A Self-Resonant Foreign Object Detection System for Metal and Living Object Detection in Electric Vehicle Wireless Charging Systems

In the application process of wireless charging for electric vehicles, foreign object detection (FOD) is one of the necessary measures to address safety issues. This letter proposes a self-resonant FOD method for metal object (MO) and living object (LO) detection. It is possible to detect an MO and an LO without being affected by the 85-kHz power transmission, without the need for a detection coil specifically designed to decouple from the power transmission coil and a high-pass filter. Each self-resonant detection coil consists of a unipolar coil and a comb-shaped capacitor plate. This letter describes a method that can identify an MO and an LO by scanning frequencies within a small range and detecting the slope of the output voltage as it changes with frequency. When there are no foreign objects, the absolute value of the output voltage slope is less than 0.15. The voltage slope less than -0.15 indicates the presence of MOs, while a slope greater than 0.15 indicates the presence of an LO. To verify the feasibility of the proposed method, an experimental prototype has been constructed.