| With the development of wireless power transmission technique and the expansion of its applications,more stringent requirements have been put forward for the electromagnetic safety standard of the system.Because wireless power transmission technique has electromagnetic fields that diffuse outward during its operation,the coupling structure needs to be equipped with electromagnetic shielding facilities.In order to reduce the weight of electromagnetic shielding structure,control the cost and improve the shielding effect,it is necessary to optimize the electromagnetic shielding structure applied in the wireless power transmission system.The common shielding structures for wireless power transmission technique have some problems,such as magnetic flux leakage at the edge of shielding,magnetic field lines cannot be returned completely due to a single magnetic shielding material,and transmission efficiency of the system is affected by excessive eddy current loss.It is in order to obtain a better shielding effect of wireless power transmission system,make up for the use of shielding materials in which too single deficiency.In this paper,from the perspective of multi-layer shielding composite structure,combined with the wireless power transmission system of electric vehicle in practical application,the composite magnetic material structure for wireless power transmission system is studied.This paper first describes the working principle of the wireless power transmission system for electric vehicles,the principle of magnetic shielding and electric shielding in electromagnetic shielding is analyzed.Different shielding materials and calculation methods of shielding effectiveness to measure shielding effectiveness are analyzed.The key points of shielding structure design are put forward.Secondly,referring to the electromagnetic field calculation formula of ring coil in the presence of single-layer shield plate,by analogy,the equations of electromagnetic fields in various regions of space under the condition of multi-layer shielding are listed.According to the boundary conditions of multilayer metal plates,the theoretical formula of shielding effectiveness in the case of multilayer shielding is derived.The proposed formula is simulated and calculated.The theoretical basis for the subsequent shield structure design is proposed.The ferrite + aluminum plate structure model commonly used in the wireless power transmission system of electric vehicles is simulated and calculated in the simulation software.A novel edge thickened nanocrystalline composite shielding structure is proposed.According to the characteristics of nanocrystalline materials,multilayer material structure modeling is carried out.According to the simulation,it can be seen that the edge thickened nanocrystalline composite shielding structure reduces the amount of materials on the basis of ensuring the shielding effect.The mutual inductance between the coupling coils is enhanced and the magnetic flux leakage in the shielding edge space is reduced.Finally,a space magnetic measurement device is built in this paper,experiments are carried out on different shielding structures,the experimental results show that the simulation is scientific and correct.The edge thickening nanocrystalline shielding structure designed in this paper can not only compensate for the influence of aluminum plate on mutual inductance between coupling systems,enhance the magnetic field between coupling coils,the shielding effectiveness is also increased compared with the commonly used ferrite + aluminum structure.The research results show the feasibility and superiority of the edge thickened nanocrystalline shielding structure for the shielding of electric vehicle wireless power transmission system.It can be used for reference for the shield design of the wireless power transmission system of electric vehicle. |
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