• Journal of IKEEE
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• v.24 no.1
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• pp.208-215
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• 2020

In this study, the output 380V direct current DC-DC converter for low-voltage direct current(LVDC) distribution was designed in three types, and the voltage and current characteristics of the three types of DC-DC converter were compared and analyzed through simulation. When the converter was configured using a parallel structure with the power metal-oxide semiconductor field-effect transistor and two current suppression insulated-gate bipolar transistors(IGBTs), the time when the output voltage was stabilized at DC 380V was relatively short with 9ms and the range of output current changes was also between 44.8A and 50.2A, indicating that the width of change was much smaller and the effect of current suppression was greater compared to when IGBT was not applied(68~83A). These results suggest that the proposed DC-DC converter for LVDC distribution is likely to be applied to smart grid construction.

• Journal of Power Electronics
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• v.16 no.1
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• pp.340-350
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• 2016

A cascaded hybrid multilevel inverter including a reconfiguration technique for low voltage dc distribution applications is proposed in this paper. A PWM generation fault detection and reconfiguration paradigm after an inverter cell fault are developed by using only a single-chip controller. The proposed PWM technique is also modified to reduce switching losses. In addition, the proposed topology can reduce the number of required power switches compared to the conventional cascaded multilevel inverter. The proposed technique is validated by using a 3-kVA prototype. The switching losses of the proposed multilevel inverter are also investigated. The experimental results show that the proposed hybrid inverter can improve system efficiency, reliability and cost effectiveness. The efficiency of proposed system is 97.45% under the tested conditions. The proposed hybrid inverter topology is a promising method for low voltage dc distribution and can be applied for the multiple loads which are required in a data center or telecommunication building.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.6
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• pp.911-917
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• 2016

DC-based power system is paid attention as interests in energy efficiency and power quality are increased. However, standardization and researches for commercializing Low Voltage DC(LVDC) distribution system are still insufficient. Protection system, which is closely related with reliability, power quality, safety, and life expectancy of components in power system, is also included. This paper therefore analyzes fault response characteristics in LVDC distribution system as a preliminary study on protection schemes. A stepwise analysis on fault current from both AC/DC converter and DC/DC converter is performed and related expressions are derived. And then, modeling and simulation with various conditions are conducted by using ElectroMagnetic Transients Program (EMTP) to verify analysis results. Based on research results in the paper, direction for development of protection schemes for LVDC distribution system is suggested.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.6_3
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• pp.1259-1267
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• 2023

In recent years, as the demand for distributed power has increased, the need for microgrids connected to grid power and renewable power generation sources has emerged. In the case of DC microgrids, reactive power does not occur, and power conversion losses are reduced compared to AC when connecting to the load and power grid[2]. With the revitalization of the DC distribution network industry, various studies and demonstrations of DC microgrids have been carried out. In the case of the recent unit distribution, its stability and effectiveness have been verified through empirical and research analysis. However, there is a lack of empirical tests to prevent chain accidents for the protection of the power grid circuits and the misoperation of the distributed power system caused by individual accidents when connecting various distributed power sources and power grids. In this paper, the operation plan of a stable multi-circuit DC distribution connection for the demonstration site was verified through the protection cooperation and operation algorithm for the stable linkage management of the DC distribution network composed of such a multi-circuit.

• Journal of IKEEE
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• v.22 no.3
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• pp.754-758
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• 2018

Analysis methods in the power system are static analysis, dynamic analysis and online analysis, offline analysis. The static analysis is used for the existing power system analysis method and the static analysis is mainly used for PSS / E. However, in the real system where the value changes in real time which we are using, dynamic analysis is required which can be analyzed in real time for accurate analysis. Therefore, attention is focused on EMS (Energy Management System) and importance is increasing. Among the various EMS systems, we will cover state estimation, which is a static on-line analysis that can receive and interpret data from the acquisition point in real time. DC systems are spreading in various fields such as DC load, DC distribution, renewable energy. As such, much attention and attention are focused on the DC system. In this paper, we have studied the feasibility through the case study and the interpretation of the state estimation that can be applied to the DC system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.1-12
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• 2021

Technologies for an MVDC(medium voltage direct current) distribution system are being considered as an effective alternative to overcome the interconnection delay issues of PV systems. However, the implementation of a DC distribution system might lead to economic problems because of the development of DC devices. Therefore, this paper deals with the scale of a PV plant based on its capacity and proposes hosting-capacity models for PV systems to establish a network to evaluate the feasibility of an MVDC distribution system. The proposed models can be classified as AC and DC distribution systems by the power-supply method. PV systems with hundreds of MW, dozens of MW, and a few MW can be categorized as large-scale, medium-scale, and small-scale models, respectively. This paper also performed modeling for an economic evaluation of MVDC distribution system by considering both the cost of AC and DC network construction, converter replacement, operation, etc. The profit was composed of the SMP and REC rate of a PV plant. A simulation for economic evaluation was done for the MVDC distribution system using the present worth and equal-principal costs repayment method. The results confirmed that the proposed model is a useful tool to evaluate economic issues of a DC distribution system.

• Journal of Electrical Engineering and Technology
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• v.8 no.5
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• pp.1212-1220
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• 2013

In general, for a large power system like DC distribution system for buildings, several power converters are modularized for parallel operation. However, in parallel operation, inconsistency of parameters in each module causes circulating current in the whole system. Circulating current is directly related to loss, and, therefore, it is most important for the safety of the power system to supply the suitable current to each module. This paper proposes a control method to reduce circulating current caused during parallel operation. Accordingly, the validity of parallel operation system including response characteristics and normal state was verified by simulation and experiment result.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.2
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• pp.75-81
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• 2015

At the end of the 19th century, Edison's DC power system and Tesla's AC power system was debated in power market. Finally, AC system became the primary system of the power market because both step-up and step-down of voltage by using transformer and long-distance power transmission are easily possible. However, nowadays the power market takes some action for introducing DC system. Both domestic and foreign researchers are conducting the study on the DC system as well. Some researchers have conducted the studies on power quality and economic evaluation of the DC distribution system but DC distribution system is still controversial in terms of the effectiveness and reliability. In this paper, we calculate the reliability indices of the Low Voltage Direct Current(LVDC) distribution system considering arrangement of power electronics, layout of the distribution system, and distance between load points.

• Progress in Superconductivity and Cryogenics
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• v.19 no.1
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• pp.26-29
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• 2017

We studied the distribution of the current density and its magnetic-field dependence in GdBCO coated conductors with AC bias currents using low temperature scanning Hall probe microscopy. We selectively measured magnetic field profiles from AC signal obtained by Lock-in technique and calculated current distributions by inversion calculation. In order to confirm the AC measurement results, we applied DC current corresponding to RMS value of AC current and compared distribution of AC and DC transport current. We carried out the same measurements at various external DC magnetic fields, and investigated field dependence of AC current distribution. We notice that the AC current distribution unaffected by external magnetic fields and preserved their own path on the contrary to DC current.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.516-517
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• 2015

This paper proposes the feedforward compensation method of output voltage with 3phase AC/DC PWM converter on DC distribution system for improved response. AC/DC PWM converter on DC distribution is required power supply of high quality because of renewable energy sources and load links. In general, Feedforward compensation method of 3phase AC/DC PWM converter receives the sensor input to the output current, load power. Resulting, error of the sensing values and communication cause time delay. Therefore, Feedforward compensation method through only the output voltage is proposed in this paper. The feedforward compensation method through only the output voltage can be applied to the two-level AC/DC PWM converters, as well as multi-level converter or inverter.