Anti-islanding Schemes Research Articles

Bagged tree based anti-islanding scheme for multi-DG microgrids

Microgrids are becoming a prevalent part of the grid due to its’ numerous advantages on energy management system. Microgrids are perceived as the gate way for systematic inclusion of multiple renewable based distributed generations. One of the key concerns for these types of microgrids is detection of absence of the grid. This paper demonstrates a dual use line relay (DULR) based passive detection technique which uses an intelligent electronic device (IED) platform to confirm the islanding condition. Bagged tree ensemble classifier based on synchrophasor measurements has been used in IED as a decision making algorithm. Assorted range of non-islanding and islanding state of affairs have been considered to train the classifier. The measurements obtained from DULR can be used for further analysis at any level of the smart-grid communication hierarchy. The proposed scheme has been seen as fast, effective, economic, and having zero non-detection zone, compared to some of the existing techniques.

Field Verification of Autonomous Anti-Islanding Schemes and Grid Support Functions of an Inverter-Based Microturbine Distributed Generator

Canada-wide climate change plans have been put in place in the form of legislation and emission reduction programs. As part of these measures, reduced amounts of natural gas can be vented, incinerated, or flared. These programs have a direct impact on the Canadian oil and gas industry. Other measures mandate the decommissioning of high-emission thermal power plants, such as coal-fired generation. At the same time, governments are encouraging the wide-scale adoption of distributed energy resources (DERs). Because of these changes, natural gas fired DERs have been proliferating in oilfields to consume the byproduct natural gas and most major oil and gas companies are diversifying their portfolio to include generation assets. It is a more sustainable and environmentally friendly scenario as compared to the previous status quo. From an electric utility standpoint, this represents a change in paradigm, because distribution systems are traditionally planned to be radial and only experience power flowing from the substation to the load centers. This change requires utilities to adapt to new concerns and requirements, which span from operation to health and safety hazards. Among these, anti-islanding is likely the most important concern to allow the safe and reliable operation of a distribution system. The standard method to avoid unintended islanded operation is the direct transfer trip. Under exceptional circumstances, the utility may waive this requirement if an alternative acceptable method is in use. This article addresses existing anti-islanding schemes and covers in detail an alternative anti-islanding method native to many inverters. This article contains the philosophy of such method and measurement results captured during commissioning of a DER containing the scheme. Furthermore, this article highlights the evolution of inverter-based generator technologies and how the revision of applicable standards (IEEE 1547) can improve the reliable operation of such DERs.

Methodology for Assessing the Risk of Unintentional Islanding of Distributed Wind Generators Using Passive Schemes

Anti-islanding protection of distributed generation is usually performed by passive schemes, which are based on local measurements of voltage. However, these schemes may fail in detecting the islanding occurrence for some specific operating conditions. For a distributed wind generator connected to a specific grid, these operating conditions depend on the load curve and the wind speed distribution. Thus, this paper proposes a methodology to assess the risk of a passive anti-islanding scheme not being able to detect an islanding occurrence in a distributed wind generator. This risk level may be used in cost–reliability evaluations carried out to select the most suitable protection scheme.

Active Cross-Correlation Anti-Islanding Scheme for PV Module-Integrated Converters in the Prospect of High Penetration Levels and Weak Grid Conditions

This paper introduces a new cross-correlation anti-islanding detection scheme for module-integrated converters (MICs) with pseudo dc-link. The proposed scheme periodically injects a second-order harmonic current component of low magnitude (in open-loop mode) and evaluates grid response by means of correlation. The proposed scheme is highly reliable, providing nondetection-zone free operation, fast detection, and compliance with the relevant power quality and anti-islanding standards. Additionally, it excels in lower computational cost, reduced fault detection zone, and higher output power quality, compared to the referenced anti-islanding schemes that are compatible with MICs. Last but not least, it can be implemented in MIC platforms without requiring an output current sensor, being an easily upgradable solution in software level. A firm theoretical framework that considers both high penetration levels of PV systems and weak grid conditions is also included in this paper. The theoretical framework, as well as the effectiveness of the proposed scheme, is verified through extensive experimental results for various electrical-network parameters and nonlinear loading conditions. Finally, a comprehensive comparison between the proposed method and the most common anti-islanding techniques (compatible with MICs) is performed, leading to some valuable conclusions from MICs perspective.

On Harmonic Injection Anti-Islanding Techniques Under the Operation of Multiple DER-Inverters

This paper studies the significant impact of distributed-energy-resource (DER) inverters (which are connected to the same node) on anti-islanding protection of DER-installations. As it concerns the harmonic injection-based schemes, the induced harmonic voltage component that is provoked by each inverter is compromised, as synchronous injection (injection at the same time intervals) among the inverters cannot be reassured. Therefore, harmonic injection-based anti-islanding schemes will fail if the harmonic voltage component falls below a certain level. In this framework, a novel metric (i.e., the upgrade factor, UF ) is introduced, indicating the supplementary power (of DERs) that can be installed in the same point of common coupling without compromising the effectiveness of the harmonic injection scheme. As this metric enables the evaluation of harmonic injection schemes prior to the future integration of DERs, it could be a substantial addendum into the relevant standards that evaluates the anti-islanding features of grid-tied DER-inverters. Finally, this paper proposes a technique (implemented in the software level), which maximizes UF and reassures the effectiveness of the harmonic injection schemes under the power variations of installed inverters. Extensive simulations and experimental tests have been conducted that verify the effectiveness of the proposed strategy under various penetration-levels and islanding-network conditions.

On the Injection of Sub/Inter-Harmonic Current Components for Active Anti-Islanding Purposes

Active anti-islanding schemes that are based on the injection of harmonic currents, such as the measurement of the impedance at a specific frequency or similar techniques, have been proposed for anti-islanding protection in photovoltaic (PV) systems due to their low impact on inverter active power, their fast detection response in island, and reduced non-detection zone (NDZ). Integer multiples of the fundamental frequency as well as sub/inter-harmonics have both been used for the implementation of those schemes. Although utilization of sub/inter-harmonics present significant advantages, they also present significant limitations. This work investigates those limitations, particularly the ones that are caused by the parallel operation of multiple inverters. In addition, the distortion effect that is caused in the output current of the widely used PV microinverters with pseudo dc-link (PV Pdc-MICs) is discussed and thoroughly analyzed. It is concluded that when the injection is performed asynchronously (without communication among the inverters) sub/inter-harmonics are unsuitable for utilization under the parallel operation of multiple inverters. It is worth noting that a strategy is proposed in the current work that retains the effectiveness of the harmonic injection scheme under the injection of integer multiples of fundamental frequency. On the other hand, the distortion effect that is caused by the sub/inter-harmonics on PV Pdc-MICs output current, has been evaluated as insignificant when harmonics are used for anti-islanding purposes. Finally, the theoretical/mathematical outcomes of this work are supported by simulation and experimental results.

Autonomous microgrid operation subsequent to an anti-islanding scheme

A microgrid is a scaled-down power grid, comprising of distributed power generations (DPGs) and loads. It generally operates in conjunction with the utility grid, but can also isolate to operate in “islanded mode” and serve independently according to the physical and/or economic circumstances. However, while incorporating the DPGs with the main grid, anti-islanding becomes a vital operational requirement. Thus, a novel anti-islanding scheme based on harmonic distortion is proposed in this study. To realize the full benefit of high DPGs penetration, stable operation of an islanded microgrid becomes a vital concern after the detection of an islanding event. Hence, this paper also investigates the capability of DPG units to sustain the transition, along with the post-islanding stability. Furthermore, the study also investigates the problem of power sharing during post-islanding condition and incorporates an intelligent power sharing technique for power balance, satisfying both voltage and frequency constraints. The studies show that the proposed approach not only ensures quick islanding detection with a reduced non-detection zone but also the stability of the microgrid, even during islanding transients. The time domain simulation results are found through MATLAB/SIMULINK environment and the corresponding analysis are presented to justify the efficacy of the proposed technique.

Anti-islanding and Distributed Generation System

This paper proposes an anti-islanding control for a grid connected distributed generation system. The proposed control is based on d-q frame. The scheme using current command reference as positive feedback is utilized to drift the PCC voltage beyond the threshold limits to detect islanding within 2 seconds as prescribed by IEEE 1547. The test system configuration and parameters for anti-islanding study is prepared on IEEE 929 standards. The effectiveness of proposed anti-islanding scheme is validated by simulation done in MATLAB platform.

Incorporation of Harmonic Injection in an Interleaved Flyback Inverter for the Implementation of an Active Anti-Islanding Technique

Over recent years, the output power of micro-inverters [module-incorporated inverter (MIC)] is progressively pushed to higher levels, following the current photovoltaic (PV) modules market trends. The interleaved Flyback inverter—under discontinuous conduction mode of operation (DCM)—is an appealing solution for PV applications which are based on MIC technology. This topology provides increased power level for distributed PV generation exploitation with simple control configuration, high efficiency, and reduced filter size. In this paper, the harmonic injection capability is incorporated into the interleaved Flyback inverter for the implementation of an active anti-islanding scheme. A suitable technical solution is proposed that bypasses the unfolding H-bridge, without affecting the active power generation of the inverter and without requiring any hardware modification. In addition, a mathematical model based on the instantaneous power balance theory is presented, being a powerful analysis tool for inverters operating under complete magnetic discharge such as the Flyback inverter (either conventional or interleaved) under DCM or boundary conduction mode of operation. The proposed model predicts accurately the steady-state operational behavior of the Flyback inverter under current harmonic injection, either in grid-tied or islanding operation. The proposed technical implementation method and mathematical model are verified through simulation and experimental results. Finally, an anti-islanding set-up based on the proposed harmonic injection technique is presented and implemented into the Flyback micro-inverter. The proposed set-up is verified through experimental results on various quality factor values, as well as for weak grid conditions.

The Anti-islanding Scheme for a Number of Grid-connected Inverters Under Parallel Operation

The Anti-islanding Scheme for a Number of Grid-connected Inverters Under Parallel Operation

周波数フィードバック方式を用いた単独運転検出機能が引き起こすPV用PCS出力ハンチング現象の解明とその対策

周波数フィードバック方式を用いた単独運転検出機能が引き起こすPV用PCS出力ハンチング現象の解明とその対策

Adapative Load Anti-islanding Method of Large Distributed Photovoltaic Power Grid

A large number of distributed photovoltaic power grid, islanding problems become more prominent. This paper first analyzes some existing anti-islanding scheme, and analyzes its advantages and disadvantages. Then, this paper proposes adaptive anti-islanding scheme by using the load, i.e. load automatic switching, changing the characteristics of the whole load, make the passive anti-islanding without dead-zone. Then using PSCAD simulation of the program, to verify the usefulness of the proposed scheme. To minimize the distributed photovoltaic power grid investment, saving the scheme relies on a new generation of distributed photovoltaic (pv) grid interface device. Then the paper introduces the overall structure and function of the device configuration, the device not only can solve the problem of area of backup protection, also save on investment, convenient for on-site equipment installation and maintenance, for the widespread promotion of distributed photovoltaic power grid to lay a solid foundation.

불검출영역이 없는 새로운 단독운전 검출기법

Unintentional islanding results in safety hazards, reliability, and many other issues. Therefore, the islanding detection of a power conditioning system of a distributed generation, such as a grid-connected photovoltaic inverter, is a key function for standard compliance. Currently, many anti-islanding schemes have been examined, but existing anti-islanding schemes have poor power quality and non-detection zone issues. Therefore, this study analyzes the non-detection zone in a more deliberate manner than the existing analysis of the non-detection zone and proposes a new anti-islanding scheme, which has negligible power quality degradation and no non-detection zone. Simulation and experimental results validate that the proposed scheme shows much better performance than other existing schemes.

A Practical Method for Nondetection Zone Estimation of Passive Anti-Islanding Schemes Applied to Synchronous Distributed Generators

Unintentional islanding detection is a primary requirement for the interconnection of synchronous distributed generators (DGs). For this purpose, voltage and frequency-based relays are largely employed due to their low cost and simplicity However, these devices are not totally reliable due to their associated nondetection zone (NDZ). The NDZ is an effective tool to evaluate the performance of these relays against islanding occurrence. In this context, this paper presents a simple and practical analytical method to estimate the NDZ of frequency and voltage-based relays without relying on numerous, time-consuming electromagnetic transient (EMT) simulations. The main contribution is that one can easily estimate the NDZ of these protection systems based on a few analytical expressions. The effectiveness and generality of the analytical method are verified by comparing its results with those obtained by repeated, intensive EMT simulations for different power distribution networks and different relay types.

Islanding Detection in Microgrids Using Harmonic Signatures

In recent years, there has been a growing interest in incorporating microgrids in electrical power networks. This is due to various advantages they present, particularly the possibility of working in either autonomous mode or grid connected, which makes them highly versatile structures for incorporating intermittent generation and energy storage. However, they pose safety issues in being able to support a local island in case of utility disconnection. Thus, in the event of an unintentional island situation, they should be able to detect the loss of mains and disconnect for self-protection and safety reasons. Most of the anti-islanding schemes are implemented within control of single generation devices, such as dc-ac inverters used with solar electric systems being incompatible with the concept of microgrids due to the variety and multiplicity of sources within the microgrid. In this paper, a passive islanding detection method based on the change of the 5th harmonic voltage magnitude at the point of common coupling between grid-connected and islanded modes of operation is presented. Hardware test results from the application of this approach to a laboratory scale microgrid are shown. The experimental results demonstrate the validity of the proposed method, in meeting the requirements of IEEE 1547 standards.

분산전원 시스템의 주파수 변동을 통한 단독운전 방지기법 분석

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.

단독운전 방지를 위한 능동적 주파수 변환 기법의 검출 성능 및 THD 분석

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.

향상된 고조파 검출 능력을 갖는 계통연계 인버터의 하이브리드 단독운전 방지기법

향상된 고조파 검출 능력을 갖는 계통연계 인버터의 하이브리드 단독운전 방지기법

Anti-Islanding Scheme for Synchronous DG Units Based on Tufts–Kumaresan Signal Estimation Method

Considering safety and reliability problems of distribution networks, an exact distinction method is required to discriminate the loss of the main network from the existing parallel operation. Hence, this paper introduces a new islanding detection method for synchronous DGs. This method uses a noniterative signal estimation algorithm for the estimation of the damping factor and oscillation frequency of synchronous DG. The Tufts-Kumaresan (TK) signal estimation method is used in this study to detect the islanding conditions. Simulation results under various scenarios, such as different types of faults, load changes, and capacitor bank switching are used to evaluate the performance of the proposed method. This method has a high capability in islanding detection, even in cases with near to zero active power imbalances. To show the effectiveness of the proposed method, it is compared with the performance of ROCOF and ROCOFOP methods.

Anti-islanding Protection of Distributed Generation Using Rate of Change of Impedance

Abstract Distributed Generation (DG), which is interlinked with distribution system, has inevitable effect on distribution system. Integrating DG with the utility network demands an anti-islanding scheme to protect the system. Failure to trip islanded generators can lead to problems such as threats to personnel safety, out-of-phase reclosing, and degradation of power quality. In this article, a new method for anti-islanding protection based on impedance monitoring of distribution network is carried out in presence of DG. The impedance measured between two phases is used to derive the rate of change of impedance (dz/dt), and its peak values are used for final trip decision. Test data are generated using PSCAD/EMTDC software package and the performance of the proposed method is evaluated in MatLab software. The simulation results show the effectiveness of the proposed scheme as it is capable to detect islanding condition accurately. Subsequently, it is also observed that the proposed scheme does not mal-operate during other disturbances such as short circuit and switching event.