Dealing with magnetization effects in EV positioning systems based on periodic magnetic signals

Abstract

This paper presents the general solution to the accuracy problems in magnetic field based positioning systems needed for inductive charging of electric vehicles. These systems process a periodic magnetic signal emitted by the charging coil for its localization. The amplitude is highly distorted by the ferromagnetic vehicle according to an unknown transformation f. Thus, this paper discusses how f is affected by the magnetization process in the material. It is shown that f is proportional to the incremental permeability μΔ which depends on the non-deterministic operating point on the material’s hysteresis curve. However, in this research the same problem is described for the first time from the perspective of Hopkinson’s law, showing that the hysteresis curve is extremely flattened. As a consequence μ△ has in all possible operating points the same value, meaning that f is reproducible, measurable and depends only on the distance d to the coil. Further, it is deduced that f(d) is a strictly monotonously decreasing function, which enables unambiguous coil detection. Finally, the non-monotonous structure of f close to the coil is discussed, and why it is negligible for positioning.