• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1332-1336
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• 2009

If water-chillers are arranged in series-series counterflow, compressor lift of each chiller will be decreased in comparison with water-chillers in parallel. That means that compressor power of the chillers in series will be lower than that of chillers in parallel. However, the pressure drop of the water flow through the chillers in series will increase, and thus increase the power of water pumps. This disadvantage will be made good by increasing the temperature difference of water flow through evaporator and condenser, but the water flow rates will decrease. This paper explores the optimal parameters in system of series-series counterflow for central chilled water plants such as the leaving chilled water temperature, the leaving condenser water temperature, condenser water flow rate and number of chillers in series.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.182-183
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• 2010

풍력발전 시스템은 무제한적인 공간에 설치가 가능하다는 점과 기후 변화에 대응할 수 있는 원천적인 에너지원으로 각광을 받고 있다. 본 논문에서는 영구자석 동기형 풍력발전 시스템의 구성요소인 풍력발전기, 컨버터, 인버터를 모델링하고, 풍력발전 시스템의 성능 해석을 위한 PSIM 시뮬레이터를 개발하였다. 제안된 시뮬레이터는 PSIM 시뮬레이션을 통해 제안된 풍력발전 시스템 모델링과 시뮬레이터의 타당성을 검증하였다.

• Proceedings of the KIEE Conference
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• 1998.07e
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• pp.1684-1686
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• 1998

Gas Insulated Switchgear(GIS) acts as an indispensible part in power transmission network. In order that GIS may have its high reliability, it is necessary to pay careful attention to its whole process e.g., designing, manufacturing, installation, and operation. The main hazard in GIS comes from free conducting particles, which can move and cause breakdown under the influence of the electric field. Although the concentration on protecting the GIS inner part against the free conducting particles is made, it is, actually, almost impossible to avoid the hazard from the particles throughly. In this paper, using the EHV test chamber, partial discharge quantity in GIS was measured when free conducting particles initiate to discharge for providing fundamental data for the purpose of developing predictive diagnosis technology on site GIS.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.358-359
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• 2013

LED는 우수한 특성으로 인하여 차세대 조명으로 각광받고 있지만, 높은 비용에 따른 시장 활성화가 더딘 상태로서 저가격화 노력이 꾸준히 이루어지고 있다. 현재는 LED조명을 구동하기 위한 정전류 Driver, AC-DC컨버터를 배제시킬 수 있도록 AC 입력으로 LED를 구동하는 기술이 선보이고 있지만, AC성분 특성상 낮은 효율과 역률, 높은 THD의 문제점을 가지고 있다. 본 논문에서는 직렬 콘덴서를 통해 AC 입력전압으로 LED를 구동하는 방식에서 입출력변동에 따른 정전류 제어와 높은 THD를 개선하기 위한 스위칭 기법을 제안하였고, 이러한 회로의 용량성 역률을 보상하기 위하여 유도성 부하인 방전램프(고압나트륨램프)와 결합을 통한 역률을 보상하는 하이브리드 조명회로를 제안하였다.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.58-62
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• 2001

A numerical investigation was performed to determine the effect of airfoil on the optimum flap. height using NACA 0006, 0009, 0012, 0015, 0018, 0021 and 0024 airfoils. The six flaps which have 0.5% chord height difference were used. A Navier-Stokes code, FLUENT, was used to calculate the flow field of the airfoil. The code was first tested as a benchmark by modelling flow around a NACA 4412 airfoil. Predictions of local pressure coefficients are found to be in good agreement with the result of the experimental result. For every NACA 00XX airfoil, flap heights ranging from 0.0% to 2.5% chord were changed by 0.5% chord interval and their effects were also studied. Representative results from each case are presented graphically and discussed. It is concluded that this initial approach gives a promise for the future development of wind turbine optimum design.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.312-313
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• 2017

전력계통 주파수를 증대시키면 변압기를 비롯하여 전력변환기의 사이즈는 감소하나 부하에 따른 선로전압 강하가 크게 나타난다. 전력계통의 주파수는 전력전송이 이루어지는 거리에 따라 최적의 주파수로 운용한다면 전체시스템의 구성단가를 낮출 수 있다. 해외에서는 장거리전송을 위해 20[Hz] 전력전송에 대한 연구가 활발히 연구되고 있다. 항공모함과 같은 단거리 전력전송에서는 400[Hz] 전력전송을 사용하고 있다. 본 논문은 배전시스템의 주파수설정에 따른 변압기 및 전력변환기영역에서 장단점을 비교하여 경제성을 분석하여 마이크리드 시스템에 따라 그 적용 타당성을 연구하였다.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.360-361
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• 2019

본 논문에서는 연료전지용 전력변환 장치에서 높은 승압비를 구현하기 위하여 절연형 풀브릿지 컨버터의 고주파 변압기 2차측을 직렬로 연결한 새로운 DC/DC 컨버터와 이에 적합한 가변 위상변위 스위칭 방식을 제안하였다. 제안된 컨버터는 기존 방식에 비해 정류부와 필터부의 일원화가 가능한 구조로 출력레벨의 증가를 위해 컨버터의 수를 증가 하더라도, 수동소자의 수를 대폭 줄일 수 있다. 제안된 직렬 방식의 컨버터의 출력전압은 기존의 일정위상변위 스위칭 방식으로는 극성이 반대로 되는 구간이 발생하므로, 제안된 전력변환기에 적합한 간단한 가변 위상 변위 스위칭 방식을 적용함으로써, 출력전압의 감소문제를 해결하였으며, 시뮬레이션과 실험을 통하여 제안된 방식의 타당성을 검증하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.799-809
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• 2020

In this study, the supercavitating flow of a high-velocity moving body near air-water surface is calculated and analyzed based on a commercial CFD software ANSYS Fluent. The effect of regular wave parameters including both wave height and wavelength on the cavitating flow and force characteristics of a body at different velocities is investigated. It is found that the cavity shape, lift coefficient and drag coefficient of the body vary periodically with wave fluctuation, and the variation period is basically consistent with wave period. When the wavelength is much greater than the cavity length, the effect of wave on supercavitation is the alternating effect of axial compression and radial compression. However, when the wavelength varies around the cavity length, the cavity often crosses two adjacent troughs and is compressed periodically by the two wave troughs. With the variation of wavelength, the average area of cavity shows a different trend with the change of wave height.

• The KSFM Journal of Fluid Machinery
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• v.11 no.5
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• pp.15-21
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• 2008

In modem wind power system of large capacity above 1MW, horizontal axis wind turbine(HAWT) is a common type. And, the optimum design of wind turbine to guarantee excellent power performance and its reliability in structure and longevity is a key technology in wind Industry. In this study, mathematical expressions based upon the conventional BEMT(blade element momentum theory) applying to basic 1MW wind turbine blade configuration design. Power coefficient and related flow parameters, such as Prandtl's tip loss coefficient, tangential and axial flow induction factors of the wind turbine analyzed systematically. X-FOIL was used to acquire lift and drag coefficients of the 2-D airfoils and we use Viterna-Corrigan formula to interpolate the aerodynamic characteristics in post-stall region. In order to predict the performance characteristics of the blade, a performance analysis carried out by BEMT method. As a results, axial and tangential flow factors, angle of attack, power coefficient investigated in this study.

• Journal of Power Electronics
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• v.14 no.1
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• pp.194-201
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• 2014

To increase the capacity of secondary cells, an appropriate serial composition of the battery modules is essential. The unbalance that may occur due to the series connection in such a serial composition is the main cause for declines in the efficiency and performance of batteries. Various studies have been conducted on the use of a passive or active topology to eliminate the unbalance from the series circuit of battery modules. Most topologies consist of a complex structure in which the Battery Management System (BMS) detects the voltage of each module and establishes the voltage balancing in the independent electrical power converters installed on each module by comparing the module voltage. This study proposes a new magnetic flux sharing type DC/DC converter topology in order to remove voltage unbalances from batteries. The proposed topology is characterized by a design in which all of the DC/DC convertor outputs connected to the modules converge into a single transformer. In this structure, by taking a form in which all of the battery balancing type converters share magnetic flux through a single harmonic wave transformer, all of the converter voltages automatically converge to the same voltage. This paper attempts to analyze the dynamic properties of the proposed circuit by using a Programmable Synthesizer Interface Module (PSIM), which is useful for power electronics analysis, while also attempting to demonstrate the validity of the proposed circuit through experimental results.