• 한국산학기술학회논문지
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• 제22권1호
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• pp.768-776
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• 2021

LVDC 배전계통에서 DC전원의 공급을 위한 컨버터나 DC차단기의 보호동작은 AC 보호기기 보다 훨씬 빠르기 때문에, 기존의 T-C곡선의 반 한시특성에 의한 보호기기간의 보호협조 운용이 어려운 문제점을 가지고 있다. 따라서, 본 논문에서는 LVDC 배전계통에서 사고지점에 따라 다양하게 나타날 수 있는 사고전류의 경사각 개념에 대하여 정의하고, 이를 바탕으로 컨버터와 보호기기간의 협조동작을 신속 정확하게 수행하고, 정전구간의 범위를 최소화할 수 있는 LVDC 배전계통의 사고구간분리 보호협조 알고리즘을 제안한다. 즉, LVDC 배전계통에서의 사고전류가 선로정수에 의해 사고지점에 따라 비례적으로 변하는 경사각의 특성을 이용하여 메인 컨버터가 탈락되기 전에 사고구간을 선택적으로 분리하도록 한다. 또한, 본 논문에서는 배전계통 상용해석 프로그램인 PSCAD/EMTDC를 이용하여 배전용 변전소, LVDC용 컨버터 그리고 LVDC 배전선로로 구성된 1.5kV급 LVDC 배전계통 모델링을 수행한다. 이를 바탕으로 사고지점에 따른 경사각 특성 및 보호협조 운용알고리즘을 분석한 결과, 메인 컨버터가 탈락하기 전 사고구간만을 2ms 이내에 분리하고 건전구간의 수용가에 미치는 영향을 최소화 할 수 있어, 본 논문에서 제안한 사고구간분리 보호협조 운용 알고리즘이 유용함을 확인하였다.

• 전기학회논문지P
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• 제67권3호
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• pp.119-124
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• 2018

Recently, LVDC distribution network and DC microgrid with many advantages are being built. However, this LVDC distribution is an IT grounded or ungrounded system, and it is difficult to detect a ground fault because the fault current is small. In this paper, we propose a signal injection method for unipolar LVDC distribution network to detect ground fault in ungrounded LVDC distribution, and various analyzes were performed for ground fault detection.

• 조명전기설비학회논문지
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• 제29권4호
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• pp.54-61
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• 2015

Recently, DC-based power system is being paid attention as the solution for energy efficiency. As the example, HVDC (High Voltage DC) transmission system is utilized in the real power system. On the other hand, researches on LVDC (Low Voltage DC) distribution system, which are including digital loads, are not enough. In this paper, reliability in LVDC distribution system is analyzed according to the specific characteristics such as the arrangement of DC/DC converters and the number of poles. Furthermore, power quality is also taken account of since LVDC distribution system includes multiple sensitive loads and electric power converters. In order to achieve this, LVDC distribution systems are modeled using ElectroMagnetic Transient Program (EMTP) and both the minimal cut-set method and Customer Interruption Cost (CIC) are used in the reliability analysis.

• 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.

• 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.

• 전기학회논문지
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• 제65권1호
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• pp.158-164
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• 2016

That's the reason why LED lighting has to employ AC power inlet. However, LED is a kind of diode, semiconductor, it's driven by DC power. With whis reason all of LED lighting should have AC/DC converter in its systems. This converter causes energy loss, it's the target for lesson the energy loss. To reduce this energy loss, DC power distribution structure can be used. LED lighting system using LVDC is a kind of DC power distribution structure, but LVDC has severe voltage drop which makes non-uniform brightness in lighting system. In this paper, we suggest a novel structure for the uniform brightness in LVDC LED lighting system using IoT based network system. The constructed test-bed system of suggested structure shows this structure can con control the brightness with uniformity.

• 전기학회논문지
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• 제63권5호
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• pp.608-614
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• 2014

Recent developments and trends in the electric power consumption clearly indicate an increasing use of DC in end-user equipment. According to the trends, new DC power distribution systems have been researched and developed although we presently enjoy a predominantly AC power distribution system. We can use various grounding schemes in DC distribution system as well as in AC distribution system to protect human body and equipments. However, we need to evaluate carefully which grounding scheme is appropriate for a specific system before applying those schemes. In this paper, we analyze the human safety and system effect according to various grounding schemes in Low Voltage DC (LVDC) distribution system. Some components in LVDC distribution system are modeled and computer simulations are conducted by using ElectroMagnetic Transient Program (EMTP).

• 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.

• 한국산학기술학회논문지
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• 제20권4호
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• pp.25-34
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• 2019

최근, 출력전압의 제어가 가능하고 양방향 운용이 가능한 PWM(Pulse Width Modulation) 정류기가 도입되고 있다. 그러나, PWM 정류기가 적용될 경우, 전력계통측에서 사고발생하면, 회생전력에 의한 사고전류 공급으로 기존의 사고전류 크기 및 방향이 바뀔 가능성이 있다. 또한, 경전철용 급전시스템에서는 장거리 지점에서 사고가 발생하는 경우, 사고전류의 크기가 크게 감소되고, 부하전류와 비슷하거나 더 작은 경우가 발생할 수 있기 때문에 이에 대한 적절한 보호협조 운용 방안이 필요한 실정이다. 따라서, 본 논문에서는 상기의 문제점들을 해결하기 위하여, 경전철용 LVDC 배전선로의 보호기기 운용 방안을 제안한다. 구체적으로는 LVDC 배전선로에서의 거리 및 단락저항별 사고특성을 분석하여, 다양한 조건에서 사고를 적절하게 판별하는 직류선택계전기의 보호협조 운용방안을 제안한다. 또한, 배전계통 상용 해석 프로그램인 PSCAD/EMTDC를 이용하여 AC 계통, PWM 정류기, LVDC 배전선로로 구성된 경전철용 급전시스템의 모델링을 제시한다. 한편, 제안한 보호협조 알고리즘과 모델링을 이용하여 LVDC 배전선로의 보호기기 특성을 분석한 결과, 제안한 운용방식에서는 전류 경사각의 급격한 감소를 판정하는 보호요소를 추가한다. 따라서, 사고지점의 단락저항이 높거나 장거리 선로인 경우에도, 보호기기가 사고전류와 부하전류를 적절히 판별할 수 있어, 본 논문에서 제안한 보호협조 운용알고리즘의 유용성을 확인하였다.

• 전기학회논문지
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• 제67권10호
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• pp.1286-1291
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• 2018

In recent years, the proliferation of DER (distributed energy resources) is progressing rapidly. In particular, research on LVDC distribution grid with various advantages has begun. In order to commercialize this LVDC grid, direct current protection method should be established by analysis of DC faults. Recently, the development of HSCB (high-speed circuit breaker) for new ${\pm}750[V]$ LVDC grid has been researched. This paper deals with the calculation of the maximum short-circuit fault current of the HSCB as a part of the development of HSCB for the LVDC distribution grid. First, modeling using PSCAD was carried out for PV array with BESS on the Gochang Power Test Center system. Next, to calculate the rated capacity of HSCB, fault currents were calculated and the characteristics were analyzed through fault simulations. Thus, this study results can help to establish short-circuit capacity calculation of HSCB and protection plan for DC protection relay system.