• 전기학회논문지
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• 제58권9호
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• pp.1720-1727
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• 2009

This paper presents that generation and propagation mechanism of low frequency current ripples generated by a rectification effect of an inverter in fuel cell generation system is analyzed. The ripple reduction methode using hardware components such as capacitors and inductors is examined to reduce low frequency current ripples. A new fast and robust low frequency current ripple elimination algorithm is then proposed to incorporate a single loop current controller, which directly controls fuel cell current, without any extra hardware. The proposed algorithm can completely eliminate this current ripple as well as an overshoot or undershoot is significantly reduced. And the de link voltage and output current are well regulated by inverter controller. The validity of proposed algorithm is verified both computer simulation using PSIM 6.0 and experiment with a 1kW laboratory prototype.

• 전기학회논문지P
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• 제59권4호
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• pp.473-476
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• 2010

In this paper, we analyzed the short circuit current of a low voltage direct current distribution system. For the analysis, we performed the modeling of the low voltage direct current distribution system with a 6-pulse three-phase thyristor rectifier using the PSCAD/EMTDC, surveyed impedance of sources, transformers and distribution lines to run a simulation. A result of the simulation is that short circuit currents of the direct current distribution system with the rectifier decreased due to a thyristor-ON-resistance(Ron). But in case of the low thyristor-ON resistance, output fault current of the rectifier increased over three-phase short circuit current of an AC power system without a rectifier by regular ratio of the rectifier. Because the output fault current of the rectifier can increase over interrupting the capacity of circuit breakers, studying short circuit currents of a low voltage direct current distribution system with a rectifier is necessary for introducing the direct current distribution systems.

• E2M - 전기 전자와 첨단 소재
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• 제9권10호
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• pp.1001-1007
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• 1996

The conduction mechanisms of the off-current in low temperature (.leq. >$600^{\circ}C$) processed polycrystalline silicon thin film transistors (LTP poly-Si TFT'S) have been systematically studied. Especially, the temperature and bias dependence of the off-current between hydrogenated and nonhydrogenated poly-Si TFT's were investigated and compared. The off-current of nonhydrogenated poly-Si TF's is because of a resistive current at low gate and drain voltage, thermally activated current at high gate and low drain voltage, and Poole-Frenkel emission current in the depletion region near the drain at high gate and drain voltage. After hydrogenation it has shown that the off -current mechanism is caused mainly by thermal activation and that the field-induced current component is suppressed.

• 대한물리의학회지
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• 제6권3호
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• pp.353-360
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• 2011

Purpose : The purpose of this study was to compare the effect of muscle strength by stimulation of russian current and low frequency. Methods : The subjects were thirty young healthy volunteers who were divided into two groups including russian current group(n=15) and low frequency group(n=15). The intervention was applied totally 12 times (1 time, 10 minute) for 4weeks in each group. The peak torque and average power were measured and analysed using Biodex system 4 before the treatment, after 2 weeks, 4 weeks. Results : As a result, russians currents and low frequency stimulation increased significantly average power and peak torque with the lapse of time. However, there were not significant differences of the average power and peak torque between the groups in all periods. Conclusion : In conclusion, russians currents and low frequency stimulation had no differences in the increase of muscle strength.

• 전자공학회논문지C
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• 제35C권5호
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• pp.33-40
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• 1998

In this paper, a design of current-mode continuous-time filters for low voltage and low frequency applications using complementary bipolar current mirrors is presented. The proposed current-mode filters consist of simple bipolar current mirrors and capacitors and are quite suitable for monolithic integration. Since the design method of the proposed current-mode filters are based on the integrator type of realization, it can be used for a wide range of applications. Since the input impedance of simple bipolar current mirror is small, in this paper, negative feedback amplifier is used to realize is designed by cascade method. The cutoff frequency of the designed filter can be easily tunable by the DC controlling current from 60kHz to 120kHz. The characteristics of the designed current-mode filters are simulated and examined by SPICE using standard bipolar transistor parameters.

• JSTS:Journal of Semiconductor Technology and Science
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• 제4권4호
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• pp.269-274
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• 2004

Current delivery system, in which the analog current produced by a unique DAC circuit is stored into a current-memory circuit and delivered in a time-divided sequence, shows variation of output current as low as 4% in a current source data-driver IC for AM-OLED driven by a current-programmed method without any fuse repairing after fabrication. This driver IC has 54 outputs and can sink constant current as low as 3 ${\mu}A$ with 6-bit analog levels. Such a low current level without variation can hardly be obtained by an ordinary MOS transistor because the current level is in the sub-threshold region and changes exponentially with threshold voltage variation. Thus we adopted a current mirror circuit composed of bipolar transistors to supply well-controlled current within a nano-ampere range.

• Journal of Electrical Engineering and Technology
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• 제5권2호
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• pp.307-318
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• 2010

In this work, an accurate analysis of low frequency current ripple in residential fuel cell power generation systems is performed based on the proposed residential load model and its unique operation algorithm. Rather than using a constant dc voltage source, a proton exchange membrane fuel cell (PEMFC) model is implemented in this research so that a system-level analysis considering the fuel cell stack, power conditioning system (PCS), and the actual load is possible. Using the attained results, a comparative study regarding the discrepancies of low frequency current ripple between a simple resistor load and a realistic residential load is performed. The data indicate that the low frequency current ripple of the proposed residential load model is increased by more than a factor of two when compared to the low frequency current ripple of a simple resistor load under identical conditions. Theoretical analysis, simulation data, and experimental results are provided, along with a model of the load usage pattern of low frequency current ripples.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 합동 추계학술대회 논문집 정보 및 제어부문
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• pp.550-553
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• 2002

A source meter is a basic instrument to perform a measurement of DC characteristic of semiconductor devices. the source meter can be used as variable voltage source, variable current source, voltage meter, or current meter. The accuracy of the low current measurement can be improved with the compensation of leakage current and charge and discharge current. In the low current measurement, the RC time constant is extremely big, so the measurement speed is very low. In this thesis, the analysis of the behavior of the measurement current according to the RC time constant and output capacitance and the method to accelerate the measurement speed.

• 한국수소및신에너지학회논문집
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• 제18권2호
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• pp.157-163
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• 2007

During PEMFC operation, low current and low humidity conditions accelerate the degradation of perfluorosulfonic acid membrane. But, there have been no studies that clearly explain why these conditions accelerate the membrane degradation. In this study, the hydrogen permeability through the membrane, I-V polarization of MEA, fluoride emission rate(FER) in effluent water were measured during cell operation under low current densities and low relative humidity(RH). The experimental results were evaluated with oxygen radical mechanism the most commonly known for membrane degradation. It seems that low RH of anode is a good condition for $H{\cdot}$ radical formation on the Pt catalyst and the low current condition accelerates the $H{\cdot}$ to form $HO_2{\cdot}$ radical attacking the polymer membrane.

• 한국전자통신학회논문지
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• 제8권10호
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• pp.1477-1483
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• 2013

연속시간 전류모드 기저대역 채널선택 필터 설계를 위하여 전류이득과 단위이득 주파수를 개선시킨 저전압 선형 캐스코드 전류모드 적분기를 제안하였다. 제안된 전류모드 적분기는 CMOS 상보형 회로로 구성된 완전 차동 형태의 입 출력단으로 구성하였으며, 여기에 캐스코드 트랜지스터를 추가시킴으로써 바이어스 단을 구성하여 선형영역에서 동작시켜 저전압 구조에 적합하도록 설계하였다. 이 때 바이어스 전압을 선택적으로 제어하여 주파수 대역이 가변될 수 있도록 설계하였다. 시뮬레이션 결과를 통해 설계한 선형 캐스코드 전류모드 적분기가 저전압 동작, 전류 이득 및 단위이득 주파수 등 모두 만족할 만한 특성을 가지고 있음을 확인하였다.