Equivalent-Circuit-Based Design of Symmetric Sensing Coil for Self-Inductance-Based Metal Object Detection

Van X Thai,Seog Y Jeong,Yun-Su Kim,Chun T Rim,Jun H Park

doi:10.1109/access.2020.2995210

Abstract

A symmetric sensing coil design is proposed and adapted for the self-inductance-based metal object detection (MOD) of wireless electric vehicle (WEV) charging. Compared to conventional non-symmetric sensing coils, the proposed sensing coil provides symmetric detection sensitivity and ease of manufacturing, pertaining blind-zone-free characteristics. Moreover, it is found that the design of the proposed symmetric sensing coil is very different from that of the symmetric sensing coil for conventional induced voltage sensing (IVS) based MOD method due to different principles of MOD methods. Therefore, an analysis based on a newly proposed equivalent circuit, is used to design a high sensitivity symmetric sensing coils, considering many aspects such as metal object covering, metal object size, and mutual inductance between sensing coils. Based on the analysis, an optimized sensing coil design created through a finite element method simulation is proposed to achieve highest sensitivity with the lowest number of sensing coils. It can be readily applied to a cost-effective MOD system that can be used for high-power WEV charging. Experiments on a metal object 20 mm $\times20$ mm in size with a 20Arms Tx current verified high detection sensitivity of 38% without any blind zones.

Highlights

Inductive power transfer (IPT) for wireless electric vehicle (WEV) charging involves managing significant technical issues, such as the power transfer capability, efficiency, and tolerances [1]–[11]
While electromagnetic field (EMF) cancellation provides safety for humans by reducing or shielding the EMF generated by an IPT system, foreign object detection (FOD) is mainly related to the safety and reliability of IPT systems themselves by detecting objects which may harm the system
With the symmetric sensing coil design, every sensing coil has an identical number of turns; induced voltage becomes zero automatically, manufacture and design the sensing coil become much easier, the adjustment of the number of turns is unnecessary, and most importantly, the detection sensitivity over the entire Tx pad can become symmetric, which reduces the risk of blind-zone existence

Summary

INTRODUCTION

Inductive power transfer (IPT) for wireless electric vehicle (WEV) charging involves managing significant technical issues, such as the power transfer capability, efficiency, and tolerances [1]–[11]. The blind-zone problem can be solved by modifying the sensing coils, the IVS type still has a big disadvantage since it cannot work when the IPT system is turned off, as the magnetic field does not exist. With the symmetric sensing coil design, every sensing coil has an identical number of turns; induced voltage becomes zero automatically, manufacture and design the sensing coil become much easier, the adjustment of the number of turns is unnecessary, and most importantly, the detection sensitivity over the entire Tx pad can become symmetric, which reduces the risk of blind-zone existence It stems from the symmetric sensing coil idea in [32], the design of the symmetric sensing coil proposed in this paper is very different from the sensing coil design for IVS type due to the fact that the principle of IVS and SIRC methods are different. The analysis and optimization are verified by the FEM simulations and power experiments with 3.3 kW IPT system for WEV charging at the Tx current of 20 Arms

CONCEPT OF THE PROPOSED SYMMETRIC SENSING COIL

DESIGN OF THE PROPOSED SYMMETRIC SENSING COILS

EXPERIMENTAL VERIFICATION

Findings

CONCLUSION