Non-detection Zone Research Articles

Space Vector Rotation-Based Controlled Decaying Current Injection for Islanding Detection of Inverter-Interfaced DG

Continuous injection-based islanding detection of Inverter-Interfaced Distributed Generator (IIDG) has been a general trend. The major issues in previous islanding detection methods are large Non-Detection Zone (NDZ), poor Power Quality (PQ), high implementation cost, and lack of real-time validation. Further, the threshold in most methods is not generic and depends on the system’s rating. Hence, this paper proposes a local voltage and current measurement-based islanding detection method for IIDGs. It utilizes parameters estimated from the fundamental phasors of voltage and current at the Point of Common Coupling (PCC) of IIDG using Space Vector Rotation (SVR) and a controlled self-decaying current injection. The proposed disturbance is injected only after disturbance detection by SVR parameters to mitigate the impact on PQ. Disturbance identification is easy due to the combined PCC voltage and current effects on parameter estimation. Real-Time Digital Simulator (RTDS) and Controller Hardware In the Loop (CHIL) setup-based results from the proposed method have been obtained and compared with previous methods. These results indicate the proposed method’s real-time efficacy (low islanding detection time) with no NDZ and negligible impact on PQ for different islanding events. Also, the proposed method is independent of the microgrid’s rating and reliable for non-islanding events.

A model predictive Goertzel algorithm based active islanding detection for grid integrated photovoltaic systems

A microgrid is a cluster of several energy sources and interconnected loads which are synchronized to operate either in grid connected or islanded mode. To attain higher efficiency and improved power control the microgrid is integrated with power electronic devices. But various problems arise related to protection among which the major issue to be focused on is islanding detection. Whenever an islanding condition arises the balance between load and generation in the islanded circuit can be violated, thereby leading to abnormal frequencies and voltages. This hazardous state observed in the system can be prevented by early detection of occurrence. In this paper, an active islanding detection with integrated PV system for grid based on Predictive Goertzel algorithm is proposed. The proposed single-phase single stage photovoltaic system injects a small harmonic component of the output of the grid and checks point of common coupling (PCC). The Predictive Goertzel algorithm is a discrete Fourier transform that resolve Non detection Zone (NDZ) and detection time. The highlight of this work is to demonstrate the performance of proposed islanding detection method, a single-stage single-phase grid integrated PV system embraces of 1-Φ full bridge inverter, LCL filter and local load (RLC parallel load) is considered. This algorithm is implemented in MATLAB Simulink environment. From the results obtained, the detection time for real time environment has reduced by 200ms compared to existing algorithm.

A Novel Approach for Secure Hybrid Islanding Detection Considering the Dynamic Behavior of Power and Load in Electrical Distribution Networks

In the arena of modern electrical power distribution systems, distributed generators (DGs) are emerging as a manifestation of electric power personalization. Even though DGs have various advantages, unintentional islanding phenomena caused by DGs during abnormal grid operations can damage equipment connected to the grid. Therefore, islanding detection mechanisms are essential for DGs in grid-connected mode to disconnect the DG from the grid in case of grid abnormalities by obeying to specific grid codes. In this regard, a novel approach to develop a secure hybrid islanding detection method (IDM) is presented in this paper. The proposed hybrid IDM is developed by combining two passive IDMs known as rate of change of active power and rate of change of reactive power with an active IDM called load connecting strategy. An 11 kV Malaysian distribution system integrated with three types of DGs, namely synchronous generator, photovoltaic, and biomass, has been chosen as a testbed for the verification of the proposed hybrid IDM. Seven different case studies have been conducted in the PSCAD/EMTDC platform to validate the performance of the proposed IDM for islanding and non-islanding events. The simulation results confirm that the proposed IDM can detect islanding within 0.09 s, which is within 2 s complying with IEEE and IEC standards. Further, a comparative study based on the detection time and non-detection zone has been carried out, which has confirmed that the proposed IDM demonstrates better performance compared to the previously developed hybrid IDMs.

A Passive Islanding Detection Method for Distribution Power Systems With Multiple Inverters

The high penetration of grid-connected distributed energy resources (DERs) leads to a need for smart inverters to enhance their performance and minimize the negative impacts of these resources on grid behavior. However, the interconnection of these smart inverters may interfere with their anti-islanding algorithms, which creates detection difficulties. Advanced islanding detection techniques are therefore required to detect and disrupt islanding operations under such an environment with system’s disturbances and interferences. Even though various islanding detection methods have been developed in recent literature to identify islanding operations with high detection accuracy and minimized nondetection zone, these methods mainly focus on a single inverter system, which is incompatible in modern power system with high penetration of grid-connected inverters. In this article, an advanced passive islanding method is proposed for a single-phase distribution power system taking account of the interferences and disturbances brought by these grid-connected inverters. The effectiveness of the proposed passive islanding method is validated through experiments in a laboratory platform. Also, the experimental results have verified that the proposed methods can effectively terminate the islanding operation even with rich inverters’ interferences.

Application of copy number variation squencing for prenatal diagnosis

To assess the value of next-generation sequencing-based copy number variation sequencing (CNV-seq) for the detection of copy number variations (CNVs) in prenatal diagnosis. The results of single nucleotide polymorphism array (SNP-array) for prenatal diagnosis from May 2018 to December 2020 were reviewed. Selected cases of CNVs of clinical significance or low-percentage mosaic aneuploidies were included. Preserved DNA samples of amniotic fluid DNA were detected by CNV-seq. The results of CNV-seq and CMA were analyzed. A total of 16 488 data of SNP-array were re-analyzed, and 343 DNA samples were selected for the CNV-seq assay. All samples were successfully analyzed. Compared with the SNP-array, the proportion of full concordance, partial concordance and missed detection was 91.5% (314/343), 1.2% (4/343) and 7.3% (25/343), respectively. The non-detection zones of CNV-seq were confirmed, which have encompassed the SHOX gene and AZFc region. With a high accuracy and wide genome-wide coverage, CNV-seq is worthy for a wide application in prenatal diagnosis, though the limitation of testing should be taken into consideration, and the appropriate prenatal diagnosis method should be selected for different populations to reduce the occurrence of birth defects.

Performance of a new hybrid approach for detection of islanding for inverter-based DGs

This paper proposes a new hybrid method for islanding detection and minimizes the Non-Detection Zone (NDZ), for an inverter-based grid-connected distributed generation (DG) system. The proposed hybrid method is an integration of the modified active Sandia Frequency Shift (SFS) method and the passive reactive power variation technique. The modified active SFS method is obtained by adaptive tuning of the gain parameter Ksfs, using the Adaptive Particle Swarm Optimization (APSO) technique. The proposed hybrid method produces a significant reduction of NDZ and is suitable for more accurate detection of islanding condition. The effect of NDZ for the proposed hybrid method has been derived analytically and the system performance has been assessed, under various power mismatch conditions for a DG-grid interface. The overall system performance has been found to be superior under the presence of constant power control strategy. The effect of frequency and voltage variations at the common coupling point during islanding have also been considered. Finally, the performance of the proposed method under the IEEE standard 1547 islanding test condition has been investigated for different load factors and load variations.

Review on islanding detection methods for grid‐connected photovoltaic systems, existing limitations and future insights

The connection of renewable energy sources (RESs) to the distribution network has been rising at a steady pace over the past decades. The great penetration of RESs such as grid-connected photovoltaic system brings new technical challenges to the distribution networks such as unintentional islanding. Conceptually, this situation occurs when a portion of the network that has been isolated from the main grid remains energised by the embedded RESs. This unexpected scenario should be thereby identified effectively to avoid frequency and voltage deviations and their hazardous effects. The aim of this paper is to provide a comprehensive review on the recently developed islanding detection methods for grid-following/grid-connected photovoltaic system, analyse their existing limitations, and suggest possible future research implementations. In this context, an in-depth comparison is provided considering the main features used in islanding detection methods such as non-detection zone, detection time, implementation cost and complexity, and power quality degradation. Finally, the main technical requirements established by the current grid codes are recalled identifying potential multi-functional approaches to expand the current islanding detection capabilities.

Angular symmetrical components-based anti-islanding method for solar photovoltaic-integrated microgrid

ABSTRACT This article examines how an innovative Angular Symmetrical Components of Voltages be applied to islanding detection and voltage unbalance factor estimation at a photovoltaic inverter-based distribution unit. Positive and Negative Sequence Components are converted into a polar form such as Line Aggregate RMS (LARMS) Voltage and Tangent Angle of Unbalance (TAU) which are determined from two line voltage signals. Three voltage relays are replaced with a single relay which compares the LARMS voltage and TAU with threshold limits to identify the condition of balance. ASCOV relay does not generate the trip signal in a non-islanding situation such as linear load switching and nonlinear load switching. The Non-Detection Zone (NDZ) of this ASCOV relay is very low compared to other relays. The proposed anti-islanding method is tested in a SPV powered microgrid using MATLAB/SIMULINK and the performance was studied under islanding and non-islanding events. Consequently, the simulation outcome indicates that the proposed technique effectively identifies the islanding condition with less computation time as 1 s and the performance of the proposed relay is compared with existing relays. The voltage unbalance factor determined by the proposed method is very close to the actual value in all types of unbalance conditions.

A Hybrid Islanding Detection Method for One Cycle Controlled PV Inverter System

Features like phase locked loop free implementation, simple-structure, grid voltage sensor-less operation, and its feedback response make one cycle control (OCC) inverters suitable and cost-effective for small single-phase photovoltaic distributed generator units. The feedback nature of OCC makes passive islanding detection more effective in comparison with other control methods. A novel hybrid islanding detection method (IDM), which is suitable for OCC inverters, is proposed in this article. The hybridization is done in two levels and is aimed at reducing the nondetection zone of the existing feedback-based passive IDM. The passive first level defense, which is always present, is due to the feedback nature of OCC. When islanding is suspected, the active second level defense is initiated by injecting a short real power disturbance. This accelerates the feedback action and helps in timely detection of islanding. Unlike other active methods, the disturbance is injected only when an islanding condition is suspected. The induced disturbance in real power is momentary, and the inverter goes back to the normal operation under nonislanded conditions. Simulation and experimental studies are performed to verify the effectiveness of the proposed IDM.

Analysis of Passive Islanding Detection Techniques for Double Line Fault in Three Phase Microgrid System

Microgrids are able to dispatch power to distribution systems with the advancement of power electronics-based inverters. As per IEEE-1547-2018 standards, Microgrid has to maintain voltage of 0.88 < V < 1.1 p.u (per unit) and frequency of 58.8< f_0 < 61.2 Hz and detect un-intentional faults in less than 2 seconds to bring Microgrid into islanding mode seamlessly. Unless these faults are detected and Microgrid is islanded, the system stability cannot be maintained and Microgrid cannot feed the connected loads. To detect these unsymmetrical faults, to bring the Microgrid to islanding mode and to be stable during non-islanding cases like loads switch on and throw off at Point of Common Coupling (PCC), a passive islanding detection method, Rate Of Change Of Voltage Phase Angle (ROCOVPA) is proposed. The methodology is simple. First, the voltage phase angle of generator bus and the grid is monitored. Then, absolute value is found and finally differentiated to get ROCOVPA and detect islanding. Also, this technique is compared with the widely used method of Rate Of Change Of Frequency (ROCOF) at different percentage active and reactive power mismatches. It also avoids nuisance tripping so that Microgrid's stability is maintained. This method is tested for un-symmetrical double line fault, for islanding cases and switch on or throw off, for non-islanding cases with linear and non-linear loads. In this method, the power quality is also not affected because of no perturbations during testing and the Non-Detection Zone (NDZ) is almost zero. The proposed method is verified by simulating islanding and non-islanding conditions in MATLAB/Simulink and by comparing with ROCOF method and found effective.

A new hybrid islanding detection method for mini hydro-based microgrids

This paper proposes a fast and reliable hybrid islanding detection method (IDM) for mini-hydro-based distributed generations (DGs) with zero non-detection zone (NDZ). The proposed IDM aims to tackle the islanding events caused by a self-excited induction generator (SEIG) when it is driven by a mini-hydro turbine system utilising the transient dynamic response of the governor for the first time. To achieve such a goal, it takes advantage of a two-stage process in which both passive and active techniques are combined. Thus, if the rate of change of frequency (ROCOF)-based threshold of the first stage is exceeded, the power reference of the mini-hydro unit is modified, implying a change in the turbine governor gate position. The mechanical torque applied to the prime mover is accordingly shifted to a new state so that both frequency and its derivative will exceed the established thresholds in the second stage in the islanding mode. Conversely, the effect of imposed disturbance is eminently negligible in the grid-connected mode since the frequency is strictly dictated by the main grid. The proposed IDM has been evaluated through numerous islanding and non-islanding case studies considering both single and multi-DG scenarios in MATLAB/Simulink. The outcomes highlight the outstanding performance of the proposed algorithm with zero NDZ and 473 ms average detection time, indicating the capability of the governor system as a reliable tool to identify islanding operations. The proposed technique does not degrade the power quality (PQ) of the grid, requires a low level of computational complexity and provides a high degree of reliability. Therefore, it is a robust and cost-effective solution for future microgrids with great penetration of mini-hydro units.© 2017 Elsevier Inc. All rights reserved.

Implementation and Critical Analysis of the Active Phase Jump with Positive Feedback Anti-Islanding Algorithm

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.

An impedance identification-based islanding detection method for droop control inverters based on RDFT and positive–negative notch filters

Droop control inverters are widely used because of their plug-and-play characteristics, no need for communication, and adaptability to weak power grids. However, because of the difficulty of islanding detection, after the grid is restored, drooping control inverters may cause security problems. In order to address this issue, this paper proposes an islanding detection method for droop control inverters based on impedance identification. By injecting current disturbance into common coupling points (PCC), the impedance is identified by the current response, and then the islanding can be determined by the impedance change. On the one hand, a signal extraction method based on positive–negative notch filters is proposed to reduce the content and impact on the power quality of the disturbance injection. On the other hand, this paper uses a signal processing method based on recursive discrete Fourier transform (RDFT), which can effectively reduce the computational burden. Moreover, the proposed method can eliminate the non-detection zone of the island detection. The experimental results verify the effectiveness of the proposed method.

A simplified passive islanding detection technique based on susceptible power indice with zero NDZ

Distributed energy resources (DER’s) incorporation in power system brings economical, technical and environmental benefits. Besides these benefits, excess penetration of DER’s elevates technical concerns. Islanding detection is one of main issue and is essential for personnel safety and protection of equipment. This work introduces a passive islanding detection scheme based on phase angle of positive sequence voltage (PAOPSV). The PAOPSV was selected on the basis of rigorous investigation of 13 different indices. Comparative analysis demonstrates that PAOPSV has the best sensitivity and accuracy for islanding detection among all other parameters. An extensive case study considering worst-case scenarios is accomplished in order to check the working efficacy of the suggested scheme that easily discriminates islanding events from non-islanding events such as load switching, different fault types switching, capacitor and motor switching. The suggested scheme is simple with fast execution and easy to implement that is established on IEEE 1547 generic test system in MATLAB/SIMULINK environment. Islanding is detected within 0.10 s even with a zero non-detection zone.

An innovative hybrid method for islanding detection using fuzzy classifier for different circumstances including NDZ

Distributed energy resources (DERs) are an alternative to conventional fossil fuel-based energy resources for a pollution-free operation. But the integration of these DERs to the main grid comes with certain challenges, out of which unintentional islanding detection is of prior importance. A lot of techniques have been used for detecting islanding, among these techniques, passive and active. Passive islanding detection methods have drawbacks in the form of the existence of large non-detection zones whereas active detection methods have devastating effects on power quality. To overcome these drawbacks, a proposed hybrid passive-active systematic methodology based on a smart classifier that decides to use an active method instead of a passive one; is presented. The simulation results confirm that the proposed scheme is accurate, robust, fast, simple to implement for inverter-based DGs, and is able enough to perform effective and rapid detection of islanding in all the circumstances for the chosen system model without degrading power quality. The proposed scheme was simulated using the MATLAB/Simulink platform, and the results reflect its potential with a comparative study.

A non-array customizable tactile sensor based on spraying process

PurposeThe tactile sensor with array structure normally has the defects of existing nondetection zone, complex and nonstretchable structure. It is difficult to seamlessly attach to the surface of the robot. For this reason, this paper proposes a method to prepare nonarray structure tactile sensor directly on the surface of the robot by spraying process.Design/methodology/approachBased on the principle of gradient potential distribution, the potential fields are constructed in two different directions over the conductive film in time-sharing. The potentials at touching position in the two directions are detected to determine the coordinate of the touching point. The designed tactile sensor based on this principle consists of only three layers. Its bottom layer is designed as a weak conductive film made of graphite coating and used to construct the potential field. It can be sprayed either on PET substrate or directly on robot surface.FindingsThe radial basis function neural network is used for remodeling the potential distribution, which can effectively solve the problem of nonlinear potential distribution caused by irregular sensor shape, and uneven conductivity at different points of the spraying coating. The simulation and experimental results show that the principle of the proposed tactile sensor used for touching position detection is feasible to be applied to complex surfaces of the robot.Originality/valueThis paper proposed a nonarray customizable tactile sensor based on the spraying process. The sensor has a simple structure, and only five lead wires are needed to realize the coordinate detection of the touch position.

Zero Non-Detection Zone for Islanding Detection Based on a Novel Hybrid Passive-Active Technique with Fuzzy Inference System

Distributed generation (DG) has reformed the meaning of power generation from large scale to small scale, but unintentional islanding is the main issue when connecting DG and the utility grid. A lot of techniques have been used for detecting islanding, among these techniques, there are passive and active. The main problem of passive techniques is their large non-detection zone (NDZ), while the main drawback of active techniques is their undesirable effect on power quality. In this paper, a proposed hybrid passive–active systematic methodology based on a smart classifier that decides to use an active method instead of a passive one is presented. In the proposed scheme, sensors are used for measuring the reactive power at three terminals: the DG terminal, grid terminal, and load terminal. The novelty in this paper is the accurate detection of islanding within a shorter time either in the normal case or NDZ; also it can differentiate between islanding and grid faults without degrading the power quality of the overall system as the active technique does not have to be used continuously, and so total harmonic distortion does not exceed the standard value (5%) detected by IEEE standards. The proposed scheme was simulated using the MATLAB/Simulink platform, and the results reflect its potential with a comparative study.

Validation of Passive Islanding Detection Methods for Double Line-to-Ground Unsymmetrical Fault in a Three-Phase Microgrid System

Distributed generators (DG),double line-to-ground fault (L-L-G-Fault),non-detection zone (NDZ),point of common coupling (PCC),rate of change of frequency (ROCOF),rate of change of voltage phase angle (ROCOVPA)

Novel Passive Islanding Detection Technique by Monitoring Reverse Power at PCC

Power System of the age has included remarkable contribution of distributed energy resources (DERs). This inclusion has opened new era of research and studies. Islanding detection has become one of the important events in power system that is to be detected precisely. This study introduces a single-parameter-based passive technique for islanding detection which has zero nondetection zone without involvement of any signal processing tool. The proposed technique is tested for various islanding and nonislanding events. The simulation results prove that the suggested technique detects islanding event accurately and it is capable of distinguishing islanding and nonislanding events by an economical and simpler method.

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.