1,720,961 research outputs found
Modulation Techniques for Three-Phase Three-Level NPC Inverters: a Review and a Novel Solution for Switching Losses Reduction and Optimal Neutral-Point Balancing in Photovoltaic Applications
No full textA number of modulation strategies have been proposed in literature in the particular case of three-phase three-level NPC inverter, each one focusing on the optimization of specific aspects and performance of the converter. Nevertheless a comprehensive analysis of state-of-art techniques and their specific features suitable for a photovoltaic (PV) applications is still missing, such a study being highly desirable.
Both carrier-based and space vector modulation techniques are analyzed in this paper, highlighting specific features and limitations, especially related to PV applications. Basic issues are considered and compared among modulation strategies, namely: switching losses, low-frequency oscillations of the neutral-point (NP) voltage, total harmonic distortion (THD) and weighted total harmonic distortion (WTHD) of the phase currents and line voltages, dynamic response of the neutral-point voltage control loop under imbalance conditions and modulation algorithm complexity. A hybrid modulation strategy assisted by an optimal neutral-point voltage controller is then proposed aiming at both the reduction of the switching losses with a limited deterioration of the output voltage/current quality and fast dynamics control of the neutral point voltage. Those features allow the development of reduced dc bus capacitance PV inverters with optimized efficiency and quality of the output waveforms. Simulation and experimental results based on a TMS320F28069 DSP controller and a PV inverter are presented to confirm the effectiveness of the proposal
Applicazione di algoritmi di State Estimation per il controllo di reti attive di distribuzione
No full textLa crescente penetrazione della Generazione Distribuita (GD) nel sistema elettrico di distribuzione renderà necessaria l’adozione di tecniche di controllo attivo per la regolazione del funzionamento della rete. Ciò significa poter agire dinamicamente su una o più risorse di regolazione al fine di mantenere entro i limiti prefissati le grandezze di rete, fra cui tensione ai nodi e flussi di potenza, conferendo la massima capacità di connessione di impianti GD.
Tali modalità di gestione della rete richiedono la conoscenza, in tempo reale, dello stato di funzionamento della rete stessa.
Nel presente lavoro viene formulato un algoritmo di State Estimation avente il compito di fornire una stima dello stato della rete partendo dall’acquisizione di poche misure on-line e da una stima dei consumi/generazioni di carichi e generatori.
Saranno presentati alcuni risultati significativi ottenuti dalle simulazioni condotte su un modello realistico di rete MT, in particolare l’influenza sull’incertezza con cui è possibile pervenire alla stima dello stato derivante dal numero e posizione delle misure disponibili on-line
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Renewables contributing to Primary Control Reserve: The role of Battery Energy Storage Systems
No full textExtending the Primary Control Reserve to all the renewable generating plants could be an interesting solution to preserve the electrical power system stability. With this measure, the grid enhances its frequency regulation effectiveness and is consequently able to maintain stable operating conditions in case of sudden variations of either load or generation. In this scenario, instead of intentionally throttling the renewable plant output for providing upward reserve, the use of Battery Energy Storage Systems is introduced. This solution allows the renewable plant to maximize the primary source exploitation, reducing the costs for supplying the ancillary service. Taking into account the operative constraints of storage devices, the paper discusses a procedure to optimally design the storage system through a technical-economic analysis based on the investment profitability optimization. Some of the most diffused renewable generators are considered, such as wind plants, photovoltaic generators and hydroelectric run-of-river units. Results confirm how partially or entirely providing the primary reserve by means of storage systems (e.g., making use of Lithium-ion batteries) could be very interesting, especially in the case of renewable plants having access to incentives that increase the equivalent selling price of generated energy
Variations on the Author
Full text link“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
Full text linkWe 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
Full text linkWe 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
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