Research On Detection Of Foreign Obstacle In Wireless Charging Based On Impedance Analysis Of Transmitting Coil

There is an urgent problem to be solved in the wireless charging technology of electric vehicles that hinders its own development.That is the problem of foreign body intrusion between the transmitting and receiving coils.If metallic foreign objects invade the wireless transmission area,the temperature rise caused by its eddy current effect and magnetic effect will bring potential safety hazards to the system and affect the system efficiency and operating characteristics.To this end,many detection methods have been proposed at home and abroad,such as sound wave detection,video detection,electrical detection,etc.,most of them need to add additional devices,increasing the installation complexity and system cost.In this paper,a wireless charging foreign object detection method based on the analysis of the impedance of the transmitting coil is studied.No additional devices are needed,which makes the foreign object detection function more convenient to implement,easier to embed and compatible.Through theoretical analysis and simulation,this paper analyzes the influence of metal foreign objects on the coil and its magnetic field,and summarizes the influence of metal foreign objects on the self-inductance and mutual inductance of the system transmission coil.And,through the analysis and formula derivation of the wireless energy transmission system topology,the formula relationship between the transmission coil self-inductance and mutual inductance on the system impedance and efficiency is obtained.In addition,Maxwell and Simplorer electromagnetic co-simulation was done to the wireless energy transmission system,and the influence of metals with different properties and sizes on the phase and amplitude of the output waveform of the transmitting coil of the wireless energy transmission system was explored.Finally,based on the analysis of the output impedance of the transmitting coil,a new hardware and software solution for foreign object detection in wireless electric vehicles is proposed,and the effectiveness of its metal foreign object detection function is verified through the wireless energy transmission hardware platform.The experimental results show that the metal foreign object detection function is realized on the 3k W wireless energy transmission system experimental platform without installing any external foreign object detection device.Finally,the detection method detected 30mm~2×0.2 iron pieces successfully,and its detection area accuracy reached 1.2% of the area of the transmitting coil.