Noncooperative Metal Object Detection Using Pole-to-Pole EM Distribution Characteristics for Wireless EV Charger Employing DD Coils

Abstract

Metal object detection (MOD) is indispensable for wireless electric vehicle charging (WEVC) systems for safety concerns. Most recently, interests are growing in MOD by electromagnetic (EM) sensing. However, current works based on EM sensing rarely target the systems with DD coils, a promising coil type for commercialization. Additionally, EM sensing schemes are mostly derived from a mindset, viz., cooperation between two sensing coils to obtain the voltage difference as a MOD criterion. Hence, undesired out-of-phase incident becomes an inherent problem jeopardizing the success rates of detection. In this article, noncooperative MOD, which solely relies on the voltages of individual sensing coils rather than cooperative ones, is proposed with absolute confidence in detection results. A unique sensing coil array is devised to suit the field characteristics of DD coils perfectly. Size-modulated patch coils are created to eliminate the undetectable zones with proper polarity configuration. Moreover, virtual double-layer sensing coils are constructed to enhance MOD's reliability. Tested by 13 different positions and three types of MOs using a 3.0-kW WEVC prototype, the induced voltages reach at least four times the threshold value. Moreover, the stability of the proposed method is verified successfully no matter the system operates in light-load or heavy-load conditions.