Impact and Detection of Foreign Metal Objects in Multi-User Wireless Power Transfer System

Abstract

Presence of foreign metal object in multi-user wireless power transfer (WPT) system has a negative impact on the performance of the system. In this paper we evaluate impact of foreign metal object on the performance of the WPT system. Measurements have shown that metal object placed in the magnetic field of the transmitter coil decreases the transmitter coil inductance for up to 12%. It also decreases the quality factor of the transmitter coil up to 58 %. This increases the losses in transmitter and lowers the overall efficiency of the WPT system. Eddy currents in foreign metal objects cause the increase of induced voltage on the receiver coil up to 30%. Different methods for foreign metal object detection are discussed in paper. Measurements have confirmed that proposed step response method can be used to accurately detect foreign metal objects in multi-user WPT system. The method can be used on-the-fly and can be implemented on the transmitter side without any modification on the receiver circuits.