A Misalignment Tolerant Foreign Object Detection for EV Wireless Charging Applications

This paper presents a new foreign object detection (FOD) sensor coil layout that is robust against the misalignment of the wireless charging system. In a wireless charging system, it is important to detect the presence of metal objects to avoid overheating them due to eddy losses generated by the magnetic field of the transmitter coil. Conventionally, an array of symmetrically placed coils is used to detect metal objects. The voltage difference between complementary pairs of coils is measured and compared with previous measurements. The presence of the metal object changes the induced voltage across the sensor coil facing the metal object. If any deviation from previously measured differential voltages between complementary coils is detected, the FOD system will trigger, and the metal object will be detected. In an EV wireless charging application, misalignment of the charging pads is inevitable due to driver inaccuracy. Conventional FOD methods fail to operate under misalignment conditions due to unsymmetrical design with respect to the misalignment of the coils. In this paper, by designing the sensor coils symmetrical with respect to the misalignment direction, the proposed FOD system can operate indifferently to charging coil misalignment.