• Title/Summary/Keyword: Frequency drift

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Modeling and Analysis of Modified Active Frequency Drift Method (개선된 AFD기법의 모델링 및 분석)

  • An, Jin-Ung;Yu, Gwon-Jong;Choy, Ich;Choi, Ju-Yeop;Lee, Ki-Ok
    • The Transactions of the Korean Institute of Power Electronics
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    • v.16 no.2
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    • pp.145-151
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    • 2011
  • In this paper, among the active islanding detection techniques, the modified active frequency drift method was analyzed, which is relatively easy to apply to the single-phase grid-connected PV PCS. The existing designs for turbulences in these applications were empirically conducted, and do not have sufficient reliability and performance. Therefore, three application forms of the modified active frequency drift technique were modeled, based on which the proper magnitude of turbulence, which is the frequency acceleration component, was calculated. Using the results, the magnitude of and injection method for turbulence for ensuring the islanding detection performance and improving the output power quality were proposed, and they were verified via simulations and experiment to prove that the reliable islanding detection technique can be developed merely by measuring the basic output power quality, without the need for expensive islanding simulation equipment.

Analysis of vortex induced vibration frequency of super tall building based on wind tunnel tests of MDOF aero-elastic model

  • Wang, Lei;Liang, Shuguo;Song, Jie;Wang, Shuliang
    • Wind and Structures
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    • v.21 no.5
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    • pp.523-536
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    • 2015
  • To study the vibration frequency of super high-rise buildings in the process of vortex induced vibration (VIV), wind tunnel tests of multi-degree-of-freedom (MDOF) aero-elastic models were carried out to measure the vibration frequency of the system directly. The effects of structural damping, wind field category, mass density, reduced wind velocity ($V_r$), as well as VIV displacement on the VIV frequency were investigated systematically. It was found that the frequency drift phenomenon cannot be ignored when the building is very high and flexible. When $V_r$ is less than 8, the drift magnitude of the frequency is typically positive. When $V_r$ is close to the critical wind velocity of resonance, the frequency drift magnitude becomes negative and reaches a minimum at the critical wind velocity. When $V_r$ is larger than12, the frequency drift magnitude almost maintains a stable value that is slightly smaller than the fundamental frequency of the aero-elastic model. Furthermore, the vibration frequency does not lock in the vortex shedding frequency completely, and it can even be significantly modified by the vortex shedding frequency when the reduced wind velocity is close to 10.5.

Analysis of Anti-Islanding Schemes using Frequency Drift in Distributed Generation System (분산전원 시스템의 주파수 변동을 통한 단독운전 방지기법 분석)

  • Jo, Yeong-Min;Cho, Sang-Yoon;Song, Seung-Ho;Choy, Ick;Choi, Ju-Yeop;Lee, Young-Kwoun
    • The Transactions of the Korean Institute of Power Electronics
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    • v.20 no.3
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    • pp.247-254
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    • 2015
  • Unintentional islanding results in safety hazards, power quality degradation, and many other issues. Thus, islanding detection of grid-connected distributed generation system is a key function for standards compliance. Many anti-islanding schemes are currently being studied; however, existing anti-islanding schemes used in inverters have power quality degradation and non-detection zone issues. Therefore, this paper analyzes existing anti-islanding schemes by using frequency drift in accordance with both islanding detection performance and power quality. This paper also proposes a new anti-islanding scheme by using frequency drift. Both simulation and experimental results show that the proposed scheme has negligible power quality degradation and no non-detection zones compared with other existing schemes.

Active Frequency Drift Positive Feedback Method for Anti-islanding applied Digital Phase-Locked-Loop (Digital PLL을 이용한 Active Frequency Drift Positive Feedback에 관한 연구)

  • Lee, K.O.;Choi, J.Y.;Choy, I.;Jung, Y.S.;Yu, G.Y.;Song, S.H.
    • 한국신재생에너지학회:학술대회논문집
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    • pp.250-254
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    • 2007
  • As photovoltaic(PV) power generation systems become more common, it will be necessary to investigate islanding detection method for PV systems. Islanding of PV systems can cause a variety of problems and must be prevented. However, if the real and reactive powers of the load and PV system are closely matched, islanding detection by passive methods becomes difficult. Also, most active methods lose effectiveness when there are several PV systems feeding the same island. The active frequency drift positive feedback method(AFDPF) enables islanding detection by forcing the frequency of the voltage in the island to drift up or down. In this paper the research for the minimum value of chopping fraction gain applied digital phase-locked-loop (DPLL) to AFDPF considering output power quality and islanding prevention performance are performed by simulation and experiment according to IEEE Std 929-2000 islanding test.

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Novel Islanding Detection Method using Frequency Drift for Grid-connected PV System (계통연계형 태양광발전 시스템의 주파수 변동에 의한 새로운 고립운전 검출기법)

  • Eun Suk-Jun;;;Lee Dong-Chun
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.54 no.6
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    • pp.294-302
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    • 2005
  • PV system's islanding occurs when the uitilty grid is removed but local sources continue to operate and provide power to local loads. Islanding is one of the serious problems in an electric power system connected with dispersed power sources. Also, this can present safety hazards and the possibility of damage to other electric equipments. If the real and reactive power of RLC load and PV system are closely matched, islanding detection by passive methods becomes difficult. This paper shows the simulation and comparision for the previous active methods and novel islanding detection method using frequency drift is proposed for grid-connected PV system.

THD Analysis of Output Current for Active Frequency Drift Method in Anti-islanding (능동적 주파수 변환기법의 출력전류 고조파 왜형율 분석)

  • Lee, Ki-Ok;Choi, Ju-Yeop;Choy, Ick;Yu, Gwon-Jong;An, Jin-Ung
    • Journal of the Korean Solar Energy Society
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    • v.30 no.1
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    • pp.7-12
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    • 2010
  • As many grid-connected photovoltaic power conditioning systems (PVPCS)are installed in many residential areas simultaneously, these have raised potential problems of network protection on electrical power system. One of the numerous problems is an Islanding phenomenon. In this paper, active frequency drift (AFD) method, one of the anti-islanding methods which is analyzed by current magnitude compensation and calculation of the fundamental component. Both harmonic component and RMS value of the output current for THD analysis are provided and verified by simulation.

Output Power Analysis of Active Frequency Drift Method for Anti-Islanding (단독운전방지를 위한 능동적 주파수 변환기법의 출력전력 분석)

  • Lee, Ki-Ok;Choi, Ju-Yeop;Choy, Ick;Yu, Gwon-Jong;An, Jin-Ung
    • Journal of the Korean Solar Energy Society
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    • v.29 no.6
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    • pp.75-80
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    • 2009
  • Recently, as the grid-connected photovoltaic power conditioning systems (PVPCS) are installed in many residential areas, these have raised potential problems of network protection on electrical power system. One of the numerous problems is an Islanding phenomenon. In this paper, active frequency drift (AFD) method, one of the anti-islanding methods which is analyzed by current magnitude compensation and calculation of RMS value of the output power is proposed and verified by simulation.

Active Frequency Drift Positive Feedback Method for Anti-islanding using Digital Phase-Locked-Loop (디지털 위상검출기법을 적용한 능동적 주파수 변화 정궤환기법)

  • Lee, Ki-Ok;Young, Young-Seok;Choi, Ju-Yeop;Choy, Ick;Song, Seung-Ho;Ko, Moon-Ju
    • Journal of the Korean Solar Energy Society
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    • v.27 no.2
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    • pp.37-44
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    • 2007
  • As photovoltaic(PV) power generation system becomes more common, it will be necessary to investigate islanding detection method for PV systems. Islanding of PV systems can cause a variety of problems and must be prevented. However, if the real and reactive power of the load and PV system are closely matched, islanding detection by Passive methods becomes difficult. Also, most active methods lose effectiveness when there are several PV systems feeding the same island. The active frequency drift positive feedback method(AFDPF) enables islanding detection by forcing the frequency of the voltage in the island to drift up or down. In this paper the research for the minimum value of chopping fraction gain applied digital phase-locked-loop (DPLL) to AFDPF considering output power quality and islanding prevention performance are performed by simulation and experiment according to IEEE Std 929-2000 islanding test.

Detection Performance and THD Analysis of Active Frequency Drift for Anti-Islanding (단독운전 방지를 위한 능동적 주파수 변환 기법의 검출 성능 및 THD 분석)

  • Jo, Yeong-Min;Choi, Ju-Yeop;Song, Seung-Ho;Choy, Ick;Lee, Young-Kwoun
    • Journal of the Korean Solar Energy Society
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    • v.35 no.2
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    • pp.11-19
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    • 2015
  • Islanding is a phenomenon that EPS(Electric Power System) is continuously energized by PV PCS(Photovoltaic Power Conditioning System) even when EPS is isolated from the grid. Unintentional islanding will result in safety hazard, power quality degradation and many other issues. So, islanding protection of grid-connected PV PCS is a key function for standards compliance. Nowadays, many anti-islanding schemes are researched. But existing anti-islanding schemes used in PV PCS have power quality degradation and non-detection zone issues. This paper analyses not only detection performance of existed anti-islanding schemes using active frequency drift but also THD of PCS output current according to each value disturbance for anti-islanding. In addition, the lowest value of disturbance in each scheme was tabulated under guarantee of anti-islanding condition.

Active Frequency Drift Method for Islanding Detection Applied to Micro-inverter with Uncontrollable Reactive Power

  • Kwak, Raeho;Lee, June-Hee;Lee, Kyo-Beum
    • Journal of Power Electronics
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    • v.16 no.5
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    • pp.1918-1927
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    • 2016
  • This paper proposes active frequency drift (AFD) as an anti-islanding method applied to micro-inverters with uncontrollable reactive power. When using ordinary inverter topologies, such as full bridge inverters in photovoltaic systems, the islanding phenomenon can be detected with reactive power-based methods, such as reactive power variation. However, when the inverter topology cannot control the reactive power, conventional anti-islanding methods with reactive power cannot be utilized. In this work, the topology used in this paper cannot control the reactive power. Thus, an anti-islanding method that can be used in topologies that cannot control the reactive power is proposed. The conventional anti-islanding method of the topology that cannot control reactive power is introduced and analyzed. Unlike the conventional AFD method, the proposed method extends a zero current interval every predetermined cycle. The proposed method offers certain advantages over conventional AFD methods, such as total harmonic distortion. The proposed method is validated through simulation and experiment.