Research On Passive Electromagnetic Inductive Metal Foreign Object Detection Of Vehicle WPT System

Wireless Power Transfer(WPT)system has the advantages of convenient use,no dust,no mechanical wear and so on,and has been widely used in the field of electric vehicle charging.Due to the strong magnetic field between the coupling mechanisms of WPT system,the mixed metal foreign object will produce eddy current effect and magnetic effect,which will change the electrical parameters and charging performance of the system,meanwhile,the metal body will also produce rapid temperature rise due to eddy current heating,resulting in potential safety hazard.Therefore,the effective and reliable metal foreign object detection function is the precondition to ensure the normal charging and safe charging of WPT system.In this paper,based on the passive electromagnetic inductive detection theory,the relevant research on the metal foreign object detection method of the WPT system is carried out.Firstly,the influence of metal eddy current effect and magnetic effect on the magnetic field intensity and distribution of WPT was simulated by Maxwell software;The equivalent circuit model of metal foreign object detection is established,and the mathematical relationship between the voltage variation of the detection coil and the mutual inductance between the detection coil and metal foreign object is obtained,which provides a theoretical basis for the coil structure design and optimization to improve the mutual inductance between the coil and metal foreign object.Secondly,the calculation and comparison of the mutual inductance and change trend of the circular,square,rectangular coil and the metal foreign object have obtained the conclusion that the rectangular coil is more suitable for large-area inspection;theoretical analysis and simulation have proved that the rack coil can enhance the mutual inductance with electricity wire.The mutual inductance between the rack coils and the PCB detection coil board was optimized using Maxwell software,and the tooth height and thickness of the rack coil,as well as the wire diameter,wire spacing and copper thickness of the PCB board,were clarified.Thirdly,through Multisim simulation and experimental debugging,a conditioning circuit with the functions of signal gating,amplification,filtering and peak detection is designed;using DSP28335 development board,the functions of AD conversion,linear Kalman digital filter,scanning detection and serial communication of multi-channel detection signal are programmed;in order to facilitate the data acquisition and graphical display of the output signal from the detection coil during experiments,the PC software with the functions of serial-port data receiving,format conversion,storage and display has been developed.Finally,using the automotive WPT system experimental platform,experiments were carried out on small metal foreign objects such as coins and paper clips,and the adaptability of the detection coil,conditioning circuit and DSP processing program to the strong magnetic field environment and the detection ability of small metal foreign objects were tested.Verified the relationship between the output voltage change of the detection coil and the position of the foreign object,the intensity of the magnetic field and the height of the detection coil,and realized the point positioning function of the metal foreign object by using double-layer coil.