Based on the principle of electromagnetic induction,the electric energy can be transferred between the power source and the vehicles contactlessly by means of the wireless charging technology(WCT).The WCT has the advantages of convenience and flexibility.However,in the high power condition,the electromagnetic field(EMF)around the coupled coils might exceed the safety levels with respect to human exposure.Thus,effective EMF reduction methods,which could reduce the EMF inside and around the vehicles to the safety levels,should be studied.Focused on the electric vehicles wireless charging system(EVs WCS),this paper conducts research in three directions,i.e.modeling of the coupled circuits,modeling of the EMF for the WCS,and the EMF reduction method design.First of all,the coupled circuit topologies of the WCS are studied and analyzed.Based on the circuit theory,the circuit models of the coupled coils and the compensation network for the WCS are built up.At the same time,their properties are analyzed and sumarized respectively.Further,the coupled-mode model for the two coupled lossy resonant circuits driven by extrinsic power is built up based on the coupled-mode theory.Then,the relevance of the circuit model and the coupled-mode model,and their equivalence on the efficiency analysis,are analyzed.The accuracy of the coupled circuit model is verified by the test results of the power transfer efficiency on the four-coil WCS prototype and the LCC-CCL compensated WCS prototype.Next,focused on the EMF modeling,the cause of the electromagnetic radiation problem for the EVs WCS and the key area for EMF reduction is studied based on the finite element analysis(FEA).Moreover,the EMF dictribution characteristics and the EMF models of a single turn circular coil,multi-turn circular coils and the inductive coupled two-coil system are studied respectively based on the Biot–Savart law.This has provided a theoretical basis for the calculation of electromagnetic field intensity around the WCS.Finally,focused on the EVs WCS electromagnetic radiation safety issue,the coil turns optimization based EMF reduction method is proposed.The coil turns optimization procedure is designed and the principles of the the optimized coil turns configuration regarding the change of the charging distance,the load and the turns number of the transmitting coil are summarized.On this basis,the EMF test experiments are conducted on the two-coil inductive coupled WCS prototype.The magnetic flux intensities around the coupled coils for the optimized coil turns configuration and the symmetrical coil turns configuration are measured respectively.Based on the comparison and analysis of the test results,the EMF reduction effectiveness of the proposed coil turns optimization method for EVs WCS has been verified.This paper will provide reference and the theoretical basis for the EMF reduction of the EVs WCS. |