• ETRI Journal
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• 제33권4호
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• pp.648-651
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• 2011

This letter presents a highly efficient rack-level DC power architecture combined with a node-level DC uninterruptible power supply (UPS). The proposed system can provide almost the equivalent power efficiency of a high-voltage DC data center without any change in the existing power infrastructure. The node-level DC UPS combined with a power distribution board provides high power efficiency as well as lower UPS installation costs. Implemented on a rack, the entire power system can be monitored through a network.

• Journal of Electrical Engineering and Technology
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• 제13권5호
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• pp.1852-1863
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• 2018

Direct current(DC) systems have recently attracted attention due to the increase in DC loads and distributed generations, such as renewable energy sources. Among these technologies, there has been much research into DC distribution systems or DC microgrids. Within this body of research, the main topics have been about optimum control and operation methods in terms of improving power efficiency. When DC systems are controlled and operated using power electronic devices such as converters, it is necessary to design and analyze them by considering the power electronics sections. For this reason, we propose a scalable DC system analysis algorithm, which considers various system configurations depending on the operating mode and location of the converter. The algorithm consists of power flow fault current calculations, and the results of the algorithm can be used for designing DC systems. The algorithm is implemented using MATLAB with defined input and output data. The verification of the algorithm is mainly performed using ETAP software, and the accuracy of the algorithm analysis can be confirmed through the results.

• 전력전자학회논문지
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• 제18권2호
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• pp.138-144
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• 2013

Most of the DC loads have had the sensitive characteristics electrically for input voltage. In this system, power converter is operated after connecting with DC loads to minimize the overshoot of the control voltage that may occur during connection of the loads. But whenever starting the power converter, parameters in circuit are different because power converter has been connected with diverse load types at each startup time. This is cause of a disadvantage to PI controller design of power converter. In this paper, the novel voltage control method using sliding mode control theory has proposed. This control method minimizes the overshoot of control voltage at startup of power converter. Despite the variations of the system parameters, the proposed voltage controller has fast response and robustness characteristics such as PI and sliding mode controllers. The proposed controller was applied to the three-phase AC/DC converter and each performance of controller was verified.

• 전기학회논문지
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• 제60권9호
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• pp.1674-1683
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• 2011

More than 80% of electric loads need DC electricity rather than AC at the moment. If DC power could be supplied directly to the terminal loads, power conversion stages including rectifiers, converters, and power adapters can be reduced or simplified. Therefore, DC microgrids may be able to improve energy efficiency of power distribution systems. In addition, DC microgrids can increase the penetration level of renewable energy resources because many renewable energy resources such as solar photovoltaic(PV) generators, fuel cells, and batteries generate electric power in the form of DC power. The integration of the DC generators to AC electric power systems requires the power conversion circuits that may cause additional energy loss. This paper discusses the capability and feasibility of DC microgrids with regard to energy efficiency analysis through detailed dynamic simulation of DC and AC microgrids. The dynamic simulation models of DC and AC microgrids based on the Microgrid Test System in KEPCO Research Institute are described in detail. Through simulation studies on various conditions, this paper compares the energy efficiency and advantages of DC and AC microgrids.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1569-1571
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• 1999

In this work, we have performed the application experiment for real distribution line to diagnose the underground power cables using DC voltage decay measurement system. We have also performed the Isothermal Relaxation Current test for the same distribution line using KDA-l. We could confirmed possibility of grading the insulation aging state of underground power cables. Therefore, we conclude that it is possible to apply DC voltage decay method to the real distribution line.

• 조명전기설비학회논문지
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• 제18권5호
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• pp.174-182
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• 2004

높은 생산성, 시스템 설계의 단순화 및 미래 확장에 대비한 여분의 전원 확보 등의 병렬운전 방법의 장점으로 인해 대전력 전원장치에 있어 컨버터 시스템의 병렬운전에 대한 요구가 점점 증가되어 왔다. DC-DC 컨버터의 소신호 모델을 토대로 하여, 병렬운전 시스템의 모델을 제안하였으며 각 컨버터 모듈간의 균일한 전류분배를 위해 제안된 균등 전류 분배법을 사용한 병렬운전 시스템에 대하여 논의하였다. 모의실험 프로그램을 사용하여, 서로 특성이 다른 컨버터 모듈로 구성된 병렬운전 시스템에서 마스터와 슬레이브 모듈의 위치가 자동적으로 변하면서 전류분배 오차는 제한 값 이내로 유지됨을 확인하였다. 병렬운전을 위한 제안된 컨버터 시스템의 운전 특성을 확인하기 위하여 1[kW]의 DC-DC 컨버터 모듈 2대를 제작 실험하였으며 모의실험 결과는 과도특성 및 기동특성에 있어 실험 결과와 잘 일치됨을 확인하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.606-615
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• 2006

This study identifies the comparison of Technical specification and Characteristics of DC Protection Relay(ETCPU200) used in DC Distribution System in Korea. ETCPU200 has completed Field Test and approved its capability by finding out causes of recent operations through lately developed digital DC protection relay in parallel operation at Maebong-Substation, Nakseongdae-Substation, Euljirosaga-Substation, Jegi-Substation and Chongryangri T/P area. It also examines additional features for efficient System Analysis and Operations.

• KIEE International Transactions on Electrophysics and Applications
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• 제4C권2호
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• pp.68-72
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• 2004

The performance of copper-tungsten for electrodes used in an ultra high voltage interruption system was evaluated by means of an interruption test, which requires a large-scale apparatus and high cost. In this study, prior to the interruption test, the characteristics of a Cu-W electrode were estimated through the DC arc test, which is a simple, low cost procedure. The DC arc characteristics of a 20wt%Cu-80wt%W electrode were investigated with the change of tungsten powder size distribution and the addition of nickel. In specimens containing a high volume fraction of large sized tungsten particles, the relative density and hardness of sintered Cu-W electrodes increased while the electrical conductivity and the DC arc resistance decreased. Furthermore, the relative density became enhanced with the increase of the amount of nickel while the hardness and electrical conductivity diminished and the DC arc resistance worsened.

• 한국항행학회논문지
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• 제18권2호
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• pp.165-169
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• 2014

손쉬운 제어성, 운용성 등 다양한 이유로 디지털 부하가 급증하고 있고 이와 함께 부하의 소비 패턴은 직류화 되고있다. 그러나 공급되는 전력은 교류 전원이므로 실질적으로 필요로 하는 부하의 공급 전원인 직류 전원을 만족하기 위하여 교류 전원을 다시 직류로 변환하여 사용하고 있다. 태양광, 풍력, 연료전지 등 신재생 에너지원의 경우 직류 발전을 하는 발전원으로 교류로 변환을 통해 계통에 유입되고 다시 직류로 변환되어 부하에 공급하게 되는 다단 변환을 하게 되어 손실은 지속적으로 증가하게 된다. 에너지원의 효율적인 사용을 위한 직류 기반의 배전 시스템이 필요로 하나, 부하뿐만 아니라 보호 기능을 구현하기 위한 직류 배선용 누전 차단기의 개발이 필요하다. 이에 본 연구에서는 직류 누설 전류에 대한 검출 알고리즘을 구현하고, 이를 위하여 센서에 대한 성능을 검증하고 이를 활용하여 직류를 기반으로 하는 누전 차단기에 적용함으로써 직류 배전 시스템 운용에 있어 보호가 가능할 것으로 기대된다.

• 전력전자학회논문지
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• 제18권3호
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• pp.256-262
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• 2013

In the large system such DC distribution for building, the method that a number of modules converters operation in parallel is commonly used. When parallel operation, circulating current is directly related to the loss of the entire system. Accordingly, each module to share the same current is the most important for the safety of the power system. In this paper, control method for reducing circulating current in parallel operation is proposed. furthermore response and operation of steady-state with parallel system was verified by simulation and experiment results.