• Journal of Power Electronics
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• v.17 no.1
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• pp.200-211
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• 2017

Conventional boost-full-bridge and boost-hybrid-bridge two-stage inverters are widely applied in order to adapt to the wide dc input voltage range of photovoltaic arrays. However, the efficiency of the conventional topology is not fully optimized because additional switching losses are generated in the voltage conversion so that the input voltage rises and then falls. Moreover, the electrolytic capacitors in a dc-link lead to a larger volume combined with increases in both weight and cost. This paper proposes a higher efficiency inverter with time-sharing synchronous modulation. The energy transmission paths, wheeling branches and switching losses for the high-frequency switches are optimized so that the overall efficiency is greatly improved. In this paper, a contrastive analysis of the component losses for the conventional and proposed inverter topologies is carried out in MATLAB. Finally, the high-efficiency under different switching frequencies and different input voltages is verified by a 3 kW prototype.

• KIEE International Transactions on Power Engineering
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• v.3A no.4
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• pp.198-205
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• 2003

This paper proposes the adaptive relaying of protective devices applied in the neighboring distribution feeders for reliable and efficient operations of a wind farm interconnected with distribution networks by dedicated lines. A wind farm connected to an electric power network is one of the greatest alternative energy sources. However, the wind turbine generators are influenced by abnormal grid conditions such as disturbances occurring in the neighboring distribution feeders as well as the dedicated power. Particularly, in cases of a fault happening in the neighboring distribution feeders, a wind farm might be accelerated until protective devices clear the fault. Therefore, the delayed operation time of protective devices for satisfying the coordination might overly expose the interconnected wind turbine generators to the fault and cause damage to them. This paper describes the proper delayed operation time of protective relay satisfying the coordination of the distribution networks as well as reducing damage on the interconnected wind farm. The simulation results for the Hoenggye substation model composed of five feeders and one dedicated line using PSCAD/EMTDC showed that the proper delayed time of protective devices reflecting the fault condition and the power output of the wind farm could improve the operational reliability, efficiency, and stability of the wind farm.

• Proceedings of the KIEE Conference
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• 2004.07d
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• pp.2307-2309
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• 2004

This paper presents a modeling and simulation of a fuzzy controller for maximum power extraction of a grid-connected wind energy conversion system with a link of a rectifier and an inverter. It discusses the maximum power control algorithm for a wind turbine and proposes, in a graphical form, the relationships of wind turbine output, rotor speed, power coefficient, tip-speed ratio with wind speed when the wind turbine is operated under the maximum power control. The control objective is to always extract maximum power from wind and transfer the power to the utility by controlling both the pitch angle of the wind turbine blades and the inverter firing angle. Pitch control method is mechanically complicated, but the control performance is better than that of the stall regulation method. The simulation results performed on MATLAB will show the variation of generator's rotor angle and rotor speed, pitch angle, and generator output.

• Journal of computational fluids engineering
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• v.2 no.1
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• pp.117-128
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• 1997

Effects of dam and weir on the fluid flow and behavior of inclusions in the continuous casting tundish have been studied using the CFD (Computational Fluid Dynamics) technique. Inclusions affecting the quality of steel products have been considered to be passive: the fluid flow has been obtained for unstaggered grid points defined on body-fitted generalized cuvilinear coordinates with no attention on inclusions, and the spatial propagation of inclusions has been determined by using the flow field data. The result show that the dam and weir direct the flow to the free surface and increase the residence time of inclusions significantly, and thereby that inclusions have much more chance to be floated to the free surface of the tundish where it is eliminated. It is also found that they offer more margin on the geometric design of exit nozzles connected to moulds. This finding is particularly important for twin casting operations where the quality of steel products from the two moulds be kept uniformly.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.5
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• pp.2221-2235
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• 2020

Compared to the past infrastructure networks, the current smart grid network can improve productivity and management efficiency. However, as the Industrial Internet of Things (IIoT) and Internet-based standard communication protocol is used, external network contacts are created, which is accompanied by security vulnerabilities from various perspectives. Accordingly, it is necessary to develop an appropriate cybersecurity guideline that enables effective reactions to cybersecurity threats caused by the abuse of such defects. Unfortunately, it is not easy for each organization to develop an adequate cybersecurity guideline. Thus, the cybersecurity checklist proposed by a government organization is used. The checklist does not fully reflect the characteristics of each infrastructure network. In this study, we proposed a cybersecurity framework that reflects the characteristics of a microgrid network in the IIoT environment, and performed an analysis to validate the proposed framework.

• Bulletin of the Korean Chemical Society
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• v.32 no.7
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• pp.2193-2198
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• 2011

We prepared polycatenar 1H-imidazole amphiphiles having a structure in which a 1H-imidazole head was connected through a benzene ring to a pheny group having two or three oligo(ethylene glycol) chains and studied their supramolecular assembly by fluorescence spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). When the aqueous solutions of the amphiphiles ($5{\times}10^{-5}M{\sim}10^{-3}M$) were deposited onto a carbon-coated copper grid and dried, twisted structures with diameters of ~200-300 nm were imaged by TEM and AFM. We presume that the structures comprised a chain of the amphiphile dimers formed via successive hydrogen bonding between the 1H of the imidazole group and 3N of the neighboring one. In a solution of pH 4, entangled fibers with diameters of several nanometers were observed by TEM. In a pH 10 solution, film-like aggregates formed exclusively. The 1H-imidazole amphiphiles hydrolyzed tetraethoxysilane to induce gelation to form fibrous and spherical silica structures at neutral pH in aqueous solutions. No silica was formed when imidazole was used instead of the amphiphiles, suggesting that the selfassembled aggregates of the amphiphiles were responsible for the gelation.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.153-159
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• 2012

In photovoltaic system, the characteristic of photovoltaic module such as open circuit voltage and short circuit current will be changed because of cell temperature and solar radiation. Therefore, a boost converter of the PV system connects between the output of photovoltaic system and DC link capacitor of grid connected inverter as controlling duty ratio for maximum power point tracking(MPPT). This paper shows the dynamic characteristic of the boost converter by comparing single-loop control algorithm and two-loop control algorithm using both analog and digital control. The proposed both compensation method has been verified with computer simulation and simulation results obtained demonstrate the validity of the proposed control schemes.

• Journal of the Korean Solar Energy Society
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• v.34 no.4
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• pp.1-7
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• 2014

The microgrid system is the combination of photovoltaic(PV) array, load, and battery energy storage system. The control strategies were defined as multi-modes of operation, including rest operation without use of battery, power charging, and power discharging, which enables grid connected mode or islanded mode. Photovoltaic power is a problem of the uniformity of power quality because the power generated from solar light is very sensitive to variation of insolation and duration of sunshine. As a solution to the above problem, energy storage system(ESS) is considered generally. There fore, in this study, we did basic research activities about optimization method of the amount of energy used, using a smart microgrid test-bed constructed in building. First, we analyzed the daily, monthly and period energy pattern amount of power energy used, and analyzed PV power generation level which is built on the roof. Utilizing building energy pattern analysis data, we was studied an efficient method of employing the ESS about building power consumption pattern and PV generation.

• Journal of the Korean Solar Energy Society
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• v.37 no.6
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• pp.59-68
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• 2017

In accordance with the policy of local government, the large scale of wind farms have been installed in Jeju power system. However, The intermittent characteristics of wind power output may cause grid voltage and frequency variation, especially in weak power system. One of the solution to solve this problem is installation of Energy storage system (ESS). In this case, the ESS will regulate the active power generated from wind farm to mitigate fluctuation. Actually, the local government of Jeju island constructed ESS connected to Hangwon wind turbine in 2016. From this point, this paper analyzes requirement capacity of ESS to mitigate wind power fluctuation based on measured data from Hangwon wind turbine and ESS. The simulation results will be carried out by Matlab program.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.249-250
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• 2008

본 논문은 고창 전력품질 실증시험장에서 실 계통 연계를 위해 시험 중인 1.5M급 풍력발전 시뮬레이터의 선로정수를 PSCAD/EMTDC를 이용하여 모의하고 선로정수에 따른 풍력발전시스템이 계통에 미치는 영향을 분석하는데 중점을 두었다. 현재 고창에 설치되어있는 전력품질 실증시험장은 22.9kV 급전선에 SSTS(Synchronous Static Transfer Switch)의 한쪽 스위치로 직접 연결되어있으며 다른 한 쪽은 전력계통에서 발생되는 다양한 형태의 이벤트를 발생시키는 SSHG(Sag Swell Harmonics Generator)를 통하여 연결되어있다. 전력품질 향상기기중 하나인 DVR(Dynamic Voltage Restorer)는 SSTS의 부하쪽으로 직렬로 연결되어있으며 delta-wye 변압기를 통해 정류기 부하와 APF(Active Power Filter), 그리고 순저항부하와 유도성부하가 연결되어 있고 또한 SSHG를 통하여 연결된 배전선에는 DSTATCOM(Distribution Static Compensator)가 병렬로 연결되어있다. 본 논문에서는 고창에 있는 풍력발전 시뮬레이터와 동일하게 PSCAD/EMTDC로 구성하였으며 선로정수를 모델링 하기 위해 선로모델을 10Km, 20Km, 30Km, 40Km,로 설정하여 선로정수에 따른 계통영향을 분석하여 풍력발전 시뮬레이터에서 모의가능 한 선로정수 값을 제시한다.