• Journal of Power Electronics
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• 제18권4호
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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.

• 전기학회논문지
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• 제64권11호
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• pp.1651-1657
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• 2015

In MHz operating wireless power transfer systems, skin- and proximity-effect losses in the transmitter and the receiver coils dominate the coil-to-coil efficiency of the system. A Litz-wire was regarded as a common solution for minimizing such Ohmic losses in high frequencies. In this paper, equivalent series resistances of 12 different cables including Litz-wire and copper tubing have been calculated and measured for a 6.78 MHz, 100W, 30 cm wireless power transfer system. It has been shown that the copper tubing has lower resistances compared to the Litz-wire in that frequency and a wireless power transfer system with the copper tubing was able to achieve much higher efficiency than a system using the Litz-wire. Calculations of the resistances and efficiencies were accomplished with analytical equations and those calculations were evaluated by experimental results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.1037-1039
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• 2002

가전산업과 연계하여 유도가열 기술을 응용한 대표적인 시스템으로 IH압력밥솥을 예로 들 수 있다. 유도가열 코일에서 고주파 자속의 의해 발생된 와전류가 결합된 밥솥을 가열하기 때문에 유도가열 코일에는 고주파 손실을 줄이기 위해 Litz wire가 사용된다 이에 본 논문은 특히 IH압력밥솥에 사용되는 Litz wire를 선정하는 데 있어 중요한 요소가 되는 소선경, 가닥수별 AC DC 저항 및 손실계산 그리고 Cost 예측 방법을 제안한다.

• 한국초전도ㆍ저온공학회논문지
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• 제25권4호
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• pp.45-49
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• 2023

CORC, which is being studied as one of the conductors for large currents, is manufactured by symmetrically arranging several strands of high-temperature superconducting wires on a cylindrical former. It allows current to flow evenly between wires and has the advantage of being manufactured in a multi-layer structure to increase current capacity. In order to apply CORC to AC power devices, it is necessary to review the material of the former, which is the frame around which the superconducting wire is wound. In the case of metal formers, they are difficult to apply because eddy currents are generated in the former, and they do not have the flexibility to be manufactured into coils by winding them with CORC. In this paper, we compare and analyze the magnetization loss caused by an external alternating magnetic field of Litz wire, which is being considered as a former material for CORC, with the results from formers made of other materials. In addition, we experimentally examine the effect of reducing magnetization loss due to an external magnetic field in CORC using a split wire made by dividing a high-temperature superconducting wire into two using an etching method, and in CORC made with a non-split wire.

• 한국산학기술학회논문지
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• 제12권3호
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• pp.1302-1307
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• 2011

본 논문은 코일 제작 시 고려사항인 1, 2차측 코일 인덕턴스, 턴수, 크기, 두께, 차폐지 등을 고려하여 리쯔 와이어로 나선형 코일을 제작하는데 이때 반자동화 권선기를 사용하게 된다. 1, 2차측 코일 사양을 정하여 코일을 제작할 때 다양한 사양의 리쯔 와이어와 나선형 코일을 필요로 하게 되는데, 이때 제작 비용, 기간, 제작 시 발생하는 불량 등으로 인해 코일 샘플 제작에 어려움이 발생하고 원하는 사양의 코일 품질 관리에도 어려움이 생기게 된다. 이를 개선하기 위해 2차측의 정류부를 개선함으로써 코일 설계 및 제작 시 다양한 코일 제작 사양의 범위를 좀더 포괄적으로 할 수 있으며 제작 시 발생하는 비용을 줄이고, 기간 단축 및 코일의 품질 관리를 개선하고자 한다.

• 전기전자학회논문지
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• 제27권4호
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• pp.587-600
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• 2023

본 논문에서는 315W급 65인치 UHD-TV용 LLC DC to DC 공진 컨버터에 사용되고 있는 Slim형 고주파 변압기의 최적화 설계에 대해서 나타낸다. 또한 본 논문에서는 LLC 공진 변압기의 코어 손실 분석, AC 권선 손실 분석 및 권선 배치 최적화 설계를 통해 Slim형 고주파 변압기의 최적화 설계를 수행한다. 특히 본 논문에서는 이론적으로 해석하여 얻어진 결과를 토대로 고효율 및 Slim형 고주파 변압기는 교류 권선 손실 최소화 및 권선 자동화를 위하여 인터리브 및 수직형 권선 구조로 구성한다. 본 논문 제안한 수직형 권선 구조 방식의 Slim형 고주파 변압기의 1차측 권선은 Litz 권선을 2차 권선은 PCB와 동판 권선을 사용하였다. 최종적으로 Maxwell 2D 및 3D Tool을 이용한 시뮬레이션 결과를 토대로 이론 해석의 정당성을 입증하기 위해서 실험 결과를 통해 본 논문에서 제안한 Slim형 고주파 변압기의 최적화 설계를 수행하였다.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2003년도 춘계학술발표논문집
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• pp.267-270
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• 2003

All artificial infernal organs which are using electric energy supply energy with inductive couple. Transcutaneous energy transmission system enhance survival chance of the patients and quality of life by reducing volume and mass. In this research, we used both tune in transmission system in state of fixing cycle in order to increase the voltage gain and the current gain and to reduce effect of leakage inductance. Also to maximize the effect of resonance, a constant frequency duty cycle control method is used. Test is progressed with litz wire which is set up with various sizes of core to minimize size of converter. This research aimed in analysis of transcutaneous energy transmission system and in measuring of stability and efficiency of Lithium-ion battery charge which are using transmitted energy.

• 한국전자파학회논문지
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• 제22권9호
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• pp.820-826
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• 2011

본 논문에서는 자기 공명 방식의 무선 전력 전송 시스템에서 효율 향상 방안을 제시하였다. 공진 코일은 헬리컬과 스파이럴 형태가 결합된 구조를 제안하였으며, 소스와 디바이스 코일은 단일 원형 루프 형태로 설계하였다. 측정 결과, 송수전 코일이 120 mm의 거리로 이격되어 있을 때 헬리컬과 스파이럴 구조를 결합한 공진기는 기존의 헬리컬 구조의 공진기보다 효율이 13 % 향상되는 결과를 보였다. 뿐만 아니라, 크기도 기존 공진기에 비해 33 % 소형화할 수 있었다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제48권8호
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• pp.400-407
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• 1999

This paper treated the design, manufacture and the performance characteristics under each mode of high speed motor/generator for an electro-mechanical battery(EMB). This machine is employed as an integral part of a flywheel energy storage system(FESS), i.e., a modular flywheel system to be used as a device for storing electrical or mechanical energy. In this machine, the magnetic field system is constructed by using special magnet array, dipole Halbach array with 16 permanent magnet segments and the armature is composed of a plastic bobbin and multi-phase windings with Litz wire. The magnet array produces a highly uniform dipole field without back iron. The motor/generator is 3-phase machine in which the dipole Halbach array surrounding the winding is rotating. Since there are no iron laminations, this field system offers some unique advantages for the simplicity of the design and the theoretical prediction of characteristics of a high speed electric machine. This paper describes the results obtained when EMB system was tested in the laboratory.

• Journal of Power Electronics
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• 제17권3호
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• pp.835-847
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• 2017

A transmitting coil with an optimal topology and number of turns can effectively improve the performance of the wireless power transfer (WPT) systems for endoscope robots. This study proposes the evaluation parameters of the transmitting coils related to the performance of the WPT system to standardize the design of the transmitting coils. It considers both the quality factor of transmitting coils and the coupling factor between the two sides. Furthermore, an analytical model of transmitting coils with different topologies is built to exactly estimate the evaluation parameters. Several coils with the specified topologies are wound to verify the analytical model and the feasibility of evaluation parameters. In the case of a constant power received, the related evaluation parameters are proportional to the transfer efficiency of the WPT system. Therefore, the applicable frequency ranges of transmitting coils with different topologies are determined theoretically. Then a transmitting coil with a diameter of 69 cm is re-optimized both theoretically and experimentally. The transfer efficiency of the WPT system is increased from 3.58% to 7.37% with the maximum magnetic field intensity permitted by human tissue. Finally, the standardized design of the transmitting coil is achieved by summing-up and facilitating the optimization of the coils in various situations.