• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.250-255
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• 2018

This paper presents a method for minimizing standby power consumption in wireless power transfer (WPT) system via magnetic resonance coupling (MRC) that operates at 6.78 MHz. The proposed circuit controls the required capacitance according to operational condition in order to reduce standby power consumption. Based on an impedance characteristic of the class-E power amplifier, operational principles of the proposed circuit are analyzed. Moreover, to verify the effectiveness of the proposed class-E power amplifier, an 8 W prototype for WPT system is implemented. The measured input power of the proposed class-E power amplifier at standby condition is reduced from 5.81 W to 3.53 W.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.152-153
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• 2014

본 논문에서는 이차전지의 특성비교/분석을 위해 이산 웨이블릿 변환(DWT;discrete wavelet transform)과 웨이블릿 패킷 변환(WPT;wavelet packet transform)을 적용한 연구를 소개한다. 다해상도 분석(MRA; multi resolution analysis)의 시간-주파수 분석을 통해 저주파 성분(approximation;$A_n$)과 고주파 성분(detail;$D_n$)로 분해되는 것은 두 방법 동일하다. 하지만, 이산 웨이블릿 변환이 단순히 저대역 부분만 계속 분해하는 것과 달리 웨이블릿 패킷 변환은 저대역과 고대역을 모두 분해하여 높은 분해성능을 가지는 웨이블릿의 일반화이다. 웨이블릿 패킷 변환을 자세히 소개하고 이를 이차전지에 적용하여 이산 웨이블릿 변환과의 상관성을 정리하였다.

• Journal of Power Electronics
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• v.19 no.2
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• pp.602-611
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• 2019

The major drawbacks of magnetic resonant coupled wireless power transfer (WPT) to the embedded sensors on spindles are transmission instability and low efficiency of the transmission. This paper proposes a novel double-loop coil design for wirelessly charging embedded sensors. Theoretical and finite-element analyses show that the proposed coil has good transmission performance. In addition, the power transmission capability of the double-loop coil can be improved by reducing the radius difference and width difference of the transmitter and receiver. It has been demonstrated by analysis and practical experiments that a magnetic resonant coupled WPT system using the double-loop coil can provide a stable and efficient power transmission to embedded sensors.

• 전기의세계
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• v.66 no.1
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• pp.32-37
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• 2017

본 고에서는 무선전력전송(WPT) 분야에 메타재질(Metamaterial)구조 기술이 어떻게 접목되고 있는지가 다뤄진다. 전기공학의 중요한 테마가 된 무선전력전송과, 주로 고주파 영역에서 등장하는 메타재질구조와는 괴리가 있다고 느껴질 수도 있으나, 근원이 전류이고 자기장에 의한 송수신 사이의 결합이라는 점에 기반을 두고 있다는 점에서 접목 가능성은 충분하다. 따라서, 자속과 유효 투자율 증가가 가능한 자기장형 메타재질구조에 의한 무선전력전송 시스템의 성능향상법을 국외 사례 및 필자의 WPT 과제수행 경험을 근간을 제시한다.

• JOURNAL OF ELECTRICAL WORLD
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• s.442
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• pp.64-66
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• 2013

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.4
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• pp.684-688
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• 2016

The magnetic resonance method requires high quality factor(Q-factor) of resonators. Superconductor coils were used in this study to increase the Q-factor of wireless power transfer(WPT) systems in the magnetic resonance method. The results showed better transfer efficiency compared to copper coils. However, as superconducting coils should be cooled below critical temperatures, they require cooling containers. In this viewpoint, shielding materials for the cooling containers were applied for the analysis of the WPT characteristics. The shielding materials were applied at both ends of the transmitter and receiver coils. Iron, aluminum, and plastic were used for shielding. The electric field distribution and S-parameters (S11, S21) of superconducting coils were compared and analyzed according to the shield materials. As a result, plastic shielding showed better transfer efficiency, while iron and aluminum had less efficiency. Also, the maximum magnetic field distribution of the coils according to the shielding materials was analyzed. It was found that plastic shielding had 5 times bigger power transfer rate than iron or aluminum. It is suggested that the reliability of superconducting WPT systems can be secured if plastic is used for the cooling containers of superconducting resonance coils.

• Journal of electromagnetic engineering and science
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• v.11 no.3
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• pp.166-173
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• 2011

In this paper, we implemented and analyzed a wireless power transfer (WPT) system with a CSPR topology. CSPR refers to constant current source, series resonance circuit topology of a transmitting coil, parallel resonance circuit topology of a receiving coil, and pure resistive loading. The transmitting coil is coupled by a magnetic field to the receiving coil without wire. Although the electromotive force (emf) is small (about 4.5V), the voltage on load resistor is 148V, because a parallel resonance scheme was adopted for the receiving coil. The implemented WPT system is designed to be able to transfer up to 1 kW power and can operate a LED TV. Before the implementation, the EMF reduction mechanism based on the use of ferrite and a metal shield box was confirmed by an EM simulation and we found that the EMF can be suppressed dramatically by using this shield. The operating frequency of the implemented WPT system is 30.7kHz and the air gap between two coils is 150mm. The power transferred to the load resistor is 147W and the real power transfer efficiency is 66.4 %.

• Journal of electromagnetic engineering and science
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• v.19 no.1
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• pp.48-55
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• 2019

Unmanned aerial vehicles (UAVs) using communications, sensors, and navigation equipment will play a key role in future warfare. Currently, UAVs are monitored to prevent misfire and accidents, and the conventional method adopted uses wires for data transmission and power supply. The repeated connection and disconnection of cables increases maintenance time and harms the connector. For convenience and stability, a wireless power transfer system to power UAVs is needed. Unlike other wireless power transfer (WPT) applications, the size of the receiving coils must be small, so that the WPT systems can be embedded inside space-limited UAVs. The small size reduces the coupling coefficient and transfer efficiency between the transmitting and the receiving coils. In this study, we propose a toroidal-shaped coil for a WPT system for UAVs with high coupling coefficient with minimum space requirements. For validation, conventional coils and the proposed toroidal-shaped coil were used and their coupling coefficient and power transfer efficiency were compared using simulated and measured results. The simulated and measured results were strongly correlated, confirming that the proposed WPT system significantly improved efficiency with negligible change in the space requirement.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.3
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• pp.485-489
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• 2018

Studies have been actively conducted on the magnetic-resonance wireless power transmission (WPT) for commercialization. Such studies are essential for improving the transmission efficiency. In the magnetic-resonance WPT, the inductance (L) and capacitance (C) vary significantly depending on the design of the coils, and the efficiency sharply changes accordingly. To address this problem, studies on the coil design are required. In this study, the S-parameter characteristics according to the number of turns of the coil were analyzed to improve the efficiency of the superconducting WPT. Superconducting coils were designed, and the reflection coefficient ($S_{11}$) according to the turns was analyzed. It was confirmed that the power transmission characteristics were improved as the reactance approached $0{\Omega}$

• Journal of Power Electronics
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• v.18 no.4
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• pp.1268-1277
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• 2018

A relatively high operating frequency is required for efficient wireless power transfer (WPT). However, the alternating current (AC) resistance of coils increases sharply with operating frequency, which possibly degrades overall efficiency. Hence, the evaluation of coil AC resistance is critical in selecting operating frequency to achieve good efficiency. For a Litz wire coil, AC resistance is attributed to the magnetic field, which leads to the skin effect, the proximity effect, and the corresponding conductive resistance and inductive resistance in the coil. A numerical calculation method based on the Biot-Savart law is proposed to calculate magnetic field strength over strands in Litz wire planar spiral coils to evaluate their AC resistance. An optimized frequency can be found to achieve the maximum efficiency of a WPT system based on the predicted resistance. Sample coils are manufactured to verify the resistance analysis method. A prototype WPT system is set up to conduct the experiments. The experiments show that the proposed method can accurately predict the AC resistance of Litz wire planar spiral coils and the optimized operating frequency for maximum efficiency.