• 전력전자학회논문지
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• 제25권5호
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• pp.333-342
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• 2020

Power exchanges between the grid and the battery through a bidirectional DC-DC converter are essential for DC microgrid systems. In general, the battery is charged when the grid is connected, and the system is powered by the battery when the grid is disconnected. In this mode transition, the saturation of the voltage controller slows down output response and produces large transient errors in DC link voltage. To solve this problem, a novel anti-windup design is proposed to improve anti-windup performance further. The proposed method stabilizes DC bus voltage through a wider range of battery voltage with faster transition compared with that of conventional methods. The proposed method is verified through an experimental setup composed of a 125 W laboratory-scale DC microgrid system.

• 전력전자학회논문지
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• 제12권3호
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• pp.258-266
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• 2007

자기부상열차는 초기부상에서 정상상태에 이르는 짧은 시간동안 전류변화가 매우 큰 단점이 있다. 본 연구에서는 이를 안정적으로 제어하기 위해서 다중루프제어를 적용하였다. 제어기가 포함된 전체시스템에 상태방정식의 특성방정식을 구하여 원하는 특성의 제어이득을 쉽게 구할 수 있도록, Bessel function 원형모델을 도입하여 극점을 설정하였다. 설정된 극점을 바탕으로 제어기를 구성하고, 시스템의 특성방정식을 구하여 계수비교 함으로써, 시스템의 안정된 제어 특성을 확인하였다.

• 자원ㆍ환경경제연구
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• 제17권3호
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• pp.167-199
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• 2008

세계 각지에서 전력망 연계를 통한 전력부문의 협력과 전력시장의 통합이 추진되어 가시적인 성과를 거두고 있다. 동북아 지역은 상당한 경제적 편익이 기대됨에도 불구하고 역내 국가들의 다양한 이해관계와 현실적 제약요인 등으로 인해 전력협력의 성과가 제대로 나타나지 않고 있다. 미국 에너지부 산하의 아르곤연구소(Argonne National Laboratory)에서 개발한 발전 및 송전을 모의하는 프로그램인 GTMax를 통하여 러시아로부터 값 싼 전력이 국내에 수입되는 경우를 분석하였다. 러시아로부터의 수전량이 2,000MW(2017년의 국내 설비용량은 약 90,000MW 이상으로 2,000MW는 2%에 해당)일 경우 절대량이 미미하여 국내 전력시장에 미치는 영향이 거의 없다. 전력망 연계에 의해 큰 폭의 비용 절감을 도모하기 위해서는 수전량이 전체의 10% 수준이 될 정도로 커질 필요가 있음을 보여주고 있다. 또한 경인지역으로 직접 연계되는 것이 비용절감을 크게 하며, 영동지역과 연계되는 경우 영동-경인 간 선로용량의 증설이 불가능하다면 수전전력은 중부지역의 발전량을 대체하게 되어 수전의 상대적 이득이 감소하는 것으로 나타났다.

• Journal of Advanced Marine Engineering and Technology
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• 제32권5호
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• pp.691-697
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• 2008

Heat exchangers are commonly used in practice in a wide range of application, from heat and air-conditioning system in a household, to chemical processing and power production in large plant. An Experimental study was conducted to investigated the fluid flow and heat transfer around four circular cylinders of in-line in a cross flow of air. The local and average heat transfer characteristics for tube banks are investigated in the present study. Heat transfer in a heat exchanger usually involves convection in each fluid and conduction through the wall separating the two fluid. The in-line pitch ratio was in the range $1.5{\leq}L/d{\leq}4.0$, where L is the center distance and d the cylinder diameter, and in the Reynolds number $8,000{\leq}Re{\leq}50,000$. The local and mean Nusselt numbers were estimated. Subsequently, the heat transfer characteristics of four circular cylinders are found to exhibit a strong dependency upon the separation point of their upstream cylinders.

• 설비공학논문집
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• 제25권11호
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• pp.624-630
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• 2013

A truck refrigeration system using phase change material (PCM) is expected to have a lower noise level, reduced energy cost, and much lower local greenhouse gas emission. Recently, a forced convection type PCM refrigeration module has been developed. As the operation time increases, the PCM around the air inlet melts, because of a large temperature difference between the PCM and air. Therefore, the latent heat transfer area decreases and the heat transfer rate of the module decreases even though there is a lot of PCM which does not melt around the air outlet. A computational fluid dynamic modeling of the PCM refrigeration module was developed and validated by the experiment. Using the CFD, the design parameters, such as the mass flow rate of the air and roughness of the slab, were investigated to improve the heat transfer inhomogeneity. As a result, the adoption of partial roughness on the slabs improved the heat transfer inhomogeneity and reduced a fan power.

• 대한기계학회논문집
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• 제16권8호
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• pp.1566-1574
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• 1992

본 연구에서는 원형수직 충돌분류에 의한 가열평판의 전열특성을 해석하기 위 하여 최근 표면온도 측정에 많이 사용되고 있는 liquid crystal을 이용하였다. 즉 liquid crystal의 감온특성과 영상처리 기법을 이용하여 레이놀즈수 및 노즐과 충돌판 사이의 거리(L/D) 변화에 따른 전열면의 온도장 변화를 측정하였다.

• Nuclear Engineering and Technology
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• 제53권12호
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• pp.3990-4002
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• 2021

CSPACE (Core meltdown, Safety and Performance Analysis CodE for nuclear power plants) for a simulation of severe accident progression in a Pressurized Water Reactor (PWR) is developed by coupling of verified system thermal hydraulic code of SPACE (Safety and Performance Analysis CodE for nuclear power plants) and core damage progression code of COMPASS (Core Meltdown Progression Accident Simulation Software). SPACE is responsible for the description of fluid state in nuclear system nodes, while COMPASS is responsible for the prediction of thermal and mechanical responses of core fuels and reactor vessel heat structures. New heat transfer models to each phase of the fluid, flow blockage, corium behavior in the lower head are added to COMPASS. Then, an interface module for the data transfer between two codes was developed to enable coupling. An implicit coupling scheme of wall heat transfer was applied to prevent fluid temperature oscillation. To validate the performance of newly developed code CSPACE, we analyzed typical severe accident scenarios for OPR1000 (Optimized Power Reactor 1000), which were initiated from large break loss of coolant accident, small break loss of coolant accident, and station black out accident. The results including thermal hydraulic behavior of RCS, core damage progression, hydrogen generation, corium behavior in the lower head, reactor vessel failure were reasonable and consistent. We demonstrate that CSPACE provides a good platform for the prediction of severe accident progression by detailed review of analysis results and a qualitative comparison with the results of previous MELCOR analysis.

• 한국컴퓨터정보학회논문지
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• 제25권1호
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• pp.45-53
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• 2020

기존의 CNN 알고리즘은 위성영상과 같은 대형 이미지에서 소형 객체를 식별하는 것이 불가능하다는 문제점을 가지고 있었다. 본 연구에서는 이러한 문제를 해결하기 위해 관심영역 설정 및 이미지 분할 기법을 적용한 CNN 알고리즘 개선방안을 제시하였다. 실험은 비행장 및 항공기 데이터셋으로 전환학습한 YOLOv3 / Faster R-CNN 알고리즘과 테스트용 대형 이미지를 이용하여 진행하였으며, 우선 대형 이미지에서 관심영역을 식별하고 이를 순차적으로 분할해 나가며 CNN 알고리즘의 객체식별 결과를 비교하였다. 분할 이미지의 크기는 실험을 통해 최소 분할로 최대의 식별률을 얻을 수 있는 최적의 이미지 조각 크기를 도출하여 적용하였다. 실험 결과, 본 연구에서 제시한 방안을 통해 CNN 알고리즘으로 대형 이미지에서의 소형 객체를 식별하는 것이 충분히 가능함을 검증하였다.

• 전기학회논문지P
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• 제66권4호
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• pp.182-187
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• 2017

Synchronous generators have been significantly applied in large-scale power plants and its monitoring systems are additionally established to sequentially observe states and outputs. We develop a computer based monitoring device for three-phase synchronous power generators in this paper. First, a test-bed of such generator system is created and then a interface board is constructed to transfer electric signals including the output voltage and the current from generators into a computer system via a data acquisition device. Its RMS(root-mean-square) values are continuously shown on a screen of computer systems and its time-histories graphs are additionally illustrated under a graphic user interface(GUI) mode. Lastly, we carry out real-time experiments using the generator system with the monitoring device to demonstrate its reliability and superiority by comparing results of a generic power analyzer which is well-used in measuring various power systems practically.

• 한국정밀공학회지
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• 제14권3호
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• pp.35-40
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• 1997

The traction drive has advantages of having high efficiency and transmitting the power without blacklash. However, when high ratio of speed reduction is desired, excessively large size is required. In this study, a new type of traction drive is invented, designed and manufactured so that stable speed reduction mech- anisms are available by adopting a cross roller type drive. It has a simple structure, but produces high speed reduction ratio. Power loss is observed, and also, driving torque and torque transfer efficiency are calculated. Pre-loads are needed in order that the traction drive transfers power without slipping, and the spacer is enlarged due to the pre-loading. After all, the key point of pre-load mechanism is that the spacer's diameter becomes larger as pre-loads are applied.