• 한국수소및신에너지학회논문집
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• 제24권4호
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• pp.311-319
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• 2013

A clear understanding on cell voltage-reversal behavior due to local hydrogen starvation in a stack is of paramount importance to operate the fuel cell vehicle (FCV) stably since it affects significantly the cell performance and durability. In the present study, a novel experimental method to simulate the local cell voltage-reversal behavior caused by local hydrogen starvation, which typically occurs only one or several cells out of several hundred cells in a stack of FCV, has been proposed. Contrary to the conventional method of overall fuel starvation, the present method of local hydrogen starvation caused the local cell voltage-reversal behavior in a stack very well. Degradation of both membrane electrode assembly (i.e., pin-hole formation) and gas diffusion layer due to an excessive exothermic heat under voltage-reversal condition was also observed clearly.

• Journal of Magnetics
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• 제18권1호
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• pp.50-56
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• 2013

In this paper, the 6-switch inverter for the Flux-Reversal Motor (FRM) has been presented and compared to the 4-switch inverter for the FRM, which is more popular in cost effective applications. To analyze the FRM, we adopted the two-dimensional time-stepped voltage source finite element method (FEM) that uses the actual pulse width modulation (PWM) voltage waveforms as the input data. As the FRM characteristic analysis of actual pwm voltage input, the torque ripples and iron losses (eddy current and hysteresis loss) of the FRM can be precisely calculated. With the simulated and experimental results, the performance and limitations of the 4-switch FRM which is the cost effective drive compared to the 6-switch FRM drive are provided in more detail.

• 대한수의학회지
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• 제32권4호
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• pp.543-553
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• 1992

Properties of unitary ATP-sensitive $K^+$ channels were studied using planar lipid bilayer technique. Vesicles were prepared from bullfrog (Rana catesbeiana) skeletal muscle. ATP-sensitive $K^+$ (K (ATP)) channels were identified by their unitary conductance and sensitivity to ATP. In the symmetrical solution containing 200mM KCI, 10mM Hepes, 1mM EGTA and pH 7.2, single K (ATP) channels showed a linear current-voltage relations with slight inward rectification. Slope conductance at reversal potential was $60.1{\pm}0.43$ pS(n=3)). Micromolar ATP reversibly inhibited the channel activity when applied to the cytoplasmic side. In the range of -50~＋50 mV, the channel activity was not voltage-dependent, but the channel gating within a burst was more frequent at negative voltage range. Varying the concentrations of external/internal KCl(mM) to 40/200, 200/200, 200/100 and 200/40 shifted reversal potentials to $-30.8{\pm}2.9$(n=3), $-1.1{\pm}2.7$(n=3), 10.5 and 30.6(mV), respecrivety. These reversal potentials were close to the expected values by the Nernst equation, indicating nearly ideal selectivity for $K^+$ over $Cl^-$. Under bi-ionic conditions of 200mM external test ions and 200mM internal $K^+$, the reversal potentials for each test ion/K pair were measured. The measured reversal potentials were used for the calculation of the releative permeability of alkali cations to $K^+$ ions using the Goldman-Hodgkin-Katz equation. The permeability sequence of 5 cations relative to $K^+$ was $K^+$(1), $Rb^+$(0.49), $Cs^+$(0.27), $Na^+$(0.027) and $Li^+$(0.021). This sequence was recognized as Eisenman's selectivity sequence IV. In addition, modelling the permeation of $K^+$ ion through ATP-sensitive $K^+$ channel revealed that a 3-barrier 2-site multiple occupancy model can reasonably predict the observed current-voltage relations.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권5호
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• pp.203-210
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• 2003

This paper describes high voltage and high energy density capacitor developed for pulsed power applications. The rated voltage of the developed capacitor is DC 22 [kV], the capacitance is 206 [$\mu$F] and the energy density is about 0.7 [kJ/kg]. Polypropylene film and kraft paper were used as the dielectrics. The ratio of the thickness of each dielectric material which consists of the composite dielectric structure, stacking factor and the termination method were determined by the charging and discharging tests on model capacitors. In terms of energy density, the developed capacitor has higher energy density compared with the products of foreign leading companies. In addition, it has been proved that the life expectancy can be more over 2000 shots through the charging and discharging test. The voltage reversal factor was 20%. This capacitor can be used as numerous discharge applications such as military, medical, industrial fields.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.1552-1553
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• 2011

The HVDC transformer which is one of the main equipments for HVDC(High Voltage Direct Current) electric power transmission systems is exposed to not only AC voltage but also the inflowing DC voltage which comes from the DC-AC converter systems. Therefore, the HVDC transformer insulation system is required to withstand the electric field stress under AC, DC and DC polarity reversal conditions. However the electric field distributions under those conditions are different because the AC electric field and DC electric field are governed by permittivity and conductivity, respectively. In this study, the changes of electric potential and electric field of conventional AC transformer insulation system under DC polarity reversal test condition were analyzed by FEM(Finite Element Method). The DC electric field stress was concentrated in the solid insulators while the AC electric field stress was concentrated in the mineral oil. In addition, the electric stress under that condition which is affected by the surface charge accumulation at the interfaces between insulators was evaluated. The stress in some parts could be higher than that of AC and DC condition, during polarity reversal test. The result of this study would be helpful for the HVDC transformer insulation system design.

• 한국전자파학회논문지
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• 제29권4호
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• pp.285-289
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• 2018

본 논문에서는 지능적인 원거리 무선전력전송의 방식으로 시간 역전(time reversal) 기반 전파 집속 방법을 제시하였다. 시간 역전 기반의 무선전력전송은 복잡한 전파환경에서도 기기의 위치에 상관없이 전파를 선택적으로 집속하여 높은 peak 전력을 전달할 수 있다. 현실과 가까운 전파환경 시뮬레이션을 통하여 시간 역전 기반의 시 공간 전파 집속 현상을 검증하였고, 집속된 RF를 정류하여 전달된 DC 전압을 확인하였다. 또한 일반적인 협대역 신호(CW) 대비 시간 역전 신호의 peak 향상률과 정류 전력비를 확인한 결과, 최대 12 dB 향상된 peak 전력이 전송되었으며, 따라서 보다 높은 효율로 전력전송이 이루어짐을 확인하였다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권12호
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• pp.709-717
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• 2004

Flux-reversal machine (FRM) is a new brushless doubly salient permanent magnet machine. Its operation is similar to that of the brushless DC motor, so it can be driven by 120 degree square wave voltage and use PWM pulse patterns in two-phase feeding scheme to control the speed. In this driving method, the back electromotive force (BEMF) current in the open phase is generated by the BEMF. It can be appeared or disappeared according to the changes of the neutral voltage of the machine. In this paper, the time-stepped voltage source finite-element method taking BEMF current into account is proposed. Its influences on the performances of the FRM are also investigated. To prove the propriety of the proposed analysis method, a Digital Signal Processor (DSP) installed experimental devices are equipped and the experiment is performed.

• 한국응용과학기술학회지
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• 제35권4호
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• pp.1206-1212
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• 2018

본 연구에서는 강유전성 고분자를 이용하여 제작된 100 nm 이하 두께를 가지는 박막형 커페시터의 측정 주파수에 따른 분극 반전 특성을 측정, 분석하였다. 고정된 박막 두께에 대해, 인가되는 최고 전기장의 세기가 증가할수록 더 높은 항전계에서 분극 반전이 발생되었다. 고정된 최고 전기장에 대해, 박막의 두께에 무관하게 같은 항전계에서 분극 반전이 발생되었다. 모든 측정에서 로그스케일 전기장 및 로그스케일 주파수의 관계에서 약 $0.12{\pm}0.01$의 비례 상수를 보였다. 결과적으로, 강유전체 고분자 커페시터가 40 nm 두께까지는 size effect 없이 일정한 분극 반전 특성을 보였다. 본 연구는 저전압 동작 고분자 메모리 소자의 동작 예측에 유용할 것이므로 저전압에서 동작 가능한 고분자 메모리 소자의 가능성을 보여준다.

• Journal of Magnetics
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• 제17권2호
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• pp.124-128
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• 2012

Many different converter topologies have been developed with a view to use the minimum number of switches in order to reduce construction costs. Among this research, the four-switch converter topology with a novel PWM control technique based on the current controlled PWM method is thought to be a good solution. In this paper, a two dimensional time-stepped voltage source finite-element method (FEM) is used to analyze the characteristics of a Flux-Reversal Machine (FRM) with a 4-switch converter. To validate the proposed computational method, a digital signal processor (DSP) installed controller and prototype FRM are built and experiments performed.

• 전자공학회논문지A
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• 제32A권1호
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• pp.185-192
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• 1995

In this study, very fine photoresist pattern was examined using the image reversal process. And very fine photoriesist pattern (less than 0.2um) was obtsined by optimizing the exposure and reversal baking condition of photoresist. The produced pattern does not show the loss of thickness, and has a sparp negative edge profile. also, the ion implanted 0.25um T-shaped gate MESFET was fabricated using this resist pattern and the directional evaporation of gate metal. The fabricated MESFET has the maximum transconductance of 302 mS/mm, and the threshold voltage of -1.8V, and the drain saturation current of this MESFET was 191 mA/mm.