A survey of islanding detection methods for microgrids and assessment of non-detection zones in comparison with grid codes

Detection of unintentional islanding is critical in microgrids in order to guarantee personal safety and avoid equipment damage. Most islanding detection techniques are based on monitoring and detecting abnormalities in magnitudes such as frequency, voltage, current and power. However, in normal operation, the utility grid has fluctuations in voltage and frequency, and grid codes establish that local generators must remain connected if deviations from the nominal values do not exceed the defined thresholds and ramps. This means that islanding detection methods could not detect islanding if there are fluctuations that do not exceed the grid code requirements, known as the non-detection zone (NDZ). A survey on the benefits of islanding detection techniques is provided, showing the advantages and disadvantages of each one. NDZs size of the most common passive islanding detection methods are calculated and obtained by simulation and compared with the limits obtained by ENTSO-E and islanding standards in the function of grid codes requirements in order to compare the effectiveness of different techniques and the suitability of each one

Performance Evaluation of Active Islanding-Detection Algorithms in Distributed-Generation Photovoltaic Systems: Two Inverters Case

Grid-connected photovoltaic (PV) inverters employ an islanding-detection functionality in order to determine the status of the electrical grid. In fact, the inverter must be stopped once the islanding operating mode is detected according to standards and grid-code limits. Diverse islanding-detection algorithms have been proposed in literature to cope with this safety requirement. Among them, active methods based on the deliberate perturbation of the inverter behavior can minimize the so-called nondetection zone, which is a range of conditions in which the inverter does not recognize that it is operating in an undesired island. In most cases, the performances of these methods have been analyzed considering a highly dispersed generation scheme, where only one distributed-generation power system is connected to the local electrical power system (EPS). However, in some studies, it has been highlighted that if two or more PV inverters are connected to the same local EPS, their anti-islanding algorithms do not behave ideally and can fail in detecting the islanding condition. However, there is no systematic study that has investigated the overall capability of different anti-islanding methods employed on several inverters connected to the same EPS to detect islanding condition. This paper is a first attempt to carry out a systematic study of the performances of the most common active detection methods in a case of two inverters connected to the same EPS. In order to evaluate the global capability of the two systems to detect islanding condition, a new performance index is introduced and applied also to the case when the two inverters employ different anti-islanding algorithms

Assessment of non-detection zone of different active anti-islanding methods for single and multi-inverters grid connected photovoltaic power systems

This paper attempts to carry out a systematic study of the performance of the most common active detection methods, Active frequency drift (AFD) ,Sandia frequency shift (SFS) method and slip mode shift frequency (SMS) method. These methods are used to explain their global capability in developing photovoltaic system that are improved by including a boost converter MPPT technique and PID controller. Their effectiveness and limits in detection of islanding phenomenon are studied in details using Matlab/Simulink environment. In addition to that, the “no detection zone” of each method is basically investigated. The implementation of these methods shows that they can work perfectly under normal/islanded modes. Moreover, the results show that islanding mode can conditionally be detected and prevented successfully using the three common active methods when adequate parameters are adapted for the local load and for the grid. Moreover, the results show that there is an interaction between the used methods at the level of detection/prevention obtained in terms of time and non-detection zone.Cet article tente de réaliser une étude systématique de la performance des méthodes de détection active les plus courantes, la méthode Active frequency drift (AFD) et Sandia frequency shift (SFS) et la méthode slip mode shift frequency (SMS). Ces méthodes sont utilisées pour expliquer leur capacité globale à développer des systèmes photovoltaïques améliorés en incluant une technique de convertisseur élévateur MPPT et un contrôleur PID. Leur efficacité et leurs limites dans la détection du phénomène d’îlotage sont étudiées en détail dans l’environnement Matlab / Simulink. En plus de cela, la «zone de non détection» de chaque méthode est fondamentalement étudiée. La mise en œuvre de ces méthodes montre qu'elles peuvent parfaitement fonctionner en mode normal / en îlot. De plus, les résultats montrent que le mode d'îlotage peut être conditionnellement détecté et empêché avec succès en utilisant les trois méthodes actives courantes lorsque des paramètres adéquats sont adaptés à la charge locale et au réseau. De plus, les résultats montrent qu'il existe une interaction entre les méthodes utilisées au niveau de la détection / prévention obtenu en termes de temps et de zone de non-détectio

An active Anti-islanding method based on phase-PLL perturbation

This paper presents a new active anti-islanding detection method for distributed power generation systems. This method is based on introducing a disturbance at the inverter output and observing the behavior of the voltage at the point of common coupling (PCC), which depends on the impedance connected to the PCC in an islanding situation. The islanding detection is based on the Goertzel algorithm.Velasco De La Fuente, D.; Trujillo Rodríguez, CL.; Garcerá Sanfeliú, G.; Figueres Amorós, E. (2011). An active Anti-islanding method based on phase-PLL perturbation. IEEE Transactions on Power Electronics. 26(4):1056-1066. doi:10.2089643S1056106626

Anti-Islanding Detector based on a Robust PLL

As required by international standards, the distributed energy generators, connected to the grid by an inverter, have to detect an islanding condition within a suitable time interval. In this paper, a phase-locked loop (PLL), based on a third-order prediction-correction filter, is proposed to implement an islanding detector with reduced detection time. Such a feature is obtained using the estimation of the grid angular frequency and acceleration provided by the PLL with a negligible time delay. The proposed approach is implemented on an industrial grade DSP and validated through the experimental comparison among different detection methods, such as rate of change of frequency (ROCOF) and Slip Mode frequency Shift (SMS). The combined use of ROCOF and SMS is also illustrated and discussed