• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -1
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• pp.333-336
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• 2000

We discuss the direct methods (Gauss-Jordan and Gaussian eliminations) to solve linear systems on distributed memory parallel computers. It will be shown that the so-called row-cyclic storage gives rise to the best performance among the standard three (row-cyclic, column-cyclic and cyclic-cyclic) data storages. We also show that Gauss-Jordan elimination, rather than Gaussian elimination, is highly efficient for the direct solution of linear systems in parallel processing, though Gauss-Jordan elimination requires a larger number of arithmetic operations than Gaussian elimination. Numerical experiment is performed on HITACHI SR12201 with the standard libraries MPI and BLAS.

• Asia pacific journal of information systems
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• 제1권1호
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• pp.49-62
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• 1991

This paper examines the problems of database partitioning and file allocation in a fixed topology distributed computer network. The design objective is to make files as collections of attributes and to allocate these files to network nodes so that a minimum total transmission cost is achieved subject to storage capacity constraints. A mathematical model for solving the problem is formulated and, the resulting optimization problem is shown to fall in a class of NP-complete problems. A new heuristic algorithm is developed which uses the idea of allocating attributes according to the transaction requirements at each computer node and then making files using the allocated attributes. Numerical results indicate that the heuristic algorithm yields practicable low cost solutions in comparison with the existing methods which deal with the file allocation problems and database partitioning problems independently.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권6호
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• pp.2429-2449
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• 2018

Dynamic data possession verification is a common requirement in cloud storage systems. After the client outsources its data to the cloud, it needs to not only check the integrity of its data but also verify whether the update is executed correctly. Previous researches have proposed various schemes based on Merkle Hash Tree (MHT) and implemented some initial improvements to prevent the tree imbalance. This paper tries to take one step further: Is there still any problems remained for optimization? In this paper, we study how to raise the efficiency of data dynamics by improving the parts of query and rebalancing, using a new data structure called Rank-Based Merkle AVL Tree (RB-MAT). Furthermore, we fill the gap of verifying multiple update operations at the same time, which is the novel batch updating scheme. The experimental results show that our efficient scheme has better efficiency than those of existing methods.

• 한국컴퓨터정보학회논문지
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• 제14권4호
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• pp.9-17
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• 2009

본 논문에서는 운영체제 수준에서 에너지 절감과 함께 I/O 성능 개선을 목적으로 하여 소형 하드 디스크와 플래시 메모리를 이종의 저장 장치로 가지는 모바일 시스템에 대해 동적 부하 분산 기법을 제안한다. 제안 기법은 부하가 에너지 및 성능 효율적인 방법으로 하드디스크와 플래시 메모리의 이종성의 저장 장치 구성에 대해서 어떻게 효율적으로 분산될 수 있을 것인지를 발견하기 위하여 파일 배치 기법과 버퍼 캐시 관리 기법을 결합하는 접근법을 취한다. 제안한 기법은 폭넓은 시뮬레이션을 통해서 기존의 기법들과 비교하여 이종의 모바일 저장장치들에 대해서 더 개선된 실험 결과를 보이는 것으로 나타났다.

• 한국정보시스템학회지:정보시스템연구
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• 제27권2호
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• pp.95-114
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• 2018

Purpose The recent concern over environmental problems such as greenhouse gas emission and fine dust contributes increasing interest in renewable energies. However the intrinsic characteristics of renewable energies, intermittent and stochastic generation, might cause serious problems to the stability and controllability of power grid. Therefore countermeasures such as virtual power plant (VPP) must be prepared in advance of the spread of uncontrollable distributed renewable energy resources to be one of major energy sources. Design/methodology/approach This study deals with the design concept of the VPP platform. we proposed as a technology solution for achieving the stability of power grid by guaranteeing a single power profile combining multiple distributed power sources with ICT. The core characteristics of VPP should be able to participate in the grid operation by responding to operation instructions from the system operator, KPX, as well as the wholesale electricity market. Findings Therefore this study includes energy storage device(ESS) as a controllable component as well as renewable energy resources such as photovoltaic and wind power generation. Based on this configuration, we discussed core element technologies of VPP and protype design of VPP solution platform according to system requirements. In the proposed solution platform, UX design for the integrated control center and brokerage system were included as well as ancillary service function to respond to KPX's operation instruction with utilizing the capability of ESS. In addition, a simulator was suggested to verify the VPP operations.

• 전기학회논문지P
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• 제58권2호
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• pp.116-121
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• 2009

Distributed power systems (DPSs) has been widely used various industrial/military applications due to their various advantages. Furthermore, the "All electric" concept, in conjunction with DC DPS, appears to be more advanced and mature in the AEV(All-Electric Vehicular) industry. Generally, AEV carry many loads with varied functions. However, there may be large pulsed loads with short duty ratios which can affect the normal operation of other loads. In this paper, a converter with spilt capacitors and a simple adaptive controller is proposed as a active damping device to mitigate the voltage transients on the bus. The proposed converter allows the smaller capacitive storage. In addition, the proposed control approach has the advantage of requiring only one sensor and performing both the functions of mitigating the voltage bus transients and maintaining the level of energy stored. The control algorithm has been implemented on a TMS320F2812 Digital Signal Processor (DSP). Simulation and experimental results are presented which verify the proposed control principle and demonstrate the practicality of the circuit topology.

• 한국기록관리학회지
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• 제19권3호
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• pp.271-292
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• 2019

최근 중앙행정기관은 업무관리시스템을 클라우드 기반의 온나라2.0으로 변경하였다. 국가기록원은 클라우드 업무관리시스템의 기록을 이관받아 관리할 수 있도록 클라우드 기반의 기록관리시스템을 개발하여 보급하고 있다. 클라우드 컴퓨팅의 이점을 극대화하여 기록관리가 보다 효과적 효율적으로 이루어지도록 재설계할 수 있는 기회이다. 전자기록 관리의 프로세스와 방법이 종이기록 관리방식을 단순히 전자화하는 것에서 탈피하여 디지털 기술에 따른 변환(Transformation)의 수준으로 나아갈 수 있는 기회이기도 하다. 첫째, 이관의 방식을 변환해 볼 수 있다. 업무관리시스템과 기록관리 시스템이 클라우드 저장소를 공유하게 되면 처리과에서 기록관으로 기록물 이관 시 콘텐츠 파일들을 물리적으로 이동시키지 않고 메타데이터만 복사하는 방식으로 이관할 수 있어 비용이 줄고 무결성 훼손 위험이 줄어들 수 있다. 둘째, 기록물의 저장공간 할당에 대한 전략을 구상해 볼 수 있다. 클라우드 저장소를 업무관리시스템과 기록관리시스템이 공유하는 것을 전제로 한다면 콘텐츠 파일들을 저장할 때 기록의 보존기간에 따라 저장하는 위치를 구분함으로써 이점을 얻을 수 있다. 셋째, 기록의 생산시스템, 기록관리시스템, 정보공개시스템 등 콘텐츠에 접근하는 시스템들이 클라우드 저장소를 공유하게 되면 콘텐츠의 중복을 최소화하는 방향으로 설계를 전환할 수 있다.

• 정보처리학회논문지:소프트웨어 및 데이터공학
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• 제2권2호
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• pp.91-96
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• 2013

바이오 응용과 같은 대용량 데이터 처리와 고성능 계산을 동시에 지원하는 발판으로 슈퍼컴퓨팅 시스템의 활용 분야가 변화하고 있다. 이러한 응용에서는 발생하는 대용량의 데이터를 고속으로 처리하고 효율적으로 저장 관리하기 위한 고성능의 분산 파일 시스템이 요구된다. 본 논문에서는 대용량의 데이터 처리와 고성능 계산을 동시에 지원하는 슈퍼컴퓨팅 시스템을 위해 우수한 메타데이터 연산 성능 및 입출력 성능을 제공하는 MAHA-FS를 소개한다. 아울러 성능 분석을 통해 MAHA-FS가 메타데이터 연산 처리 성능 및 random 입출력 성능이 우수함을 보인다.

• 전기학회논문지
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• 제60권6호
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• pp.1112-1121
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• 2011

A microgrid is an aggregation of multiple distributed generators (DGs) such as renewable energy sources, conventional generators, and energy storage systems that provide both electric power and thermal energy. Generally, a microgrid operates in parallel with the main grid. However, there are cases in which a microgrid operates in islanded mode, or in a disconnected state. Islanded microgrid can change its operational mode to grid-connected operation by reconnection to the grid, which is referred to as synchronization. Generally, a single machine simply synchronizes with the grid using a synchronizer. However, the synchronization of microgrid that operate with multiple DGs and loads cannot be controlled by a traditional synchronizer, but needs to control multiple generators and energy storage systems in a coordinated way. This is not a simple job, considering that a microgrid consists of various power electronics-based DGs as well as alternator-based generators that produce power together. This paper introduces the results of research examining an active synchronizing control system that consists of the network-based coordinated control of multiple DGs. Consequently, it provides the microgrid with a deterministic and reliable reconnection to the grid. The proposed method is verified by using the test cases with the experimental setup of a microgrid pilot plant.

• Journal of Power Electronics
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• 제18권4호
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• pp.1111-1126
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• 2018

In modern power systems, distributed generators (DGs) result in high stress on system frequency stability. Apart from the intermittent nature of DGs, most DGs do not contribute inertia or damping to systems. As a result, a new control method referred to as a virtual synchronous machine (VSM) has been proposed, which brought new characteristics to inverters such as synchronous machines (SM). DGs employing an energy storage system (ESS) provide inertia and damping through VSM control. Meanwhile, energy storage presents some physical constraints in the VSM implementation level. In this paper, a VSM mathematical model is built and analyzed. The dynamic responses of the output active power are presented when a step change in the frequency occurs. The influences of the inertia constant, damping factor and operating point on the ESS volume margins are investigated. In addition, physical constraints are proposed based on these analyses. The proposed physical constraints are simulated using PSCAD/EMTDC software and tested through RTDS experiment. Both simulation and RTDS test results verify the analysis.