• 전력전자학회:학술대회논문집
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• 전력전자학회 2005년도 전력전자학술대회 논문집
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• pp.436-438
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• 2005

This paper presents a Zero-Current Switching(ZCS) two-transformer phase-shift full-bridge(TTFB) converter using voltage ripple. The proposed converter provides Zero-Voltage Switching(2VS) of leading leg switches and ZCS of lagging leg switches using volt-age ripple. Especially, circulating current Is reduced by ZCS operation and there are no additional components required for the soft switching of power switches. Furthermore, in case of light load, ZVS operation of lagging leg can be achieved. The operations, analysis and design consideration of proposed converter are presented. To verify the validity of the proposed converter, experimental results for a flow (205V, 2A) prototype are presented.

• Journal of Electrical Engineering and Technology
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• 제2권1호
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• pp.19-28
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• 2007

The paper discussed various techniques for islanding detection and described in detail the working principles of ROCOF and vector shift relays. A simulator was used to investigate why the stability of both types of relays maybe affected by network and load switching, short-circuit faults and in the case of a ROCOF relay the loss of bulk generation or the tripping of a transmission feeder. Finally, to enhance the reliability of Loss of Mains protection, a new islanding detection technique based on a GPS synchronized phasor measurement system was proposed.

• 한국통신학회논문지
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• 제40권11호
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• pp.2121-2130
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• 2015

본 논문에서는 단일 RF 단을 사용하여 다중 스트림을 전송할 수 있는 LM-MIMO (load-modulation multiple-input multiple-output) 시스템에 대하여 알아보고, 이 시스템에서 사용하는 부하변조 (load modulation) 방법이 고차 m-PSK (phase shift keying) 심볼이나 고차 m-QAM (quadrature amplitude modulation) 심볼을 효과적으로 생성할 수 있는지 확인한다. 그리고 부하변조를 사용하는 LM-MIMO 시스템의 성능을 평가한다. LM-MIMO 시스템은 안테나가 확장되어도 단일 RF 단만을 요구하기 때문에 저복잡도, 저전력의 시스템 구성을 할 수 있다. 시뮬레이션의 결과를 살펴보면, T 모델 (model)을 사용하는 부하변조는 고차 m-PSK 변조와 고차 m-QAM 변조를 효과적으로 지원할 수 있다. 또한 부하변조를 사용하는 LM-MIMO 시스템이 기존의 이상적인 m-PSK나 m-QAM 변조를 사용하는 MIMO 시스템과 유사한 성능을 낼 수 있음을 확인하였다. 또한 $4{\times}4$ LM-MIMO 시스템이 기존의 $4{\times}4$ MIMO 시스템과 유사한 성능을 내는 것을 확인하였다.

• 태양에너지
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• 제19권3호
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• pp.63-73
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• 1999

Ice storage systems are used to shift the peak load in day time into night time in summer. This paper describes a system simulation of partial ice storage system composed of an encapsulated ice storage tank, a screw compressor chiller, a heat exchanger, and a brine pump. For the system simulation, a one-dimensional model of ice storage tank is developed and validated by comparison with the performance data from measurements of an ice storage tank installed at a building. The control strategies considered in this study are chiller priority and storage priority being used commercially. The system is simulated with design cooling load of 600 RT peak load in design day and with off-design day cooling load, and the electric energy costs of the two control strategies for the same system size are compared. As a result of calculation, the energy consumption in a week for storage priority is higher than that for chiller priority control. However due to lower cost of night electric charge rate, energy cost for storage priority control is lower than chiller priority.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.281-284
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• 2006

ASCE-ACI Committee 426 and 445, on Shear and Torsion, well noted in their report that recent research work regarding shear and torsion had been devoted primarily to members. But it was not logical approach of PSC members applied by axial force based on the shear deformation in web element. And it was not included that the effect of axial is to shift the shear strain(or crack width) in the web element versus the applied shear curve up or down by the amount by which the biaxial tension-compression state varies. The shear strength also increases or decreases, so that the change in shear strain at service load due to the presence of axial load is to some extent changed. Generally, in corresponding beams the shear strain at service load is less in the beam subject to axial compression and greater in the beam subject to axial tension, than in the beam without axial load. In particular, however, no research were available on the shear deformation in shear of PSC members with web reinforcement, subject to axial force in addition to shear and bending. Therefore, this study was basically performed to develop the program for the calculation of the shear deformation based on the shear effect of axial force in prestressed concrete members.

• 한국전자파학회논문지
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• 제24권6호
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• pp.602-612
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• 2013

본 논문에서는 주파수 5.3 GHz에서 소형화된 branch line 커플러와 $360^{\circ}$ 이상의 위상천이를 보일 수 있는 가변 리액턴스 부하를 결합하여 소형화된 위상천이기의 설계를 보였다. 위상천이기의 소형화를 위하여, branch line 커플러의 새로운 구조를 제안하였다. 새로운 branch line 커플러는 전송선의 T 및 ${\pi}$형 등가회로 변환 방법을 이용하여 소형화하였다. 소형화된 branch line 커플러는 일반적인 구조에 비해 50 % 이상 소형의 크기를 가진다. 넓은 위상천이량을 갖기 위하여 전송선에 버렉터 다이오드 두 개를 입력과 출력에 연결한 부하 구조를 채택하였다. 특히, 조정 전압에 대한 위상천이량이 완만하도록 임피던스 변환기 역할을 하는 전송선을 설계된 부하 구조에 추가하여 구조를 보완하였다. 추가된 임피던스 변환기에 사용된 전송선 및 선정된 부하 구조의 전송선은 소형화에 장애가 되기 때문에 이를 집중 소자로 등가하여 소형화하였다. 제작된 위상천이기는 $15{\times}15mm^2$의 소형의 크기를 가지며, 조정 전압 0~10 V 범위의 경우, 중심 주파수 5.3 GHz에서 삽입 손실은 약 -4~-6 dB, 반사 손실은 -20 dB 이하, 약 $480^{\circ}$의 넓은 위상천이를 보였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1824-1827
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• 2005

For application to micro fluid control systems such as ${\mu}TAS$ (Micro Total Analysis Systems) and DDS (Drug Delivery Systems), it is very significant to handle precise and minute flow rates with low pressure pulsation. In this study, a novel valveless piezoelectric pump using peristaltic motion with three disk type PZT actuators is presented. The newly devised pump with an effective size of $70mm{\times}60mm{\times}55mm$ has three actuator layers connected in series from inlet to outlet. The PZT actuator has a maximum displacement of 240 ${\mu}m$ and a maximum force of 1.6 N. When the driving voltage for PZT actuators is sequentially applied with a certain phase shift, the pumping is performed by peristaltic motion of liquid volume. The working fluid is shut off without the driving voltage. Three methods for sequential driving are proposed and experimentally investigated. First and second methods utilize an intermittent sinusoidal waveform with phase shift of $90{\circ}\;and\;120^{\circ}$, respectively. Third method uses a rectangular waveform with phase shift of $90^{\circ}$. A controller with multi-phase shifter is designed and fabricated. Then, frequency and voltage-flow rate characteristics and load pressure-flow rate characteristics are experimentally investigated to verify the validity of the developed pump.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.1282-1285
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• 2004

The high voltage driving system with multi-phase shifter including piezoelectric actuators comprised a driving power unit for outputting the driving power by converting input alternate current into direct current, a frequency shifting unit for supplying the direct current power and shifting or generating a frequency, a high-voltage amplification unit for amplifying the input signal outputted from the driving power unit and the frequency shifting unit into a high-voltage signal, and a phase shifting unit for shifting the phase difference of the amplified signal applied to the high-voltage amplification unit and driving plural piezoelectric actuators sequentially. The results that the operating voltage was stable, the voltage loss ratio was low and the response velocity was fast could be obtained. An experiment on performance of the high voltage driving system with multi-phase shifter designed and manufactured as above described was conducted by using a piezoelectric pump having 3 sheets of round unimorph piezoelectric actuators laminated respectively in a rectangular case. It sucks any fluid by causing the first piezoelectric actuator to shift from the inlet porter side, the phase delay of 60$^{\circ}$ causes the second piezoelectric actuator to begin to shift, and the phase delay of 120$^{\circ}$ causes the third piezoelectric actuator to begin to shift. As a result of measuring each change in the outlet flow rate of the piezoelectric pump, it was shown that the frequency-flow rate characteristic, the voltage-flow characteristic, and the load pressure-flow rate characteristic were improved.

• 전력전자학회논문지
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• 제12권2호
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• pp.107-114
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• 2007

계통 연계형 태양광 발전 시스템이 정전 혹은 사고 등으로 계통으로부터 분리되었을 때 태양광 발전 시스템이 배전선 부하를 떠맡아 운전을 계속하는 현상을 고립운전이라 하는데 이런 상태가 지속되면 선로 유지보수자의 안전사고를 야기할 수 있으며 전기설비에 나쁜 영향을 줄 수도 있다. 수동 검출법은 연계점(PCC:Point of Common Coupling)의 전압이나 주파수를 측정하여 한계치를 벗어나면 고립운전으로 판단하는데 RLC 부하의 유효전력과 무효전력이 각각 PV 시스템의 유효전력, 무효전력과 서로 비슷하면 검출할 수 없다. 이 경우 고립운전을 검출하기 위한 다양한 능동 검출법이 제안되었으며 가장 효과적인 방법은 미국 샌디아 연구실(Sandia National Lab)에서 제안한 SFS법(Sandia Frequency Shift method)이다. 본 논문에서는 자동 위상 이동을 이용한 새로운 능동 검출기법을 제안하고 Matlab 시뮬레이션과 실험을 통하여 타당성을 검증하였다.

• 전자공학회논문지A
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• 제31A권3호
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• pp.39-46
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• 1994

CMOS LCD driving circuits using poly-Si TFT have been designed and basic blocks including test patterns have been fabricated. Column driver drives the pixels by block because polu-Si TFT can not operate at the speed of video signal. Row driver has mode selection circuit which can select a mode between interlacing mode and non-interlacing mode. Experimental results show shift register can operate at 1MHz colck frequency with 4pF load.