Negligible Non-detection Zone Research Articles

Fast Islanding Detection of Nested Grids Including Multiple Resources Based on Phase Criteria

Smart grid enables integration of distributed generations (DGs) to contribute to support the network. In the islanding condition, a section of the system and at least one DG become separated from the main grid and can continue to operate autonomously. This paper proposes a passive islanding detection algorithm using just the DG power factor angle to extract an indicator for islanding detection with a negligible non-detection zone (NDZ). The proposed algorithm guarantees reliable detection of islanding condition even where the system is composed of multiple DGs including different types. In this paper, islanding and non-islanding events are discriminated using the proposed algorithm even in a nested microgrid which is operated autonomously. Moreover, the proposed algorithm provides secure detection in the noisy condition. Also, the proposed algorithm allows reaching the frequency and voltage ride-through requirements quickly by correctly discriminating grid-connected disturbances from islanding condition. The performance of the proposed algorithm is validated by performing extensive simulations and scenarios in different test systems. The results of the IEEE 34 bus test system have been presented in this paper.

Islanding detection method for distributed generation with wavelet based nuisance tripping suppression

This paper deals with modified reactive power control (RPC) for islanding detection. The RPC approach is an effective technique for detecting islanding in distributed generation (DG). However, existing RPC methods have limitations of injecting/drawing unnecessary reactive power into/from the grid. Furthermore, RPC methods may be affected by disturbances such as power system transients resulting in false islanding detection. This paper proposes a new controller’s reference reactive power based on the positive sequence voltage of the point of common coupling (PCC) and a reactive mismatch coefficient to overcome the aforementioned drawbacks. Furthermore, the Discrete Wavelet Transform (DWT) of the difference between the amplitude of actual and nominal PCC voltages is incorporated in the decision criteria. An entropy function based on DWT is defined to improve the reliability of the RPC method under disturbances. The proposed islanding detection method (IDM) is evaluated under various load and disturbance conditions to show its performance. Simulation and experimental finding indicate that the proposed IDM can detect islanding quickly and with a negligible Non-Detection Zone. Moreover, the DG and load reactive powers are nearby matched during the normal operation, and non-islanding events are effectively prevented.

Methods for protecting network from islanding danger

The process of energizing loads from other sources like a distributed generator with a total disconnection of utility grid at the point of common coupling is called islanding. The islanding phenomenon affects the network by safety issues and bad impact on the utility and connected loads, especially the workers on the utility. Hence, it must be detected by a suitable anti-islanding (AI) technique which is needed to be faster in terms of time detection and smaller or negligible nondetection zone. To detect this phenomenon, there are local and remote AI techniques. In this paper, local AI techniques are illustrated, which are used for improving the performance regarding the size of the nondetection zone and detection speed.

Permutation Entropy Thresholding: A Non-Linear Signal Processing Method for Islanding Detection

ABSTRACT A novel passive method based on Permutation Entropy (PE) is proposed for fast, efficient, and differential detection of islanding from other disturbance events in power system. The extremely remarkable attributes of PE such as efficient and fast detection of change in dynamics as well as computational and conceptual simplicity can be appropriately utilized to devise a thresholding system that can differentiate the change in dynamics of islanding event from the non-islanding ones with negligible Non-Detection Zone (NDZ). As NDZ is the most critical issue of existing passive islanding detection methods, which overshadows its beneficial characteristics, this new approach can prove to be a suitable alternative with an added benefit of faster detection. The method is evaluated with grid connected single as well as multi-DG systems and its robustness against effects of load quality factors, active and reactive power mismatches is investigated. Results show that this method can detect the islanding disturbance and differentiate it from other disturbances within half a cycle. The performance of the proposed method is evaluated with photovoltaic (PV) sources and also validated on IEEE 14 bus model. Results indicate the suitability of the PE method for the common DG source of PV for a wide range of power mismatches including the worst cases and also its robustness against false tripping during DG switching. The results verify the credibility and advantage of the proposed PE thresholding method and its suitability for adopting into existing networks for passive islanding detection.

Maximum Power Point Tracking Injection Method for Islanding Detection of Grid-Connected Photovoltaic Systems in Microgrid

This paper proposes a novel islanding detection method (IDM) for grid-connected photovoltaic systems (GCPVSs) through a disturbance injection in the maximum power point tracking (MPPT) algorithm. When an absolute deviation of the output voltage exceeds a threshold, the applied disturbance shifts system operating point from its maximum power point (MPP) condition. This leads to a sharp active power output reduction and consequently, a significant voltage drop in islanded mode beyond the standard voltage limit. The proposed algorithm is defined in a way that the distributed generator (DG) can be restored to MPP after islanding classification. It is thereby effective in microgrid in where the power injection at maximum level to cater the critical loads and maintain the stability of the isolated area are pursued. An intentional time delay has also been considered to avoid nuisance tripping in short-circuit faults which do not require tripping. The assessment of the proposed technique has been conducted for a sample network containing two GCPVSs in a real-time platform including actual relays in hardware-in-the-loop (HiL). The provided results under extensive islanding scenarios defined in islanding standards endorse timely and accurately detection with negligible non-detection zone (NDZ) as well as no false tripping in non-islanding disturbances. The comparative analysis of the presented scheme with a few recent IDMs for GCPVS highlights its overall superiorities, including very small NDZ, fast detection, thresholds self-standing determination, no adverse effect on power quality, and simple and inexpensive integration.

A Feedback-Based Passive Islanding Detection Technique for One-Cycle-Controlled Single-Phase Inverter Used in Photovoltaic Systems

Single-stage, single-phase photovoltaic (PV) distributed generation (DG) systems rated below 5 kW are becoming popular because of the reduction in the cost of PV panels and also due to various policy initiatives. One cycle control (OCC) based inverters are ideally suitable for such DG systems because of its cost-effectiveness, simple structure, and phase-locked loop free implementation. These inverter-based DG systems should have a robust islanding detection method (IDM) incorporated into it and should fulfill the recent standard requirements. This article proposes a novel feedback-based passive IDM, which is suitable for OCC-based grid-connected PV inverter system. The proposed method relies on the inbuilt feedback nature of OCC-based system, which drives the voltage at the point of common coupling outside the normal range of operation during an islanding condition. The proposed IDM works effectively under the new standard requirements with negligible nondetection zone. The IDM does not rely on additional computational effort or injection of external disturbance into the grid. Simulation studies are performed to verify the effectiveness of the proposed IDM. A laboratory prototype has been developed, and experimental studies are conducted to ascertain the viability of the proposed method.

Kriging Empirical Mode Decomposition via support vector machine learning technique for autonomous operation diagnosing of CHP in microgrid

Combined Heat and Power (CHP) is the one of new energy resources which has been added to power system in recent years. High efficiency, Loss reducing of power system and etc, are the main advantages of CHP as same as other distributed generations. But, unwanted islanding is one of the main problems for this generation. This article presents a novel technique for CHP unit islanding detection using Kriging Empirical Mode Decomposition (KEMD) and Support Vector Machine (SVM) pattern learning technique. In this technique the variation of Intrinsic Mode Functions (IMF) of local signals in two-dimensional mode is utilized as input data of relay. An optimal signal selection model is applied to the proposed relay in order to Non-Detection Zone (NDZ) and fails detection reducing. The best signal selection is introduces based on mean square value between islanding and non-islanding conditions. Also, by considering Optimal SVM model for the proposed relay as a pattern recognizing and weighing it using shark smell optimization, this technique has overcome the threshold selection problem. This relay is applied to CHP system in a microgrid system contains various types of DGs. Many islanding and non-islanding situation in various operation conditions in the studied microgrid are simulated. The results of simulation results are show that the proposed relay is suitable for microgrid application. Negligible NDZ, high detection time, zero fail detection and low cost of this relay are the main advantages of the proposed technique.

Islanding detection using sparse S-transform in distributed generation systems

Anti-islanding protection is a mandatory requirement for grid-connected distributed generation system so as to avoid the adverse effect of islanding. In order to achieve the objective of negligible non-detection zone along with fast detection and to reduce the computational burden, sparse S-transform (SST) is proposed here. The SST matrix is computed by considering the selected frequency components containing substantial information about signal irregularities caused by islanding and ignores the irrelevant data. The modal voltage signal of the voltage at point of common coupling is processed through the SST. The energy, standard deviation and entropy values are obtained from the transformed signal for islanding detection. The proposed scheme is validated for islanding cases under closely matched power scenarios and simultaneous occurrence of islanding event with power quality disturbances. Similarly, scheme is tested for normally occurring non-islanding disturbances. The performance of the scheme is validated in IEEE-13 bus distribution system. From the simulation results, it is found that the proposed scheme performs satisfactorily under almost all practical network disturbances. The SST technique reduces the computational burden and memory requirement significantly; hence, it is more suitable for real-time implementation.

Islanding detection approach with negligible non-detection zone based on feature extraction discrete wavelet transform and artificial neural network

Summary The paper presents a novel detection method based on feature extraction discrete wavelet transform (DWT) combined with artificial neural network (ANN) for identification of islanding condition in distributed generation (DG) system. Islanding detection methods can be classified into two major categories as active and passive methods. The main disadvantages of the passive methods are determined threshold value and related to their large non-detection zone. The emphasis of the proposed approach is eliminating the aforementioned drawbacks. The DWT allows revealing various hidden features of the signal. The aim of this paper is to determine the best wavelet basis function in order to identify islanding occurrence with higher accuracy and lower decomposition level. The proposed approach requires the measure rate of change of frequency at the DG's terminal, and various features are extracted from DWT then these features used as input into ANN. Also, the performance of the different structures of ANN such as feed-forward neural network, radial basis function, and probabilistic neural network are compared for islanding detection purpose. The proposed method is simulated and tested in various operation conditions such as islanding conditions, motor starting, capacitor bank switching, and nonlinear load switching. The test results showed that the proposed method correctly detects the islanding operation and does not mal-operate in the other situations. Copyright © 2016 John Wiley & Sons, Ltd.

Islanding detection method for inverter‐based distributed generation with negligible non‐detection zone using energy of rate of change of voltage phase angle

A simple technique is proposed in this study, aimed at the islanding detection of an inverter-based distributed generation (DG). The main advantage of the proposed technique is its reliance on a simple approach for islanding detection with negligible non-detection zone and keeping the unchanged output power quality. This work attempts to detect islanding conditions through computing the rate of change of voltage phase angle (ROCOVPA) of the point of common coupling by phase-locked loop (PLL) in inverter controllers. Because almost all inverter systems are equipped with the PLL, its implementation for inverter-interfaced DGs is simple and economical. Simulation results show that the durability energy of ROCOVPA is different for islanding and non-islanding conditions. In fact, in non-islanding condition the energy of ROCOVPA reduces to a negligible value after a certain time, but in islanding conditions it has considerable variation. The proposed method is evaluated using the conditions dictated by the IEEE 1547 and UL 1741 standards. The simulation results are presented to highlight the effectiveness of the proposed technique. In addition, the proposed method is compared with several passive and intelligent methods and it is confirmed that the proposed method has better performance and more accuracy.

Performance analysis of a new fast negative sequence power injection oriented islanding detection technique for photovoltaic photovoltaic based voltage source converter based micro grid operation

This study presents a new study on islanding detection method for photovoltaic (PV) based voltage source converter (VSC) system incorporated with multiple distributed energy resources-based microgrid. The VSC system is basically controlled by positive sequence power–voltage loop, where dc-link capacitor voltage and point of common coupling power components are measured parameters. During grid disconnection an islanding detection loop is further implemented with existing control, based on negative sequence active and reactive powers of coupling bus. The threshold for the feedback sequence voltage is determined to maintain a negligible non-detection zone and to avoid false detection during other power quality issues. A binary tree classifier is adopted for threshold filter design to perturb disturbance parameters only during islanding events. Worst-case scenario is considered by implementing a PV-based VSC system from IEEE UL 1741 standard. The performance of the proposed islanding detection technique is investigated in MATLAB/ Simulink environment. The efficient detection of islanding with a fast run on time is ensured by the result analysis, where no significant effect in power quality during normal operating condition has been maintained.

Development of Dynamic Estimators for Islanding Detection of Inverter-Based DG

In this paper, a new islanding detection method (IDM) is proposed to dynamically estimate islanding occurrence. The proposed dynamic estimators estimate amplitudes and phase angles of the current injected by the grid at the point of common coupling with the distributed generation (DG) in addition to the DG's bus voltage. A distributed two-level algorithm is proposed to detect an islanding condition for single and multi-DG configurations. Analytical design and transient analysis are carried out for the islanding detection problem to determine the nondetection zone (NDZ) of the proposed islanding detection algorithm. A local low-frequency meshed communication network is sufficient to achieve distributed islanding detection capability for a general multi-DG network with negligible NDZ. It is shown through simulations that the proposed IDM can successfully distinguish an islanding condition from other disturbances that may occur in power system networks.

Integrated Autonomous Voltage Regulation and Islanding Detection for High Penetration PV Applications

This paper proposes an autonomous unified var controller to address the system voltage issues and unintentional islanding problems associated with distributed photovoltaic (PV) generation systems. The proposed controller features the integration of both voltage regulation (VR) and islanding detection (ID) functions in a PV inverter based on reactive power control. Compared with the individual VR or ID methods, the function integration exhibits several advantages in high PV penetration applications: 1) fast VR due to the autonomous control; 2) enhanced system reliability because of the capability to distinguish between temporary grid disturbances and islanding events; 3) negligible nondetection zone (NDZ) and no adverse impact on system power quality for ID; and 4) no interferences among multiple PV systems during ID. As the VR and ID functions are integrated in one controller, the controller is designed to fulfill the requirement of VR dynamic performance and ensure small ID NDZ simultaneously. The interaction among multiple PV systems during VR is also considered in the design procedure. Finally, the feasibility of the proposed controller and the controller design method is validated with simulation using a real-time digital simulator and a power hardware-in-the-loop testbed.

A Simple Technique for Islanding Detection With Negligible Nondetection Zone

Although active islanding detection techniques have smaller nondetection zones than passive techniques, active methods could degrade the system power quality and are not as simple and easy to implement as passive methods. The islanding detection strategy, proposed in this paper, combines the advantages of both active and passive islanding detection methods. The distributed-generation (DG) interface was designed so that the DG maintains stable operation while being grid connected and loses its stability once islanded. Thus, the over/undervoltage and over/underfrequency protection method would be sufficient to detect islanding. The main advantage of the proposed technique is that it relies on a simple approach for islanding detection and has negligible nondetection zone. The system was simulated on PSCAD/EMTDC and simulation results are presented to highlight the effectiveness of the proposed technique.

A $Q$– $f$ Droop Curve for Facilitating Islanding Detection of Inverter-Based Distributed Generation

This paper presents a new method for islanding detection of distributed generation (DG) inverter that relies on analyzing the reactive power versus frequency (Q-f) characteristic of the DG and the islanded load. The proposed method is based on equipping the DG interface with a Q-f droop curve that forces the DG to lose its stable operation once an islanding condition occurs. A simple passive islanding detection scheme that relies on frequency relays can then be used to detect the moment of islanding. The performance of the proposed method is evaluated under the IEEE 1547 and UL 1741 antiislanding test configuration. The studies reported in this paper are based on time-domain simulations in the power systems computer-aided design (PSCAD)/EMTDC environment. The results show that the proposed technique has negligible nondetection zone and is capable of accurately detecting islanding within the standard permissible detection times. In addition, the technique proves to be robust under multiple-DG operation.

Islanding detection of inverter-based distributed generation

An active islanding detection technique for an inverter-based distributed generator (DG) is presented. Two control strategies are studied: one in which the DG only supplies active power and one in which the DG supplies both active and reactive power to improve the power factor. The nondetection zone (NDZ) of the over/under voltage and frequency protection (OVP/UVP and OFP/UFP) method for each control strategy is determined. For the presented interface control, it is observed that the NDZ of the OVP/UVP and OFP/UFP is larger when the DG interface is designed to improve the power factor. In order to decrease the NDZ, an islanding detection method is designed that is based on creating a mismatch between the load and DG reactive power, thus forcing the frequency to deviate outside the OFP/UFP limits. It is shown that the proposed islanding detection technique is robust and has a negligible NDZ.