Phase-detection-based metal objects and pick-up coils detection scheme without malfunction in wireless power transfer system

Metal object detection (MOD) and detection of position (DoP) of pick-up coils are increasingly critical to the commercialisation of the wireless power transfer system. In this study, a detection scheme based on phase-detection, which can both realise the function of MOD and DoP, is newly introduced. The method is based on the principle that the presence of metal objects and pick-up coils both affect the impedance phase of the detection coil loop. Comparing with the traditional detection methods, which is based on measuring the absolutely value of impedance in detection loop, the malfunction is avoided by adopting phase difference as the criterion of the existence of metal objects and pick-up coils. An inexpensive and high-precision sensing circuit is newly designed to acquire the phase difference accurately. Simulation models and experiments are conducted to verify the feasibility of the proposed detection scheme. The Δ δ of the detection coil circuit with a coin placed reaches −5.17, while the Δ δ of other detection coils without metal objects keeps zero. In the meantime, the position of the pick-up coil is identified because the Δ δ of these detection coils closer to the centre of the pick-up coil varies more significantly while other coils vary slightly.