• Title/Summary/Keyword: In-grid Condition

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Comparison of Two Reactive Power Definitions in DFIG Wind Power System under Grid Unbalanced Condition

  • Ha, Daesu;Suh, Yongsug
    • Proceedings of the KIPE Conference
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    • 2014.07a
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    • pp.213-214
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    • 2014
  • This paper compares two instantaneous reactive power definitions in DFIG wind turbine with a back-to-back three-level neutral-point clamped voltage source converter under unbalanced grid conditions. In general, conventional definition of instantaneous reactive power is obtained by taking an imaginary component of complex power. The other definition of instantaneous reactive power can be developed based on a set of voltages lagging the grid input voltages by 90 degree. A complex quantity referred as a quadrature complex power is defined. Proposed definition of instantaneous reactive power is derived by taking a real component of quadrature complex power. The characteristics of two instantaneous reactive power definitions are compared using the ripple-free stator active power control algorithm in DFIG. Instantaneous reactive power definition based on quadrature complex power has a simpler current reference calculation control block. Ripple of instantaneous active and reactive power has the same magnitude unlike in conventional definition under grid unbalance. Comparison results of two instantaneous reactive power definitions are verified through simulation.

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Free-surface Boundary Condition in Time-domain Elastic Wave Modeling Using Displacement-based Finite-difference Method (시간영역 변위근사 유한차분법의 자유면 경계조건)

  • Min Dong-Joo;Yoo Hai Soo
    • Geophysics and Geophysical Exploration
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    • v.6 no.2
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    • pp.77-86
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    • 2003
  • We designed a new time-domain, finite-difference, elastic wave modeling technique, based on a displacement formulation. which yields nearly correct solutions to Lamb's problem. Unlike the conventional, displacement-based, finite-difference method using a node-based grid set (where both displacements and material properties such as density and Lame constants are assigned to nodal points), in our new finite-difference method, we use a cell-based grid set (where displacements are still defined at nodal points but material properties within cells). In the case of using the cell-based grid set, stress-free conditions at the free surface are naturally described by the changes in the material properties without any additional free-surface boundary condition. Through numerical tests, we confirmed that the new second-order finite differences formulated in the cell-based grid let generate numerical solutions compatible with analytic solutions unlike the old second-order finite-differences formulated in the node-based grid set.

Islanding detection algorithm for a micro-grid based on the active and reactive power in the time domain (시간영역에서의 유효/무효전력을 이용한 마이크로그리드의 단독운전의 판단 알고리즘)

  • Lee, Young-Gui;Lee, Hye-Won;Kim, Yeon-Hee;Zheng, Tai-Ying;Kang, Yong-Cheol
    • 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.

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An Output Voltage Balance Control of Grid Connected Inverter by Phase Current Control at Critical Load Unbalanced Condition (계통연계 인버터의 주요 부하 불평형 시 상전류 제어를 통한 부하 상전압 평형 제어)

  • Tae-Hyeon Park;Hag-Wone Kim;Kwan-Yuhl Cho;Joon-Ki Min;Won-Il Choi
    • The Transactions of the Korean Institute of Power Electronics
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    • v.28 no.1
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    • pp.22-29
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    • 2023
  • A grid-connected inverter can be used in grid-connected or stand-alone modes. Generally, a grid-connected inverter operates in a grid-connected mode, but the inverter operates in stand-alone mode if grid faults occur. In the stand-alone mode, the grid-connected inverter must supply electric power to a critical load that needs to receive stable power even though grid faults occur. Generally, three-phase loads are used as critical loads, but a single phase is configured in some cases. In these conditions, the critical load is required to unbalance the load power consumption, which makes the three-phase load voltage unbalancd. This unbalanced voltage problem can cause fatal problems to the three-phase critical loads, and thus must be addressed. Hence, this paper proposes an algorithm to solve this unbalanced voltage problem by the individual phase current control. The proposed method is verified using Psim simulation and experiments.

A Robust PLL of PCS for Fuel Cell System under Unbalanced Grid Voltages (불평형 계통전압에 강인한 연료전지용 전력변환시스템의 PLL 방법)

  • Kim, Yun-Hyun;Kim, Wang-Rae;Lim, Chang-Jin;Kim, Kwang-Seob;Kwon, Byung-Ki;Choi, Chang-Ho
    • Proceedings of the KIPE Conference
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    • 2008.06a
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    • pp.103-105
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    • 2008
  • In grid-interconnection system, a fast, robust and precise phase angle detector is most important to grid synchronization and the active power control. The phase angle can be easily estimated by synchronous dq PLL system. On the other hand under unbalanced voltage condition, synchronous dq PLL system has problem that harmonics occur to phase angle or magnitude of grid voltage because of the effect of the negative sequence components. So, To eliminate the negative sequence components, the PLL method using APF (All Pass Filter) in a stationery reference frame to extract positive sequence components under unbalanced voltage condition is researched. In this paper, we propose a new PLL method with decoupling network using APF in a synchronous reference frame to extract the positive sequence components of the grid voltage under unbalanced grid. The cut-off frequency of APF in a synchronous reference frame can be set to twice of the fundamental frequency comparing with that of APF in a stationery reference frame which is the fundamental frequency. The proposed PLL strategy can detect the phase angle quickly and accurately under unbalanced gird voltages. Simulation and experimental results are presented to verify the proposed strategy under different kind of voltage dips.

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DEVELOPMENT OF CFD PROGRAM BASED ON UNSTRUCTURED GRID SYSTEM (비정렬 기반의 CFD 프로그램 개발)

  • Lee, Jung-Hee;Lee, Sang-Hyuk;Lee, Myung-Sung;Hur, Nahm-Keon
    • 한국전산유체공학회:학술대회논문집
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    • 2010.05a
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    • pp.524-529
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    • 2010
  • In the present study, a CFD program is developed for the Fluid-Structure Interaction(FSI) analysis. The non-staggered, non-orthogonal, and unstructured grid system was also used to handle the complicated geometries in the program. In order to validate the capabilities of the developed CFD program, various models are investigated by using unstructured and nonorthogonal meshes. The predicted results are a good agreement with analytic solution, experimental data and commercial software. And also PISO algorithm is applied for transient flow analysis. The cyclic boundary condition and baffle cell are developed in order to improve the effectiveness of the calculation for complex geometry.

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Specifications of 22.9kV HTS cables and FCLs considering protection systems in Korean power distribution system (국내계통 보호시스템을 고려한 22.9kV 초전도케이블/한류기 설계사양 제안)

  • Lee, Seung-Ryul;Park, Jong-Young;Yoon, Jae-Young;Lee, Byong-Jun;Yang, Byeong-Mo
    • Progress in Superconductivity and Cryogenics
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    • v.11 no.3
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    • pp.50-54
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    • 2009
  • In Korea, 22.9kV 50MVA HTS (High Temperature Superconducting) cables and 630A/3kA hybrid SFCLs (Superconducting Fault Current Limiters) have been or are being developed by LS Cable, LS Industrial System, and Korea Electric Power Research Institute. They will be installed at Icheon 154kV Substation for real-power-distribution-system operation in 2010. This paper proposes specification of current limiting resistor/reactor for the SFCL and fault current condition of the HTS cable for applying the superconducting devices to Korean power distribution system, from the viewpoint of power system protection.

Performance Improvement of Grid-Connected Inverter Systems under Unbalanced and Distorted Grid Voltage by Using a PR Controller

  • Lee, Jong-Hyun;Jeong, Hae-Gwang;Lee, Kyo-Beum
    • Journal of Electrical Engineering and Technology
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    • v.7 no.6
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    • pp.918-925
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    • 2012
  • This paper proposes a control method for grid-connected inverter systems under unbalanced and distorted grid voltage. The proposed method can reduce the power ripple caused by the unbalanced condition and compensate for the low-order harmonics of the output currents caused by the distortion of grid voltage. To reduce the power ripple, our method replaces the two conventional PI controllers with one PR controllers in the stationary frame. PR controllers can implement selective harmonic compensation without excessive computational requirements; the use of these controllers simplifies the method. Both the simulated and experimental results agree well with the theoretical analysis.

A Study of Automatically Authentication System for Virtual Resource Organization on Grid (그리드상의 가상 자원 조직에 대한 자동 인증 시스템 연구)

  • 최병선;이원구;이재광
    • Proceedings of the Korea Contents Association Conference
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    • 2004.05a
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    • pp.301-306
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    • 2004
  • The Grid VO(Virtual Organization) is temporary VO where gather indivisual, authority, or system resource, differ from previous VO concept that controled by internal principal and policy set. It have many problems in case of indivisuals, authorities, or system resources that became member\ulcorner of some Grid VO at same time and combination followed changing condition of system resource for building Grid VO. This paper propose lightweighted Grid VO authentication system based on XML security to solve the authentication of the problems occuring in building Grid VO. In this paper, Grid VO authentication system is including Grid VO authentication module that is intermediate management system in PH to previous authentication service structure and provide effective authentication service to Grid VO.

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A Study of Automatically Resources Authentication over Grid VO (그리드 VO 상에서의 자동화된 자원 인증 시스템 연구)

  • 이원구;이재광
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2004.05b
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    • pp.739-743
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    • 2004
  • The Grid VO(Virtual Organization) is temporary VO where gather indivisual, authority, or system resource, differ from previous VO concept that controled by internal principal and policy set. It have many problems in case of indivisuals, authorities, or system resources that became member of some Grid VO at same time and combination followed changing condition of system resource for building Grid VO. This paper propose lightweighted Grid VO authentication system based on XML security to solve the authentication of the problems occuring in building Grid VO. In this paper, Grid VO authentication system is including Grid VO authentication module that is intermediate management system in PKI to previous authentication service structure and provide effective authentication service to Grid VO.

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