• Title/Summary/Keyword: Islanding

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Reactive Power Variation Method for Anti-islanding Using Digital Phase-Locked-Loop (DPLL을 이용한 능동적 단독운전방지를 위한 무효전력변동법)

  • Lee, Ki-Ok;Yu, Byung-Gu;Yu, Gwon-Jong;Choi, Ju-Yeop;Choy, Ick
    • Journal of the Korean Solar Energy Society
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    • v.28 no.2
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    • pp.64-69
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    • 2008
  • 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. There has been an argument that it may be a non-issue in practice because the probability of islanding is extremely low. However, there are three counter-arguments: First, the low probability of islanding is based on the assumption of 100% power matching between the PVPCS and the islanded local loads. In fact, an islanding can be easily formed even without 100% power matching (the power mismatch could be up to 30% if only traditional protections are used, e.g. under/over voltage/frequency). The 30% power-mismatch condition will drastically increase the islanding probability. Second, even with a larger power mismatch, the time for voltage or frequency to deviate sufficiently to cause a trip, plus the time required to execute a trip (particularly if conventional switchgear is required to operate), can easily be greater than the typical re-close time on the distribution circuit. Third, the low-probability argument is based on the study of PVPCS. Especially, if the output power of PVPCS equals to power consumption of local loads, it is very difficult for the PVPCS to sustain the voltage and frequency in an islanding. Unintentional islanding of PVPCS may result in power-quality issues, interference to grid-protection devices, equipment damage, and even personnel safety hazards. Therefore the verification of anti-islanding performance is strongly needed. In this paper, improved RPV method is proposed through considering power quality and anti-islanding capacity of grid-connected single-phase PVPCS in IEEE Std 1547 ("Standard for Interconnecting Distributed Resources to Electric Power Systems"). And the simulation results are verified.

Development Tendency of Sliding Mode Frequency Shift Type Anti-Islanding of Japanese Companies

  • Jeong, Ji-Won;Kim, Dong-Hee;Lee, Byoung-Kuk
    • Journal of international Conference on Electrical Machines and Systems
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    • v.3 no.2
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    • pp.222-228
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    • 2014
  • As tightened the grid connection related regulation for a distributed power generation Japan, islanding of the distributed power generation should be detected more rapidly. In this paper, it is introduced the development tendency of sliding mode frequency shift type anti-islanding technology in Japanese companies.

Comparision for Islanding Method of Grid-connected PV System (태양광발전 시스템의 단독운전법 비교)

  • Eun Seog-Jun;Choi Jong-Woo;Kim Heung-Geun
    • Proceedings of the KIPE Conference
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    • pp.92-96
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    • 2004
  • Islanding of PV systems can cause a variety of problems and must be prevented. However, if the real and active powers of RLC load and PV system are closely matched, islanding detection by passive methods becomes difficult. Active methods enables islanding detection by forcing the frequency of the voltage in the island to drift up/down. This paper shows the simulation and comparision by Matlab for the active methods.

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Islanding Detection for Distributed Generation

  • Ding, X.;Crossley, P.A.;Morrow, D.J.
    • Journal of Electrical Engineering and Technology
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    • v.2 no.1
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    • pp.19-28
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    • 2007
  • The paper discussed various techniques for islanding detection and described in detail the working principles of ROCOF and vector shift relays. A simulator was used to investigate why the stability of both types of relays maybe affected by network and load switching, short-circuit faults and in the case of a ROCOF relay the loss of bulk generation or the tripping of a transmission feeder. Finally, to enhance the reliability of Loss of Mains protection, a new islanding detection technique based on a GPS synchronized phasor measurement system was proposed.

Active Frequency with a Positive Feedback Anti-Islanding Method Based on a Robust PLL Algorithm for Grid-Connected PV PCS

  • Lee, Jong-Pil;Min, Byung-Duk;Kim, Tae-Jin;Yoo, Dong-Wook;Yoo, Ji-Yoon
    • Journal of Power Electronics
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    • v.11 no.3
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    • pp.360-368
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    • 2011
  • This paper proposes an active frequency with a positive feedback in the d-q frame anti-islanding method suitable for a robust phase-locked loop (PLL) algorithm using the FFT concept. In general, PLL algorithms for grid-connected PV PCS use d-q transformation and controllers to make zero an imaginary part of the transformed voltage vector. In a real grid system, the grid voltage is not ideal. It may be unbalanced, noisy and have many harmonics. For these reasons, the d-q transformed components do not have a pure DC component. The controller tuning of a PLL algorithm is difficult. The proposed PLL algorithm using the FFT concept can use the strong noise cancelation characteristics of a FFT algorithm without a PI controller. Therefore, the proposed PLL algorithm has no gain-tuning of a PI controller, and it is hardly influenced by voltage drops, phase step changes and harmonics. Islanding prediction is a necessary feature of inverter-based photovoltaic (PV) systems in order to meet the stringent standard requirements for interconnection with an electrical grid. Both passive and active anti-islanding methods exist. Typically, active methods modify a given parameter, which also affects the shape and quality of the grid injected current. In this paper, the active anti-islanding algorithm for a grid-connected PV PCS uses positive feedback control in the d-q frame. The proposed PLL and anti-islanding algorithm are implemented for a 250kW PV PCS. This system has four DC/DC converters each with a 25kW power rating. This is only one-third of the total system power. The experimental results show that the proposed PLL, anti-islanding method and topology demonstrate good performance in a 250kW PV PCS.

A New Anti-Islanding Method for Utility Interconnection of Distributed Power Generation System (분산전원시스템의 계통연계를 위한 새로운 단독운전 방지기법)

  • Hwang In-Ho
    • The Transactions of the Korean Institute of Power Electronics
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    • v.9 no.6
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    • pp.568-576
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    • 2004
  • This paper presents a new anti-islanding method for distributed power generation system (DPGS) using renewable energy. Based on the concept of real and reactive power mismatch, three different islanding conditions are analyzed. It is shown via analysis that islanding voltage is a function of real power alone, where as its frequency is a function of both real and reactive power. Using this analysis, a new anti-islanding method is developed. The proposed protection algorithm continuously perturbs ($\pm$5%) the reactive power supplied by DPGS while simultaneously monitoring the utility voltage and frequency. If a measurable frequency deviation took place by islanding, the real power of DPGS is further reduced to 80%. This detection method is shown to be fast acting under resonant loads. Possible islanding conditions are simulated and verified with analysis. Experimental results on a 0.5kW utility-interactive fuel cell system are suggested.

Islanding Detection Method for Inverter-based Distributed Generation Systems using a Signal Cross-correlation Scheme

  • Bae, Byung-Yeol;Jeong, Jong-Kyou;Lee, Ji-Heon;Han, Byung-Moon
    • Journal of Power Electronics
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    • v.10 no.6
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    • pp.762-768
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    • 2010
  • This paper describes the development of a new islanding detection method for inverter-based distributed generation systems, which uses a signal cross-correlation scheme between the injected reactive current and the power frequency deviation. The proposed method injects 1% of the reactive current to the rated current which brings about a negligible degradation of the power quality. It discriminates the islanding state, when the calculated cross-correlation index is larger than 0.5. The operational feasibility was verified through computer simulations with PSCAD/EMTDC software and experimental research with a hardware prototype. The proposed method can detect the islanding state without degrading the power quality at the point of common connection. Further study is required to overcome the cancellation of the injected reactive current from multiple distributed generation units interconnected with the utility grid.

Islanding Detection Method for Inverter-Based Distributed Generation through Injection of Second Order Harmonic Current

  • Lee, Yoon-Seok;Yang, Won-Mo;Han, Byung-Moon
    • Journal of Power Electronics
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    • v.18 no.5
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    • pp.1513-1522
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    • 2018
  • This paper proposes a new islanding detection method for inverter-based distributed generators by continuously injecting a negligible amount of 2nd order harmonic current. The proposed method adopts a proportional resonant (PR) controller for the output current control of the inverter, and a PR filter to extract the 2nd order harmonic voltage at the point of common coupling (PCC). The islanding state can be detected by measuring the magnitude ratio of the 2nd order harmonic voltage to the fundamental voltage at the PCC by injecting a 2nd order harmonic current with a 0.8% magnitude. The proposed method provides accurate and fast detection under grid voltage unbalance and load unbalance. The operation of the proposed method has been verified through simulations and experiments with a 5kW hardware set-up, considering the islanding test circuit suggested in UL1741.

A Novel Method for Anti-Islanding Using Reactive Power (무효전력 제어를 이용한 새로운 독립운전 방지 기법)

  • Choi, Bong-Joo;Jeong, Jin-Beom;Kim, Hee-Jun;Baek, Soo-Hyun;Lee, Ju;Ahn, Kang-Soon
    • Proceedings of the KIEE Conference
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    • pp.203-206
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    • 2004
  • An islanding occurs when the utility grid is removed but distributed sources continuo to operate and provide power to local loads and grid. This can cause a significant risk to safety and equipment. This report present a novel anti-islanding method to prevent an islanding phenomenon. The proposed method changes the reactive power of the load. Therefore the phase difference between output voltage and current is periodically changed within decided value. When the utility-grid is removed, the frequency of output voltage and current will increase or decrease. And the proposed system will detect the change of frequency and shut down the distributed source. While the conventional methods have some difficulties in detecting particular islanding condition such as a small change in loading, the proposed method can detect most conditions. The performance was verified through experiments.

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

  • Eun Seog-Jun;Choi Jong-Woo;Kim Heung-Geun
    • Proceedings of the KIPE Conference
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    • pp.133-137
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    • 2004
  • 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 m 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. Novel islanding detection method using frequency drift is proposed for grid-connected PV system.

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