• 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.

• 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.

• 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.

• 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.

• 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.

• 전력전자학회논문지
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• 제21권6호
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• pp.486-496
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• 2016

The voltage unbalance of an LVDC bipolar distribution system was controlled for high power quality. Voltage unbalance may occur in a bipolar distribution system depending on the operation of the converter and load usage. Voltage unbalance can damage sensitive load and lead to converter accidents. The conditions that may cause voltage unbalance in a bipolar distribution system are as follows. First, three-level AC/DC converters in bipolar distribution systems can lead to voltage unbalance. Second, bipolar distribution systems can be at risk for voltage unbalance because of load usage. In this paper, the output DC link of a three-level AC/DC converter was analyzed for voltage unbalance, and the bipolar voltage was controlled with algorithms. In the case of additional voltage unbalance according to load usage, the bipolar voltage was controlled using the proposed converter. The proposed converter is a dual half-bridge converter, which was improved from the secondary circuit of a dual half-bridge converter. A control algorithm for bipolar voltage control without additional converters was proposed. The balancing control of the bipolar distribution system with distributed power was verified through experiments.

• Journal of Electrical Engineering and Technology
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• 제9권5호
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• pp.1501-1510
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• 2014

Low voltage direct current (LVDC) distribution system is a suitable techno-economic candidate which can create an innovative solution for distribution network development with respect to rural electrification. This research focuses on the use of LVDC distribution system to replace some of KEPCO's existing traditional medium voltage alternating current (MVAC) distribution network for rural electrification in South Korea. Considering the technical and economic risks and benefits involved in such project, a comparative techno-economic analysis on the LVDC and the MVAC distribution networks is conducted using economic assessment method such as the net present value (NPV) on a discounted cash flow (DCF) basis as well as the sensitivity analysis technique. Each would play a role in an economic performance indicator and a measure of uncertainty and risk involved in the project. In this work, a simulation model and a computational tool are concurrently developed and employed to aid the techno-economic analysis, evaluation, and estimation of the various systems efficiency and/or performance.

• 조명전기설비학회논문지
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• 제28권6호
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• pp.113-121
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• 2014

At the end of the 19th century, a battle known as the War of the Currents was fought over how electricity would be generated, delivered, and utilized. In this day and age, there has been a growing interest in Green Growth policies as countermeasures against global warming. As a result of these policies, the use of new and renewable energy needed a power converter to replace fossil fuels has expanded. To reduce power consumption through high efficiency of conversion, Low Voltage DC (LVDC) distribution systems are suggested as an alternative. In a DC distribution system, DC loads are very efficient due to decrease the stages of power conversion. If the LVDC distribution system is adopted, not only DC load but also existing AC loads should be connected with LVDC system. Thus, the modeling of two loads is needed to analyze the DC distribution system. This paper, especially, is focused on the modeling of resistive load and electronic load including power electronic converters using ElectroMagnetic Transient Program (EMTP) software.