Research And Application Of Foreign Object Detection In Wireless Power Transfer System

Wireless power transfer(WPT)technology get more attentions in recent years especially in electric vehicle(EV)charge field.Foreign object detection(FOD)becomes bottleneck for application of WPT.In EV charge field,resonant magnetic field is high frequency and time-varying.Due to eddy effect,metal in WPT working field could reduce efficiency of system and be with high temperature rise.This paper works for fast,effective and accurate metal foreign object detection method in WPT system.Firstly this paper introduces magnetic resonant WPT system.Then analyzes how metal get heated in alternating magnetic field,and how various factors which contains material of metal,shape of metal,size of metal,direction of magnetic field,frequency of magnetic field,direction of magnetic field effects metal heated.This offers some considerable way to find which metal is the most harmful for system.Magnetic detection is chose as detection method.Standard SAE-J2954 was set for WPT system in EV charging.So take coil which described in SAE-J2954 as a typical case for WPT system space magnetic field analysis.The analysis of magnetic field distortion distribution that created by metal eddy current is divided into two cases:magnetic field distortion created by nonferromagnetic metal and magnetic field distortion created by ferromagnetic metal.According to difference between two cases,fluxmeter would be the most suitable detection method for distorted magnetic field detection.In fluxmeter detection method,detection coil of detection system is the most important part for it would effects detection result directly.After analyzing of flatwise winding,an optimistic way to arrange winding which arrange winding symmetrically to Tx magnet field could strength anti-interference performance.To eliminate environment magnetic field effect absolutely,standing winding could be proposed.Standing winding also has less detection blind plot.Finally an experience system is established for verifying feasibility and effectiveness of detection method.Experience proves symmetrically arranged flatwise winding can avoid most environment magnetic field affect and detect metal successfully.Proposed standing winding could avoid environment magnetic field affect and detect metal successfully too.What's more,standing winding could reduce number of blind plot simply by arrange malposed winding.