Novel design and control methods for EMF/EMI reduction in automotive wireless power transfer systems

Abstract

Wireless power transfer (WPT) technology is expected to deliver new levels of convenience and safety for the charging of electric vehicles. However, a major problem is that a high-power automotive WPT system is a kind of the intentional magnetic field source generating relatively intense electromagnetic fields (EMFs) to transfer the high power through a large air gap between transmitting and receiving coils. The EMFs can adversely affect human tissues and interfere with vehicle's on-board and adjacent off-board electronics. The aim of this dissertation is to propose novel design and control methods to reduce the magnetic field emission from a loosely-coupled series-resonant WPT system using the magnetic coupling.Firstly, this dissertation proposes a coil design methodology for high efficiency and low magnetic field emission of the WPT system. The results show that the designed coils met the relevant EMF safety guidelines (ICNIRP 1998/2010), and achieved the high power transfer efficiency (PTE) over 95% even underneath the lossy automotive body. After that, for the first time, this study presents the derivation and experimental verification of the minimum conditions of the leakage magnetic fields with a given coil structure.The minimum EMF condition is also reviewed from the magnetic energy perspective, and it is shown that the EMF and PTE reach their optimal values in almost the same condition. Finally, a novel synchronous phase-shift control scheme is proposed and demonstrated by simulation for the selective harmonic elimination of the leakage magnetic fields from the WPT system.