1,720,953 research outputs found
Linear simulation of large scale regional electricity distribution networks and its applications: Towards a controllable electricity network
No full textThe volatility of renewable energy sources pose a significant challenge for Distribution Network Operators (DNOs) as it makes planning and maintaining a reliable electricity grid more complex. An essential tool in dealing with the uncertain behavior of renewable energy resources is the load flow simulation, i.e., the standard electricity network simulation in network design and operation. There is, however, still much untapped potential of applying these kind of simulations. The thesis presents improvements to the theory on linear load flow approximations. The resulting algorithms are then applied to various real world problems: control of a community battery, handling very large simulations, coping with low sensor coverage and evaluating strategic scenario's with high uncertainty. Firstly, theory is presented for the control of a community battery. It is shown how such a battery can be used for grid congestion reduction, backed up by a live experiment. A charge path optimization problem is posed as a linear problem and subsequently solved by an Linear Programming (LP) algorithm. It was found that the voltages and currents can be controlled to a great degree, increasing the grid capacity significantly. Network design formulas are described with which a DNO can quickly estimate the potential (de)stabilizing effect caused by a community battery on the steady-state voltages and currents in the grid. Next, load flow simulations are improved by applying numerical analysis techniques and the accuracy and efficiency of a linear load flow approach is investigated. The resulting fast load flow algorithm is then applied to a very large problem: integrally simulating the low and medium voltage network of Alliander DNO, a grid with over 22 million cable segments with a total combined length of over 88,000 km, built according to international standards. It is shown that this integral simulation can identify voltage problems much more accurately. Next, Bayesian state estimation is considered. A mathematical model is proposed to complement a limited set of real-time measurements with voltage predictions from forecast models. This method relies on Bayesian estimation formulated as a linear least squares estimation problem. The model is then applied to an IEEE benchmark and on a real network test bed. An observability analysis suggests strategies for optimal sensor placement. Next, theory is presented on coping with uncertain long-term scenarios for strategic simulations. A stochastic profile model is proposed based on copulas which can be calibrated by technology adoption data. Using a Monte Carlo approach, the stochastic profiles of all DNO assets are then simulated, identifying parts of the network with heavy loads. Finally, the thesis concludes by demonstrating additional applications of the presented methods, such as fast network capacity checks and reducing losses via network reconfiguration. It concludes by giving suggestions for future research.Cognitive Robotic
Low voltage power grid congestion reduction using a community battery: Design principles, control and experimental validation
No full textBy installing a battery storage system in the power grid, Distribution Network Operators (DNOs) can solve congestion problems caused by decentralized renewable generation. This paper provides the necessary theory to use such a community battery for grid congestion reduction, backed up by experimental results. A simple network model was constructed by linearizing the load flow equations using a constant impedance load model. Using this model, an accurate estimate of voltage and overload problems is fed into a receding horizon charge path optimizer. The charge path optimization problem is posed as a linear problem and subsequently solved by an LP solver. The algorithms have been applied and validated on a real-world community battery installation. It was found that the voltages and currents can be controlled to a great degree, increasing the grid capacity significantly. The proposed control framework can be used to safeguard network constraints and is compatible with other battery control goals, such as energy trading or energy independence. Network design formulas are described with which a DNO can quickly estimate the potential (de) stabilization of a community battery on the steady-state voltages and currents in the grid.Cognitive Robotic
Combined Medium Voltage and Low Voltage simulation to accurately determine the location of voltage problems in large grids
No full textDistribution Network Operators (DNOs) traditionally treat Low Voltage (LV) and Medium Voltage (MV) networks as two separate entities. Both voltage levels have their own set of assumptions and design policies. This paper proposes a fast load flow algorithm suitable to simulate both the LV and MV network in a single simulation. The algorithm is applied to the grid of Alliander DNO. Using this method, congestion problems in both the LV and MV grid can be determined with greater detail. Using a case study it was shown that identical customer load scenarios produce vastly differently results if the MV network is taken into account. While the absolute number of voltage problems was in the same order of magnitude, the location of these problems overlapped only 20\%. The lack of overlap has a severe implication, namely that searching for congestion by only simulating LV networks yields the wrong voltage problems. This conclusion calls for network design using integral MV/LV simulations.Support Cognitive RoboticsCognitive Robotic
Evaluating electricity distribution network reconfiguration to minimize power loss on existing networks
No full textThis paper applies the distribution network reconfiguration problem to existing networks. The medium voltage distribution network of the Dutch DSO Alliander is operated using a radial topology. By optimizing this topology it is possible to reduce the energy losses caused by the cable impedances. Various solutions algorithms have been compared for this distribution network reconfiguration problem, while taking into account network capacity and voltage levels. A Genetic algorithm combined with a Greedy demeshing starting condition yields the best results. Applying the algorithm on real life distribution networks shows with 226 buses and 406 buses yield a reduction in power losses of 15% and 27% respectively.Support Delft Center for Systems and Contro
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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