• 조명전기설비학회논문지
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• 제29권5호
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• pp.71-79
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• 2015

Recently, new Low Voltage DC (LVDC) power distribution systems have been constantly researched as uses of DC in end-user equipment are increased. As in conventional AC distribution system, High Impedance Fault (HIF) which may cause a failure of protective relay can occur in LVDC distribution system as well. It, however, is hard to be detected since change in magnitude of current due to the fault is too small to detect the fault by the protective relay using overcurrent element. In order to solve the problem, this paper presents an algorithm for detecting HIF using accumulated energy in LVDC distribution system. Wavelet Singular Value Decomposition (WSVD) is used to extract abnormal high frequency components from fault current and accumulated energy of high frequency components is considered as the element to detect the fault. LVDC distribution system including AC/DC and DC/DC converter is modeled to verify the proposed algorithm using ElectroMagnetic Transient Program (EMTP) software. Simulation results considering various conditions show that the proposed algorithm can be utilized to effectively detect HIF.

• 조명전기설비학회논문지
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• 제22권8호
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• pp.38-44
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• 2008

급격한 IT 산업 발전의 산물인 인터넷데이터센터(IDC)는 서버 시스템이 집적된 고밀도 디지털 부하로 구성되는 특징을 가지고 있다. IDC의 디지털 부하 특성을 고려하여 직류배전시스템을 도입하는 경우 전력 변환 체계의 단순화로 효율 향상의 가능성이 일부 제기되어 왔으나, 국내 IDC 환경에서의 효율성이 검증된 사례는 없었다. 본 논문에서는 교류배전방식을 적용한 KT 분당 IDC와 직류배전방식을 적용한 KT 남수원 IDC의 전력 효율을 비교 분석함으로써 국내 IDC 배전체계의 직류화에 따른 효율 개선 효과를 제시하였다. DC 48[V]를 배전하였을 때 직류배전 방식의 효율이 13.2[%] 높은 것으로 도출되었으며, DC 380[V]의 공급을 가정하였을 때에는 25[%] 이상의 효율 향상을 기대할 수 있었다.

• 전력전자학회논문지
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• 제22권1호
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• pp.44-52
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• 2017

This paper describes a 100 kW high-efficiency isolated DC-DC converter for DC distribution system. The DC-DC converter consists of two dual-active-bridge (DAB) converters in parallel. The operating principle of the DAB converter is explained, and the algorithm for parallel operation of the DAB converters is proposed. Simulation and experiments are conducted to verify the performance of the proposed system. Experimental results demonstrate that the developed converter excellently marks 97.4 percent of peak efficiency under its normal operating condition.

• 전력전자학회논문지
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• 제25권6호
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• pp.503-510
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• 2020

The importance of DC breakers as key protection equipment is increasing in accordance with growing concerns on MVDC distribution network systems without DC/AC conversion. Different from the situation in AC systems, no natural zero-crossing point exists in DC systems. Thus, DC breaker technology is more difficult than AC breaker technology. The solutions for DC breakers can be divided into three types: mechanical, power electronics, and hybrid. In this study, the operating principles of several topologies of hybrid circuit breakers and that of the proposed DC breaker are analyzed and simulated by sorting two types. The breakers are compared in terms of the type and number of semiconductors, volume, power loss, auxiliary components, isolation, and other aspects. The advantages and disadvantages of the breakers are also analyzed.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1805-1811
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• 2017

Recently, DC systems are considered as efficient electric power systems for renewable energy based clean power generators. This discloses several critical issues that are required to be considered before the installation of the DC systems. First of all, voltage/current switching stress, which is aggravated by large fault current, might damage DC circuit breakers. This problem can be simply solved by applying a superconducting fault current limiter (SFCL) as proposed in this study. It allows a simple use of insulated-gate bipolar transistors (IGBTs) as a DC circuit breaker. To evaluate the proposed resistive type SFCL application to the DC circuit breaker, a DC distribution system is composed of the practical line impedances from the real distribution system in Do-gok area, Korea. Also, to reflect the distributed generation (DG) effects, several DC-to-DC converters are applied. The locations and sizes of the DGs are optimally selected according to the results of previous studies on DG optimization. The performance of the resistive type SFCL applied DC circuit breaker is verified by a time-domain simulation based case study using the power systems computer aided design/electromagnetic transients including DC (PSCAD/ EMTDC(R)).

• 전기학회논문지P
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• 제65권3호
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• pp.219-223
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• 2016

DC microgrid system is attracted attention in the world, because DC distribution system is more energy efficient than AC distribution system. To analyse the contribution effects of distributed generation(DG) in LVDC distribution system through modeling the Rectifier, DC/DC converter, Energy Storage System(ESS) and Photovoltaic(PV). using PSCAD/EMTDC. This paper analyses fault response characteristics in LVDC distribution system according to the interconnection and islanding operation of DG. Based on research results on the paper, direction for development of fault current reduction method for LVDC distribution system is suggested.

• 전력전자학회논문지
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• 제19권3호
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• pp.233-239
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• 2014

This paper proposes that each converter supplies the power using the proposed droop control for the parallel operation of the converters. The proposed method is easy to increase the power as parallel system in DC distribution. By improving conventional droop-control method used in AC grid newly, a droop controller is designed to apply droop control in DC grid. And the control method of the proposed droop controller is explained particularly. In this paper, by applying the proposed control method to DC distribution system, propriety is verified through the simulation and the experiment.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권12호
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• pp.646-652
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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, Sangbong-Substation, Nakseongdae-Substation, Euljirosaga-Substation, Jegi-Substation and Chongyangri T/P area. It also examines additional features for efficient System Analysis and Operations.

• 전력전자학회논문지
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• 제26권5호
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• pp.315-324
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• 2021

A solid state transformer (SST) that can interface an MVAC of three-phase 13.2 kV and a 1.5 kV DC distribution. SST consists of an AC/DC converter and a DC/DC converter with a high-frequency isolation transformer (HFIT). The AC/DC converter consists of cascaded NPC full-bridge to cope with the MVAC. The DC/DC converter applies a quad active bridge (QAB) topology to reduce the number of the HFIT. Topology analysis and controller design for this specific structure are discussed. In addition, the insulation of HFIT used in DC/DC converters is considered. The discussion is validated using a 300 kVA three-phase SST prototype.

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1459-1473
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• 2018

This paper focuses on voltage control schemes for multi-terminal low-voltage direct current (LVDC) distribution systems. In a multi-terminal LVDC distribution system, there can be multiple AC/DC converters that connect the LVDC distribution system to the AC grids. This configuration can provide enhanced reliability, grid-supporting functionality, and higher efficiency. The main applications of multi-terminal LVDC distribution systems include flexible power exchange between multiple power grids and integration of distributed energy resources (DERs) using DC voltages such as photovoltaics (PVs) and battery energy storage systems (BESSs). In multi-terminal LVDC distribution systems, voltage regulation is one of the most important issues for maintaining the electric power balance between demand and supply and providing high power quality to end customers. This paper focuses on a voltage control method for multi-terminal LVDC distribution system that can efficiently coordinate multiple control units, such as AC/DC converters, PVs and BESSs. In this paper, a control hierarchy is defined for undervoltage (UV) and overvoltage (OV) problems in LVDC distribution systems based on the control priority between the control units. This paper also proposes methods to determine accurate control commands for AC/DC converters and DERs. By using the proposed method, we can effectively maintain the line voltages in multi-terminal LVDC distribution systems in the normal range. The performance of the proposed voltage control method is evaluated by case studies.