Vehicle position measurement and misalignment-effect-eliminated metal object detection for wireless EV charging system: A dual-purpose design of sensing coils

Vehicle Position Measurement (VPM) and Metal Object Detection (MOD) are indispensable to facilitate the commercialization of wireless charging systems for electric vehicles (EVs). In this paper, these two functions are integrated to the charging systems by simply adding a set of two-layer sensing coils. The proposed MOD method takes the advantage of symmetrical magnetic field produced by coupling coils and the uniform field distribution in the center area. By detecting the induced voltage difference of sensing coils, not only the existence of metal objects is checked, but also their positions could be obtained. Moreover, this method also provides a superior performance in view of easy fabrication, high sensitivity and no-blind-zone characteristic. More importantly, this method takes the effect of misalignment of EVs on the object detection accuracy into account by introducing a self-zero-setting method. The VPM function is realized by calculating the mutual inductance of receiving coils and sensing coils online with the virtue of the inherent resonance nature of charging circuit. The proposed design is verified by finite element simulations. When an iron nail appears in the transmitting coils, the voltage difference of corresponding sensing coil exceeds 0.4 V, which is normally lower than 0.1 V.