Research On Technology Of Metal Foreign Object Detection In Wireless Charging Device

As the new energy vehicles are popularized and supported in China,electric vehicles(EV)hold a big part of the vehicle market.The Wireless charging technology of EV is developing significantly in recent years,and has the advantages of convenient and flexible,realizing the intelligence and automation in the charge process.However,the wireless charging process is easily disturbed by the metal foreign objects(MFO),which can cause the charging efficiency decrease and a series of security problems caused by the eddy thermal effects.Therefore,the automatic detection technology of MFO has become a critical issue to be solved in the field of wireless charging of EV.In order to solve the problems above,an active method for MFO detection based on the principle that MFOs can cause mistuned resonance of detecting coil resonant circuit is proposed.The principle of detecting MFO by variation of coil equivalent impedance is analyzed.The general scheme of the automatic MFO detecting system for EV wireless chargers is presented.The factors of influencing the detection coil performance are analyzed.By using the finite element electromagnetic simulation tool,t he principle feasibility of the MFO detection method proposed is verified,and the influence of the coil parameters on the electromagnetic characteristics of the detecting coil is analyzed.The design scheme of the detecting coils suitable for the small MFO detection in the EV wireless charging large region is presented.The distribution of voltage noise from charging magnetic field in frequency domain is analyzed,and the method of choosing detecting coil excitation frequency to decouple detecting magnetic field from charging magnetic field is proposed.The method of designing high frequency time-sharing driving circuit and resonant circuit for detecting coils is introduced.The design scheme of time-sharing signal processing circuit is presented,and the method of filtering the coupled voltage noise from charging magnetic field is proposed.The design schemes of the MFO detecting programs are presented.Finally,the MFO detection system experimental platform is constructed.The anti-disturbance experiment and the MFO detection experiment of the detecting system in the wireless charging environment are designed to verify the effectiveness of the filter scheme and the MFO detection method proposed.A series of experiments of exploring the MFO detection sensitivity are designed to analyze the detection sensitivity differences in the different conditions.The sensitivity of detecting system is tested in the different charging conditions,and the results of testing are presented.