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In this era, distributed energy resources are sustainable solution to the energy crisis. Distributed generation generates power for local loads as well as sharing it to the main grid. The system may get islanded after the occurrence of fault. It is necessary to detect islanding earlier. It is necessary to detect islanding and provide trip signal earlier. Also, the oscillations should be damped out as early as possible to prevent instability. Harmonics are injected due to the introduction of a disturbance signal hence; total harmonic distortion should be as minimum as possible. Here adaptive network-based fuzzy inference system is used for the CEGRE LV system for the purpose of islanding detection and anti-islanding protection. An active oscillatory disturbance signal is injected in controller. Generally, proportional integral controller and fuzzy logic controller are used for anti-islanding protection. But an adaptive network-based fuzzy inference system can be used for earlier detection of islanding and also it gives better performance than a proportional-integral controller and fuzzy logic controller. System analysis is discussed by comparing Adaptive network-based fuzzy interference system performance with proportional gain controller and fuzzy logic controller by considering zero power mismatch condition. The simulation results of this proposed method is evaluated by using MATLAB Software. [ABSTRACT FROM AUTHOR]

This paper presents a novel Ensemble Kalman Filter (EnKF)-based passive anti-islanding method designed to enhance the reliability and stability of AC microgrids amid increasing integration of distributed energy resources (DERs). The dynamic and nonlinear characteristics of AC microgrids pose significant challenges to conventional passive islanding detection methods. To address these limitations, the proposed approach employs the EnKF as a state observer to accurately estimate the point of common coupling (PCC) voltage. In this framework, two robust indices are generated: 1) the Ensemble Kalman Filter residual (EnKFR), derived from the discrepancy between the estimated and measured PCC voltages, and 2) the 3rd harmonic distortion (3rdHD), computed from the 3rd harmonic signal estimated by the EnKF. By applying an OR operation to both the EnKFR and the 3rdHD, the proposed method reliably detects islanding events while effectively differentiating them from non-islanding events. Extensive simulations were conducted on various standards such as the IEEE and UL-1741 microgrid test networks under a range of operating conditions. Results reveal that the EnKF-based method delivers enhanced detection accuracy, swift response times, a minimized non-detection zone (NDZ), and robust immunity to false positives. The findings underscore the superiority of this approach over conventional methods, with successful detection demonstrated under both balanced and unbalanced load and generation conditions. This novel scheme offers a rigorous and innovative solution to islanding detection, providing substantial improvements in microgrid stability and operational reliability.

AC microgrids (ACMGs) represent a promising evolution of traditional distribution systems, driven by environmental advantages and concerns over power quality. However, detecting islanding events within ACMGs poses a significant challenge. In this study, we propose the utilization of the Cubature Kalman Filtering Algorithm (CKFA) to address this challenge by leveraging voltage signals at the point of common coupling (PCC). Initially, CKFA is applied to voltage signatures to compute Voltage Residuals (VR) and Voltage Harmonic Signatures (VHS) through state estimation. These estimated VR and VHS indices are then compared against pre-defined threshold settings to identify islanding states. Subsequently, a tripping decision is made based on the OR operation of both estimated VR and VHS. The proposed method demonstrates efficacy in detecting islanding occurrences under both balanced and unbalanced load/generation conditions and effectively discriminating between islanding and non-islanding conditions. Extensive simulations conducted on MATLAB/Simulink-based IEEE 13-bus test bed and UL-1741 test bed validate the effectiveness of the presented scheme. Results signify a high accuracy rate of 99.9%, tied with low computational complexity and the smallest non-detection zone (NDZ). Additionally, the time of operation for the suggested scheme is less than 1 millisecond, without any false operations, emphasizing its effectiveness in practical application.

The risk of unintentional islanding creation in distributed energy systems poses a significant security concern since unintentional islanding formation could lead to a supply of energy outside of the optimal quality limits. This constitutes a risk for users, maintenance personnel, infrastructure, and devices. To mitigate this problem, anti-islanding protections are widely used to prevent the distributed generator from feeding a portion of the radial distribution grid when a protection device trips upstream. However, the effectiveness of these protections heavily relies on properly tuning protection setting thresholds (such as time delay and pickup). This work proposes a novel approach that utilizes entropy as a model and metric of the uncertainty associated with a particular protection setting. By minimizing entropy, the proposed method aims to improve stability and sensitivity, consequently improving the overall performance of anti-islanding protection. Simulation results demonstrate that the Bayesian entropy methodology (BEM) approach achieves enhanced stability in various scenarios, including frequency transients, and demonstrates a notable reduction in the size of the dataset and computational burden, ranging between 91% and 98%, when compared to related works, with an improvement of the uncertainty achieved. The findings of this study contribute to the development of more robust and reliable anti-islanding protections. [ABSTRACT FROM AUTHOR]

Featured Application: Grid Connected Inverter. As the proportion of distributed generation (DG), including Photovoltaic (PV) generation, in the power grid system increases, there are dropouts of large-scale distributed power generation sources due to some transient conditions that negatively affect the power grid stability and power quality. Accordingly, the inverter for DG generation is in a transition period, requiring more complex control performance. Anti-islanding function requirements in particular are becoming more strict because sophisticated grid-connection requirements are demanded, such as voltage ride-through, frequency ride-through, rate of change of frequency, and other functions. Thus, highly advanced anti-islanding methods are required to detect the islanding condition quickly and accurately to stop the inverter. This paper presents the improved anti-islanding method based on reactive power variation (RPV) under grid-support environments for single-phase DG inverters. In order to verify the validity of the proposed method, PSIM simulation was conducted. The proposed method meets the requirements of IEEE Std. 1547-2018 and KS C 8564:2021 by preventing islanding within 0.007 s under the newly adopted voltage/frequency trip setting, while the conventional RPV method fails. [ABSTRACT FROM AUTHOR]

The protection against the unintentional islanding of Grid-Tied inverters is an important electrical security issue addressed by the main Standards. This concern is justified in face of the fact that unintentional islanding can lead to abrupt variations of voltage and frequency, electrical damages, professional accidents, power quality degradation, and out-of-phase reclosure. In response to the islanding concern, the literature has proposed several Anti-Islanding Protection (AIP) schemes that can be divided in passive and active methods. Many of the active AIP is based on the insertion of some disturbance in the inverter current in order to deviate the frequency out of the allowed thresholds, tripping the inverter internal disconnection system. Thus, the main objective of this paper is to analyze the performance of the Active Phase Jump with Positive Feedback (APJPF) algorithm compared to other well-known frequency drift-based solutions. More than that, this work covers the Non-Detection Zone (NDZ) problem, analyzing its main mapping methodologies and the normative requirements, exposing the minimum normative recommendations a given AIP must reach to be considered functional. The last contributions of this paper are the proposal of a parametrization criterion for the Active Frequency Drift with Pulsating Chopping Factor (AFDPCF) and for the APJPF. [ABSTRACT FROM AUTHOR]

As the proportion of distributed generation (DG), including Photovoltaic (PV) generation, in the power grid system increases, there are dropouts of large-scale distributed power generation sources due to some transient conditions that negatively affect the power grid stability and power quality. Accordingly, the inverter for DG generation is in a transition period, requiring more complex control performance. Anti-islanding function requirements in particular are becoming more strict because sophisticated grid-connection requirements are demanded, such as voltage ride-through, frequency ride-through, rate of change of frequency, and other functions. Thus, highly advanced anti-islanding methods are required to detect the islanding condition quickly and accurately to stop the inverter. This paper presents the improved anti-islanding method based on reactive power variation (RPV) under grid-support environments for single-phase DG inverters. In order to verify the validity of the proposed method, PSIM simulation was conducted. The proposed method meets the requirements of IEEE Std. 1547-2018 and KS C 8564:2021 by preventing islanding within 0.007 s under the newly adopted voltage/frequency trip setting, while the conventional RPV method fails.

With the evolution of smart grid system (SGS), many issues associated with traditional grid network, i.e., power system security, monitoring and control, energy efficiency and aging of system's equipment are resolved. The smart system is flexible enough to integrate many DGs without violating its hosting capacity. However, during and after the integration of DGs into SGS, still many other technical problems exist in the system especially islanding and stability of system. This research proposes a modified Thevenien Equivalent model for voltage stability analysis of smart grid system. With the help of phasor measurement units (PMUs), the data is collected globally and thus voltage stability margin is determined. The dS/dV algorithm is then used to determine voltage stability at all the system nodes. The proposed scheme also provides online monitoring and control of voltage stability of Smart Grid System and results in a new efficient and economical anti-islanding technique based on WSNs. Since, WSNs are already being distributed along the entire structure of Smart Grid Systems for effective communication but can also be used as sensor nodes to record the changes in system voltage and its angle, called sag calculations. The data from sensor nodes, with the help of routing nodes will be then transferred to SCADA center for operating respective circuit breaker of affected DG wirelessly. Power-Hardware-In-Loop setup is used to validate the efficacy of propositions. The analysis is carried for normal as well as for faulty conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a reactive power variation method based on positive feedback to improve islanding detection for distributed generation. The proposed strategy has a simple structure. The first part involves injecting a constant reactive power and the second part involves injecting a continuously increasing reactive power with positive feedback. Under the islanding condition, the first part serves to initially activate positive feedback by shifting the point of common coupling frequency into a certain operating point. Then the second part plays an important role in accelerating the frequency shift into the over/under threshold level direction. This method does not have a non-detection zone due to the combination of the two parts, and it has good performance regardless of the load conditions. The performance of the proposed method is verified through experiments in a 1.7 kW system, where the detection time is 53 ms with an over-threshold value of 60.5 Hz and 150 ms with an under-threshold value of 57 Hz. [ABSTRACT FROM AUTHOR]

Featured Application: Grid Connected Inverter. Islanding phenomenon of distributed generation (DG), such as photovoltaic (PV) generation, is undesirable because it causes safety issues for utility service personnel and power system equipment. Many anti-islanding methods have been studied since DG appeared in electric power systems (EPSs). Most anti-islanding methods focus on disconnecting DG from the grid using functionality to detect islanding under narrow frequency trip settings, because safety issues have a higher priority. However, as DG plays a key part of an EPS, a significant loss of DG due to a short disturbance could result in a reliability issue for the EPS. Corresponding to this matter, new international standards, such as IEEE standard 1547–2018, require more sophisticated and complex functionalities for grid-connected DGs by adopting ride-through technologies and wider voltage/frequency trip settings. Since most anti-islanding functions of inverter-based DG have been based on the frequency of the inverter voltage, it is more difficult to detect islanding under wider frequency trip settings. This paper presents a correlation-based anti-islanding method (AIM) without depending on the frequency trip of inverter-based DGs. Simulation results are provided to verify the performance of the correlation-based anti-islanding method. As a result, the proposed method detects islanding at 0.116 s under wider frequency trip setting by the IEEE Std. 1547–2018 test condition, while the popular active frequency drift method with positive feedback does not detect islanding using the same current disturbance. [ABSTRACT FROM AUTHOR]

Anti-islanding detection methods have been part of a secure operation for distributed energy resource inverters, avoiding the creation of non-intentional energization when the mains are lost. These detection mechanisms were conceived historically for current-controlled inverters. New control possibilities have broken ground, and current- or voltage-controlled inverters are a reality; however, special attention must be paid to detection strategies when applied to the latter ones. This paper addresses two topics: it exposes the lack of effectiveness of those detection algorithms based on the voltage/frequency displacement concept under voltage-controlled inverters and evaluates the applicability limits of the others based on the impedance measurement (IM). The IM is presented as a valid mechanism to achieve the islanding detection, but the exploration of its limits drives the concept of detection frequency bandwidth (DFBW), introduced in this paper. The DFBW is suggested as a practical approach to select the proper injection frequency to measure. Therefore, an improved strategy based on the IM and DFBW is proposed to allow achieving the detection towards (non-)resonant loads considering low computational burden. The results were experimentally validated in a 90-kVA four-wire voltage-controlled inverter, offering detection times of less than 100 ms in any case. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In Korea, there is a rule for Renewable Energy Certification with weighting 5.0, to expand grid linkage capacity and to improve the stability of the grid to accommodate photovoltaic (PV) systems in a distributed power system. Due to this rule, many power companies and operators are trying to install electrical energy storage systems that are able to operate in conjunction with PV system power. These systems operate in parallel at the same grid connection point. This paper presents the results of case studies on the failure to detect islanding operation. Test evaluation devices that could be bi-directionally charged and discharged were implemented for an islanding detection test. Testing was conducted under a variety of operating conditions. When a single inverter was operated under the islanding condition, it was stably stopped within 0.5 s using the Korean grid-code standard. However, when two inverters were operated at the same time under the islanding condition, islanding detection failed and the two inverters continued to feed the connected RLC (resistor, inductor, capacitor) loads in the isolated section known as an island. Different algorithms used by PCS (power conversion system) manufacturers to detect islanding might cause this phenomenon. Therefore, it is necessary for a new PCS test standard to detect islanding. [ABSTRACT FROM AUTHOR]

This paper presents an improved model of multi-DGs system for enhancing the stability. The distributed generations (DGs) in the system are equipped with the additional active power controller as the technique of enhancing the wind-thermal-bundled system stability. Firstly, the influence of multi-DGs system on the oscillation of the system is analysed. Then, the conditions for DGs producing positive damping to the power system are obtained. Secondly, taking the wind farm as the study object, the increment of the frequency of the point of common coupling (PCC) in the wind farm is feedback to the active control loops for regulating the active power of wind turbine. At the same time, the multi-DGs system holds a positive damping effect on the power system which enables the dynamic behaviour of the wind farm to be improved. Thirdly, the effect of time delay on control performance is further considered and two propositions for solving critical time-delay are put forward and proved, which are used as the constraint condition of additional active power control. Finally, the time domain simulation is implemented and the correctness of the proposed method is verified by the root locus analysis and frequency domain simulation. The results show that the additional active power control can significantly enhance the power system damping. However, the wind farm will provide negative damping and even the whole system will not maintain the power angle stability when the time-delay increases and exceeds the critical time-delay.

Islanding phenomenon of distributed generation (DG), such as photovoltaic (PV) generation, is undesirable because it causes safety issues for utility service personnel and power system equipment. Many anti-islanding methods have been studied since DG appeared in electric power systems (EPSs). Most anti-islanding methods focus on disconnecting DG from the grid using functionality to detect islanding under narrow frequency trip settings, because safety issues have a higher priority. However, as DG plays a key part of an EPS, a significant loss of DG due to a short disturbance could result in a reliability issue for the EPS. Corresponding to this matter, new international standards, such as IEEE standard 1547–2018, require more sophisticated and complex functionalities for grid-connected DGs by adopting ride-through technologies and wider voltage/frequency trip settings. Since most anti-islanding functions of inverter-based DG have been based on the frequency of the inverter voltage, it is more difficult to detect islanding under wider frequency trip settings. This paper presents a correlation-based anti-islanding method (AIM) without depending on the frequency trip of inverter-based DGs. Simulation results are provided to verify the performance of the correlation-based anti-islanding method. As a result, the proposed method detects islanding at 0.116 s under wider frequency trip setting by the IEEE Std. 1547–2018 test condition, while the popular active frequency drift method with positive feedback does not detect islanding using the same current disturbance.

The islanding phenomenon of a distributed resource (DR), like a photovoltaic (PV) system or an energy storage system (ESS), is one of the major issues about the increased DR in distributed power networks because it causes a safety hazard to a power system's service personnel and the related power facility by unexpected powering. To prevent islanding, many anti-islanding methods have been developed and evaluated by the international and domestic grid-interconnection standards, but they have mostly focused on a single DR unit. Until now, evaluating the anti-islanding function for multiple DRs connected to the same power grid has received little attention. The rapid deployment of the PV micro-inverter in recent years has substantially increased the likelihood and concerns associated with islanding, especially with multiple operations in the same grid. This paper presents an anti-islanding performance analysis of multiple PV micro-inverter operations. Various islanding cases for multiple PV micro-inverter systems are evaluated based on the existing standard with the appropriate modification. [ABSTRACT FROM AUTHOR]

Different issues will be raised and highlighted by emerging distributed generations (DGs) into modern power systems in which the islanding detection is the most important. In the islanding situation, a part of the system which consists of at least one DG, passive grid, and local load, becomes fully separated from the main grid. Several detection methods of islanding have been proposed in recent researches based on measured electrical parameters of the system. However, islanding detection based on local measurements suffers from the non-detection zone (NDZ) and undesirable detection during grid-connected events. This paper proposes a passive islanding detection algorithm for all types of DGs by appropriate combining the measured frequency, voltage, current, and phase angle and their rate of changes at the point of common coupling (PCC). The proposed algorithm detects the islanding situation, even with the exact zero power mismatches. Proposed algorithm discriminates between the islanding situation and non-islanding disturbances, such as short circuit faults, capacitor faults, and load switching in a proper time and without mal-operation. In addition, the performance of the proposed algorithm has been evaluated under different scenarios by performing the algorithm on the IEEE 13-bus distribution system.

Anti-islanding detection methods have been part of a secure operation for distributed energy resource inverters, avoiding the creation of non-intentional energization when the mains are lost. These detection mechanisms were conceived historically for current-controlled inverters. New control possibilities have broken ground, and current- or voltage-controlled inverters are a reality; however, special attention must be paid to detection strategies when applied to the latter ones. This paper addresses two topics: it exposes the lack of effectiveness of those detection algorithms based on the voltage/frequency displacement concept under voltage-controlled inverters and evaluates the applicability limits of the others based on the impedance measurement (IM). The IM is presented as a valid mechanism to achieve the islanding detection, but the exploration of its limits drives the concept of detection frequency bandwidth (DFBW), introduced in this paper. The DFBW is suggested as a practical approach to select the proper injection frequency to measure. Therefore, an improved strategy based on the IM and DFBW is proposed to allow achieving the detection towards (non-)resonant loads considering low computational burden. The results were experimentally validated in a 90-kVA four-wire voltage-controlled inverter, offering detection times of less than 100 ms in any case.

Owing to rapid depletion of fossil fuels and environmental hazard, different non-conventional sources of energy like wind, geothermal, nuclear, photovoltaic etc, have been taken into consideration for power generation. Environmental familiarness, reduced installation cost, improved power quality, abundant availability of source makes photovoltaic based distributed generation as one of the most popular alternative source of energy production. Improvement in power electronics technology makes synchronization of PV system with grid more viable. Power output from the PV module changes continuously with time depending upon the climatic condition. In order to get maximum output from the PV system different types of MPPT algorithm present in literature are studied and improvement proposed are described in this paper. Furthermore, different types of inverter topologies along with different grid synchronization technique and PWM topologies used to connect the PV system with the 3-phase AC grid are presented. In order to minimize the harmonic content of the inverter output, different types of filters used are presented in the proceeding section. Nextly different commonly used advanced islanding detection techniques for the safety purpose of PV based distribution generation system have been addressed and based on advantages and limitation of anti-islanding techniques, a comparison table has been presented. Afterward based on parameters like input, output voltage & current, MPP range, used standards etc, a comparison table between different commercially available grid tied PV inverters are presented in this paper. Finally, drawbacks of the prevailing grid connected PV system have been discussed. [ABSTRACT FROM AUTHOR]

SUMMARY Although computer simulation is certainly a powerful tool for power system stability assessment, manual analysis is more helpful for understanding mechanism of unstable phenomena. Among unstable phenomena, oscillatory stability must be the most complex one. The paper analyzes the impact of recently developed Japanese RE's standard active anti-islanding function named 'frequency feedback with step injection' on power system oscillatory stability. Since active anti-islanding makes islanded system unstable, it also makes stability of large interconnection worse. The question is how serious is the impact and how the impact can be mitigated. The paper presents a method for oscillatory stability analysis considering induction motor load, RE, and anti-islanding function on RE so minutely as readers can reproduce. Analyses are performed as case studies on aggregated power sending and receiving systems in existing interconnection of Japan. The analyses results are verified by simulation results on the same case studies. [ABSTRACT FROM AUTHOR]

Large distributed generators (DGs) are usually connected to medium voltage (MV, typically up to 50 kV) feeders directly. Their anti-islanding protections mainly rely on transfer trips from upstream substations through communication media, which are expensive and time-consuming because of infrastructure. This paper presents a local anti-islanding protection relay (LPR) as an alternative for the traditional transfer trip in MV feeder applications. The basic idea of the proposed LPR is to short phase to neutral or phase to phase voltages by thyristors at the point of common coupling (PCC) of each DG when either of them is crossing zero; then both variations of the thyristor current and voltage harmonic distortion at the PCC are observed and measured, and they are able to indicate the operating mode of the DG unit in either grid-connected or islanding. Further, this approach is analyzed and discussed based on a single DG scenario and a complicated scenario with two DGs and one shunt capacitor bank. Finally, a lot of experiment results with different scenarios are obtained based on a scale-down testing platform, which has been built in our lab by using per-unit method from an actual MV feeder system. [ABSTRACT FROM PUBLISHER]

In Korea, there is a rule for Renewable Energy Certification with weighting 5.0, to expand grid linkage capacity and to improve the stability of the grid to accommodate photovoltaic (PV) systems in a distributed power system. Due to this rule, many power companies and operators are trying to install electrical energy storage systems that are able to operate in conjunction with PV system power. These systems operate in parallel at the same grid connection point. This paper presents the results of case studies on the failure to detect islanding operation. Test evaluation devices that could be bi-directionally charged and discharged were implemented for an islanding detection test. Testing was conducted under a variety of operating conditions. When a single inverter was operated under the islanding condition, it was stably stopped within 0.5 s using the Korean grid-code standard. However, when two inverters were operated at the same time under the islanding condition, islanding detection failed and the two inverters continued to feed the connected RLC (resistor, inductor, capacitor) loads in the isolated section known as an island. Different algorithms used by PCS (power conversion system) manufacturers to detect islanding might cause this phenomenon. Therefore, it is necessary for a new PCS test standard to detect islanding.

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.

The capacity to provide ancillary services has become more and more important for generators in the distribution grid. New grid codes have been implemented which regulate inverter behavior regarding different aspects of system safety and stability. This mainly includes the frequency-dependent power reduction or the allocation of reactive power. These standards affect mains monitoring because the power control directly changes penetration after the generator has islanded. In this paper, equations for active and reactive power balance are set up and developed further. Non-Detection Zones for different control methods are shown. These are then described and interpreted in detail to show how different effects that result from grid codes interfere with one another. Frequency-dependent power reduction was found to change the size and shape of the Non-Detection Zones. Reactive power control results in a shift of the Non-Detection Zones. In fact, even the initial operating point before loss of mains has an impact on inverter behavior after islanding. Islanding operating points are sometimes undefined which leads to oscillation. An interpretation of the results and advice for future revisions of grid codes conclude the paper. [ABSTRACT FROM PUBLISHER]

This paper proposes active frequency drift (AFD) as an anti-islanding method applied to micro-inverters with uncontrollable reactive power. When using ordinary inverter topologies, such as full bridge inverters in photovoltaic systems, the islanding phenomenon can be detected with reactive power-based methods, such as reactive power variation. However, when the inverter topology cannot control the reactive power, conventional anti-islanding methods with reactive power cannot be utilized. In this work, the topology used in this paper cannot control the reactive power. Thus, an anti-islanding method that can be used in topologies that cannot control the reactive power is proposed. The conventional anti-islanding method of the topology that cannot control reactive power is introduced and analyzed. Unlike the conventional AFD method, the proposed method extends a zero current interval every predetermined cycle. The proposed method offers certain advantages over conventional AFD methods, such as total harmonic distortion. The proposed method is validated through simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper seeks to improve the computational time needed to solve transmission switching problems. Transmission switching provides an effective way to reduce operating costs in power system operations by altering the topology of the transmission network. However, determining the optimal set of lines to switch creates an enormous computational burden. Transmission switching formulations add binary decision variables for many transmission lines in the system to indicate if they are switched. This creates a very weak formulation that is difficult to solve. Altering the transmission topology by switching lines can affect the reliability of the network, for instance, by creating islands. Additional reliability constraints need to be added to the problem formulation. These constraints can potentially make an already difficult problem even harder. This paper takes a different approach to the transmission switching problem. Rather than preventing islanding by using constraints in the problem formulation, we look at how they can be used to improve the solution process. Specifically, we develop a cutting plane algorithm to generate valid inequalities and fix variables based on the fact that optimal solutions to the transmission switching problem that do not contain islands exist. [ABSTRACT FROM AUTHOR]

In this paper enhanced multi-criteria-based passive islanding detection scheme is presented. Multi-criteria based islanding detection is based on measuring the change of voltage unbalance and voltage total harmonic distortion of all phase-to-phase voltages which are also multiplied by voltage sequence components dependent value. In this new scheme islanding verification logic is further improved, so that it can separate real islanding (healthy island i.e. no fault in the islanded part of the network) case from all the other network disturbances more reliably including also cases where islanding happens after fault in HV or MV network. Also the effect of recent grid code requirements as well as change in voltage positive sequence angle has been considered and taken into account in the proposed islanding detection scheme with improved islanding verification logic. [ABSTRACT FROM AUTHOR]

An active anti-islanding method for three-phase grid-tied inverters is proposed in this paper. The method is based on asymmetric injection of the converter currents at a subharmonic frequency. This method allows an accurate detection of the islanding condition, thus it minimizes the perturbation to the power system. The theoretical analysis have been confirmed by simulation and by experimental tests conducted on a 40-kW one-cycle control grid tied inverter according to the test procedure outlined in the standard IEEE Std. 1547. The experiments have demonstrated negligible perturbation to the power system, with an increase in the total harmonic distortion of the current of less than 0.1% at full load. [ABSTRACT FROM AUTHOR]