Research On Metal Foreign Object Detection Technology In Electric Vehicle Wireless Charging System

With the increasingly serious energy crisis and environmental problems,electric vehicle is becoming more and more popular as a kind of environmental protection and clean means of transportation.Most electric vehicles use the traditional wired plug charging method,which has some safety problems such as unreliable contact,heavy charging head,cumbersome plug-in,and easy to generate charging sparks.However,the wireless charging method can solve the above problems of the wired charging.Wireless charging mode of electric vehicle refers to the technology of charging electric energy in wireless form without direct electric contact through wires.Inductively coupled power transfer(ICPT)is a kind of wireless power transfer technology.Because of its low working frequency,low electromagnetic radiation and easy to shield,and easier realization of high-power transmission,it is widely used in the electric vehicle wireless charging system.When the electric vehicle wireless charging system works,there will be a magnetic field coupling area.When the metal foreign object enters the area,it will cause the change of the electrical parameters of the system,affect the normal operation of the charging system,and the rise of the temperature of the metal foreign object will bring serious security risks.The existing detection technologies of metal foreign object mainly have the following problems: greatly affected by the working state of wireless charging system,low detection accuracy,poor anti-interference and so on,therefore,this paper aims to research a new detection technology of metal foreign object.The main research work is as follows:Firstly,starting from the basic principle of electric vehicle wireless charging system,the basic circuit structure,such as rectifier filter circuit,high frequency inverter circuit,resonance compensation circuit,and the theoretical basis of electromagnetic coupling mechanism are studied,and the mathematical model of electric vehicle wireless charging system is established and analyzed.Secondly,the basic principle of metal foreign object affecting the coil is studied.The influence of metal foreign object in different position,size and material on the electromagnetic coupling mechanism is simulated and analyzed.The characteristics of the electromagnetic coupling mechanism influenced by metal foreign object are analyzed and studied to lay a theoretical foundation for the detection of metal foreign object.Then,based on the previous theoretical research,combined with the design requirements and indicators of the metal foreign object detection system,a detection method of metal foreign object with additional detection coil is proposed,and based on the detection mechanism of the additional coil,a reference basis for evaluating the performance of the detection coil is proposed.In order to improve the sensitivity and accuracy of detection,the parameters such as wire diameter,wire spacing and turns of detection coil are optimized.A detection circuit with resonance capacitance is designed and optimized.The design method of balance coil and differential circuit is introduced.The improved structure of detection coil without blind area is proposed.Finally,the hardware design and device selection of the system inverter circuit and its driving circuit,primary and secondary side resonance circuit,coupling mechanism and detection circuit are carried out,and the overall simulation model and experimental verification platform of the system are built.The simulation and experimental results show that when there is metal foreign object in the system,the existence of metal foreign object can be judged by the output signal of the detection system,which verifies the feasibility of the detection technology of metal foreign object with detection coil proposed in this paper.72 figures,8 tables and 75 references are included in this paper.