• 조명전기설비학회논문지
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• 제18권4호
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• pp.118-123
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• 2004

분산전원의 단독운전 검출에 관한 기존의 연구들은 사고위치에 따른 다양한 상황을 고려하지 않고 조건들만 만족되면 분산전원측을 무조건 분리시켰다. 하지만 분산전원이 연계되어 있지 않은 인근선로사고의 경우에는 인근선로측 보호기기의 동작으로 전원 측으로부터 정상적인 전원이 공급되기 때문에 분산전원을 분리시킬 필요가 없다. 또한 연계선로 사고의 경우일지라도 분산전원이 즉시 분리돼야 하는 경우인지, 단독운전인지, 정상운전의 경우인지 과부하차단에 의한 보호기기 동작의 경우인지를 고려해야 한다. 본 논문에서는 이러한 고려사항들을 계통의 전력상태 변화를 통해 구분하고 단독운전 시 및 분산전원을 분리해야 되는 상황을 찾아서 분산전원을 분리시키는 단독운전 상태 검출 알고리즘을 제안하였다. 고립운전 상태 검출 알고리즘을 검증하기 위하여 PSCAD/EMTDC를 이용하여 사례별로 시뮬레이션을 수행하였다.

• Journal of Power Electronics
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• 제16권4호
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• pp.1526-1540
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• 2016

This work mainly discusses an accurate and fast islanding detection based on fractional wavelet packet transform (FRWPT)for multibus microgrid systems. The proposed protection scheme uses combined desirable features retrieved from discrete fractional Fourier transform (FRFT) and wavelet packet transform (WPT) techniques, which provides precise time-frequency information on minute perturbation signals introduced in the system. Moreover, this study focuses on the design of decoupling control with a distributed controller based on state feedback for the efficient operation of microgrid systems that are transitioning from the grid-connected mode to the islanded mode. An IEEE 9-bus test system with inverter based distributed generation (DG) units is considered for islanding assessment and smooth operation. Finally, tracking errors are greatly reduced with stability improvement based on the proposed controller. FRWPT based islanding detection is demonstrated via a time domain simulation of the system. Simulated results show an improvement in system stability with the application of the proposed controller and accurate islanding detection based on the FRWPT technique in comparison with the results obtained by applying the wavelet transform (WT) and WPT.

• 전력전자학회논문지
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• 제17권4호
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• pp.315-321
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• 2012

The utility-interactive inverter with critical loads should supply continuous and stable voltage to critical loads even during the grid fault. The conventional control method which performs current control for grid-connected mode and voltage control for stand-alone mode undergoes the critical load voltage variation during grid fault. The critical load voltage may have large transient when the inverter performs mode transfer after the islanding detection. Recently, the indirect current control method which does not have the transient state during not only islanding detection but also the mode transfer has been proposed. However, since the voltage control is maintained even during the grid-connected mode it is difficult to detect the islanding. This paper proposes an active anti-islanding method suitable for the indirect current control method which does not have NDZ(Non-Detection Zone).

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.240-241
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• 2006

Islanding operations of DG usually occur when power supply from the main utility is interrupted due to several reasons but the DG keeps supplying power into the distribution networks. These kinds of islanding conditions cause negative impacts on protection, operation, and management of distribution systems. Therefore, it is necessary to effectively detect the islanding conditions and swiftly disconnect DG from distribution network. This paper proposes the islanding detection algorithm for DG using the change of the voltage unbalance and the output power of DG. The proposed method effectively combines the conventional parameters for detecting the islanding conditions. The proposed methods were verified using the radial distribution network of IEEE 34 bus.

• 전기학회논문지
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• 제64권9호
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• pp.1315-1322
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• 2015

This paper proposes an active islanding detection method for the BESS (Battery Energy Storage System) with 3-phase inverter which is connected to the AC grid. The proposed method adopts the DDSRF (Decoupled Double Synchronous Reference Frame) PLL (Phase Locked-Loop) so that the independent control of positive-sequence and negative-sequence current is successfully carried out using the detected phase angle information. The islanding state can be detected by sensing the variation of negative-sequence voltage at the PCC (Point of Common Connection) due to the injection of 2-3% negative-sequence current from the BESS. The proposed method provides a secure and rapid detection under the variation of negative-sequence voltage due to the sag and swell. The feasibility of proposed method was verified by computer simulations with PSCAD/EMTDC and experimental analyses with 5kW hardware prototype for the benchmark circuit of islanding detection suggested by IEEE 1547 and UL1741. The proposed method would be applicable for the secure detection of islanding state in the grid-tied Microgrid.

• Journal of Electrical Engineering and Technology
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• 제11권3호
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• pp.551-559
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• 2016

The present trend of increasing the penetration levels of Distributed Generator (DG) in the distribution network has made the issue of Islanding crucial for the reliable operation of the network. The islanding, if not detected early may lead to the collapse of the system as it can drive the distribution system to the cascaded failure. In this paper, an extensive study of the effect of DG placement and sizing is performed by dividing the system into different zones to obtain a reduced effect of islanding. The siting and sizing of DG is carried out to improve the overall voltage profile or/and reduction in active power loss using two stage Genetic Algorithm (GA). In the first stage a basic knockout selection is considered and the best population is taken for next stage, where roulette selection for crossover and mutation is performed for optimal placement and sizing of DGs. The effect of the islanding, due to load variations is reduced by optimal siting and sizing of DG. The effectiveness of the proposed scheme is tested on the IEEE 33 and 69 radial bus systems and the results obtained are promising.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.599-607
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• 2018

Distributed generation (DG) is being highlighted as an alternative for future power supplies, and the number of DG systems connected to conventional power systems is steadily increasing. DG generators are designed using power electronics and can give rise to various power quality problems, such as overvoltage or overcurrent. Particularly, unintentional islanding operation can occur in a conventional power system when the power grid is separated from the DG systems. Overvoltage may occur in this situation, depending on the power generation and power consumption. However, overvoltage phenomena might not happen even when islanding occurs. Therefore, it is necessary to analyze the fault characteristics during islanding. In this study, a fault analysis of islanding operation was carried out using PSCAD/EMTDC, and a countermeasure for the overvoltage problem is proposed.

• 전력전자학회논문지
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• 제12권1호
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• pp.37-49
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• 2007

계통연계형 PV 시스템의 중요한 보호기능인 단독운전 검출기능은 시스템의 안전성 및 전기적 안정성 측면에서 매우 중요하다. 단독운전 검출기법으로는 크게 수동적 방식과 능동적 방식으로 분류되는 다양한 기법들이 있다. 본 연구에서는 IEEE 929-2000에서 제시하는 단독운전 시험조건 하에서 현재 널리 사용되는 능동적 방식 중 무효전력 변동 방식(RPV method)과 능동적 주파수 변동 방식(AFD method)을 채용한 시스템의 연계점에서 주파수 변동 특성을 해석하였다. 그리고 해석결과를 바탕으로 RPV 방식 및 AFD 방식의 설계법을 제시하였다. EMTP를 이용한 시스템 시뮬레이션을 통하여 제안된 해석 및 설계법의 타당성 및 유효성을 검증하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1085-1086
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• 2008

Shunt active filter can compensate harmonic current of utility results from non-linear loads such as rectifiers, cycloconverters and arc furnaces. It has the same structure as photovoltaic(PV) generation system. So, It was proposed the system that generates PV power and also has active filter function. It is called PV-AF(Photovoltaic and Active Filter) power generation system. Islanding can be occurred in an inverter based dispersed generation system, when the system disconnected from utility and loads are entirely supplied by PV system only. Islanding may result in interference to grid protection devices, equipment damage, and even personnel safety hazards. Therefore, islanding has to be detected and protected. The conventional anti-islanding methods have NDZ(None-Detection Zone) or power quality degradation. But PV-AF power generation system has the function of not only shunt active filter but also anti-islanding method without NDZ. In this paper, a novel anti-islanding method for PV-AF system is proposed and analysed in detail.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.1159-1160
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• 2006

As the grid-connected photovoltaic power conditioning systems (PVPCS) are installed in many residential areas, this has raised potential problems of network protection on electrical power system. One of the numerous problems is an Island phenomenon. There has been an argument that because the probability of islanding is extremely low it may be a non-issue in practice. 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 island 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 sufficient to cause a trip, plus the time required to execute the trip (particularly if conventional switchgear is required to operate), can easily be greater than the typical re-close time on the distribution circuit. And, 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 island. Unintentional islanding of PVPCS may result in power-quality issues, interference to grid-protection devices, equipment damage, and even personnel safety hazards. So the verification of anti-islanding performance is strongly needed. In this paper, the authors propose the improved RPV method through considering power quality and anti-islanding capacity of grid-connected three-phase PVPCS in IEEE Std 1547 ("Standard for Interconnecting Distributed Resources to Electric Power Systems"). And the simulation and experimental results are verified.