• Journal of Power Electronics
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• 제13권5호
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• pp.896-908
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• 2013

Under high grid impedance conditions, it is difficult to guarantee the stability of grid-connected inverters with an LCL filter designed based on ideal grid conditions. In this paper, the theoretical basis for output impedance calculation is introduced. Based on the small-signal model, the d-d channel closed-loop output impedance models adopting the converter-side current control method and the grid-side current control method are derived, respectively. Specifically, this paper shows how to simplify the stability analysis which is usually complemented based on the generalized Nyquist stability criterion (GNC). The stability of each current-controlled grid-connected system is analyzed via the proposed simplified method. Moreover, the influence of the LCL parameters on the stability margin of grid-connected inverter controlled with converter-side current is studied. It is shown that the stability of grid-connected systems is fully determined by the d-d channel output admittance of the grid-connected inverter and the inductive component of the grid impedance. Experimental results validate the proposed theoretical stability analysis.

• 대한조선학회논문집
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• 제58권2호
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• pp.90-96
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• 2021

In this study, the method of determining the state of grid points in the adaptable surface particle method based on grid system developed as a free-surface tracing method was improved. The adaptable surface particle method is a method of determining the state of the grid point according to the shape of the free-surface and obtaining the intersection of the given free-surface and grid line where the state of the grid point changes. It is difficult to determine the state of grid points in the event of rapid flow, such as collision or separation of free-surfaces, and this study suggests a method for determining the state of current grid points using the state of surrounding grid points where the state of grid point are known. A grid layer value was assigned sequentially to a grid away from the free-surface, centering on the boundary cell where the free-surface exists, to identify the connection information that the grid was separated from the free-surface, and to determine the state of the grid point sequentially from a grid away from the free-surface to a grid close to the free-surface. To verify the improved method, a numerical analysis was made on the problem of dam break in which a sudden collision of free-surface occurred and the results were compared, and the results were relatively reasonable.

• 한국산업정보학회논문지
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• 제9권1호
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• pp.77-84
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• 2004

최근, 국내외적으로 국가차원에서 Grid에 대한 다양한 연구가 이루어지고 Grid 컴퓨팅 기술에 대한 상용화의 추세가 보이면서 Grid 시스템에 참여하는 엔티티의 수가 날로 증가하고 있다. 따라서 Globus에 기반 한 Grid환경에서의 기존의 LDAP시스템은 늘어나는 부하를 처리하기에는 충분하지 못하게 되었고 제공할 수 있는 성능의 한계를 초과하고 있다. 이를 위하여 고성능 Grid환경에 부합되는 새로운 LDAP시스템의 설계가 필수적이고 이를 위해서는 기존 LDAP시스템에 대한 성능분석이 우선시 되어야 한다. 하지만 기존의 대부분의 연구는 읽기 동작이 대부분을 차지하는 기존의 응용들을 위한 성능향상에 목적을 두고 있어서 쓰기 동작이 대부분을 차지하는 Grid환경에 적용하기에는 부적합하다. 본 논문에서는 노드수(n), 도착율(λ), 읽기 확률(Pr)변화에 따른 분산 기반 모델과 복제 기반 모델에서 성능분석의 결과를 제시한다. 이를 위하여 M/M/l 큐잉모델을 기초로 기존 LDAP시스템에 대한 분산과 복제에 기반 한 분석모델을 도출하고, 분석모델을 통한 성능분석의 결과를 제시한다. 본 논문의 목표는 이러한 성능분석의 결과를 바탕으로 고성능 Grid환경에 부합되는 새로운 LDAP시스템의 설계방향을 제시하고자 한다. 또한 이러한 결과들은 고성능 Grid환경에서 LDAP기반의 GIS시스템의 설계에 기초자료 활용할 수 있을 것으로 사료된다.

• 한국산업정보학회:학술대회논문집
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• 한국산업정보학회 2003년도 춘계학술대회
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• pp.3-7
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• 2003

For high performance Grid environments, an efficient GIS(Grid Information Service is required In the Metacomputing Directory Service(MDS) of the Glogus middleware, the Lightweight Directory Access Protocol(LDAP), which is a distributed directory service protocol, is used. The LDAP GIS differs from general purpose LDAP directories in that most of the LDAP operations are write in Grid environments. To get an efficient design of the GIS, it is thus required to analyze the performance of the LDAP system in the context of Grid environments. This paper presents the result of a performance analysis of LDAP systems. The main objective of the evaluation is to see the performance scalability of the LDAP system in the Grid environment where the write operations prevails. Based on these results, we suggest directions of an efficient LDAP-based GIS for a high performance Grid.

• Journal of Electrical Engineering and Technology
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• 제12권2호
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• pp.522-532
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• 2017

In this study, we propose a fault analysis method for a power distribution grid with PCS-based DERs. We first explain the characteristics of a PCS-based DER. According to the characteristics, the DER is considered as a current-controlled voltage source, which produces varying voltages within a certain limit so that currents equal to given references flowing from the DER to the grid (currents controlled). So, we introduce the symmetrical equivalent models in the form of varying voltage source for fault analysis and then, construct a convex optimization problem to solve the fault problem associated with the equivalent models and grid conditions. Thus, the proposed method enables to perform a proper fault analysis considering the characteristics of the DER, which are currents controlled, voltage limited, and unity power factor achievement. To verify the validity of the proposed method, we perform computer simulations with the proposed method and with MATLAB Simulink, and the results are compared.

• 한국측량학회지
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• 제34권6호
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• pp.569-578
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• 2016

With the recent advancement of surveying and technology, the spatial data acquisition rates and precision have been improved continually. As the updates of spatial data are rapid, and the size of data increases in line with the advancing technology, the LOD (Level of Detail) algorithm has been adopted to process data expressions in real time in a streaming format with spatial data divided precisely into separate steps. The existing GRID analysis utilizes the single DEM, as it is, in examining and analyzing all data outside the analysis area as well, which results in extending the analysis time in proportion to the quantity of data. Hence, this study suggests a method to reduce analysis time and data throughput by acquiring and analyzing DEM data necessary for GRID analysis in real time based on the area of analysis and the level of precision, specifically for streaming DEM data, which is utilized mostly for 3D geographic information service.

• Journal of Power Electronics
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• 제13권2호
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• pp.313-321
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• 2013

This paper describes the operation analysis results of a communication-based DC micro-grid using a hardware simulator developed in the lab. The developed hardware simulator is composed of distributed generation devices such as wind power, photovoltaic power and fuel cells, and energy storage devices such as super-capacitors and batteries. Whole system monitoring and control was implemented using a personal computer. The power management scheme was implemented in a main controller based on a TMS320F28335 chip. The main controller is connected with the local controller in each of the distributed generator and energy storage devices through the communication link based on a CAN or an IEC61850. The operation analysis results using the developed hardware simulator confirm the ability of the DC micro-grid to supply the electric power to end users.

• Journal of Power Electronics
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• 제15권5호
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• pp.1338-1347
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• 2015

DC injection is a critical issue in transformerless grid-connected inverters. DC injection control based on virtual capacitor has the advantages of low cost, low loss, high accuracy and easy implementation. In this paper, the principle of DC injection control based on virtual capacitor was analyzed. In addition, the applicable conditions, working process, steady state error and advantages were also discussed in detail. The design of the control parameters based on virtual capacitor was proposed in a grid-connected inverter with LCL filter. The robustness of the control parameters was also discussed. Simulation and experimental results verify the validity of the analysis and demonstrate that this research has a certain value in engineering applications.

• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2017년도 제55차 동계학술대회논문집 25권1호
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• pp.75-78
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• 2017

This paper compares operational and network analysis of centralized and distributed repository for big data solutions in the IoT enabled Smart Grid environment. The comparative analysis clearly depicts that centralize repository consumes less memory consumption while distributed locality-based repository reduce network complexity issues than centralize repository in state-of-the-art Big Data Solution.

• Nuclear Engineering and Technology
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• 제38권4호
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• pp.375-382
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• 2006

Characterization tests (load vs. displacement curve) are conducted for the springs of Zirconium alloy spacer grids for an advanced LWR fuel assembly. Twofold testing is employed: strap-based and assembly-based tests. The assembly-based test satisfies the in situ boundary conditions of the spring within the grid assembly. The aim of the characterization test via the aforementioned two methods is to establish an appropriate assembly-based test method that fulfills the actual boundary conditions. A characterization test under the spacer grid assembly boundary condition is also conducted to investigate the actual behavior of the spring in the core. The stiffness of the characteristic curve is smaller than that of the strap-wised boundary condition. This phenomenon may cause the strap slit condition. A spacer grid consists of horizontal and vertical straps. The strap slit positions are differentiated from each other. They affords examination of the variation of the external load distribution in the grid spring. Localized legions of high stress and their values are analyzed, as they may be affected by the spring shape. Through a comparison of the results of the test and FE analysis, it is concluded that the present assembly-based analysis model and procedure are reasonably well conducted and can be used for spring characterization in the core. Guidelines for improving the mechanical integrity of the spring are also discussed.