Chiuk Song

Coil Design and Measurements of Automotive Magnetic Resonant Wireless Charging System for High-Efficiency and Low Magnetic Field Leakage

For wireless charging of electric vehicle (EV) batteries, high-frequency magnetic fields are generated from magnetically coupled coils. The large air-gap between two coils may cause high leakage of magnetic fields and it may also lower the power transfer efficiency (PTE). For the first time, in this paper, we propose a new set of coil design formulas for high-efficiency and low harmonic currents and a new design procedure for low leakage of magnetic fields for high-power wireless power transfer (WPT) system. Based on the proposed design procedure, a pair of magnetically coupled coils with magnetic field shielding for a 1-kW-class golf-cart WPT system is optimized via finite-element simulation and the proposed design formulas. We built a 1-kW-class wireless EV charging system for practical measurements of the PTE, the magnetic field strength around the golf cart, and voltage/current spectrums. The fabricated system has achieved a PTE of 96% at the operating frequency of 20.15 kHz with a 156-mm air gap between the coils. At the same time, the highest magnetic field strength measured around the golf cart is 19.8 mG, which is far below the relevant electromagnetic field safety guidelines (ICNIRP 1998/2010). In addition, the third harmonic component of the measured magnetic field is 39 dB lower than the fundamental component. These practical measurement results prove the effectiveness of the proposed coil design formulas and procedure of a WPT system for high-efficiency and low magnetic field leakage.

Shielded coil structure suppressing leakage magnetic field from 100W-class wireless power transfer system with higher efficiency

In this paper, the shielded coil structure using the ferrites and the metallic shielding is proposed. It is compared with the unshielded coil structure (i.e. a pair of circular loop coils only) to demonstrate the differences in the magnetic field distributions and system performance. The simulation results using the 3D Finite Element Analysis (FEA) tool show that it can considerably suppress the leakage magnetic field from 100W-class wireless power transfer (WPT) system with the enhanced system performance.

An Investigation of Electromagnetic Radiated Emission and Interference From Multi-Coil Wireless Power Transfer Systems Using Resonant Magnetic Field Coupling

Wireless power transfer (WPT) technology has recently emerged as an innovative and promising technology, and its electromagnetic compatibility (EMC) has become a significant issue. In this study, we investigated the electromagnetic (EM) radiated emission and interference generated by WPT systems using resonant magnetic field coupling, especially in applications with multi-coil configurations. The change in coil resonance associated with multi-coil configurations was analyzed via the impedance profile. We measured the EM radiated emission and analyzed the results with respect to the coil resonance. An analog-to-digital converter chip was designed and fabricated to analyze the effect of electromagnetic interference (EMI). Based on measurement and simulation results, we verified that the EM radiated emission and interference increase at the series or parallel resonance peaks, depending on the source type. In addition, we verified that EMI can be reduced by using ferrite sheet shielding.

Thin PCB-Type Metamaterials for Improved Efficiency and Reduced EMF Leakage in Wireless Power Transfer Systems

Current wireless power transfer (WPT) technology can only allow power transfer over a limited distance because, as the distance between the transmitter (Tx) and receiver (Rx) coils increases, the power transfer efficiency (PTE) decreases with a steep slope, while the electromagnetic field (EMF) leakage increases. In order to increase the PTE and decrease the EMF leakage simultaneously, we need to develop a method to concentrate the magnetic fields between the Tx and Rx coils. In this paper, we proposed a novel metamaterial structure to realize high efficiency and low EMF leakage. Metamaterials can confine the magnetic fields between the Tx and Rx coils by negative relative permeability. We designed and fabricated a thin metamaterial using a 1.6-mm dual layer printed circuit board (PCB) with a high dielectric constant substrate and a fine pattern to achieve a negative relative permeability with low loss at 6.78 MHz. The thin PCB-type metamaterial has a wide range of applications with low fabrication cost, light weight, and a simple fabrication process. We demonstrated a 44.2% improvement in the PTE and 3.49-dBm reduction in the EMF leakage around the WPT system at 20-cm distance. Furthermore, we first analyzed metamaterials from an EMF point of view using the 3-D magnetic field scanner. Finally, we discussed a combination of metamaterials and ferrites to further improve the PTE and reduce the EMF leakage for long-distance mobile WPT systems.

Structure of handheld resonant magnetic coupling charger (HH-RMCC) for electric vehicle considering electromagnetic field

Inductive charging is a convenient method to transfer electrical power from a source to the batteries without any electrical contact. The problem is that inductive charging technologies may have electromagnetic compatibility (EMC) issues caused by leakage magnetic field. In this paper, an inductive charger design for electric vehicles (EVs) named as Handheld Resonant Magnetic Coupling Charger (HH-RMCC) is proposed. The air gap and thickness of the ferrite core are determined considering the core saturation and leakage magnetic field. The maximum value of the simulated magnetic flux density at the distance of 200 mm away from the charger is 2.28 mG and the simulation result of the power transfer efficiency is approximately 99.5%. The simulation results using 3D Finite Element Analysis (FEA) tool show that HH-RMCC satisfies EMF regulation published by the International Commission on NonIonizing Radiation and Protection (ICNIRP) at the frequency of 20 kHz with high performance.

Design of conductive shield for wireless power transfer system for electric vehicle considering automotive body

In this paper, we quantitatively investigated the undesirable effects of the automotive body on the performance of and the magnetic field distribution around the wireless power transfer (WPT) system for electric vehicle (EV), and what is more, we found that the magnetically coupled coils of WPT system for EV can almost completely be shielded from the detrimental influences of the automotive body by employing the intermediate conductive shield only with the diameter which is at least 4 times larger than the air gap length. The simulation and measurement data show that, by employing the intermediate conductive shield, the spot value of the magnetic near field is reduced by at least 70 % and the power transfer efficiency as high as 96 % can be achieved under the automotive body.

Three-phase magnetic field design for low EMI and EMF automated resonant wireless power transfer charger for UAV

Wireless power transfer (WPT) technology enables convenient and automatic battery charging for unmanned aerial vehicles (UAVs). However, in WPT charging systems, strong electromagnetic fields (EMFs) are inevitably generated and the power source contains a wide range of harmonics. In this paper, we propose an automated resonant wireless power transfer charger for UAV with three-phase magnetic field for electromagnetic interference (EMI) and EMF reduction. The simulation results show that the proposed six-step three-phase resonant WPT system for UAV charging reduces the total harmonic distortion (THD) of the Tx and Rx currents by 14.21% and 7.45%, respectively. The strength of magnetic field from the UAV three-phase resonant WPT charging system also can be reduced compared to the single-phase resonant WPT system.

Electromagnetic interference and radiation from wireless power transfer systems

Wireless power transfer (WPT) technology is becoming increasingly popular for wireless charging of mobile phones and electrical vehicles. Because high power energy is transferred via air, however, the problem of electromagnetic radiated emission from WPT systems is expected to be serious. In this paper, an electromagnetic interface (EMI) and radiation from WPT systems are discussed. Three example technologies for suppressing the electromagnetic-field (EMF) noise and EMI noise from WPT systems are presented. EMF noise from different receiving (RX) coil topologies is characterized and an EMF noise suppression technology using a ferromagnetic material and metallic shielding is analyzed. A handheld resonant magnetic coupling charger (HH-RMCC), a WPT system with very low EMI noise, is then introduced. The proposed technologies for suppressing EMF and EMI noise from a WPT system will be helpful to design engineers.

Electromagnetic interference reduction method from handheld resonant magnetic field charger (HH-RMFC) for electric vehicle

The proposed handheld resonant magnetic field charger (HH-RMFC) is a convenient method of charging batteries in electric vehicle (EV) without any electrical contact. With close distance between Tx and Rx windings, high mutual inductance causes large reflected impedance seen by the power source. The large reflected impedance can cause distortion of current flowing through Tx and Rx windings. In frequency-domain, the distortion of current produces large current harmonics, which may have electromagnetic compatibility (EMC) issues caused by leakage magnetic field. To quantify the distortion of current, the total harmonic distortion (THD) is used. In this paper, the design method for low EMI from the HH-RMFC for EV are proposed and verified using a circuit simulator. The circuit simulation results show that THD of Tx and Rx current is below 5% using proposed method.

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.