Showing papers on "Islanding published in 2000"

Determining the impact of distributed generation on power systems. I. Radial distribution systems

Abstract: Distributed generation (DG) has much potential to improve distribution system performance and it should be encouraged. However, distribution system designs and operating practices are normally based on radial power flows and this creates a special challenge to the successful introduction of distributed generation. This paper has described a few of the issues that must be considered to insure that DG will not degrade distribution system power quality, safety or reliability. This paper focused on radial systems, although some of the issues discussed are common to low voltage distribution networks.

Determining the relative effectiveness of islanding detection methods using phase criteria and nondetection zones

Abstract: Islanding of a utility-interactive photovoltaic (UIPV) system occurs if the UIPV system continues to power a section of the utility system after that section has been disconnected from the utility source. Since islanding creates hazards for personnel and equipment, UIPV systems are required to detect and prevent it. It is desirable to have a simplified method of determining which islanding detection methods (IDMs) are most effective. In this paper, a previously described method for finding the nondetection zones (NDZs) of IDMs is experimentally verified. This method is used to determine the NDZs of several common IDMs. These results indicate that, of the IDMs discussed in this paper: (1) Sandia Frequency Shift (SFS) is most effective; and (2) the worst-case loads are low-power loads that are near resonance at the line frequency and have a large capacitance and small inductance (a high value of the quality factor Q).

Development and Testing of an Approach to Anti-Islanding in Utility-Interconnected Photovoltaic Systems

Abstract: This report documents the development of an inverter control method that detects and avoids islanding in utility-interconnected photovoltaic installations. This method is applicable to single and multiple inverters connected to a single utility distribution line. The anti-islanding approach is described and its performance is demonstrated on both a theoretical basis and with results from tests conducted at Sandia National Laboratories and Ascension Technology, a division of Applied Power Corporation. It has been demonstrated that this approach is effective for single and multiple photovoltaic inverter installations for the special case where the inverter contains a version of anti-islanding software compatible with IEEE Std 929-2000.The report also describes the anti-islanding technique so that it can be incorporated into photovoltaic systems lacking this feature. A test procedure that ascertains whether an anti-islanding capability exists in a PV inverter is also presented. This page intentionally left blank

Predicting islanding operation of grid connected PV inverters

Abstract: Increasing numbers of photovoltaic arrays are being connected to the power utility through power electronic inverters. This has raised potential problems of network protection. If, due to the action of the inverter or inverters, the local network voltage and frequency remain within regulatory limits when the utility is disconnected, then islanding is said to occur. Many methods to prevent this have been proposed and a SPICE-based model and analysis of the system are presented. Specifically aimed at predicting the effectiveness of two of these. These are: active frequency drift, which causes the inverter current to be generated slightly lower or higher in frequency than the frequency of the terminal voltage; and slip mode frequency shift, which controls the phase angle of the inverter current as a function of the frequency deviation of the terminal voltage from that of the normal network frequency. Experimental verification of the model is provided. Active frequency drift using frequency speed-up rather than speed-down is shown to be preferable for inductive loads, but conditions that resulted in islanding could be predicted. Slip mode frequency shift proved to be a more robust anti-islanding protection technique.

Using power line carrier communications to prevent islanding [of PV power systems]

Abstract: Islanding of grid-connected photovoltaic (PV) power systems jeopardizes personnel and equipment and must therefore be prevented. Existing islanding prevention schemes are undesirable because they fail for certain relatively common customer loads and when more than one PV power system is present, degrade PV power quality, reduce system efficiency, and increase system complexity. These problems can be overcome using power line carrier communications. (PLCC) and an inexpensive, purpose-designed receiver. The use of PLCC for islanding prevention is discussed. In this paper, including considerations for maximum anti-islanding effectiveness. Also, a low-cost receiver for a commercial PLCC system is described and demonstrated. This receiver demonstrates the feasibility of PLCC-based islanding prevention.

Islanding detection method of distributed generation units connected to power distribution system

Abstract: In this paper, as an active technique for detecting the islanding, voltage magnitude variation method of distributed generation (DG) unit is proposed. The proposed new algorithm detects the islanding by distinguishing the differences in the system characteristic between those experienced when the DG unit is running in parallel with the utility supply and when it is operating independently. In the parallel operation mode, due to the high capacity of the utility system, any change in the voltage magnitude of DG unit produces smaller change in the voltage at the inter-tie point than that in islanding operation mode, and larger change in the injecting reactive power at the inter-tie point than that in islanding operation mode. That is, when the small change on the voltage magnitude of DG unit is made within 0.01 per unit, if the voltage at the inter-tie point changes as much as the small change and the injecting reactive power at the inter-tie point has almost no change, that operation state can be decided to be islanding operation mode. This proposed method is proved through computer simulations.

Wide bandwidth single and three-phase PLL structures for grid-tied PV systems

Abstract: This paper presents a detailed description of a three-phase PLL (phase-locked loop) structure that fits the requirements of utility connected PV systems. The tuning of the PLL structure is discussed as well as its under utility distorted conditions. A new single-phase PLL topology is introduced. Its dynamic behavior is evaluated and its quasi-instantaneous ability to detect phase, frequency and amplitude of the utility voltage is highlighted. The analysis of the performance of the introduced single-phase PLL topology under islanding condition is also presented. Simulation and experimental results are included to support the theoretical study.

A new approach to islanding detection of dispersed generators with self-commutated static power converters

Abstract: In this paper, an islanding detection approach for dispersed generators with a self-commutated static power converter is proposed. This method is suggested based on the monitoring of the magnitude and sign change in /spl part/f/sub B//|/spl part/P/sub L/. To facilitate the detection process, a designated circuit for generating the output power deviation is also developed. The proposed method has been tested under various scenarios in order to examine the detection performance and operation reliability. It is found that the proposed method effectively detects the islanding event when different amount of power mismatch is considered. Moreover, by employing the simulated disturbances to the test system, the outcome reveals that the probability of false alarm is low. Test results solidify the feasibility of the method for the application considered.

Using power line carrier communications to prevent islanding

Abstract: Islanding of grid-connected photovoltaic (PV) systems jeopardizes personnel and equipment and must therefore be prevented. Existing islanding prevention schemes are undesirable because they fail for certain relatively common customer loads and when more than one PV system is present, degrade PV power quality, reduce system efficiency, and increase system complexity. These problems can be overcome using power line carrier communications (PLCC) and an inexpensive, purposedesigned receiver. The use of PLCC for islanding prevention is discussed in this paper, including considerations for maximum anti-islanding effectiveness. Also, a low-cost receiver for a commercial PLCC system is described and demonstrated. This receiver demonstrates the feasibility of PLCC-based islanding prevention.

Development of islanding early warning mechanism for power systems

Abstract: This paper discusses a computer algorithm which can be used to detect the conditions that will separate the power system into two or more islands. In order to provide an early warning mechanism for the dispatchers in the control center such that some actions can be taken before an islanding condition occurs, the proposed algorithm converts the power system topology into an undirected graph first. Based on the graph theory, the algorithm will indicate that outages occur on one or more of the transmission lines will lead to an islanding situation. The Tai-Power Company 345 kV and 161 kV systems will be used to validate the algorithm and evaluate the performance.

Islanding of grid-connected AC module inverters

Abstract: A major safety issue about grid-connected photovoltaics is to avoid nonintentional operation in islanding mode, the grid being tripped. This paper presents detailed measurements on the islanding behavior of four module inverters with a maximum rated power of 200 W. Although applying active anti-islanding measures each inverter could be forced into islanding. It could be observed experimentally what recently has been shown analytically, that some methods against islanding fail if inverters are loaded with considerable parallel capacitance. As most distribution grids contain a considerable capacitance, those methods are to be improved. One of the inverters failed totally what illustrates the need for standardized type approvals. The outcomes show where to put accents in the development and implementation of efficient protection algorithms.

An AGC Implementation for System Islanding and Restoration Conditions

Abstract: An Island AGC function has been implemented in a large-scale power system, Virginia Power Company(VP), to assist in system emergency and restoration situations. It is the first time that the conventional AGC function has been enhanced to be utilized, rather than to be suspended, under such circumstances. The Island AGC function is designed to be implemented in both the real-time and the Dispatcher Training Simulator (DTS) environments. The latter provides a realistic closed-loop simulation environment that mimics the real system behavior, offering an excellent opportunity for operators to be well-trained, aware and prepared for abnormal situations. This implementation has been tested on the VP system model, which consists of 4400 buses and 775 generators. It has successfully completed custom factory tests, and it is the user's opinion that the Island AGC will provide a valuable additional capability for use during system restoration.

Analysis of wind farm islanding experiment

Abstract: This paper deals with the problems related to an islanding experiment performed at Rejsby Hede in Denmark. During the experiment several interesting observations were made in connection to distortion of voltages and currents. Observations were also made in connection to variation of frequency and phase. In this paper the data are analyzed in three different ways and the results are related to the physics of the electric system.

Islanding phenomenon of grid connected PV systems

Abstract: Appropriate islanding prevention measures are a must for grid connected PV systems. A great variety of methods are used to prevent islanding of grid connected PV systems. Detecting native islanding characteristics in the power grid then dealing with the phenomenon is the passive method. Constantly adding some light disturbance to the grid and detecting their obvious effects during islanding is the active method. Also combinations of these methods have appeared. Any of them is effective to some extent, but none of them could be described as perfect. Based on numerous tests conducted at the Rokko Demonstrative Test Center, after shedding light on the substance of islanding, the causes of that imperfection were investigated.

A simple, high-quality output PV system aimed at peak demand reduction

Abstract: A grid connected photovoltaic system aimed at peak demand reduction in areas with hot weather is presented. It uses the "perturb and observe" technique to track the maximum power point of the cell array, and provides a high quality current waveform. The islanding of the system is avoided by injecting a small ripple in the output current. The system was tested with a 500 W cell array, and its performance was satisfactory.

Study on Power System Black Start

Abstract: The paper presents the study on problems of self-excitation over-voltage, frequency and voltage stability organizational measures and arrangement in the course of black start and restoration' of the systemThrotlgh simulation ofblack start on East China Poner System, above problems are allalyzed and solved it shows thill that working out strict blackstart scheme may not only speed up system restoration, reduce outage losses, hilt disc have important significance to emergency release or power system islanding

An active islanding-detection method for power conditioning subsystem of utility interactive photovoltaic system

Abstract: Islanding is a scenario where dispersed generators could be severed off from the grid, but continue to operate after the utility supply is disconnected. The occurrence of islanding events may complicate the orderly reconnection of the utility network and pose a hazard to utility personnel. In this paper, a novel active islanding-detection method for utility interactive photovoltaic systems is proposed. In this approach, a control circuit is developed and implemented for producing the designated amount of deviation, which can be reflected appropriately to the output of the photovoltaic system. Then, by coupling with a proposed algorithm, this amount of deviation will be a crucial indicator to detect the islanding. Besides, this method is capable of reactive power control such that system power factor can be better ensured. The proposed approach has been tested through different scenarios. By case studies with numerical simulation, the method was verified with simplicity, feasibility and efficiency for power system protection applications.

Design of an islanding detection circuit for dispersed generators with self-commutated static power converters

Abstract: In this paper, an islanding detection circuit designed for dispersed generators with self-commutated static power converters is proposed. This circuit is suggested based on the monitoring of the magnitude and sign change in the ratio of the frequency deviation to the load variation. To facilitate the detection process, an asymmetrical circuit for generating the output power deviation is developed. The proposed method has been tested under various scenarios in order to examine the detection performance. It is found that the proposed method effectively detects the islanding event while different amount of power mismatch is considered. The test results help verify the effectiveness and feasibility of the proposed approach.

The nature of islanding in the InGaAs / GaAs epitaxial system

Abstract: The interest in the phenomenon of islanding in a range of semiconductor systems is in part due to the fundamental importance of the Stranski-Krastanow transition but also driven by potential device applications of self-organized quantum dot arrays. However, the mechanism underlying the island formation is still to a significant degree unclear. In the present work, we focus on the epitaxial InGaAs / GaAs(001) system, with layer deposition by molecular beam epitaxy. Atomic force microscopy is used to measure the surface topography of nominally 4nm thick In x Ga 1-x As films. It is shown that the growth mode switches abruptly from flat layer to island growth if a critical Indium composition of x(In)≍0.25 is reached. The structure of such layers during early stages of growth is examined using energy-filtered transmission electron microscopy. Indium gradients in the islanded layers are measured and the driving force for the islanding transition itself is considered.

Islanding of grid-connected ac module inverters

Abstract: A major safety issue about grid-connected photovoltaics is to avoid nonintentional operation in islanding mode, the grid being tripped. This paper presents detailed measurements on the islanding behavior of four module inverters with a maximum rated power of 200 W. Although applying active anti-islanding measures each inverter could be forced into islanding. It could be observed experimentally what recently has been shown analytically, that some methods against islanding fail if inverters are loaded with considerable parallel capacitance. As most distribution grids contain a considerable capacitance, those methods are to be improved. One of the inverters failed totally what illustrates the need for standardized type approvals. The outcomes show where to put accents in the development and implementation of efficient protection algorithms.

Islanding Prevention Technique by the Active/Passive Series Method Applied to PV Power Generation Systems Interconnected to The Grid with High Density

Abstract: In near future, it expects that the PV systems will be interconnected to the utility distribution lines with high density beyond the range dealt with by the current Japanese guideline for grid interconnection. As for islanding prevention under the high density interconnection, not only more reliable detection of islanding but also prevention of unnecessary detection in normality are strongly required to keep safety and stability of the grid. A new isanding prevention method of' Active/Passive Series Method' was designed in the study. The sequence of the method is; (a) Inverter current is made decrease a little when I\" passive detective function operates., (b) Inverter operation is stopped when 2' passive detective function detects remarkable change of grid voltage, cased by a positive feed back effect of the current control inverter in islanding. As the results of a simulation using EMTP and an experiment, it is clear that islanding can be detected by enhancing the sensitivity of the 1 I passive detection and setting the current drop rate for 15% at most. The result also indicates that inverter current drop is restricted to less than 15% and the current can be recovered within I sec. by combination with the MPT control of inverter even when unnecessary operation of the 1I passive detective function occurs in normal condition. From above, applicability of the designed method to the high density interconnection is confirmed.