1,720,980 research outputs found
Remote islanded distribution networks supplied by BESS integrated PV generation units
No full textIn some countries, electrical distribution lines have to cross areas where the installation cost could be very high and carrying out maintenance could become extremely difficult (e.g. desert areas). As a result, frequent power disconnections and blackout heavily affect the quality of supply of end-users. Oppositely, the renewable energy sources exploitation in supplying portions of the distribution network during system disconnections is very interesting, both for reducing fossil fuel use and as backup power generator. In case the islanded local electrification makes use of discontinuous and unpredictable energy sources such as photovoltaic, a Battery Energy Storage System is required to regulate the system, supplying power balance and voltage stability. In the paper, a stand-alone distribution network, corresponding in size to a typical Libyan oasis-village, has been developed and analysed. A photovoltaic generator locally supplies the islanded network, while an integrated BESS provides the daily energy balance and the system stability. The research examines the effectiveness of the proposed control strategy, developed with the scope of coordinating the role of both the solar generation and the energy storage system in facing active and reactive power requirements of the connected loads. Specific algorithms are introduced to define the optimal electrical operating condition in terms of voltage and frequency. Power system simulations demonstrate the control strategy strengths in terms of stability and time of response. Quality of supply, evaluated in terms of frequency deviations and voltage profiles, remains considerably high also considering different scenarios and introducing quick load variations. Finally, a brief investigation on integrating photovoltaic, storage and traditional generators (making use of fossil fuels) is presented
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
Exploiting inverter-interfaced DG for Voltage unbalance mitigation and ancillary services in distribution systems
No full textGoing 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
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
The voltage control on MV distribution networks with aggregated DG UNITS (VPP)
No full textIn this paper a procedure that allows Distributed Generation plants (DGs) to be operated as a Virtual Power Plant (VPP), maintaining meanwhile the voltage profiles on Medium Voltage (MV) feeders within the permissible interval, is presented. To this aim a coordinated controller is proposed. It acts both on the On Line Tap Changer (OLTC) and on the reactive power production of specific plants so that voltage regulation is performed whatever the working condition (generation units disconnected or partially loaded or working at maximum power). In particular this controller can influence a VPP economic criteria dispatch by bounding, for example, the maximum active power generated by each unit in order to obtain the DG reactive generations required by the management of the distribution system. Thus, as a consequence some lower variable cost productions might have to limit their active outputs which represent a possible cost increase in VPP management. These automatic limitations, imposed by the controller, allow the Distribution System Operator (DSO) to control voltage on the whole distribution system and the DG plants to guarantee their connection to the network. Simulations on a realistic network case study are carried out to compare the VPP management impact on voltage profiles with a traditional voltage regulation (only OLTC action) and with a coordinated control system. Results demonstrate that the proposed procedure is able to preserve distribution network from dangerous under and over voltages with limited interferences with the VPP optimisation algorithm
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
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