• 전력전자학회논문지
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• 제24권5호
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• pp.349-355
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• 2019

A grid-connected inverter with critical loads should be able to supply a stable voltage to critical loads at mode change and during clearing time while detecting unintentional islanding. This study proposes a mode transfer method for a grid-connected inverter with critical loads. The proposed method, which integrates the grid-connected and islanded mode control loops into one control block, provides an autonomous and seamless mode transfer from the current control to the voltage control. Therefore, the proposed scheme can supply a stable voltage to critical loads at mode change and during clearing time. Experimental results are provided to validate the proposed method.

• Journal of Mechanical Science and Technology
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• 제19권4호
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• pp.1006-1017
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• 2005

In this work, we developed an accurate and efficient radiative finite volume method applicable for the complex 2D planar and 3D geometries using an unstructured-grid finite volume method. The present numerical model has fully been validated by several benchmark cases including the radiative heat transfer in quadrilateral enclosure with isothermal medium, tetrahedral enclosure, a three-dimensional idealized furnace, as well as convection-coupled radiative heat transfer in a square enclosure. The numerical results for all cases are well agreed with the previous results. Special emphasis is given to the parallelization of the unstructured-grid radiative FVM using the domain decomposition approach. Numerical results indicate that the present parallel unstruc­tured-grid FVM has the good performance in terms of accuracy, geometric flexibility, and computational efficiency.

• 인터넷정보학회논문지
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• 제7권6호
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• pp.63-77
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• 2006

다양한 그리드 커뮤니티가 생겨나면서 그리드 환경에서의 데이터 분산 전송의 요구가 증가하고 있다. 기존 LAN 환경 또는 특수 목적 네트워크망에서는 데이터 분산 전송을 위해서 멀티캐스팅 기술을 활용하여 네트워크 트래픽을 많이 줄일 수 있었다. 하지만 전송 성능이 일반 유니캐스트 전송보다 좋지 못하고, 하드웨어 지원 없이는 일반적인 WAN 환경에서 멀티 캐스팅을 적용할 수 없다는 단점을 갖고 있어서 그리드 응용에 적용하는 데는 한계가 있다. 이러한 문제점을 극복하기 위해서 본 논문에서는 데이터 분산 전송 기법인 DDMG(Data Dissemination Mechanism for Grid)를 제안하였다. DDMG는 보다 신속한 데이터 전송을 위하여 P2P 데이터 공유 방법을 활용하였으며, 또한 Globus XIO 라이브러리를 활용하여 그리드 환경의 다양한 프로토콜을 지원하도록 설계하였다. 본 논문에서는 DDMG 기법을 구현하여 LAN 환경과 WAN 환경에서 일반 유니캐스트 전송 방법과 비교 분석하였다.

• Journal of Electrical Engineering and Technology
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• 제8권1호
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• pp.20-30
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• 2013

An intelligent grid computing architecture is proposed and developed for transient stability constrained total transfer capability evaluation of future smart grid. In the proposed intelligent grid computing architecture, a model of generalized compute nodes with 'able person should do more work' feature is presented and implemented to make full use of each node. A timeout handling strategy called conditional resource preemption is designed to improve the whole system computing performance further. The architecture can intelligently and effectively integrate heterogeneous distributed computing resources around Intranet/Internet and implement the dynamic load balancing. Furthermore, the robustness of the architecture is analyzed and developed as well. The case studies have been carried out on the IEEE New England 39-bus system and a real-sized Chinese power system, and results demonstrate the practicability and effectiveness of the intelligent grid computing architecture.

• 전력전자학회논문지
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• 제19권2호
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• pp.194-200
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• 2014

In DC micro-grid system energy storage systems (ESS) are responsible for storing energy and balancing power. Also, control target of the bidirectional DC-DC converter(BDC) for ESS should be changed depending on the operating mode. During the grid connected mode, the BDC controls the battery current or voltage. When a grid fault occurs, the BDC should change the control target to regulate the DC-bus. The BDC with conventional control method may experience large transient state during the mode change. This paper proposes a control method of BDC for ESS. The proposed control method is able to provide autonomous and seamless mode transfer by a variable current limiter. To validate the proposed concept, simulation results using PSIM and experimental results from a 2kW prototype are provided.

• 한국정밀공학회지
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• 제29권11호
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• pp.1190-1198
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• 2012

A hot forming of large thick Al plate using a grid-type hybrid die is a process to make a shell plate for the production of a spherical LNG tank. This process is characterized by using a grid-typed die with an additional air cooling system for reducing the cooling time of the heated plate after hot forming. The process consists of the plate's feeding, heating, forming and cooling in detail and each of them is continuously performed along the rail. This paper was designed to propose the analytical and experimental methods for determining the convection and interfacial heat transfer coefficients required in hot forming analysis of Al plate. These values in the analysis are to reproduce numerically the cooling performance of grid-typed die and cooling device. Interfacial heat transfer was obtained from the heat transfer experiments for different pressures and inverse analysis method. To verify the efficiency of the coefficient values obtained from above methods, FE analysis and experiment of the hot spherical-forming process were conducted for a small-scaled model. The convection coefficient was also calculated from flow analysis of air released by cooling device within grid-typed die using ANSYS-CFX.

• 한국통신학회논문지
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• 제35권9B호
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• pp.1381-1389
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• 2010

동적인 전력 공급을 통해 에너지 효율을 높여줄 것으로 기대되는 스마트 그리드 기술은 최근 전기자동차 기술의 발달과 함께 차량의 배터리를 가정용 축전지로 활용하는 Vehicle-to-Grid(V2G) 기술에 대한 관심으로 이어지고 있다. 한편, 무선으로 전력을 공급해주는 비접촉 충전 방식은 직접 사용자가 전기 플러그를 콘센트에 꽂지 않고도 자기장 유도 기반으로 전력을 공급해줌으로써 사용자의 안전과 편의성을 보장해 줄 수 있다. 더욱이 이러한 무선 충전과 동시에 자기장을 활용한 통신 시스템이 구축되면 스마트 그리드의 동적 전력 공급의 영역을 이동하는 전기자동차까지 확장함으로써 보다 실용적인 V2G 기술을 제공할 수 있다. 본 논문에서는 이를 위한 자기장 통신 시스템을 제안한다. 자기장 통신 시스템은 데이터 통신 기능과 위치 인식 기능을 제공하며 비접촉식 충전인프라를 그대로 활용할 수 있는 장점이 있기 때문에 V2G 활용에 있어서 핵심적인 기술이라고 할 수 있다. 제안하는 시스템의 데이터 통신을 전력 공급 관련 정보를 패킷화하여 송수신하고, 위치 인식을 통해 차량과 충전인프라의 위치에 따른 충전 효율 및 통신 성능을 향상시킨다. 또한 테스트 베드를 개발하여 다양한 환경에서 성능 검증을 수행하였다.

• 전기학회논문지P
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• 제66권4호
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• pp.169-176
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• 2017

This paper presents research on low-voltage microgrids to maintain a continuous power supply to critical loads on grid-connected islands in Korea. The low-voltage microgrids of this paper focused on that changes public office buildings into uninterrupted microgrids by autonomous operation. For this, a microgrid controller (MGC) and a power conditioning system (PCS) that allow a seamless transfer between grid-connected and grid-isolated operation are proposed. The proposed PCS operates with a silicon controlled rectifier (SCR) switch and employs a simple structure. It supplies power continuously without operators through a coordinated operation between MGC and PCS. In addition, proposed MG has a schedule operation for minimizing electricity charges and provides ancillary services that enable the utilization of resources according to the operation purpose of utility distribution networks. To demonstrate the uninterrupted low-voltage microgrid proposed in this study, a microgrid was implemented and tested in a public office building in Anjwa Island, Jeollanam-do in Korea. A seamless, autonomous operation history, despite system disturbances, was obtained through a long-term demonstration of operation. The results showed that the proposed microgrid technology can be used to achieve energy resilience in grid-connected island areas.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2005년도 전력전자학술대회 논문집
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• pp.329-332
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• 2005

Distributed generation (DG) systems fall in islanding operation when they still in operation even when the main grid is out of electric power Islanding operation is further classified into intentional islanding and unintentional islanding operations. In intentional islanding operation, the DG backs up critical loads while it separates from the main grid on islanding detection. Intentional islanding operation increases utilization of the DG system during the islanding operation. This paper proposes reasonal inverter topology and its control algorithm for seamless transfer of DG systems in intentional islanding operation.

• Journal of Power Electronics
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• 제18권1호
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• pp.251-265
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• 2018

To enable a master-slave control independent microgrid system (MSCIMGS) to supply electricity continuously, the microgrid inverter should perform mode transfer between grid-connected and islanding operations. Transient oscillations should be reduced during transfer to effectively conduct a seamless mode transfer. This study uses a typical MSCIMGS as an example and improves the mode transfer strategy in three aspects: (1) adopts a status-tracking algorithm to improve the switching strategy of the outer loop, (2) uses the voltage magnitude and phase pre-synchronization algorithm to reduce transient shock at the time of grid connection, and (3) applies the hybrid-sensitivity $H_{\infty}$ robust controller instead of the current inner loop to improve the robustness of the controller. Simulations and experiments show that the proposed strategy is more practical than the traditional proportional-derivative control mode transfer and effective in reducing voltage and current oscillations during the transfer period.