Islanding Detection Scheme Research Articles

An active islanding detection scheme for inverter-based DG with frequency dependent ZIP–Exponential static load model

Abstract In this paper an analytical design method is proposed for constant voltage controlled inverter based DG with frequency dependent ZIP–Exponential static load model to obtain proper inverter output control and successful islanding detection. The proposed technique is aimed to eliminate the dependency of DG operation point on anti-islanding performance which is unavoidable in case of traditional control strategy. The generalized formulae are derived for calculating the upper and lower limits of the voltage gain, and it is recommended to select the voltage gain within the designed range for effective islanding detection. The proposed approach is tested in MATLAB/Simulink environment and result shows that the proposed scheme is found to be highly effective in islanding detection considering complex network configurations with single and multiple DG systems. The proposed control scheme is able to detect islanding within 10 ms (half cycle) from the event inception, showing the fastness of the developed technique. It is also observed that the percentage of voltage and current THD of the proposed scheme is within permissible limits, indicate that the power quality of the inverter is not degraded by the proposed control strategy, and thus overcomes the drawback of existing active anti-islanding techniques.

Current-based Islanding Detection Scheme in Presence of Distributed Generations

In this article, a new islanding detection technique based on dq0 transformation is presented for the power system network containing distributed generators. The proposed technique is based on the peak value of current (Is) that is obtained by dq0 transformation of current signals. Simulations of various islanding conditions have been carried out using PSCAD/EMTDC software package (Manitoba HVDC Research Centre, Winnipeg, MB, Canada) at different values of active and reactive power mismatches. Moreover, various non-islanding events have also been taken into account. The simulation results clearly point out that the proposed scheme completely eliminates the non-detection zone and rapidly detects islanding. At the same time, it also avoids nuisance tripping during various non-islanding events as well as for the system with multiple distributed generators. Comparative evaluation of the proposed scheme is also carried out with the existing scheme, and it has been observed that the proposed scheme remains stable during a non-islanding situation in which the existing scheme fails.

Islanding Detection Based on High Frequency Injection for Multi Inverter Microgrid

Islanding detection is one of the indispensable protection detections for grid-connected inverters. The detection of islanding is the key factor that should be considered in the analysis of grid-connection security. The non-detection zone is the performance index of anti-islanding plan. According to the phase feature, quantitative analyses of the non-detection zone of several frequency disturbance schemes are conducted under several different coordinate systems by increasing disturbance, namely injecting third harmonic to the modulating wave that produces inverter drive signal and detects the voltage value and the total harmonic distortion of the power grid. The active current all-disturbance islanding detection scheme has been chosen as the initiative scheme of anti-islanding detection to complete the parameter design and simulation. According to the experimental result, this method is feasible to detect the island of microgrid. In this paper, the simulation model of islanding detection of microgrid is established through MATLAB/SIMULINK, and the simulation analysis of islanding phenomenon after the injection of third harmonic wave is conducted. The simulation result verifies the validity and availability of the islanding detection method.

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.

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.

A Comparative Review of Islanding Detection Schemes in Distributed Generation Systems

A Comparative Review of Islanding Detection Schemes in Distributed Generation Systems

Enhanced Multi-Criteria-Based Passive Islanding Detection Scheme

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.

Islanding Detection of Inverter Based DG Unit Using PV System

Distributed generation (DG) units are rapidly increasing and most of them are interconnected with distribution network to supply power into the network as well as local loads Islanding operations of DG usually occur when power supply from the main utility is interrupted due to several reasons but the DG keeps supplying power into the distribution networks. a new method for islanding detection of inverter-based distributed generation (DG). Although active islanding detection techniques have smaller non detection 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 phenomenon of unintentional islanding occurs when a distributed generator (DG) continues to feed power into the grid when power flow from the central utility source has been interrupted. A simple islanding detection scheme has been designed based on this idea. The proposed method has been studied under multiple-DG operation modes and the UL 1741 islanding tests. The simulations results, carried out by MATLAB/Simulink, show that the proposed method has a small Non detection zone. DOI: http://dx.doi.org/10.11591/ijpeds.v4i4.6257

A New Rate of Change of Impedance-based Islanding Detection Scheme in Presence of Distributed Generation

—Integration of distributed generation with utility network demands satisfactory operation of an islanding detection scheme, as it can otherwise lead to such problems such enhancement in non-detection zone, out-of-phase reclosing, personnel safety, and degradation of power quality. This article presents a new islanding detection scheme based on the rate of change of impedance (dz/dt) of each phase. To calculate dz/dt, phasor computation is carried out using a half-cycle modified discrete Fourier transform algorithm. Test data are generated using the PSCAD/EMTDC software package (HVDC Research Center, Inc., Manitoba). Various islanding conditions have been simulated by disconnecting the main circuit breaker with different values of active and reactive power mismatch. At the same time, different non-islanding conditions have also been simulated through switching (ON/OFF) of load, energization/de-energization of medium transmission lines, short-circuit on an adjacent feeder, and switching (ON/OFF) of the transformer and capacitor bank in the network. The simulation results indicate that the proposed scheme is capable of providing effective discrimination between islanding and non-islanding conditions. The proposed scheme is able to detect islanding conditions within a half-cycle from event inception.

Rapid islanding detection using multi-level inverter for grid-interactive PV system

A novel reference signal generator is combined with a multi-level inverter to form a rapid islanding detection scheme for grid-interactive PV system. The reference signal generator can easily be synchronized with the utility grid signal and produced a fixed magnitude and very low total harmonic distortion (THD) sinusoidal signal which is in phase with the utility grid signal. Unlike conventional phase-locked loop (PLL) circuitry, the reference signal generator can also provide a fixed magnitude sinusoidal signal even if the utility grid is disconnected and automatically re-synchronous with the grid rapidly. Consequently, seamless transfer between grid-connected and stand-alone modes could easily be achieved if anti-islanding protection is not required. If a saturation element is applied to the raw reference signal followed by the synthesis of the truncated signal using a multi-level inverter, the distinct flat-top feature of the synthesized signal can quickly and easily be identified if the network is in islanding mode at the point of common coupling. Experimental results are included to demonstrate the effectiveness of the proposed detection scheme.

New active islanding detection scheme for constant power and constant current controlled inverter‐based distributed generation

This study presents an active islanding detection scheme based on voltage positive feedback control strategy in synchronous d–q frame with a variable voltage gain. The proposed method employs the injection of a variable voltage gain at the DG end in order to monitor the responses of the proposed islanding detection technique. In this study, a complex frequency-dependent ZIP-exponential load model is included to assess the impact of load's active power frequency dependence on the performance of the proposed islanding detection scheme. The upper and lower limits of the voltage gain are designed for constant power and constant current controlled inverter with frequency-dependent ZIP-exponential load. The complete scheme is developed and tested in MATLAB/simulink environment and the results obtained after extensive testing indicate that the proposed scheme can be reliably detect islanding events in distributed generation.

A Fast Gauss-Newton Algorithm for Islanding Detection in Distributed Generation

The paper presents a new Fast Gauss-Newton algorithm (FGNWA) for the detection of islanding condition in distributed generation systems (DGs) when they are disconnected from the main supply system or there are small load unbalances in the distribution network. During islanding conditions power system parameters like frequency, voltage magnitude, phase change, total harmonic distortion, and various sequence voltage, current, and power components do change and hence by monitoring these changes accurately, an islanding condition can be detected. A forgetting factor weighted error cost function is minimized by the well known Gauss-Newton (GN) algorithm and the resulting Hessian matrix is approximated by ignoring the off-diagonal terms to yield the new FGNW algorithm to estimate, in a recursive and decoupled manner, all the above voltage and current signal parameters accurately for realistic power systems even in the presence of significant noise. A number of test cases considering both islanding and nonislanding, for realistic, hybrid distribution networks has demonstrated the reliability and accuracy of the islanding detection scheme, when a fuzzy expert system (FES) is used in conjunction with the proposed FGNW algorithm.

Development of EN50438 compliant wavelet-based islanding detection technique for three-phase static distributed generation systems

The increased penetration of photovoltaic (PV) distributed generation (DG) often connected to grid through dc-ac interface has made islanding detection an important and challenging issue for power engineers. Several methods based on passive and active detection schemes have been proposed in the literature. Although passive schemes have a large non-detection zone (NDZ), concern has been raised about active methods because of their degrading effect on power quality. Therefore each grid-connected PV systems needs to be EN50438 compliant to ensure proper interface and power quality standard. This study proposes a db4 wavelet-based passive islanding detection scheme with almost zero NDZ for dc-ac inverter interfaced grid-connected PV DGs. The key idea is to utilise spectral changes in the higher frequency components of voltage at the point of common coupling, which occur after an islanding condition. The effectiveness of the proposed method is tested in simulation of a PV DG system and validated experimentally with an actual 7.5-kW grid-connected inverter system using the dSpace DS1104 DSP. The designed detection algorithm has been computationally less burden on the DSP.

Time-frequency transform-based islanding detection in distributed generation

This study presents a new technique for islanding detection in distributed generation (DG) using time-frequency transform such as S-transform. S-transform is an invertible time-frequency spectral localisation technique that provides the time-frequency contours of the voltage and current signals retrieved at the target DG location. The energy index (ratio of the spectral energy content of the voltage to current signals) is computed to track the islanding situation from non-islanding conditions such as sudden load change, tripping of other DG, etc. Further, to aid the islanding detection scheme, a cumulative sum detector is also computed based on the spectral energy content of the negative sequence components of the current and voltage signals. The results, based on extensive study, indicate that the proposed technique can reliably detect islanding in DGs connected to power distribution network.

A Novel Method of Impedance Measurement Used in Islanding Detection Based on Controllable Short-Circuit Technology

It is very important for a distributed generating system to have an islanding detection part. Focused on the problem of islanding, this paper proposes a new and effective islanding detection scheme: a thyristor is placed between any two phases just by the port of the distributed generator (DG). An artificial short time phase to-phase short circuit is formed by triggering the thyristor periodically when the voltage between this thyristor is almost equal to zero, so the short-circuit current and voltage pulse can be extracted out. Because that short-circuit current and voltage pulse contain plentiful frequency components, the frequency response of system can be acquired according to the theory of harmonic impedance, so that the impedance measured from DG port can be obtained. Whether the DG is islanding can be determined quickly by monitoring the changes of impedance. This method is proved to be correct and effective by theoretical analysis and simulation.

A New Method for Islanding Detection of Inverter-Based Distributed Generation Using DC-Link Voltage Control

This paper presents a new method for islanding detection of inverter-based distributed generation (DG). The main idea of this paper is to change the dc-link voltage considering the PCC voltage changes during islanding condition. A simple islanding detection scheme has been designed based on this idea. The proposed method has been studied under multiple-DG operation modes and the UL 1741 islanding tests. The simulations results, carried out by MATLAB/Simulink, show that the proposed method has a small nondetection zone. Also, this method is capable of detecting islanding accurately within the minimum standard time.

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.