Proposed Islanding Detection Method Research Articles

Passive Islanding Detection of Inverter-Based Resources in a Noisy Environment

Islanding occurs when a load is energized solely by local generators and can result in frequency and voltage instability, changes in current, and poor power quality. Poor power quality can interrupt industrial operations, damage sensitive electrical equipment, and induce outages upon the resynchronization of the island with the grid. This study proposes an islanding detection method employing a Duffing oscillator to analyze voltage fluctuations at the point of common coupling (PCC) under a high-noise environment. Unlike existing methods, which overlook the noise effect, this paper mitigates noise impact on islanding detection. Power system noise in PCC measurements arises from switching transients, harmonics, grounding issues, voltage sags and swells, electromagnetic interference, and power quality issues that affect islanding detection. Transient events like lightning-induced traveling waves to the PCC can also introduce noise levels exceeding the voltage amplitude by more than seven times, thus disturbing conventional detection techniques. The noise interferes with measurements and increases the nondetection zone (NDZ), causing failed or delayed islanding detection. The Duffing oscillator nonlinear dynamics enable detection capabilities at a high noise level. The proposed method is designed to detect the PCC voltage fluctuations based on the IEEE standard 1547 through the Duffing oscillator. For the voltages beyond the threshold, the Duffing oscillator phase trajectory changes from periodic to chaotic mode and sends an islanded operation command to the inverter. The proposed islanding detection method distinguishes switching transients and faults from an islanded operation. Experimental validation of the method is conducted using a 3.6 kW PV setup.

Improved Active Islanding Detection Technique with Different Current Injection Waveform

The active frequency drift (AFD) method is an effective method to detect islanding in grid-connected photovoltaic systems. However, it has some inherent drawbacks, such as generating higher harmonics. In order to reduce the harmonics and non-detection zone (NDZ), various improved AFD methods have been proposed, but they still suffer from high harmonics and reduced detection speed. To overcome these limitations, this paper proposes an innovative islanding detection technique based on AFD. Analysis reveals that the proposed method reduces harmonics by 68% compared to conventional AFD and has a larger chopping factor. Therefore, this technique offers several distinct advantages, including accelerated detection speed, reduced NDZ and harm caused by disturbances, and improved power quality. Furthermore, to verify the harmonic impact of this proposed islanding detection method, simulations and analyses are conducted using simulation software of Matlab/Simulink. An experimental prototype is set up in Laboratory. The simulation and experimental results demonstrate the superiority of the proposed method.

Islanding detection method for microgrids based on CatBoost

The occurrence of unintentional islanding will seriously threaten the stable operation of a microgrid (MG). Therefore, detecting the islanding of an microgrid timely is an important premise to ensure the microgrid operates safely and stably. However, the problem of dead zone exists in the traditional islanding detection process because the threshold of various electrical feature quantities of the point of common coupling (PCC) cannot be determined effectively. To solve this problem, an islanding detection method based on CatBoost is proposed for an microgrid. The novelty of this method lies in two aspects: 1) To reduce the error brought by the electrical feature quantities with weak correlation in the process of islanding detection, an analysis method based on the Spearman correlation coefficient is used to extract the electrical feature quantities closely related to islanding detection. 2) To determine the threshold of the electrical feature quantities more accurately and reduce the dead zone of island detection, an integrated learning machine is used to dig out correlations between the electrical feature quantities and the operation of an microgrid. The performance of the proposed islanding detection method is verified based on the modified IEEE13-bus system. The results of the example verify that the proposed islanding detection can achieve higher detection accuracy in cases of grid-connected interference and line faults.

Islanding Detection Scheme Using Potential Energy Function Based Criterion

Owning to the extensive enhancement of renewable energy resources in the distribution grids, the employment of such sources has also introduced various issues, such as the islanding problem. In this paper, an effective method is proposed for the detection of islanding in micro-grids. The proposed method employs the concept of potential energy function to drive the islanding detection index. Based on swing and potential energy function equations, an islanding detection criterion is derived based on the rate of change of the potential energy function. The islanding detection index (IDI) takes into account the frequency changes and the rate of change of frequency (ROCOF) of DG. The superiority of the proposed islanding detection method is manifested in the condition where the generation of distributed resources is in balance with the loading consumption. The performance of the proposed method has been evaluated considering the conditions where islanding is difficult to detect or might be mistaken for other phenomena given by loads within the Non-Detection Zone (NDZ) region, different fault types, and loads with different power factors. The performance evaluation has been carried out through simulations and, furthermore, has been compared with the state-of-the-art algorithms.

Empirical mode decomposition based algorithm for islanding detection in micro-grids

Owning to extensively enhancement of renewable energy resources in the distribution grids, the employment of such sources is also associated with various issues such as the islanding problem. In this paper, an effective method has been proposed for detection of the islanding in the micro-grids comprised of inverter or direct fed types of distributed generations. The proposed method is designed based on the intrinsic modes of the voltage signal measured at the PCC point. More specifically, through the calculation of the positive sequence of the voltage signal variation (PSVSV) and extracting the signal energy of PSVSV's intrinsic modes, the islanding can be detected. The superiority of the proposed islanding detection method is manifested in the condition where the generation of distributed resources is in balance with the loading consumption. The performance of the proposed method has been evaluated considering the conditions where islanding is difficult to detect or might be mistaken with other phenomena given by loads within the NDZ region, different fault types, and loads with different power factors. The performance evaluation has been carried out through simulations, and furthermore has been compared with the state-of-the-art algorithms.

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.

Islanding Detection Method With Load Power Factor Improvement and High Frequency Transient Suppressing

Reactive power control (RPC) strategy is a promising option for islanding detection in distributed generation (DG) systems. Existing RPC methods have drawbacks of not providing the reactive power to improve the load power factor and are not robust against high-frequency transient disturbances. This paper presents a modified RPC method to overcome these limitations in a 220/380 V distribution network. In this method, the reference of reactive power of the DG is designed to improve the load power factor and ensure a fast islanding detection. In addition, the proposed method incorporates a second decision-making criterion based on discrete wavelet transform (DWT) to avoid false islanding detection due to non-islanding events. The proposed islanding detection method (IDM) is tested under various conditions. Simulation and experimental results show that the proposed IDM can detect islanding rapidly and with zero Non-Detection Zone (NDZ) in the situation of load power factor improvement. Moreover, non-islanding events such as capacitor switching are effectively avoided.

Voltage-Based Hybrid Algorithm Using Parameter Variations and Stockwell Transform for Islanding Detection in Utility Grids

This paper has introduced an algorithm for the identification of islanding events in the remotely located distribution grid with renewable energy (RE) sources using the voltage signals. Voltage signal is processed using Stockwell transform (ST) to compute the median-based islanding recognition factor (MIRF). The rate of change in the root mean square (RMS) voltage is computed by differentiating the RMS voltage with respect to time to compute the voltage rate of change in islanding recognition factor (VRCIRF). The proposed voltage-based islanding recognition factor (IRFV) is computed by multiplying the MIRF and VRCIRF element to element. The islanding event is discriminated from the faulty and operational events using the simple decision rules using the peak magnitude of IRFV by comparing peak magnitude of IRFV with pre-set threshold values. The proposed islanding detection method (IDM) effectively identified the islanding events in the presence of solar energy, wind energy and simultaneous presence of both wind and solar energy at a fast rate in a time period of less than 0.05 cycles compared to the voltage change rate (ROCOV) and frequency change rate (ROCOF) IDM that detects the islanding event in a time period of 0.25 to 0.5 cycles. This IDM provides a minimum non-detection zone (NDZ). This IDM efficiently discriminated the islanding events from the faulty and switching events. The proposed study is performed on an IEEE-13 bus test system interfaced with renewable energy (RE) generators in a MATLAB/Simulink environment. The performance of the proposed IDM is better compared to methods based on the use of ROCOV, ROCOF and discrete wavelet transform (DWT).

An Islanding Detection Method for Multi-RES Systems Using the Graph Search Method

An islanding operation refers to the phenomenon in which a part of a power system composed of one or more power sources and loads is separated from the rest of the system for a certain period. An unintentional islanding operation may cause system instability and lead to human accidents, so it should be detected to prevent problems. Conventional various methods for determining islanding operation detect the islanding through the variation of power quality. However, these methods may not operate correctly in a power system which includes a variety of devices that improve power quality in the future. Therefore, in this study, we propose a method of determining islanding operation based on system configuration. Connection status between Renewable Energy Sources (RESs) and main source can be checked using depth first search among the graph search method. If RESs and main sources are connected, it is not an islanding operation and vice-versa. The simulation results show that the proposed islanding detection method complies with the maximum detection time of IEEE Std. 1547.

A Novel ANFIS-Based Islanding Detection for Inverter-Interfaced Microgrids

This paper presents a new islanding detection strategy for low-voltage inverter-interfaced microgrids based on adaptive neuro-fuzzy inference system (ANFIS). The proposed islanding detection method exploits the pattern recognition capability of ANFIS and its nonlinear mapping of relation between inputs. The ANFIS monitors seven inputs measured at point of common coupling (PCC), namely root-mean square (RMS) of voltage and current (RMS U and RMS I ), total harmonic distortion (THD) of voltage and current (THD U and THD I ), frequency ( ${f}$ ), and active and reactive powers ( ${P}$ , ${Q}$ ) that are experimentally obtained based on practical measurement in a real-life microgrid. The proposed method is composed of passive monitoring of the mentioned inputs. It does not influence power quality (PQ) and considerably decreases non detection zones (NDZs). In order to cover as many situations as possible, minimize false tripping and still remain selective; type and number of samples are introduced. Here, one of the primary goals is reducing NDZ while keeping PQ in order. Based on the sampled frequency and number of samples, we find that the proposed method has less detection time and better accuracy when compared to the reported methods. Simulations performed in MATLAB/Simulink software environment and several tests performed based on different active load conditions and multiple distributed generation, prove the effectiveness, authenticity, selectivity, accuracy and precision of the proposed method with allowable impact on PQ according to UL1741 standard.

Research on island detection method based on integrated impedance sequence component

Aiming at the large blind area of traditional passive island detection method, active island detection method has a certain impact on power quality. A new method of island detection based on integrated sequential impedance is proposed. In this method, the integrated impedance sequence component of the Inverter side union point is used to replace the sudden variable in the traditional impedance method. By detecting the change of the integrated impedance sequence component at the PCC point, the islanding phenomenon is determined when the value exceeds the limited range. The simulation of single-PV grid-connected inverter system verifies the correctness of the theoretical derivation and the effectiveness of the proposed islanding detection method.

Reactive Power P&O Anti-Islanding Method for a Grid-Connected Inverter With Critical Load

A grid-connected inverter with critical loads should be able to supply a stable voltage to critical loads at the instant of a mode change as well as during clearing time while quickly detecting unintentional islanding. The indirect current control has been proposed to provide not only a stable voltage to critical loads during clearing time but also a seamless transfer of inverters at the instant of a mode change. However, the conventional islanding detection methods cannot be applied to the indirect current control based inverter since the magnitude and frequency of voltage do not vary when an islanding occurs. This paper proposes a reactive power P&O anti-islanding method for the indirect current control. The proposed islanding detection method generates a small reactive power perturbation at the output of the inverter and detects the islanding by observing reactive power mismatch during the islanding. Using the proposed method, the inverter can supply high quality power to critical loads without distorting the output current during the clearing time. The proposed anti-islanding method is validated through simulation and experimental results.

Anti-Islanding Detection Method Using Phase-Shifted Feed-Forward Voltage in Grid-Connected Inverter

For safety and maintenance problems, the grid-connected inverters have been required to detect whether the utility voltage source is connected or disconnected to the grid. If the inverter continues to energize local loads while the utility voltage source is disconnected, it is called islanding operation. This paper proposes a new islanding detection method using phase shifted feed-forward voltage. In the grid- connected inverter system, the PCC voltage is simultaneously measured, and those values are used as the feed-forward values in the current controller. In this paper, the phase of feed-forward voltage is modified to detect the islanding condition. As the measured PCC frequency changes, the proposed method modifies the phase of feed-forward voltage. Because the phase angle of feed-forward voltage is determined according to the variation of measured frequency of PCC voltage, the proposed method makes positive feedback to the frequency. If the frequency variation exceeds the allowable range, it is judged to be islanding operation. Since the frequency response of the proposed method is fast, the islanding operation could be detected in 90 ms despite high quality-factor ( $Q_{f}$ ), 10. Moreover, when the grid is normal condition but grid frequency changes in allowable range, the proposed method does not produce continuous reactive power which reduces the quality of inverter output power. Lastly, proposed method has very small NDZ because there is no limitation on reactive power injection. The performance of the proposed islanding detection method was verified by a computer simulation and experiment with 600 W single/three phase grid-connected inverters.

Novel Islanding Detection Method for Multiple DGs Based on Forced Helmholtz Oscillator

This paper proposes a novel, passive-based anti-islanding method for both inverter and synchronous machine-based distributed generation units. Unfortunately, when the active/reactive power mismatch is near to zero, the majority of passive anti-islanding methods cannot detect the islanding situation. This paper introduces a new islanding detection method based on the chaos theory that can detect the islanding condition with near-zero active power mismatch. The method uses the modified frequency of the point of common coupling link as an input signal of forced Helmholtz oscillator. The obvious change between chaotic and normal motions in the forced Helmholtz oscillator is its main advantage over other oscillators. This change determines the threshold for detection index. The non-islanding transient events, which can cause a significant deviation in the frequency-based input signal of detector, are considered in simulations for two different case studies. These events include different types of faults, load changes, capacitor bank switching, and motor starting. Further, for islanding events, the capability of the proposed islanding detection method is verified by near-to-zero active power mismatches and UL 1741-based load imbalance tests.

Grid Connected Inverter for Current Control by Using Anti-Islanding Technique

The inverter with critical loads should be able to provide critical loads with a stable and seamless voltage during control mode change as well as clearing time. The indirect current control has been proposed for providing stable voltage with critical load during clearing time and seamless control mode transfer of inverters. However, the islanding detection is difficult since with the indirect current control the magnitude and frequency of voltage do not change when the islanding occurs. The conventional anti-islanding method based on the magnitude and frequency of voltage variation cannot apply to the indirect current control. This paper proposes an islanding detection method for the indirect current control. The proposed islanding detection method can detect the islanding using reactive power perturbation and observation when the frequency and magnitude of voltage don’t vary during clearing time. In order to verify the proposed anti-islanding method, the experimental results of a 600W three-phase inverter are provided.

Islanding detection scheme based on adaptive identifier signal estimation method

This paper proposes a novel, passive-based anti-islanding method for both inverter and synchronous machine-based distributed generation (DG) units. Unfortunately, when the active/reactive power mismatches are near to zero, majority of the passive anti-islanding methods cannot detect the islanding situation, correctly. This study introduces a new islanding detection method based on exponentially damped signal estimation method. The proposed method uses adaptive identifier method for estimating of the frequency deviation of the point of common coupling (PCC) link as a target signal that can detect the islanding condition with near-zero active power imbalance. Main advantage of the adaptive identifier method over other signal estimation methods is its small sampling window. In this paper, the adaptive identifier based islanding detection method introduces a new detection index entitled decision signal by estimating of oscillation frequency of the PCC frequency and can detect islanding conditions, properly. In islanding conditions, oscillations frequency of PCC frequency reach to zero, thus threshold setting for decision signal is not a tedious job. The non-islanding transient events, which can cause a significant deviation in the PCC frequency are considered in simulations. These events include different types of faults, load changes, capacitor bank switching, and motor starting. Further, for islanding events, the capability of the proposed islanding detection method is verified by near-to-zero active power mismatches.

Novel Islanding Detection Method for Distributed PV Systems with Multi-Inverters

This study proposes a novel islanding detection method for distributed photovoltaic (PV) systems with multi-inverters based on a combination of the power line carrier communication and Sandia frequency shift islanding detection methods. A parameter design method is provided for the novel scheme. On the basis of the designed parameters, the effect of frequency measurement errors and grid line impedance on the islanding detection performance of PV systems is analyzed. Experimental results show that the theoretical analysis is correct and that the novel method with the designed parameters has little effect on the power quality of the inverter output current. Non-detection zones are not observed, and a high degree of reliability is achieved. Moreover, the proposed islanding detection method is suitable for distributed PV systems with multi-inverters.

Islanding detection method based on a new approach to voltage phase angle of constant power inverters

This study presents a new islanding detection approach using the notion of active methods. A difference between the instantaneous and nominal voltage phase angle (VPA) of a distributed generation (DG) is applied to inverter-based interface control. After the islanding phenomenon, currents id and iq will be changed by adding the variation of the point of common coupling VPA to input of d–q transformation block of currents. This subsequently causes the voltage and frequency deviations using for detecting island. Active islanding detection techniques usually leave adverse effects on power quality. The considerable advantages of the proposed method include insignificant negative effects on the power quality in the normal operation of the power system. The performance of the proposed islanding detection method is evaluated by some common test presented in UL1741; in addition, the results of some tests are presented for multiple DGs that show the proposed method does not cause significant interference between two DGs in the operational mode. Analogous to the case of a single DG, the island was also detected well in the case of multiple DGs.

Islanding detection and load shedding scheme for radial distribution systems integrated with dispersed generations

This study presents a novel islanding detection and optimal load shedding scheme for radial distribution systems integrated with dispersed generation (DG). A simple and effective passive islanding detection method is developed based on the phase-space technique and using a probabilistic neural network-based classifier. After the system detects unintentional islanding state, it utilises an optimal load shedding scheme to prevent system collapse due to load-generation mismatch and voltage instability encountered in the islanded part of the system. The optimal load shedding scheme is developed based on the backtracking search algorithm. Extensive tests conducted with the DigSilent Power Factory® software and MATLAB® software on the IEEE 33-bus system with four DG units considering several scenarios of islanding condition were utilised to evaluate the effectiveness of the proposed islanding detection method and the optimal load shedding scheme. The results showed that the proposed method can effectively detect the islanding events and stabilise the islanded part of the system with minimum load curtailment.

A Test Device for Optimize PMU-based Islanding Detection Technology

Islanding detection is a necessary function for grid connected distributed generators. Islanding detection methods can be classified as two catalogues: remote detecting methods and local detecting methods. Most of them have limitation and defects when they are applied in photovoltaic power stations. Recently Synchronous measurement is proposed to be applied for islanding detecting. Although the islanding detection method is supposed to be applied in traditional bulk power systems, it is also suitable for renewable generation power plants. To do this islanding detection will be implemented on central management unit of photovoltaic power station instead of on grid-tied inverters as traditionally. In implementing, the criteria of this method and the threshold of algorithm are to be optimized. This paper develops a test device to validate the proposed islanding detection method applying in PV station, and provide a platform for the algorithm optimization.