Design of High Sensitivity Foreign Object Detection System in Wireless Charging Based on the Variation of Detection Coils Impedance

Metal foreign objects could enter the wireless power system easily due to the contactless characteristics of primary side and secondary side. Because of eddy current loss, metal foreign objects would not only reduce the system output power and efficiency, but also cause the potential safety hazard. To solve the problem that the conventional approach has low detection sensitivity and blind zone, a design method of high sensitivity foreign object detection system is proposed. Firstly, according to the magnetic induction intensity distribution of the primary coil, the distribution of detection area and the symmetrical structure of detection coils are designed. Secondly, the relationship between the parameters of detection coils and detection sensitivity is analyzed in detailed through the finite element simulation. Then, the excitation frequency of detection circuit is optimized to realize the highest detection sensitivity. Finally, the proposed design is verified by experiments on a LCC-LCC 6.6 kW prototype. As for 1 RMB yuan coin in the position of alignment, corner and 5 mm high, the variation of amplitude of detection signal are 94.1%, 31.8% and 23.18%, respectively.