A foreign object detection coil array that does not affect the power transmission capacity of the wireless power transmission (WPT) system and has no detection blind spots was proposed in view of the problem that metal foreign objects falling into the charging area of electric vehicles affect the electrical characteristics of the system and generate eddy current heating in order to ensure the safety and reliability of the WPT system. The detection coil resonance circuit and control circuit were designed to improve detection sensitivity and accuracy. An electric vehicle WPT system experimental prototype with metal foreign body detection function was built, and the effectiveness and feasibility of the detection method through more than ten common metal foreign bodies were verified. The test results verified that the output voltage of the detection circuit had obvious changes by removing the cans, paper clips and coins from the detection coil. The size and material of various metal foreign objects were different, and the output voltage change rate was different. The effectiveness of the proposed metal foreign body detection method was verified.

Keywords： wireless power transfer ; electric vehicle ; eddy current ; metal object detection