• 전력전자학회논문지
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• 제22권4호
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• pp.285-296
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• 2017

This paper proposes an improved modulation scheme for the medium voltage modular multi-level converter (MMC), which operates in the nearest level control and applies in the medium voltage direct current (MVDC) system. In the proposed modulation scheme, the offset (neutral-to-zero output) voltage is adjusted, with the phase voltage magnitude, thereby maintaining a constant value with N+1 level in the controllable modulation index (MI) range. In order to confirm the proposed scheme's validity, computer simulations for the 22.9 kV - 25 MVA MMC were performed with PSCAD/EMTDC, as well as hardware experiments for the 380 V - 10 kVA MMC. The proposed modulation scheme offers to build a constant pole voltage regardless of the MI value, and to build a phase voltage with improved total harmonic distortion (THD).

• 산업융합연구
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• 제18권4호
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• pp.51-59
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• 2020

본 연구는 만성 뇌졸중 환자를 대상으로 저항운동이 포함된 거울치료 시 tDCS(transcranial direct current stimulation)의 융합 자극을 통해 마비측 다리의 근력과 보행 능력의 개선을 알아보고자 하였다. 12명의 뇌졸중 환자는 실험군 당 6명씩 무작위로 할당하였다. 실험군I(n=6)은 NDT(neurodevelopmental treatment)와 거울치료 시 sham tDCS의 융합자극군, 실험군II는 NDT와 거울치료 시 tDCS의 융합자극군으로 나누어 각각 30분씩, 주5회, 총4주 동안 실험을 실시하였다. 모든 평가는 중재 전과 중재 4주 후에 실시하였다. 다리근력은 측정한 모든 근육에서 실험군I에 비해 실험군II에서 유의한 차이를 나타냈고(p<.05), 변화량을 통한 군 간 비교에서는 quadriceps(p<.01)와 tibialis anterior(p<.01)에서 유의한 차이를 나타냈다. 보행능력은 실험군I과 실험군II 모두에서 유의한 차이를 나타냈고(p<.05), 변화량을 통한 군 간 비교에서 유의한 차이를 나타냈다(p<.01). 거울치료와 tDCS의 융합자극은 마비측 다리 근력 및 보행능력 향상에 중첩효과를 통한 긍정적인 개선 효과를 주는 것을 알 수 있었다.

• 한국진공학회지
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• 제20권4호
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• pp.307-312
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• 2011

정상 세포로부터 암과 같은 종양세포를 제거하는 방법으로 라디오주파수의 전자파를 이용하여 세포가 사멸되는 임계온도보다 높은 온도로 국소 가열하는 발열 치료법이 임상에서 시술되고 있다. 그러나 이 기술은 임상에서 활발히 사용되기에는 여러 가지 제약 요인이 존재한다. 본 연구에서는 교류파 대신에 미소 직류전원을 사용하여 국소부위에 열을 발생하는 안전성이 증가된 방법의 실효성을 이론적으로 입증하고자 한다. 종양세포의 형태에 따라 적당한 모양의 전극을 종양조직에 삽입하고 종양조직의 형태와 유사한 열분포를 갖도록 제어하는 기술을 개발한다. 열원은 조직 내에 삽입된 전극과 매질에 형성되는 전기장에 의한 저항열이다. 종양 조직 내에 삽입된 전극에 10 V, 20 V, 30 V를 각각 인가하고 시간에 따른 열분포를 전산모의 하였다. 결과적으로, 20 V를 전극에 인가하면 1~2 분 이내에 버섯모양의 등온도 분포를 갖으며 세포를 고사시키는 온도 이상의 치료영역이 형성됨을 보였다. 4개의 전극에 대칭적인 전위를 인가하고 $50^{\circ}C$ 이상의 온도 분포를 암 조직의 모양과 유사하게 분포하도록 조절하여 효과적인 치료를 수행 할 수 있는 가능성을 제시하고자 한다.

• 한국엔터테인먼트산업학회논문지
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• 제14권6호
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• pp.269-277
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• 2020

본 연구의 목적은 감각 결손이 있는 만성 뇌졸중 환자를 대상으로 경 두개 직류 전류 자극을 체성감각피질에 적용했을 때, 감각의 회복과 상지 기능의 회복을 알아보고자 하는 것이다. 만성 뇌졸중 환자 20명을 실험군 10명, 대조군 10명으로 나누어 실시하였다. 실험군은 환측 체성감각피질에 경 두개 직류 전류 자극을 적용하였으며, 대조군은 위상 자극을 실시하였다. 중재는 총 2주간, 10회, 회기 당 20분씩 진행되었다. 체성감각 평가는 The Erasmus MC modifications to the (revised) Nottingham Sensory Assessment(EmNSA), Semmes-Weinstein monofilament examination(SWME), 상지기능 평가는 퍼글마이어평가(FMA), 운동 활동 척도(MAL), 가속도계를 사용하였다. 연구 결과, 실험군은 대조군보다 전체적인 촉각 감각과 고유수용성 감각, 피질 감각, 지각의 민감도에서 유의한 개선을 보였으며, 환측 상지의 사용량에서 통계학적 유의한 차이를 나타냈다. 본 연구 결과를 기반으로 체성감각 회복과 상지기능의 회복을 위한 tDCS의 효과적인 임상 적용의 가능성을 높일 수 있을 것으로 생각된다.

• 한국초전도ㆍ저온공학회논문지
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• 제17권3호
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• pp.37-40
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• 2015

Recently, the electrical insulation design for electrical apparatuses is important to cope with the tendency of high voltage. The degradation characteristics of a superconducting coil due to an electrical breakdown should be considered to design a high voltage superconducting coil. In this paper, the degradation characteristics of 2G high temperature superconducting (HTS) wires are studied with respect to electrical breakdown tests. To analyze the dependency of the degradation characteristics of 2G HTS wires, the electrical breakdown tests are performed with AC(alternating current) and DC(direct current) voltage. All tests are performed by applying various magnitudes of AC and DC breakdown voltages. To verify the degradation characteristics of 2G HTS wires, the tests are performed with various 2G HTS wires with respect to stabilizer materials. The degradation characteristics of 2G HTS wires, such as Ic(critical current) and index number are measured by performing electrical breakdown tests. It is found that the characteristics such as Ic and index number can be degraded by an electrical breakdown. Moreover, it is concluded that the degradation characteristics of 2G HTS wires are affected by the stabilizer material and applied voltages. The cross-sectional view of 2G HTS wires is observed by using a scanning electron microscope (SEM). As results, it is found that the degradation characteristics of 2G HTS wires are concerned with hardness and electrical conductivity of stabilizer layers.

• Journal of Electrical Engineering and Technology
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• 제9권5호
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• pp.1654-1659
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• 2014

Tunneling field-effect transistors (TFETs) are very applicable to low standby-power application by their virtues of low off-current ($I_{off}$) and small subthreshold swing (S). However, low on-current ($I_{on}$) of silicon-based TFETs has been pointed out as a drawback. To improve $I_{on}$ of TFET, a gate-all-around (GAA) TFET based on III-V compound semiconductor with InAs/InGaAs/InP multiple-heterojunction structure is proposed and investigated. Its performances have been evaluated with the gallium (Ga) composition (x) for $In_{1-x}Ga_xAs$ in the channel region. According to the simulation results for $I_{on}$, $I_{off}$, S, and on/off current ratio ($I_{on}/I_{off}$), the device adopting $In_{0.53}Ga_{0.47}As$ channel showed the optimum direct-current (DC) performance, as a result of controlling the Ga fraction. By introducing an n-type InGaAs thin layer near the source end, improved DC characteristics and radio-frequency (RF) performances were obtained due to boosted band-to-band (BTB) tunneling efficiency.

• Geomechanics and Engineering
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• 제1권4호
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• pp.275-289
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• 2009

Electroosmosis (EO) is the movement of water in a porous medium under the influence of a direct current (dc). In past decades, electro-osmosis has been successfully employed in many soil improvement and other geotechnical engineering projects. Metal electrodes, such as steel, copper and aluminum have been used traditionally to conduct current. The shortcoming of these electrodes is that they corrode easily during an EO treatment, which results in reduced effectiveness and environmental concerns. More recently, conductive polymers are developed to replace metal electrodes in EO treatment. Electrical vertical drainages (EVDs) are one of these products under trial. The goal of this study is to assess the performance of EVDs for soil improvement and to further understand the scientific principle of the EO process, including the voltage drop at the soil-EVD interface, electrical current density, polarity reversal, and changes in soil physico-chemical properties generated by electroosmosis. It is found from the study that after 19 days of EO treatment with a constant applied dc electric field intensity of 133 V/m, the soil's moisture content decreased by 28%, the shear strength and pre-consolidation pressure increased more than 400%. It is also found that the current density required triggering the water flow in the soil tested, the Korean Yulchon marine clay, is 0.7 $A/m^2$. The project demonstrates that EVDs can serve as both electrodes and drains for soil improvement in short term. However, the EVDs, as tested, are not suitable for polarity reversal in EO treatment and their service life is limited to only 15 days.

• JSTS:Journal of Semiconductor Technology and Science
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• 제12권3호
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• pp.370-376
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• 2012

In this work, design considerations for high-performance silicon photodetector are thoroughly investi- gated. Besides the critical dimensions of device, guidelines for process architecture are suggested. Abiding by those criteria for improving both direct-current (DC) and alternating-current (AC) perfor- mances, a high-speed low-operation power silicon photodetector based on p-i-n structure for optical interconnect has been designed by device simulation. An $f_{-3dB}$ of 80 GHz at an operating voltage of 1 V was obtained.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 추계학술대회 논문집
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• pp.38-43
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• 1998

Magneto Electrolytic Polishing (MEP) is a process in which metal ions are removed from a abrasive through a combination of magnetic electric current and chemical solution. The substrate is immersed into the magnetic effect, chemical solution, and DC crunt is applied. Several factors affect the rate at which the metal ions are removed from the substrate. Three of the most significant are the amount of time in which the substrate is immersed I the solution, and the amount of direct current applied in magnetic field. In this study, the surface finishing characteristics and optical finishing condition for the stainless steel were experimented upon and analyzed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.132-135
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• 2008

This paper presents a PLL(Phase Lock Loop) control method for speed control of high speed miniature BLDCM(Brushless DC Motor) using hall sensor. The Proposed PLL based speed control method uses a only phase shift between reference pulse signal according to speed reference and actual pulse signal from hall sensor. It doesn't use any speed calculation, and calculates a direct current reference from phase shift. The current reference is changed to reduce the phase shift between reference and actual pulse. So the actual speed can keep the reference speed. The proposed control scheme is very simple but effective speed control is possible.