Showing papers on "Islanding published in 2003"

Splitting strategies for islanding operation of large-scale power systems using OBDD-based methods

Abstract: System splitting problem (SS problem) is to determine proper splitting points (or called splitting strategies) to split the entire interconnected transmission network into islands ensuring generation/load balance and satisfaction of transmission capacity constraints when islanding operation of a system is unavoidable. For a large-scale power system, its SS problem is very complicated in general because a combinatorial explosion of strategy space happens. This paper mainly studies how to find proper splitting strategies of large-scale power systems using an ordered binary decision diagrams (OBDD)-based three-phase method. Then, a time-based layered structure of the problem solving process is introduced to make this method more practical. Simulation results on IEEE 30- and 118-bus networks show that by this method, proper splitting strategies can be given quickly. Further analyses indicate that this method is effective for larger-scale power systems.

A review of islanding detection methods for distributed resources

Abstract: Islanding detection methods for distributed resources are reviewed. Special emphasis is put on some of the detecting systems based on "active methods" which have been developed in Japan for rotating machine type distributed generations. Then, reduction of the islanding detection sensitivity with multiple distributed generations is discussed. Finally, a new concept of an islanded operation is introduced.

Testing the islanding protection function of photovoltaic inverters

Abstract: A major safety issue in grid-connected photovoltaics is to avoid nonintentional operation in islanding mode when the grid is being tripped. Worst-case conditions under which islanding can occur are specified analytically. The circuit that is commonly used for testing is described. The issue of appropriate test conditions with regard to reactive-power injection to the grid is discussed and the stabilizing impact of rotating machines and resonant circuits is evaluated in detail. Islanding test results for small inverters are presented. They confirm that very simple islanding protection methods that are commonly used, are likely to fail, if inverters are loaded with considerable capacitance. The obtained results support the assessment of the islanding protection function. They emphasize important points when defining new certification procedures for upcoming guidelines and standards.

Power conversion apparatus, power conversion system, and islanding operation detection method

Abstract: When islanding operation is to be detected in a power conversion apparatus for converting a DC power into an AC power and outputting the AC power to a system power supply, a plurality of variation generation means for executing, in accordance with different schemes, detection of islanding operation in which power supply from the system power supply is stopped are arranged, and at least one variation generation means is selected by selection means from the plurality of variation generation means and operated.

Method and apparatus for anti-islanding protection of distributed generations

Abstract: An apparatus for anti-islanding protection of a distributed generation with respect to a feeder connected to an electrical grid is disclosed. The apparatus includes a sensor adapted to generate a voltage signal representative of an output voltage and/or a current signal representative of an output current at the distributed generation, and a controller responsive to the signals from the sensor. The controller is productive of a control signal directed to the distributed generation to drive an operating characteristic of the distributed generation out of a nominal range in response to the electrical grid being disconnected from the feeder.

Testing the islanding protection function of photovoltaic inverters

Abstract: A major safety issue in grid-connected photovoltaics is to avoid nonintentional operation in islanding mode when the grid being tripped. Worst-case conditions under which islanding can occur are specified analytically. The circuit that is commonly used for testing is described. The issue of appropriate test conditions with regard to reactive power injection to the grid is discussed and the stabilizing impact of rotating machines and resonant circuits is evaluated in detail. Islanding test results for small inverters are presented. They confirm that very simple islanding protection methods that are commonly used, are likely to fail, if inverters are loaded with considerable capacitance. The obtained results allow the assessment of the islanding protection function. They emphasize important points when defining new certification procedures for upcoming guidelines and standards.

Intention islanding of distributed generation for reliability enhancement

Abstract: The paper investigates the coordination requirements for intention islanding to increase DG/Utility reliability in providing uninterruptible power to the connected loads. The most principal interconnection switchgear components are identified for the islanding. The argument of the intention islanding case is carried out using a hypothetical DG/Utility model. By identifying the principal switchgear, proper interfacing using programmable logic controllers are recommended to bridge the communication gap between the DG/Utility and the protection switchgear. Through the identified interface requirements and permitting DG islanding in the case of main feeder faults, greater reliability and load power continuity was achieved.

Anti-islanding device and method for grid connected inverters using random noise injection

Abstract: A device and method for detecting islanding of a grid connected inverter makes use of an injected white noise as a perturbing force on the output voltage of the inverter. The white noise is injected at least once in every cycle and can be generated at different rates in implementation. On loss of the grid, a frequency drift of the output voltage is detected and a positive feedback is activated that accelerates the drift.

International harmonization of grid connection guidelines: adequate requirements for the prevention of unintentional islanding

Abstract: Islanding is still one of the major controversial subjects in the international harmonization of grid connection requirements for distributed generation, and particularly photovoltaics. As long as islanding is not intended in order to back up a loss of mains, it should be avoided. The present study reviews the theory of unintentional islanding and assesses the probability of occurrence of the phenomenon, based on previous studies and theoretical considerations. While islanding is virtually impossible if only a small number of distributed generation units is connected to a distribution grid, with higher distributed generation densities, the possibility of islanding becomes realistic. The risk associated with unintentional islanding is estimated, and adequate requirements for functional safety of protection devices are determined in order to ensure the necessary additional degree of safety to be introduced by an islanding prevention device. Finally, a fundamental set of requirements with regard to islanding, to be included in an international grid connection guideline, is derived from the study. Copyright © 2003 John Wiley & Sons, Ltd.

Demonstrative research on grid-interconnection of clustered photovoltaic power generation systems

Abstract: The new national R&D project on PV system has been started since last year. The target of this project is to solve technical problems such as restriction of PV system output, higher harmonics and islanding operation where PV systems are clustered in a residential district. In this project, about 400 grid-connected PV systems with battery installed at residential houses and are monitored at all times. The results obtained in this project are expected to provide information and technologies to increase the further introduction of PV systems.

Application of distribution line carrier-based protection to prevent DG islanding: an investigating procedure

Abstract: The paper deals with the possibility of using the distribution line carrier (DLC) in order to prevent dispersed generation islanding. The feasibility of this technology applied to MV networks has been investigated from a theoretical as well as experimental point of view. A multiconductor matrix procedure based on bus admittance matrix allows us to predict the high frequency behaviour of MV lines (overhead and cable): the signal strength can be verified at any section of MV networks. Moreover two measurement campaigns have been performed on real MV networks in order to validate the theoretical results.

Investigation of antiislanding protection of power converter based distributed generators using frequency domain analysis

Abstract: Islanding of a grid connected distributed generation (DG) unit occurs when a section of the utility system containing such generators is disconnected from the main utility, but the independent DGs continue to energize the utility lines in the isolated section (termed as an island). Unintended islanding is a concern, primarily because it poses a hazard to utility and customer equipment, maintenance personnel and the general public. The algorithm proposed by the Sandia National Laboratories is analyzed in this study because it is considered to be effective in detecting the formation of such islands. Previously, there has not been any quantitative analysis for tuning the control gains of the algorithm based on the rating and bandwidth of the DG power converter. The paper interprets the components of the algorithm that affect the voltage magnitude and frequency into block diagrams that can be linearized and studied using continuous time approximations. The model represents DG operation while connected or disconnected from the main utility. This paper uses frequency domain approach to analyze the range for the gains required by antiislanding algorithm to effectively determine the disconnection of the mains grid within an acceptable time duration. The effect of variation of DG's operating power level is studied and demonstrated how the gains of the algorithm can be set to be effective for a wide power range. The results are validated using detailed time domain DG and power system simulations.

Control schemes of the inverter-interfaced multi-functional dispersed generation

Abstract: This paper deals with control schemes of the inverter-interfaced multi-functional dispersed generation (MDG), which focuses on improving the power quality, blocking of the reverse power flow, and ensuring the continuity of the electric power supply. Corresponding with the various system conditions, above functions can be performed in paralleling mode and in islanding mode. The configuration of the proposed system is composed of one DG and series and shunt inverters. Thus it has an ability to perform a unified power quality conditioner (UPQC). A numerical formulation of the proposed control schemes, which are based on the instantaneous power theory, is presented. Simulations of the test system will validate their effectiveness and flexibility of the proposed control schemes for the multi-functional purpose.

Splitting strategies for islanding operation of large-scale power systems using OBDD-based methods

Abstract: Summary form only given. System spitting problem (SS problem) is to determine proper splitting points (or called splitting strategies) to split the entire inter-connected transmission network into islands ensuring generation/load balance and satisfaction of transmission capacity constraints when islanding operation of system is unavoidable. For a large-scale power system, its SS problem is very complicated in general because a combinatorial explosion of strategy space happens. This paper mainly studies how to find proper splitting strategies of large-scale power systems using an OBDD-based three-phase method. Then a time-based layered structure of the problem solving process is introduced to make this method more practical. Simulation results on IEEE 30- and 118-bus networks show that by this method proper splitting strategies can be given quickly. Further analyses indicate that this method is effective for larger-scale power systems.

Intention islanding of distributed generation for reliability enhancement

Abstract: The paper investigates the coordination requirements for intention islanding to increase DG/utility reliability in providing uninterruptible power to the connected loads. The most principal interconnection switchgear components are identified for the islanding. The argument of the intention islanding case is carried out using a hypothetical DC/utility model. By identifying the principal switchgear, proper interfacing using programmable logic controllers are recommended to bridge the communication gap between the DC/utility and the protection switchgear. Through the identified interface requirements and permitting DG islanding in the case of main feeder faults, greater reliability and load power continuity was achieved.

Photovoltaic system performance statistical analysis

Abstract: PV system performance evaluation is not clear today. Performance Ratio (PR) or other performance indicators are site-dependant and in many cases systems reveal to have poorer performance than expected. Thus, the evaluation of factors of influence is very vague and a generalised method is necessary. We present a new methodology addressing performance for the overall PV system, for which all inputs are treated as stochastic variables. The methodology is explained and examples are given for different kinds of PV systems (grid connection, pumping SHS or SAPV systems with storage even PV/thermal systems). Additional applications are also presented (irradiation data generation, islanding probability, PV module matrix): Two main applications illustrate the methodology: the calculation of the battery SOC probability density function to assess the design of the PV system, and a way to evaluate the representativeness of the battery tests sequence in comparison to the field operating conditions the battery will face.

Analysis of PWM Converter for V-I Output Characteristics of Solar Cell

Abstract: Recently, photovoltaic system has been studied widely as a renewable energy system, because it does not produce environmental pollution and it has infinity energy souice from the sun A study on photovoltaic system has a lot of problems like as reappearance and repetition of some situation in the laboratory experiment for development of MPPT algorithm and islanding detection algorithm, because output characteristics of solar cell are vaned by irradiation and surface temperature of solar cell Therefore, the assistant equipment which emulates the solar cell characteristics Which can be controlled arbitrarily by researcher is require to the ieseaichers for reliable experimental data In this paper, the virtual implement of solar cell (VISC) system is proposed to solve these problems and to achieve reliable experimental result on photovoltaic system VISC system emulates the solar cell output characteristics, and this system can substitute solar cell in laboratory experiment system To realize the VISC, mathematical model of solar cell is studied for driving converter and the DC/DC converters are compared in viewpoint of tracking error using computer simulation Output dynamic characteristic of PV array is vaned by iriadiation and PWM converter performance is studied using PSIM simulator

Emergency Control and Special Protection Systems InLarge Electric Power Systems

Abstract: This chapter addresses the topic of designing a corrective control strategy after large disturbances. When a power system is subjected to large disturbances such as simultaneous loss of several generating units or major transmission lines, and the vulnerability analysis indicates that the system is approaching a catastrophic failure, control actions need to be taken to limit the extent of the disturbance. In our approach, the system is separated into smaller islands at a slightly reduced capacity. The basis for forming the islands is to minimize the generation-load imbalance in each island, thereby facilitating the restoration process. An analytical approach to forming the islands using a two-time-scale procedure is developed. Then by exploring a carefully designed load-shedding scheme based on the rate of frequency decline, we limit the extent of the disruption and are able to restore the system rapidly. We refer to this corrective control scheme as “controlled islanding” followed by load-shedding based on the rate of frequency decline. A new class of controls called special protection systems is now finding greater acceptance in power systems with their enhanced need to provide reliability in a competitive restructured utility environment. These systems are triggered only when large disturbances occur. They provide a degree of safety in preventing cascading outages. The special protection systems be presented and their potential for greater use will be examined.

The experimental results of an islanding detection method for Japanese AC modules

Abstract: Recently, AC modules are familiarized in Europe and US. However, there are still several problems, which need to be dealt with, for instance islanding that is one of major requirements for grid connection of solar modules in Japan. In this study, an islanding detection algorithm has been newly developed according to a sequential approach and its basic operation has been confirmed. The purpose of this study is to find the optimum detecting thresholds by different experiments, that means by single and multiple operations. Here, several developed inverters together with newly developed ones with the algorithm were examined regarding islanding detections. In this paper, the results including test methods, conditions, observed waveforms are presented. This paper proposes an islanding detecting function for Japanese AC module from comparison of usual MIC and PVPC point of view.

Grid-connection of PV generators: technical and regulatory issues

Abstract: Publisher Summary The integration of photovoltaic (PV) systems to electricity networks is covered at the top level in the standard, which groups the issues into two main categories: safety and power quality. Safety of personnel and protection of equipment are the most important issues concerning a grid-connected PV generator. When the source of power is disconnected from the network section to which the inverter is connected, the inverter is required to shut down automatically within a given time. An inverter that remains generating into such a network is termed to be in island operation. Such operation could critically affect the safety of electricity supply staff and the public, as well as the operation and integrity of other equipment connected to the network. Any generator or load connected to the mains network may affect the quality of the waveform. Alterations to the voltage or frequency, or variations that affect the shape of the sine wave, such as harmonics and flicker, are all important. Power factor and fault current contribution are also relevant considerations. Fortunately, with inverter connected PV systems, neither of these are a particular problem. Most modern inverters can adjust their power factor to suit the network. Fault level contributions are low as there is little stored energy in an inverter in contrast with the rotation energy of a spinning generator.

Method for determining an exclusive operation of system interconnection distribution power, concerned with detecting an exclusive operation of distribution power by analyzing various system parameters

Abstract: PURPOSE: A method for determining an exclusive operation of system interconnection distribution power is provided to increase a reliability of the method by reducing an erroneous operation of an electric measuring members caused by various reasons. CONSTITUTION: A voltage and a current are detected(S10) at a point interconnected with a distributed power system. A voltage imbalance index is calculates(S20) from the voltage and the current. A voltage imbalance change index is calculates(S40) by using the voltage imbalance change index. Whether the voltage imbalance change index exceeds a predetermined value is determined(S50). Distributed powers are determined to operate in an islanding mode and a trip signal is transmitted(S100) when the voltage imbalance change index is larger than the predetermined value.

New Applications of Multi-Agent System Technologies to Power Systems

Abstract: This chapter provides a state-of-the-art summary of multi-agent system technologies for power system applications. New applications to controlled islanding of power systems and MicroGrid with distributed generations are discussed. A new defense system concept, Strategic Power Infrastructure Defense (SPID), has been developed. Controlled islanding is an important extension of the SPID system and the multi-agent system is a promising technology for implementation of the SPID concept. The University of Washington is also developing the intelligent control system for MicroGrids. In this chapter, the multi-agent technology applications to these two topics are discussed with specific examples.

A Study of Islanding Detection of Grid-connected Three-phase Photovoltaic Power Conditioning System

Abstract: Islanding phenomenon of a grid-connected photovoltaic (PV) power conditioning system (PCS) is said to occur if the PCS 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, PCSs are required to detect and prevent it. In this paper, several islanding detection methods (IDMs) and reactive power variation method are described. Islanding test results for 9kW PCS are presented for verification.