Low EMF and EMI Design of a Tightly Coupled Handheld Resonant Magnetic Field (HH-RMF) Charger for Automotive Battery Charging

Wireless power transfer (WPT) technology is an electrically safe and convenient method of charging batteries. WPT technology allows elimination of exposed contacts, which can cause direct electrocution of human. In spite of the great advantages, the WPT system inevitably generates strong electromagnetic fields (EMFs), causing interference on the nearby electrical devices as well as harmful influence on human health. Therefore, it is important to satisfy EMF guidelines and reduce leakage magnetic field harmonics in WPT system. For the first time, in this paper, we propose a new tightly coupled handheld resonant magnetic field (HH-RMF) charger operating at 20 kHz with low EMF and high efficiency. Using a guided magnetic flux in resonance structure, 64.5 mG of EMF is reduced compared to the conventional inductive charger at a distance of 200 mm from edge of the core. In addition to the electromagnetic interference (EMI) reduction, the isolation inductor scheme is proposed as an EMI reduction method. Through a series of measurements, we experimentally verified that the proposed HH-RMF charger complies with the regulations published by the International Commission on Non-Ionizing Radiation Protection in 1998. The proposed HH-RMF charger with the isolation inductor scheme successfully reduces the third harmonic of the Tx and Rx currents by 23.4 and 11.8 dBμA, respectively. Furthermore, the third and fifth magnetic field harmonics reduce by 1.38 and 0.67 mG, respectively. The coil-to-coil power transfer efficiency and total system power transfer efficiency of the proposed structure are maintained at over 98% and 84%, respectively.