Analytical Equivalent Circuit Extraction of Foreign Metal Objects in WPT Systems

Abstract

Wireless power transfer (WPT) technologies are rapidly attracting attention because of their wide application field. Among them, inductive power transfer (IPT) technology is most promising for daily usage in households. Foreign metal detection (FMD) is indispensable for IPT applications because foreign metal heats up easily in the magnetic field generated by IPT devices and causes a dangerous situation. On the other hand, the representation of the foreign metal as an equivalent circuit model is not readily available. Therefore, we need to use finite element method (FEM)-based electromagnetic field simulators, which require massive computation time and cost. This work proposes a novel simulation method of foreign metal in the magnetic field based on theoretical analysis. We establish an equation-based theory for simulating metal pieces as circuit elements and deliver an equivalent circuit model with a virtual inductance of the metal piece and a mutual inductance between the sense coil and the metal piece. The Z parameter of the extracted circuit model is compared with that of a FEM-based simulator. Evaluation results show that the proposed method returns the result 971 times faster than the FEM-based simulator with the memory usage of 1/3863, while the simulation error is at most 3.88 %