Research On The Electromagnetic Field And Power Flow In The Wireless Power Transfer System

Wireless power transfer(WPT)is a way of transmitting power without using cables.WPT technology originated in Tesla at the end of the 19 th century.WPT technology has become one of the hot research topics in the field of energy and information.It has made great progress in the research of WPT principle,system equipment,industrial applications and other aspects.However,at present,WPT technology is still in the stage of laboratory research.Therefore,One of the possible scientific reasons behind this is that the knowlage of WPT's basic physical characteristics and energy transfer law is not enough,which needs further study.Therefore,aiming at this basic problem,this paper focuses on three aspects: electromagnetic field calculation method,electromagnetic field characteristics and power flow characteristics in WPT transmission space.The main work is as follows:?1 A direct filament method and an optimization scheme are established.Firstly,a direct filament method based on Biosavart's law for the analysis of electromagnetic field and power flow in WPT system is established.Compared with other filament methods,the direct filament method is more efficient and concise in formula expression because it aims at programming solution.Secondly,based on the principle of graph denoising,a maximum filtering method is proposed,and combined with the twodimensional feature selection validation(2D-FSV)method,an optimization scheme for the number of coil segments is proposed.The optimal number of coil segments is obtained,thus balancing the calculation efficiency and accuracy of the direct fine line method.This method can be well applied to the solution and analysis of space electromagnetic field in WPT system,which lays the foundation of theoretical calculation in this paper.?2 The electromagnetic field characteristics of WPT system are studied.Firstly,the composed magnetic field in WPT system is studied in time and complex domain.It is revealed that the composed magnetic field is a non-sinusoidal field,and the magnetic field sinusoidal distortion(MFSD)is defined by combining the complex modulus and the instantaneous maximum value.The polarization characteristics of the composed magnetic field are studied.It is found that the composed magnetic field has linear polarization,circular polarization and elliptical polarization.The non-sinusoidal and polarization characteristics of WPT system under different conditions are discussed.It is concluded that the non-sinusoidal and multi-polarization characteristics of composed magnetic field are universal and the phase difference of space magnetic field components is the direct reason.Secondly,the electric field of WPT system is studied.The dispersionfree,linear polarization and sinusoidal time-varying characteristics of the electric field of WPT system are obtained.According to the characteristics of electric field in WPT system,an electric field measurement method is designed.The study reveals the basic characteristics of electromagnetic field of WPT system,which lays a foundation for power flow analysis in this paper.?3 The power flow in WPT system is studied.The power flow of WPT system is studied in time domain and complex domain.In the analysis of instantaneous Poynting vectors,it is found that the instantaneous Poynting vectors at a certain point in space have two peaks,which can be used as the verification object of instantaneous Poynting vectors in WPT system.In the analysis of complex Poynting vectors,the characteristics of power flow are analyzed based on the active and reactive power density vectors.The active power density vector originates from the transmitting coil and terminates in the receiving coil,and forms a cylindrical ring in space.The reactive power density forms two rings.The variation of active and reactive power density in different WPT systems is discussed.It is found that the direction of the active power density vector does not change with the current amplitude ratio.One transmission power on the circular surface near the receiving coil with the cross section of the receiving coil as the size is calculated.It is found that the existence of transmission power depends on the current phase difference.The basic characteristics of power flow are obtained by studying the power flow of WPT system,which can be used as a reference for the analysis and design of WPT system,and also for the study of other near-field coupling systems.