Determination Method of Target Material and Coil Area Based on Average Magnetic Flux Density for Metal Object Detection of Dynamic WPT

Abstract

The detection of foreign metal objects is an essential technology to ensure the safety of the wireless power transfer (WPT) systems. The standards of required detection targets and areas have already been proposed for the static WPT (S-WPT) system. However, for the dynamic WPT (D-WPT) system, it is necessary to take into account that the magnetic field varies with the position of the receiver coil. This paper proposes a method to determine the detection targets and area for the D-WPT system. First, the average of the magnetic flux density during one charge in D-WPT is calculated using an electromagnetic field simulator. Next, the average magnetic flux density is applied to various metal plates using the S-WPT test bench, and its temperature is observed. The applying period is the same as the D-WPT driving situation. Finally, the magnetic flux density at the point when the saturation temperature of each metal reaches $80^{\circ}\text{C}$ is used as the threshold value, and the required detection area is determined by comparing it with the average magnetic flux density distribution. The proposal was experimentally verified using our developed WPT system, whose rated power is 20 kW. This proposal is helpful because the test can be conducted without moving the receiver coil, and can clearly define the required detection target and area for the foreign metal objects in the D-WPT system.