Development of Foreign Object Detection Systems with Blind-zone Reduction and Low-Noise for Electric Vehicle Wireless Charging

Abstract

Nowadays, with the development of wireless power transfer (WPT) technology in general and inductive power transfer (IPT) technology in particular, the commercialization of a wireless electric vehicle (WEV) is no longer a far future. However, the danger caused by foreign objects to the WEV charging system remains one of the biggest problems, which prevents the commercialization of WEV. Although there exist a variety of researches on foreign object detection (FOD) system for WEV charging, it is found that the existing FOD technology still have many drawbacks. Throughout this doctoral dissertation, essential technologies for solving the drawbacks of FOD technique, which includes reducing blind-zone and enhancing signal to noise ratio in FOD system for WEV charging, are widely researched. The dissertation can be divided into two parts, which correspond to two types of FOD technique: metal object detection (MOD) technique, and living object detection (LOD) technique. First, for MOD technique, solutions of symmetric sensing coils, which can be applied to both induced voltage sensing (IVS) type and self-inductance with resonant circuit (SIRC) type, are newly proposed. The symmetric sensing coil solutions can offer several great advantages, of which the biggest one is to reduce/eliminate the blind-zone, i.e. the region on the transmitting (Tx) pad where metal object cannot be detected. However, because of different operational principles of IVS type and SIRC type, the design and principle of symmetric sensing coils of two types are different. Therefore, to clarify the difference and to provide an insight on how to design a symmetric sensing coil, an equivalent circuit model of symmetric sensing coils for SIRC type is proposed, together with an optimized design for the sensing coils. Second, for living object detection (LOD) technique, the dissertation focuses on the method where a capacitive sensor is used for detecting the capacitance change caused by a living object. A sensing circuit based on Wheatstone bridge circuit is newly proposed in order to replace the conventional sensing circuit. The Wheatstone bridge based circuit offers many advantages such as low-cost, compact size and high signal-to-noise ratio. More importantly, to reduce/eliminate the high order harmonic noise coupled between Tx coil and the sensing electrodes of the LOD system, which is the main problem of FOD system in any high power WEV charging application, a design of a comb-pattern electrostatic shield is proposed. The design of the electrostatic shield is proved effective in reducing high frequency noise significantly on the capacitive sensor. We believe that all works in this dissertation will contribute to solving the existing problems of FOD technology, and our hope is that it will play an important role in both FOD research and commercializing WEV technology.