| In the field of passenger cars,electric vehicles(EV)have gradually become an important choice for the development of a green and environmentally friendly society.In order to meet the range of EV and alleviate the limitation of power battery storage capacity,wireless power transfer(WPT)technology for EV has gradually received attention and research from many experts and scholars.However,there are many challenges,and the electromagnetic safety of the coupler of EV wireless charging system is one of the prominent issues.This paper investigate the electromagnetic shielding problem of high-power wireless charging system under the premise of ensuring the energy efficiency of coupler,and investigate it through theoretical calculation,simulation analysis and experimental demonstration.The main research contents are as follows:(1)Electric vehicle wireless charging system composition and modeling methods.In order to match the modeling method of electric vehicle wireless charging with the applicable scenario,this article propose the wireless power transmission model based on multiple coils,and compare different modeling methods of electric vehicle wireless charging system,showing that the modeling method based on circuit theory is more suitable for the design of coupling mechanism in this paper.In view of the multiplicity and complexity of the topology of the EV wireless charging compensation circuit,the transmission characteristics of EV wireless charging under the circuit model are analyzed by taking SS-type and LCC-type compensation networks as examples;for the electromagnetic energy conversion process of EV wireless charging,the numerical calculation method of the magnetic field strength at any point in space under a given excitation source is proposed.Considering the skin effect,the impedance matrix calculation formula is given for the non-uniform distribution of current under AC field.(2)Optimization and design method of shielding layer of basic coupler for wireless charging of EV.To address the selection of coil structure parameters of the basic coupler,finite element analysis software is used to carry out simulation and analyze the influence of coil physical structure on the coupling coefficient,mutual inductance,self-inductance and magnetic induction intensity distribution,which shows that the single coil has higher coupling capacity and the combined coil has stronger misalignment tolerance adaptability;to address the electromagnetic safety of the coupler,a model with electromagnetic shielding effect is designed to meet the requirements of the national standard.The results show that about 80% of the energy loss in the wireless charging process is generated in the conductor;for the above-mentioned energy efficiency problems of the coupler,the optimization objectives and design process of the coupler are proposed,and an optimized shielding coupler is designed based on the addition of shielding layer with the optimization objectives of manufacturing cost,space occupation volume,transmission efficiency,and environmental magnetic field strength.A multi-level energy conversion wireless power transmission model from grid side to vehicle side is built to calculate the transfer efficiency of different coupler.The results show that the optimized coupler has better shielding effect and misalignment tolerance adaptability,and the system transmission efficiency reaches86.2%.(3)Research on the electromagnetic shielding characteristics and human safety of the wireless charging coupler of EV.The minimum safety limit of human exposure to wireless charging working area is given for the safety of human exposure to high frequency electromagnetic field.Adopt the passive shielding method of coupler,divide the shielding layer of coupler into double-layer structure,analyze the influence of different ferromagnetic materials and conductive metal materials on coupler coupling coefficient,transmission efficiency and surrounding electromagnetic radiation,and optimize the double-layer shielding structure.Use aluminum plate and manganese zinc ferrite as shielding layer,its shielding performance can meet the requirements of international standards without losing transmission energy efficiency;for the body shielding and human tissue heat effect of wireless charging of EV,taking into account the shielding effect of the vehicle chassis and location restrictions,introduce the human body isometric figure model,complete the human body in different positions and different angles of the wireless power transmission coupling space The results show that the ankle area is most affected by the thermal effect in the standing position,and only the magnetic field strength will exceed the minimum safety limit in some position.(4)Construction of dynamic wireless charging experimental platform for EV and testing of coupler.According to the previous study,a dynamic wireless charging experimental platform for EV with a rated power of 11 k W is built to meet various charging requirements,and the platform can realize the requirements of visualization of experimental process,measurability of experimental data and controllability of experimental equipment.In addition,no-load and full-load tests of static wireless charging and verification of dynamic wireless charging coil throwing strategy are carried out according to the actual scenario requirements in this chapter.In order to meet the rated output power conditions of the coupler around the environmental magnetic induction intensity changes and electromagnetic shielding effect,the field measurement of the equipment,the test results are consistent with the simulation experiment;for the platform transmission energy efficiency changes under the misalignment,the misalignment test with the receiving coil current and transmission efficiency as indicators,showing that under the premise of the transmission efficiency of not less than 80%,the single coil coupler with double shielding structure achieves a maximum misalignment tolerance adaptability of 13.1%. |
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