planar circular coil and the square coil as a reference,considering various factors such as the specific application environment and economic cost in the charging process.