Research On Detection Method Of Metal Foreign Body In Electric Vehicle Wireless Charging Coupling Mechanism

Wireless charging technology of electric vehicles is being paid more and more attention because of its safety,convenience and environmental protection.It is of great significance in solving the problems of charging time,maintenance and cost of plug-in charging way.However,the analysis for the current wireless charging technology is based on the ideal state.When metal foreign obj ects occur between the receiver and the transmitter,the parameters of the system will change leading to the decrease of transmission efficiency.More seriously,it will cause the heating of metal foreign objects resulting in security risks.Therefore,the detection of metal foreign objects is particularly important.In this dissertation,the wireless charging system of electric vehicle with metal foreign objects are analysed,and the array-coil detection method is studied by electromagnetic field theory and finite element simulation.(1)Based on the theory of circuit and electromagnetic field,the influence of metal foreign objects on the wireless power transfer system is analysed.Then an array-coil detection method is proposed.With analysis of detection circuit,the effects of metal on the voltage and power of the detection coil are studied.(2)The calculation model of the wireless power transfer system with the function of metal foreign objects detection is established.Based on the study of eddy current losses of metal to wireless power transfer system,the detection coil is optimized from coil shape,inner diameter and outer diameter.The influences of aluminum,copper and iron plate on the voltage of the detection coil are obtained.(3)The metal foreign obj ect detection system in wireless power transfer is built to detect the aluminium plate,copper plate,iron plate,steel plate,one yuan coin,fifty-cent piece,and paper clip.The effects of material properties of aluminium,copper,and iron on the voltage of detection coil are analysed and compared to the simulation.This dissertation proposes an array-coil detection method,and the structure design of the detection coil is studied.The results show that when the size of the metal sheet in the transmitting coil center is less than 136mmx 136mm,it is unnecessary to detect because the eddy current loss ratio is less than 10%.The circular array-coil has a better detection effects than the square array-coil.With the increase of the outer diameter,the detection effect decreases.However,it is almost unaffected by the change of the inner diameter.By the optimization,the circular coil with an inner diameter of 20mm and an outer diameter of 50mm is finally determined as the detection coil.