• 한국IT서비스학회지
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• 제7권4호
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• pp.167-178
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• 2008

This paper addresses the issue of workflow on Grid and P2P, and proposes a layered workflow architecture and its related workflow models that are used for not only distributing workflows' information onto Grid or P2P resources but also scheduling the enactment of workflows. Especially, the most critical rationale of this paper is on the fact that the nature of Grid computing environment is fitted very well into building a platform for the maximally parallel and very large scale workflows that are frequently found in very large scale enterprises. The layered architecture proposed in this paper, which we call Enterprise Workflow Grid Architecture, is targeting on maximizing the usability of computing facilities in the enterprise as well as the scalability of its underlined workflow management system in coping with massively parallel and very large scale workflow applications.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.111-114
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• 2004

CFD code that simulates stator-rotor interactions is developed applying parallel computing method. Modified Multi-Block Grid System which enhances perpendicularity in grid and is appropriate in parallel processing is introduced and Patched Algorithm is applied in sliding interface which is caused by movement of rotor. The experimental model in the turbo-machine is composed of 11 stators and 14 rotors. Analyses on two test cases which are one stator - one rotor model and three stators - four rotors model are performed. The results of the two cases have been compared with the experimental test data.

• Journal of Power Electronics
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• 제10권5호
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• pp.555-562
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• 2010

This paper presents the development of a hardware simulator for a 3-parallel grid-connected PMSG wind power system. With the development of permanent magnetic materials in recent years, the capacity of a PMSG based wind turbine system, which requires a full-scale power converter, has been raised up to a few MW. Since it is limited by the available semiconductor technology, such large amounts of power cannot be delivered with only one power converter. Hence, a parallel connecting technique for converters is required to reduce the ratings of the converters. In this paper, a hardware simulator with 3-parallel converters is described and its control issues are presented as well. Some experimental results are given to illustrate the performance of the simulator system.

• 한국태양에너지학회 논문집
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• 제37권3호
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• pp.13-22
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• 2017

Anti-islanding scheme of grid-connected inverter is a key function of standards compliance, since unintentional islanding results in safety hazards, reliability, and many other issues. Therefore, many anti-islanding schemes have been researched, however, most of them have problems, which deteriorate performance of islanding detection under parallel-operation. Therefore, this paper proves the reason of problems and proposes a new anti-islanding scheme that has precise islanding detection under parallel-operation in single-phase and three-phase system. Finally, both simulation and experimental result validate the proposed scheme.

• Journal of Power Electronics
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• 제18권5호
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• pp.1555-1566
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• 2018

Proportional capacitor-current-feedback active damping (AD) is a common damping method for the resonance of LCL-type grid-connected inverters. Proportional capacitor-current-feedback AD behaves as a virtual resistor in parallel with the capacitor. However, the existence of delay in the actual control system causes impedance in the virtual resistor. Impedance is manifested as negative resistance when the resonance frequency exceeds one-sixth of the sampling frequency ($f_s/6$). As a result, the damping effect disappears. To extend the system damping region, this study proposes a virtual resistor-inductor-capacitor (RLC) AD method. The method is implemented by feeding the filter capacitor current passing through a band-pass filter, which functions as a virtual RLC in parallel with the filter capacitor to achieve positive resistance in a wide resonance frequency range. A combination of Nyquist theory and system close-loop pole-zero diagrams is used for damping parameter design to obtain optimal damping parameters. An experiment is performed with a 10 kW grid-connected inverter. The effectiveness of the proposed AD method and the system's robustness against grid impedance variation are demonstrated.

• Journal of Radiation Protection and Research
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• 제41권2호
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• pp.111-115
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• 2016

Background: The scattered photons cause reduction of the contrast of radiographic image and it results in the degradation of the quality of the image. In order to acquire better quality image, an anti-scattering x-ray gird should be equipped in radiography system. Materials and Methods: The X-ray anti-scattering grid of the inclined type based on the hybrid concept for that of parallel and focused type was tested by MCNP code. The MCNPX 2.7.0 was used for the simulation based test. The geometry for the test was based on the IEC 60627 which was an international standard for diagnostic X-ray imaging equipment-Characteristics of general purpose and mammographic anti-scatter grids. Results and Discussion: The performance of grids with four inclined shielding material types was compared with that of the parallel type. The grid with completely tapered type the best performance where there were little performance difference according to the degree of inclination. Conclusion: It was shown that the grid of inclined type had better performance than that of parallel one.

• Journal of Electrical Engineering and Technology
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• 제7권6호
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• pp.898-904
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• 2012

This paper presents a ride-through skill of PMSG wind turbine system under the distorted and unbalanced grid voltage dips. When voltage dips occur in the grid, pitch control and generator speed control as well as a parallel resistor of DC-link help to keep the turbine's safety. Modern grid code requires a wind turbine to supply reactive currents to help voltage recovery after grid faults clearance. In order to supply reactive currents to the grid in case of the distortedly unbalanced grid voltage dips, a special PLL is needed to control the grid side converter and to regulate the grid voltages symmetrically. The proposed method is applied to 2MW multi-pole PMSG wind turbine system, and verified by simulation.

• 한국공간정보시스템학회 논문지
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• 제10권4호
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• pp.21-26
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• 2008

본 연구에서는 대용량의 항공 레이저 스캔 자료를 효율적으로 처리하기 병렬처리 기법과 가상격자 구조를 도입하였으며 제안한 방법의 실효성을 평가하기 위하여 IDW(Inverse Distance Weighting) 방식으로 정규격자 DSM을 생성하였다. 즉, 대용량 항공 레이저 스캔 자료의 신속한 보간을 위하여 병렬처리 기법을 이용하고 불규칙적으로 분포된 포인트의 검색 효율성을 제고하기 위하여 가상격자(virtual grid)를 사용하였다. 마스터 노드와 6대의 슬래이브 노드로 구성된 클러스터를 사용하여 처리 시간을 측정한 결과 노드의 수가 증가하더라도 1에 가까운 efficiency를 나타내었으며 load scalability의 특성도 만족시켰다. 또한 용량의 한계로 인하여 단일 시스템에서 처리할 수 없는 크기의 자료를 클러스터 시스템으로 처리할 수 있음을 확인하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.232-233
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• 2007

In this paper, phenomenon of islanding parallel inverters in an ac-distributed system is proposed. The paper explores the test results of the parallel-connected inverters in grid-connected system. The test results are devised and analyzed taking into account the power quality and the islanding performance. The islanding test methods applied. Experimental results are provided from two 2 kVA inverters connected in parallel, showing the features of islanding test.

• 전력전자학회논문지
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• 제27권2호
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• pp.92-99
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• 2022

Due to space and geographical constraints, the power source may be located outside the island area, resulting in the considerable length of transmission line. In these cases, when an active power is transmitted, unexpected reactive power is generated at a point of common coupling (PCC). Unlike the power transmitted from the power generation source, the reactive power adversely affects the system. This study proposes a new algorithm that controls reactive power at PCC. Causes of reactive power errors are separated into parallel and series components, which allows the algorithm to compensate the reactive current of the inverter output and control reactive power at the PCC through calculations from the impedance, voltage, and current. The proposed algorithm has economic advantages by controlling the reactive power with the inverter of the power source itself, and can flexibly control power against voltage and output variations. Through the simulation, the algorithm was verified by implementing a power source of 3 [kVA] capacity connected to the low voltage system and of 5 [MVA] capacity connected to the extra-high voltage system. Furthermore, a power source of 3 [kVA] capacity inverter is configured and connected to a mock grid, then confirmed through experiments.