• Transactions of the Korean hydrogen and new energy society
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• v.27 no.5
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• pp.547-553
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• 2016

This paper presents the effect of a grid system on the performance of a small Savonius wind turbine installed side-by-side. Turbine performance is compared using three different grid systems; tetrahedral grid having a concentrated circular grid around turbine rotors, the tetrahedral grid having a concentrated rectangular grid around turbine rotors and the symmetric grid having a concentrated tetrahedral grid near the turbine rotor blades and a hexahedral grid. The commercial code, SC/Tetra has been used to solve the three-dimensional unsteady Reynolds-averaged Navier-Stokes analysis in the present study. The Savonius turbine rotor has a rotational diameter of 0.226m and an aspect ratio of 1.0. The distance between neighboring rotor tips keeps the same length of the rotor diameter. The variations of pressure and power coefficient are compared with respect to blade rotational angles and rotating frequencies of the turbine blade. Throughout the comparisons of three grid systems, it is noted that the symmetric grid having a concentrated tetrahedral grid near the turbine rotor blades and a hexahedral grid has a stable performance compared to the other ones.

• Proceedings of the Korean Society of Computer Information Conference
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• 2011.06a
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• pp.83-86
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• 2011

2009년 7월 G8 확대정상회의에서 이태리와 공동으로 Smart Grid 선도국으로 한국이 지정되었다. 하지만 차세대 국가 성장 동력인 Smart Grid에 대한 사이버 공격 사례가 발생하고 있으며, 모의실험을 통해 보안 위협이 예측되고 있어, Smart Grid 공격을 분석하고, 안전성을 확보하기 위한 Smart Grid 보안기술에 대한 연구가 필요하다. 본 논문은 Smart Grid의 AMI, 네트워크 인프라, 시스템의 스마트 제어 및 스마트 서비스에 대한 보안성 분석과 램 공격, 주파수 크래킹, 악성코드 등의 공격과 취약점에 관한 연구를 한다. 그리고 Smart Grid 기술에 대한 공격을 방어 할 수 있는 보안 기술 및 보안 방법을 연구한다. 본 연구를 통해 Smart Grid에 대한 보안성을 강화하여 Smart Grid 보안기술 발전에 기여할 것이다.

• Proceedings of the Korean Society of Computer Information Conference
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• 2011.06a
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• pp.71-74
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• 2011

2030년까지 한국에 Smart Grid를 구축할 계획을 가지고 추진하고 있다. Smart Grid는 지능형 전력망으로 기존의 전력망에 IT를 접목시켜 통신을 실시하여 양방향성을 가지게 된다. 기존의 전력망에 부가될 IT전기기기들은 기존에 IT가 지니고 있는 취약점들이 있어 기존의 Smart Grid공격에 노출되어 있다. 본 논문에서는 한국보다 먼저 구축되어서 활용되고 있는 미국의 Smart Grid에 대한 공격사례를 분석한다. 그리고 한국 Smart Grid에 대한 전기IT기기의 취약점을 분석하여, 한국 Smart Grid에 대한 예상 공격을 분석하고, 보안 대책을 제시한다. 본 논문은 한국 Smart Grid에 안정성과 보안성을 갖춘 기술 자료로 활용할 것이다.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.1
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• pp.41-50
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• 2014

The rising penetration of renewable energy resulted in the development of grid-connected large-scale power plants. Therefore, grid stabilization, which depends on the system-type or grid of each country, plays an important role and has been strengthened by different grid codes. With this background, VDE-AR-N 4105 for photovoltaic (PV) systems connected to the low-voltage grid and the German Association of Energy and Water Industries (BDEW) introduced the medium-voltage grid code for connecting power plants to the grid and they are the most stringent certifications. In this paper, an optimal control strategy scheme for three-phase grid-connected PV system is enhanced with VDE-AR-N 4105 and BDEW grid code, where both active/reactive powers are controlled. Simulation and experimental results of 100kW PV inverter are shown to verify the effectiveness of the proposed implemental control strategy.

• Journal of the Korean Society of Radiology
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• v.9 no.7
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• pp.515-521
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• 2015

This study assessed the degradation of image quality caused by grid artifacts and $moir{\acute{e}}$ pattern artifacts in a stationary grid, and the degradation of image quality caused by cut off artifacts in a moving grid. X-ray images were acquired in a stationary grid and a moving grid with X-ray exposure conditions of 100 cm, 80 kVp, and 30 mA using a CDRAD phantom and a 24 cm thickness acrylic phantom. Observer's perception of X-ray imaging using CDRAD Analyzer was mean 49.36, standard deviation 3.76, maximum 55.56, and minimum 38.67 in the stationary grid, and 47.04, 12.69, 55.56, and 20.89, respectively, in the moving grid. The stationary grid was superior to the moving grid in terms of the mean and standard deviation of observer's perception.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.12
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• pp.948-952
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• 2009

Recently, a new distributed grid scheme, called DS-GRID(distributed S-GRID), has been proposed to manage the location information of moving objects in a spatial network[1]. However, because DS-GRID uses uniform grid cells, it cannot handle skewed data which frequently occur in the real application. To solve this problem, we propose a dynamic distributed grid scheme which splits a grid cell dynamically based on the density of moving objects. In addition, we propose a k-nearest neighbor processing algorithm for the proposed scheme. Finally, it is shown from the performance analysis that our scheme achieves better retrieval and update performance than the DS-GRID when the moving objects are skewed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.9
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• pp.1209-1216
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• 2013

Recently, there is a rising interest in smart grid operating system which manages various types of distributed generation, smart meters, and electric vehicles with power grid. Considering the features of smart grid environment, the interoperability should be one of the important factors to build smart grid environment successfully. To secure interoperability, smart grid operating system should conform to some standards in terms of the data representation and communication. CIM and OPC-UA are the international standards widely used in smart grid domain for enabling interoperability. They provide common information model and the unified architecture for communicating between each systems or applications. In this paper, we illustrate a smart grid operating system that we have developed to secure interoperability between not only applications but also numerous legacy systems(applications) by implementing CIM based information model and OPC-UA based communication interface services.

• Nuclear Engineering and Technology
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• v.39 no.6
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• pp.737-746
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• 2007

A spacer grid, which is one of the most important structural components in a PWR fuel assembly, supports its fuel rods laterally and vertically. Based on in-house design experience, scrutiny of the design features of advanced nuclear fuels and the patents of other spacer grids, KAERI has devised its own spacer grid shapes and acquired patents. In this study, a performance evaluation of KAERI's spacer grid shapes was carried out from mechanical/structural and thermohydraulic view points. A comparative performance evaluation of commercial spacer grid shapes was also carried out. The comparisons addressed the spring characteristics, fuel rod vibration characteristics, fretting wear resistance, impact strength characteristics, CHF enhancement, and the pressure drop level of the spacer grid shapes. The results show that the performances of KAERI's spacer grid shapes are as good as or better than those of the commercial spacer grid shapes.

• Journal of Power Electronics
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• v.15 no.3
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• pp.806-818
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• 2015

Based on the inherent relationship between dc-bus voltage and grid feeding active power, two dc-bus voltage regulators with different references are adopted for a grid-connected PV inverter operating in both normal grid voltage mode and low grid voltage mode. In the proposed scheme, an additional dc-bus voltage regulator paralleled with maximum power point tracking controller is used to guarantee the reliability of the low voltage ride-through (LVRT) of the inverter. Unlike conventional LVRT strategies, the proposed strategy does not require detecting grid voltage sag fault in terms of realizing LVRT. Moreover, the developed method does not have switching operations. The proposed technique can also enhance the stability of a power system in case of varying environmental conditions during a low grid voltage period. The operation principle of the presented LVRT control strategy is presented in detail, together with the design guidelines for the key parameters. Finally, a 3 kW prototype is built to validate the feasibility of the proposed LVRT strategy.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.145-146
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• 2011

A micro-grid (MG) is usually interconnected to the main grid through the dedicated line. Immediately after the removal of the grid supply, the MG should be disconnected and remain disconnected until the main grid is re-energized. It should detect islanding condition as soon as it happens to adjust the setting of the protection relays in the MG. This paper proposes an islanding detection algorithm for the MG based on the active and reactive power delivered to the dedicated line in the time domain. The performance of the proposed algorithm is verified under islanding conditions and fault conditions using the PSCAD/EMTDC simulator. The results indicate that the proposed algorithm can discriminate the islanding conditions from the various fault conditions.