Determination Scheme of Ferromagnetic Metal Objects Using Detection Coil in Wireless Power Transfer

Abstract

This paper proposes a determination scheme to identify and distinguish ferromagnetic metals from non-magnetic and conductive metals in Wireless Power Transfer (WPT) systems. Ferromagnetic metal, with high conductivity and permeability, generates more heat, but the detection signal is relatively small. In the proposed method, detection coils detect voltage changes caused by foreign objects at two frequencies. The presence and properties of objects are detected by comparing these voltages to reference values. The proposed method reduces the risk of underestimating hazards by preventing ferromagnetic materials from being mistakenly classified as non-magnetic and conductive materials. The effects of magnetization and eddy currents on the detection coil voltage are explained using a circuit model and FEA simulations, and findings are validated by experiment. Experimental results confirm the method's effectiveness in enhancing safety and material identification. © 2024 The Institute of Electrical Engineers of Japan.