1,720,995 research outputs found
Modeling, control, and stability analysis of an islanded microgrid
No full textEconomic, technical, and environmental incentives are deriving the energy sector towards a new era of smart distribution networks where coordinated clusters of Distributed Energy Resources (DERs) and local loads form a microgrid, which has a significant potential to serve as the building block of the next generation power distribution networks. This thesis focuses on modeling, control, and stability analysis of a microgrid which consists of multiple electronically interfaced DER units. An important feature of a microgrid is its capability to disconnect from the host power grid and operate in the islanded mode. In the islanded mode of operation, undesirable dynamic interactions could occur between loads and electronically interfaced DER units due to lack of rotational inertia; in the absence of appropriate controls, these dynamic interactions may result in poor transient performance or even instability of an islanded microgrid. To address these challenges, this thesis proposes a control strategy to enhance transient performance and stability of a droop-controlled microgrid and to enable it to ride through transients caused by such system disturbances as load change, DER unit switching, and change of network topology. The dependency of dynamics on the droop gains, steady-state power flow, and network/load is studied in a droop-controlled DER unit. These dependencies result in poor transient performance or even instability of the network in the event of a disturbance in the system. To eliminate these dependencies, a gain-scheduled decoupling control strategy is proposed which alters the dynamic coupling between the DER unit and the rest of microgrid for better stability and transient performance. The impact of the proposed control on the DER and network dynamics is studied by calculating the eigenvalues of a test microgrid assuming the proposed control. The proposed control is shown to stabilize the microgrid for a range of operating condition. Further, this thesis develops a stability analysis method to study dynamic interaction of loads with a DER units and its impact on small-signal stability of an islanded microgrid. The purpose of this study is to design controls that are insensitive to load dynamics. The proposed stability analysis method: i) is a frequency-domain approach which models the source-load dynamic interaction via a closed-loop system of impedances and admittances; ii) provides a less conservative stability condition compared to existing methods, in the sense of having less restriction on the control system; and iii) establishes a robust stability margin in terms of perturbations in load parameters. The proposed method is used to examine small-signal stability of a test islanded microgrid. The findings of the frequency domain analysis are illustrated through time-domain simulations around the operating point on the system under study. Next, based on the proposed stability analysis method, a controller design methodology has been proposed for a DER unit to design a controller which enhances robust stability against load dynamics.Extensive case studies, based on time-domain simulations in the PSCAD/EMTDC software environment, are conducted to evaluate performance of the proposed controllers when the microgrid is subject to various disturbances such as load change, change in network topology, and DER unit outage. Real-time case studies, using OPAL-RT, are also conducted to demonstrate feasibility of hardware implementation and validate controller performance against real-world implementation issues.Des incitatifs économiques, environnementaux, et techniques poussent le secteur énergétique vers une nouvelle ère des "réseaux de distribution intelligents" où les grappes coordonnées de ressources énergétiques distribuées (DER) ainsi que les charges locales forment un microréseau, qui a un potentiel important pour servir comme composante de base des réseaux de distribution d'énergie de la prochaine génération. Cette thèse porte sur la modélisation, le contrôle, et l'analyse de la stabilité d'un microréseau qui se compose de plusieurs unités DER interfacées électroniquement. Une caractéristique importante d'un microréseau est sa capacité à se déconnecter du réseau électrique hôte et fonctionner en mode de l'îlotage. En mode de l'îlotage, des interactions dynamiques indésirables pourraient survenir entre les charges et les unités de DER à cause du manque d'inertie de rotation; en l'absence de contrôles appropriés, ces interactions dynamiques peuvent entraîner de mauvaises performances transitoires ou même l'instabilité du microréseau.Pour relever ces défis, cette thèse propose une stratégie de contrôle pour améliorer les performances transitoires et la stabilité d'un microréseau controlé par statisme. La stratégie proposée permet au microréseau de passer à travers des transitoires causés par des perturbations du système comme un changement de charge, la commutation de DER, et un changement de topologie du réseau. Nous étudions la dépendance de la dynamique sur les gains de statisme, le flux d'énergie à l'état stationnaire, et la dynamique du réseau/charge dans une unité de DER contrôlée par statisme. Ces dépendances entraînent de mauvaises performances transitoires ou même l'instabilité du réseau dans le cas d'une perturbation dans le système. Pour éliminer ces dépendances dynamiques, nous proposons une stratégie de contrôle par découplage et séquencement de gain qui modifie le couplage dynamique entre l'unité de DER et le reste du microréseau pour une meilleure stabilité et performance transitoire. Nous étudions l'impact de la commande proposée sur la dynamique du réseau en calculant les valeurs propres d'un microréseau d'essai en supposant la commande proposée. Nous montrons que cette commande stabilise le microréseau pour une gamme de conditions de fonctionnement.De plus, cette thèse développe une méthode d'analyse de la stabilité pour étudier l'interaction dynamique entre des charges et des unités de DER et son impact sur la stabilité de petit signal d'un microréseau en mode d'îlotage. L'objectif de cette étude est de concevoir des contrôles qui sont insensibles à la dynamique des charges. La méthode proposée: est une approche dans le domaine fréquentiel qui modélise l'interaction dynamique via un système d'impédances et admittances en boucle fermée; fournit une condition de stabilité moins conservatrice par rapport aux méthodes existantes, dans le sens d'avoir moins de restrictions sur le système de contrôle; et établit une marge de stabilité robuste en termes de perturbations dans les paramètres de charge. La méthode proposée est utilisée pour examiner la stabilité de petit signal d'un microréseau d'essai en mode d'îlotage. Les résultats de l'analyse dans le domaine fréquentiel sont exposés par des simulations dans le domaine temporel autour du point d'opération du système à l'étude.Nous menons des études de cas approfondies, basées sur les simulations dans le domaine temporel dans l'environnement logiciel PSCAD, pour évaluer les performances des contrôleurs proposés lorsque le microréseau est soumis à diverses perturbations telles que le changement de charge, changement dans la topologie du réseau, et la connexion ou déconnexion de l'unité de DER. Des études de cas en temps réel, en utilisant OPAL-RT, sont également menées pour démontrer la faisabilité de la mise en œuvre matérielle et de valider les performances du contrôleur en pratique
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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