Foreign Object Detection in a Wireless Power Transfer System Using Symmetrical Coil Sets

In this paper, a foreign object detection (FOD) method based on symmetrical coil sets is proposed to prevent wireless power transfer (WPT) systems from heating, which could possibly cause an accidental fire. First, the influence of a foreign metal object on the magnetic field distribution of the WPT system is analyzed. Then, a two-layer symmetrical detection coil set is proposed considering the magnetic field characteristics. This kind of FOD method can reduce the design complexity, and the detection strategy is easily realized. The mutual inductance variation patterns are used to detect the presence and location of metal objects. Four scenarios of foreign object intrusion, including one coin with different locations, a coin on top of two adjacent detection coils with the same cover area, different test bodies, and different numbers of coins, are taken into consideration for validating the effectiveness of the proposed FOD method. Finally, a WPT system prototype with symmetrical coil sets for FOD detection is established. Both the simulation and experimental results indicate that the proposed method can effectively detect the presence and location of foreign objects.