International White Book on DER Protection : Review and Testing Procedures

This white book provides an insight into the issues surrounding the impact of increasing levels of DER on the generator and network protection and the resulting necessary improvements in protection testing practices. Particular focus is placed on ever increasing inverter-interfaced DER installations and the challenges of utility network integration. This white book should also serve as a starting point for specifying DER protection testing requirements and procedures. A comprehensive review of international DER protection practices, standards and recommendations is presented. This is accompanied by the identifi cation of the main performance challenges related to these protection schemes under varied network operational conditions and the nature of DER generator and interface technologies. Emphasis is placed on the importance of dynamic testing that can only be delivered through laboratory-based platforms such as real-time simulators, integrated substation automation infrastructure and fl exible, inverter-equipped testing microgrids. To this end, the combination of fl exible network operation and new DER technologies underlines the importance of utilising the laboratory testing facilities available within the DERlab Network of Excellence. This not only informs the shaping of new protection testing and network integration practices by end users but also enables the process of de-risking new DER protection technologies. In order to support the issues discussed in the white paper, a comparative case study between UK and German DER protection and scheme testing practices is presented. This also highlights the level of complexity associated with standardisation and approval mechanisms adopted by different countries

The effect of inrush transients on pv inverter's grid impedance measurement based on inter-harmonic injection

This paper addresses a cause for false tripping of photovoltaic inverters with antiislanding protection based on impedance measurement with inter-harmonic injection. Earlier discussions about tripping problems happening when several devices are doing the measurement at the same time are supplemented with a problem caused by inrush transients of nearby devices. A series of experiments was conducted in the Power Quality laboratory of the TU/e, on a PV inverter which complies with the DIN VDE 0126 standard. Impedance measurement was done in parallel with the inverter and measurement results are presented. A criterion for false tripping caused by transients is explored. Also, influences of network impedance and grid harmonic pollution on false tripping were analyzed. In the end, some signal processing techniques are proposed to avoid this problem

Islanding issues associated with photovoltaic inverters

One of the main barriers for the proliferation of photovoltaic (PV) systems in power distribution networks is the concern over possible islanding, i.e., when a disconnected part of the power network remains energized by the connected PV systems for a significant time interval. Islanding is undesirable for a number of reasons including safety hazards to utility personnel; and potential damage to equipment. Numerous anti-islanding techniques have been proposed and implemented in present-day grid-tie inverters. This thesis reviews some of the pros and cons of different anti-islanding techniques, and offers a solution to the Multiple Inverter Islanding Issue and also presents some experimental results conducted on two local grid-tie inverters

Reliability analysis of single-phase photovoltaic inverters with reactive power support

Reactive power support is expected to be an emerging ancillary requirement for single-phase photovoltaic (PV) inverters. This work assesses related reliability issues and focuses on the second stage or inversion process in PV inverters. Three PV inverter topologies are analyzed and their reliability is determined on a component-by-component level. Limiting operating points are considered for each of these topologies. The capacitor in the dc link, the MOSFETs in the inverting bridge, and the output filter are the components affected. Studies show that varying power-factor operation with a constant real power output increases the energy storage requirement as well as the capacitance required in the dc link in order to produce the double-frequency power ripple. The overall current rating of the MOSFETs and output filter must also be sized to accommodate the current for the apparent power output. Modeling of the inverter verifies the conditions for each of the components under varying reactive power support commands. It is shown that the production of reactive power can significantly increase the capacitance requirement, but the limiting reliability issue comes from the increased output current rating of the MOSFETs

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

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

A Discussion of Anti-islanding Protection Schemes Incorporated in a Inverter Based DG

The discussion in this paper is about the local anti-islanding protection techniques that are incorporated in a inverter based DG. The most widely used passive and active techniques along with their suitability to reduce the Non-detection zone (NDZ) are explained here. The most recent work using wavelet transform which actually reduces the NDZ to zero is also introduced in the last section of the paper

Analysis of Local Anti-Islanding Detection Methods for Photovoltaic Generators in Distribution Systems

In the current decade, technology innovations and cost reduction of inverter-based Distributed Energy Resources (DERs) have led to higher integration of distributed energy storage and photovoltaic (PV) solar power systems. Increasing growth in PV penetration to the distribution system can raise operational and safety concerns especially in case of an unintended islanding. In general, standards require distributed generators (DGs) to detect islanding from the main grid and cease to energize the local system. Multiple methods have been introduced in the literature to detect these islands reliably and quickly. In order to connect an inverter to distribution system, inverter should pass certain certification tests such as UL 1741 certification test. The anti-islanding test in UL 1741 standard tests only one type of load over a limited range of loading conditions with a single inverter and lumped load and no impedances in between them. The overall goal of this thesis is to determine those parameters to which run-on times (ROTs) are relatively insensitive and thus do not need to be emphasized in certification testing or risk of islanding studies. This thesis presents a generic MATLAB Simulink inverter model and studies sensitivity of anti-islanding tests to parameters such as inverter location, inverter operating point, load location, load type and circuit impedance. Inverters in these studies are equipped with Group 2A and Group 2B anti-islanding methods. The key contributions in this thesis can be summarized as follows: A comprehensive review of anti-islanding techniques in the literature. An anti-islanding detection model was developed in MATLAB software with at least one method from different groups of anti-islanding methods; the model can be used further for industrial applications and research purposes. The result of analyses indicated that the level of phase-phase imbalance, constant-power load, harmonic-current load and irradiance level have a low or negligible impact on anti-islanding and can be omitted from these studies. These findings are expected to lower the cost and improve the speed of these studies, in large distribution systems. Adviser: Sohrab Asgarpoo