New Islanding Detection Method with Better Performance in Presence of Non-resistive Load

Islanding detection is a mandatory component in grid-connected photovoltaic （PV） inverters. It is also a key issue in the photovoltaic agriculture. In this work, an overview on the islanding effect in grid-connected PV power systems was provided. Various islanding detection methods were introduced and their strength and weakness were dicussed. An improved islanding detection method was proposed based on active frequency drift （AFD）. The new method tolerated capacitive and inductive loads, because its perturbation signal was not offset by the non-resistive load. The new method through simulation in MATLAB/Simulink was evaluated and the advantages of the new method were demonstrated.

Improved Active Islanding Detection Technique for Multi-Inverter Power System

Due to the increased penetration of multi-inverter distributed generation(DG)systems,different DG technologies,inverter control methods,and other inverter functions are challenging the capabilities of islanding detection.In addition,multi-inverter networks connecting the distribution system point of common coupling(PCC)create islanding at paralleling inverters,which adds the vulnerability of islanding detection.Furthermore,available islanding detection must overcome more challenges from non-detection zones(NDZs)under reduced power mismatches.Therefore,in this study,a new method called parameter self-adapting active islanding detection was utilized to minimize the dilution effect and reduce NDZs in multi-inverter power systems.The method utilizes an active frequency drift(AFD)method and applies a positive feedback gain of adoption parameters,which significantly minimizes NDZs at parallel inverters.The simulation and experimental outcomes indicate that the proposed method can effectively weaken the dilution effect in multi-inverter networks connecting the distribution system PCC.

Islanding detection based on asymmetric tripping of feeder circuit breaker in ungrounded power distribution system

An islanding detection method in ungrounded power distribution system based on single-phase operating mechanisms of the circuit breaker(CB)is proposed in this paper.When CB opens three phase circuits to form an island,one phase circuit is opened firstly and the other two phase circuits are opened secondly after certain duration.During the period when only one phase circuit is opened,negative sequence voltage with certain duration is obtained at DG side because of the asymmetric operation of the system.After all three phase circuits are opened,the voltage variation direction of the two phases that are secondly disconnected from the grid follows the voltage variation direction of the firstly disconnected phase.Based on the above voltage characteristics,an islanding detection scheme is proposed to identify genuine islanding from system disturbances.The performance of the proposed scheme is tested in PSCAD/EMTDC using a 10 kV distribution network with synchronous DG interconnection.Simulation results demonstrate the proposed method is effective and reliable to detect islanding formation.

Hybrid intelligent water drop bundled wavelet neural network to solve the islanding detection by inverter-based DG

In this paper, a passive neuro-wavelet based islanding detection technique for grid-connected inverter- based distributed generation was developed. The weight parameters of the neural network were optimized by intelligent water drop （IWD） to improve the capability of the proposed technique in the proposed problem. The proposed method utilizes and combines wavelet analysis and artificial neural network （ANN） to detect islanding. Connecting distributed generator to the distribution net- work has many benefits such as increasing the capacity of the grid and enhancing the power quality. However, it gives rise to many problems. This is mainly due to the fact that distribution networks are designed without any generation units at that level. Hence, integrating distributed generators into the existing distribution network is not problem-free. Unintentional islanding is one of the encountered problems. Discrete wavelet transform （DWT） is capable of decomposing the signals into different frequency bands. It can be utilized in extracting discrimi- native features from the acquired voltage signals. In passive schemes with a large non-detection zone （NDZ）, concern has been raised on active method due to its degrading power quality effect. The main emphasis of the proposed scheme is to reduce the NDZ to as close as possible and to keep the output power quality unchanged. The simulation results from Matlab/Simulink shows that the proposed method has a small non-detection zone, and is capable of detecting islanding accurately within the minimum standard time.

Intelligent Islanding Detection of Multi-distributed Generation Using Artificial Neural Network Based on Intrinsic Mode Function Feature

The integration of distributed energy resources(DERs) into distribution networks is becoming increasingly important, as it supports the continued adoption of renewable power generation, combined heat and power plants, and storage systems. Nevertheless, inadvertent islanding operation is one of the major protection issues in distribution networks connected to DERs. This study proposes an intelligent islanding detection method(IIDM) using an intrinsic mode function(IMF)feature-based grey wolf optimized artificial neural network(GWO-ANN). In the proposed IIDM, the modal voltage signal is pre-processed by variational mode decomposition followed by Hilbert transform on each IMF to derive highly involved features. Then, the energy and standard deviation of IMFs are employed to train/test the GWO-ANN model for identifying the islanding operations from other non-islanding events. To evaluate the performance of the proposed IIDM, various islanding and non-islanding conditions such as faults, voltage sag, linear and nonlinear load and switching, are considered as the training and testing datasets. Moreover, the proposed IIDM is evaluated under noise conditions for the measured voltage signal. The simulation results demonstrate that the proposed IIDM is capable of differentiating between islanding and non-islanding events without any sensitivity under noise conditions in the test signal.

Shifting of research trends in islanding detection method-a comprehensive survey

The augmentation in electricity demand,power system privatization as well as efficacy of renewable resources has paved the way for power system companies and researchers to exploit the field of grid connected distributed generation(DG)and its issues,islanding being a dominant one.Several research works have been conducted to mitigate the issues of islanding detection(ID).In context of this,the paper gives a comprehensive review of islanding issues,standard test systems,criteria and shifting of research trends in islanding detection methods(IDMs).The significant contributions pertain to categorization of IDMs,evaluation of non-detection zone(NDZ)for each test system,disquisition on evolution and advancement of IDMs and its comparisons based on criteria such as NDZ,run on time,nuisance tripping percentage,applicability in multi DG system and implementation cost to draw out the strength and shortcomings of individual methods that will come to aid to the companies or researchers for establishing the applicability and appropriateness of such method for their concerned domain.

Power Quality Assessment of Voltage Positive Feedback Based Islanding Detection Algorithm

Islanding refers to a condition where distributed generators(DGs)inject power solely to the local load after electrical separation from power grid.Several islanding detection methods(IDMs)categorized into remote,active,and passive groups have been reported to detect this undesirable state.In active techniques,a disturbance is injected into the DG’s controller to drift a local yardstick out of the permissible range.Although this disturbance leads to more effective detections even in well-balanced island,it raises the total harmonic distortion(THD)of the output current under the normal operation conditions.This paper analyzes the power quality aspect of the modified sliding mode controller as a new active IDM for grid-connected photovoltaic system(GCPVS)with a string inverter.Its performance is compared with the voltage positive feedback(VPF)method,a well-known active IDM.This evaluation is carried out for a 1 k Wp GCPVS in MATLAB/Simulink platform by measuring the output current harmonics and THD as well as the efficiency under various penetration and disturbance levels.The output results demonstrate that since the proposed disturbance changes the amplitude of the output current,it does not generate harmonics/subharmonics.Thereby,it has a negligible adverse effect on power quality.It is finally concluded that the performance of the sliding mode-based IDM is reliable from the standpoints of islanding detection and power quality.

A new technique for islanding operation of distribution network connected with mini hydro

An islanding operation of a distribution network is a topic of interest due to the significant penetration of distributed generation(DG) in a power system network. However, controlling the frequency of an islanded distribution system remains an unresolved issue, especially when the load exceeds the generation. This paper presents a new technique for a successful islanding operation of a distribution network connected with multiple mini hydro based DGs. The proposed technique is based on three main parts. The first part uses an islanding detection technique to detect the islanding event correctly. The second part consists of a power imbalance estimation module(PIEM), which determines the power imbalance between the generation and load demand. The third part consists of a load shedding controller, which receives the power imbalance value and performs load shedding according to load priority. The proposed technique is validated on an 11 k V existing Malaysia distribution network. The simulation results show that the proposed technique is effective in performing a successful islanding operation by shedding a significant number of loads.

Grid Voltage Sensor-less Protection Scheme for One Cycle-Controlled Single-phase Photovoltaic Inverter Systems

One-cycle-controlled(OCC)inverters are suitable for small single-phase photovoltaic distributed-generator systems because of their simplicity,phase-locked-loop free structure,grid voltage sensor-less operation,and cost-effectiveness.Grid voltage sensor-less control helps reduce cost and increases reliability in operation.However various sensors are used for implementation of a protection mechanism.In this paper,a grid voltage sensorless protection scheme for OCC based single-phase inverter systems is proposed.The estimated value of voltage at point of common coupling(VPCC)is used for protecting the system during over/under voltage conditions of the grid,implementing of voltage ride through conditions,and for disconnecting the grid during islanded conditions.The VPCC is estimated from the measured inverter current,switching pulses,and the measured dc-link voltage using a second-order filter.Simulation and experimental studies are performed to verify the efficacy of the proposed voltage sensor-less protection mechanism triggered using estimated VPCC.