Capacitive power transfer (CPT) system can be employed for wireless charging of drone applications. However, in the CPT system, cross-coupling capacitance caused by coupling of the two pairs of plates on different sides, which do not form the main capacitance must be considered. Designs that do not properly consider the cross-coupling capacitance can cause decrease in the efficiency of the system. In this article, we propose a separate circular capacitive coupler for the CPT system. To reduce the cross-coupling capacitance in drone applications, the plates on the same side are separated. The circuit model of the coupler is presented; it considers a total of six coupling capacitances. For maximum power transfer efficiency, impedance of the receiver is considered to determine the parameter value of the LC resonance. Through simulation and measurement, we verified that the proposed separated circular coupler can reduce the cross-coupling capacitance. The plate-to-plate power transfer efficiency is maintained at 89.4% with 100-W output power.

Recently, maintenance applications around power lines have been actively studied. These applications usually supply power through magnetic energy harvesting(MEH) to devices around the power line. A major challenge for practical MEH is to overcome magnetic saturation, which can cause degradation of power density under a wide current range in the power line. In this paper, we propose a design methodology to harvest maximized output power by considering the saturation effect. To consider magnetic saturation, the output power model and the saturable magnetizing inductance model based on magnetizing current were comprehensively analyzed. Additionally, the critical point of saturation for the maximum harvested power was analyzed by considering different primary side current conditions. With the proposed design methodology, the accuracy and efficiency of the output model were verified with experimental results compared to the conventional model. To consider the real environment, a 150 kW class of AC resistor load bank was implemented to control the primary current from 0 to 100 A with power frequency of 60 Hz. Experimental results show that the proposed method can harvest an average power of 14.32 W on 70 A power line, which is an increase of 39.8 % compared with the conventional design method.

This article proposes transmitter coils selection method for maximum power transfer efficiency in the wireless power transfer (WPT) system with multiple transmitter coils and a single receiver coil (MTSR). The proposed method is divided into two main steps. First, transmitter coil selection criteria that can achieve maximum efficiency are derived by analyzing the relative magnitude of the coupling coefficient between each coil. Next, a method for calculating the relative coupling coefficients used for the criteria only with the input current value is presented. This method differs from previous studies in that it can be applied when some transmission coils are deactivated. Therefore, it is possible to select the optimal transmitter coil combination in consideration of the characteristics of the receiver coil using the proposed method without information on the receiver coil. By the proposed transmitter coils selection criteria, the power transfer efficiency has an average of 96.5 $\pm$ 0.5% when the output power is 300 W, even with the position change of the receiver coil. In addition, it is confirmed that the proposed coupling coefficient extraction method has a slight error of 2.5% compared to the measured value by a vector network analyzer.

For the wireless power transfer (WPT) system in implantable medical devices (IMDs), human tissue is positioned between the transmitting and receiving coils which are different from general WPT systems. Because this space is where the strongest electromagnetic field (EMF) occurs, it is essential to reduce the EMF at the interspace to reduce human exposure to the EMF. In this paper, an out-of-phase coupled WPT system for IMDs is proposed to reduce human exposure to EMF. Considering the EMF exposure and power transfer efficiency (PTE) of the proposed system, a design procedure for determining the phase difference of each capacitor is analyzed and presented. Based on the equivalent circuit model analysis of the proposed system, the EMF and PTE characteristics of the WPT system depending on the design variables are comprehensively analyzed. The proposed system is compared with conventional systems through simulation and measurements. It is verified that the proposed system can reduce the EMF by 41.05% and increase the PTE by 9.62% compared to the conventional system. In addition, through simulation, human exposure to EMFs is assessed considering the exposure environment and electrical properties of human tissues. As a result, the current density, induced electric field, and specific absorption rate were reduced by 44.10%, 38.90%, and 63.82%, respectively.

This article proposes a method of extracting the coupling coefficient and the resonant frequency of the receiving (Rx) side of a wireless power transfer system with an LCC -series topology, using only information from the transmitting (Tx) side. The proposed method has three modes, which allow the Tx coil and the Rx coil inductance and the coupling coefficient to be extracted, respectively. The coupling coefficient can be calculated while considering the tolerance of the coils. The Rx side senses the frequency of the Rx coil current, which is equal to the operating frequency of the inverter. This indicates that which mode the system is in, and the circuit on the Rx side is then modified to fit each mode. Details of the proposed method were analyzed using calculations, and simulations and experiments confirmed the effectiveness of the proposed method. Results showed that the coupling coefficient of the WPT system can be extracted with an error of less than 8%. In addition, the resonant frequency of the Rx side was accurately predicted, and then used as the operating frequency of the WPT system. Up to a 4% increase in efficiency was confirmed in the 80-W-class WPT experiment.

Wireless power transfer (WPT) systems use a magnetic field as the medium for transferring power wirelessly. During the transfer process, there are two magnetic fields, which are called the coupling magnetic field and the leakage magnetic field. The leakage magnetic field can cause electromagnetic field (EMF) and electromagnetic interference (EMI) issues. In WPT systems, when transferring power from source to load, EMF can affect humans due to the strong magnetic field. EMI can cause interference with other electronic devices due to the harmonic magnetic field. Before a WPT system can be commercialized, the EMF and EMI issues must both be solved. Additionally, EMF and EMI regulations must be met. This article proposes a method of designing resonant circuit components to suppress EMF and EMI in WPT systems for electric vehicles (EVs). The processes of suppressing EMF and EMI are explained. The proposed method was verified through simulation and experiment. Results showed that EMF can be suppressed by up to 50%, and EMI can be suppressed by up to 14 dB.