Foreign Object Detection Method For Electric Vehicle Wireless Charging System Based On Four-coil Real-time Voltage Monitoring

With the increasing shortage of non-renewable energy sources and the need to reduce pollution and protect the environment,electric vehicles are increasingly popular as a clean way of travel.The traditional plug-in type has safety hazards and there is a risk of leakage in a humid environment Wireless power transfer technology can solve the above problems well.At present,wireless charging technology is developing in the direction of high power and high efficiency.In actual use,foreign metal objects may exist between the charging coils,which affects the charging efficiency,and the metal temperature rises for a long time,which may bring a safety problem.Therefore,it is necessary to detect foreign matter in the wireless charging system of electric vehicles.The paper first introduces the basic structure of electric vehicle wireless charging system,including power frequency rectification,inverter,compensation circuit,coupling mechanism,high frequency rectification,DC/DC circuit and battery load.Combined with the circuit model,the output performance of the compensation topology and its influence on the system efficiency are analyzed.The key analysis of the LCC compensation topology is made.Combined with its output characteristics,its constant voltage characteristics and the characteristics affected by the load are analyzed.After that,the paper illustrates several common coil structures.Then,the influence of metal foreign bodies on the wireless charging system of electric vehicles is analyzed,including magnetic effect and eddy current effect.The eddy current loss and coil parameters are analyzed.The temperature changes of different metal foreign bodies in the actual wireless charging platform are compared,and the necessity of metal foreign bodies detection is summarized.By comparing the effects of metal foreign bodies of different sizes,locations and materials on coil parameters,and verifying by electromagnetic simulation and experiments,a circuit model is built in Matlab to analyze the influence of metal foreign bodies on the output of wireless charging system.Based on the previous analysis,this paper proposes a foreign object detection method based on real-time monitoring of four coil voltages.The key to metal foreign object detection in electric vehicle wireless charging systems is to cope with coil offset and load changes and accurately detect metal foreign objects.In this paper,the structure of the detection coil is designed based on the electromagnetic simulation results.The circuit model of the wireless charging system with detection coil is established.It is found that the induced voltage of the detection coil is only related to the mutual inductance of the coil and the current of the transmitting coil,and the foreign object detection process is designed.In the non-charging phase,the amplitude of the induced voltage of the detecting coil is judged;in the charging phase,the difference between the induced voltages of the four detecting coils is judged.The established circuit simulation model shows that the method used in this paper can accurately detect metal foreign objects.Finally,the composition of 3.3kW wireless charging platform is introduced,including the design of main circuit,control circuit and coupling mechanism.The correctness of foreign objects detection method is verified on the experimental platform.