• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.11
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• pp.2142-2148
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• 2009

A microgrid is defined as two or more distributed generation or storage assets configured in a networks and capable of operation in parallel or independently form a larger electric gird, while providing continuous power to one or more end users. And when microgrid are separated from grid oprating protection devices by faults of the grid side, microsources should charge electrical power needs of loads in microgrid and operate maintaining power quality. The magnitude of the switching transients will vary based on voltage phase difference between microgrid and grid, when the microgrid is resynchronized to grid. In this paper, when microgrid is resynchronized to grid, we analyzed the existing problems for reducing switching transients of SS(Static Switch).

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.380-381
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• 2019

This paper presents a grid voltage-sensorless current control design for an LCL-filtered grid-connected inverter with the purpose of enhancing the reliability and reducing the total cost of system. A disturbance observer based on the gradient steepest descent method is adopted to estimate the grid voltages with high accuracy and light computational burden even under distorted grid conditions. The grid fundamental components are effectively extracted from the estimated gird voltages by means of a least-squares algorithm to facilitate the synchronization process without using the conventional phase-locked loop. Finally, the estimated states of inverter system obtained by a discrete current-type full state observer are utilized in the state feedback current controller to realize a stable voltage-sensorless current control scheme. The effectiveness of the proposed scheme is validated through the simulation results.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.47 no.2
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• pp.54-64
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• 2010

Localization is the most important feature in the sensor network environment because it is a basic element enabling people and things to aware the circumference environment. Existing localization methods can be categorized as either range-based or range-free. While range-based is known to be not suitable because of the irregularity of radio propagation and the additional device requirement. range-free is much appropriated for the resource constrained sensor network because it can actively locate by means of the communication radio. But its location accuracy is just depended on the density of circumference nodes; it is very low in low-density sensor network environment. This paper proposes a mobile object tracking method, named DRTS(Distributed Range-hybrid Tracking Scheme), with combining range-based and range-free. It is optimally making use of the location, communication range, and received signal strength from circumference nodes. Especially, it can greatly improve the mobile tracking accuracy by adapting a new prediction method, named EGP(Estimative Gird Points) into the proposed location estimation method. The simulation results show that our method outperforms the other localization and tracking methods in the tracking accuracy point of view.

• Journal of the Korean Solar Energy Society
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• v.32 no.spc3
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• pp.228-234
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• 2012

This paper presents the algorithm of the compensation of the grid current distortion caused by the grid voltage unbalance and distortion in 3-phase bi-directional DC to AC inverter. Usually 3-phase grid system has unbalance and distortion because of connecting 1-phase and non-linear load with 3-phase load using same input node. Controlling 3-phase inverter by general method under the unbalanced and distorted grid voltage, the grid current has distortion. This distortion of the grid current cause the grid voltage distortion again. So, it need to control the grid current balanced and non-distorted, even the grid voltage gets unbalanced and distorted. There are some complex method to compensate the gird current distortion. it sugest simple method to solve the problem. PSIM simulation is used to validate the proposed algorithm.

• Journal of Welding and Joining
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• v.30 no.1
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• pp.59-63
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• 2012

The spacer grid is one of the main structural components in a fuel assembly. It supports fuel rods, guides cooling water and maintains geometry from external impact load and cyclic stress by the vibration of nuclear fuel rod, it is necessary to have sufficient strength against dynamic external load and fatigue strength. In this study, the mechanical properties and fatigue characteristics of laser beam welded zircaloy thin sheet are examined. The material used in this study is a zirconium alloy with 0.66 mm of thickness. The fatigue strength under cyclic load was evaluated at stress ratio R=0.1. S-N curves are presented with statistical testing method recommend by JSME- S002 and compared with S-N curves at R.T. and $315^{\circ}C$. As a result of the experimental approach, the design guide of fatigue strength is proposed and the results obtained from this study are expected to be useful data for spacer gird design.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1787-1791
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• 2006

수공 구조물 설계를 위한 설계홍수량의 산정은 실측홍수량의 빈도해석을 통해 빈도별 설계 홍수량을 결정하는 것이 가장 바람직하나, 관측 홍수량 자료의 부족으로 인해 대상 유역의 강우량을 강우-유출 모형에 입력하여 설계 홍수량을 구하는 것이 일반적이다. 이러한 목적을 위해 이용되는 강우-유출 모형의 효과적인 적용을 위해서는 적절한 모형 매개변수의 결정이 매우 중요하며, 이를 위해 주로 이용되는 GIS 프로그램의 경우에는 적절한 격자 크기의 결정이 매개 변수 및 홍수량의 산정에 큰 영향을 미치게 된다. 본 연구에서는 분포형 강우-유출 모형인 TOPMODEL을 이용한 분석을 실시하였으며, 격자 크기의 변화에 따른 홍수량의 변화를 실측 홍수량과 비교 분석하였다. 분석 결과 괴산댐 유역 의 경우 격자 크기 $100{\times}100m$일 때 추출된 지형학적 매개변수를 이용해서 모의한 유출량이 실측 유량과 가장 근접한 것으로 분석 되었으며, 격자 크기에 따른 홍수량의 변화를 파악할 수 있었다. 추후 대상 유역을 확대한 연구를 통해 유역특성에 따른 격자 크기 결정 기준이 수립된 다면 분포형 강우-유출 모형의 신뢰성 향상에 기여할 수 있을 것으로 기대된다.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.397_398
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• 2009

Demonstrations to deploy high temperature superconducting (HTS) cable to the real gird are actively carried out throughout the world. Power utilities have an interest in the inherent advantage of the HTS cable system, and achieve the expected results from the series of verification test. To embody the reliability in the phenomenon occurred commonly in three-phase system, we simulate the load unbalance. A 22.9 kV large scale HTS cable system with the specification of 100 m-long, 50 MVA capacity has been tested with up to 30% unbalance rate. To evaluate the effect of AC loss increase due to the unbalanced load, the cooling loads are measured by the calorimetry method. In this paper, the correlation between AC loss and load unbalance is described and investigated precisely.

• Journal of Computing Science and Engineering
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• v.9 no.2
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• pp.39-50
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• 2015

Genetic algorithm (GA) and particle swarm optimization (PSO) are two excellent approaches to multimodal optimization problems. However, slow convergence or premature convergence readily occurs because of inappropriate and inflexible evolution. In this paper, a novel optimization algorithm with a flexible grid optimization (FGO) is suggested to provide adaptive trade-off between exploration and exploitation according to the specific objective function. Meanwhile, a uniform agents array with adaptive scale is distributed on the gird to speed up the calculation. In addition, a dominance centroid and a fitness center are proposed to efficiently determine the potential guides when the population size varies dynamically. Two types of subregion division strategies are designed to enhance evolutionary diversity and convergence, respectively. By examining the performance on four benchmark functions, FGO is found to be competitive with or even superior to several other popular algorithms in terms of both effectiveness and efficiency, tending to reach the global optimum earlier. Moreover, FGO is evaluated by applying it to a parameter decision in a least squares support vector machine (LS-SVM) to verify its practical competence.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.11
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• pp.27-36
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• 2013

Islanding in a gird connected inverter of wind power generation system may influence a bad effect on equipments or yield safety hazards on grid so it should be detected rapidly and exactly. A passive method to detect islanding is comparatively simpler than an active method but suffers from non detection zone (NDZ). On the other hand, the active method can significantly reduce NDZ by injecting a disturbance into inverter output. To improve the reliability of islanding detection, this paper proposes a hybrid anti-islanding detection method combining the conventional passive method as well as the active method based on novel harmonic injection method using fourier transform. The proposed scheme is fast to detect islanding when NDZ does not exist because it has the nature of passive method. Under NDZ, the active method can detect occurrence of islanding reliably. The effectiveness and validity of the proposed scheme is proved through comparative simulations.

• Journal of the Korean Society for Railway
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• v.11 no.1
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• pp.13-18
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• 2008

In this study, unsteady wind pressure analyses on platform screen door (PSD) have been conducted considering the flow intereference effects between the moving train and the configuration of subway station. The major role of PSD prevents passenger accidents, wind pressure, polluted dust and noise when the train is entering the station platform. Computational fluid dynamic method with moving gird algorithm has been adopted to accurately predict unsteady pressure levels exerted on the PSD. Closed and open type station configuration are considered. Also, wind pressure levels for passing and stopping drive motion of the entering train are presented and practically compared each other.