1,720,974 research outputs found
Distributed vs. centralized generation: Advantages and drawbacks
No full textThis section analyses the main benefits and drawbacks of conventional centralized generation and of the new, distributed architecture of power systems, discussing first of all the reasons for this change of paradigm. Distributed generation involves primarily, but not exclusively, crowds of small-scale renewable power plants connected to low-medium voltage networks, which is a huge breakthrough toward environmental sustainability, and beyond that an epochal challenge for system reliability and security. The intermittent and scarcely predictable nature of such sources, in fact, is highly demanding for power balancing and requires the traditional “fit-and-forget” approach to be quickly substituted by a real integration of dispersed generation into the system perspectives and needs. This section also details how flexible resources like energy storage devices and dispatchable distributed generators can contribute to power quality and to the secure operation of the power system, especially if involved in new market schemes. Finally, a quick review of operational and sizing criteria of off-grid configurations is provided
Integration of Process-Side Energy Storage and Active Distribution Networks: Technical and Economical Optimisation
No full textThis paper is primarily aimed at demonstrating how
energy tariffs with a significant price difference between
day and night can make energy storage systems more
profitable for an active customer. An optimisation
procedure, based on the “energy hub” concept, has been
devised and applied for a coordinated operation of local
generation and process-side electric and thermal
storages. The optimized integrated management of these
systems enables an efficient use of primary sources,
largely resorting to co-generation (CHP) and an optimal
use of production and storage devices. Different case
studies show how supply and distribution tariffs can
influence the cost-effective operation of a CHP system,
assuming the presence of various kinds of process-side
storages
Black-start of remote areas through SCR-based HVDC Links
No full textThis paper analyses the possibility to black-start a remote area using an existing Line Commutated Converter HVDC link.To do this, a relatively small size Voltage Sourced Converter must be installed at the link receiving-end. The black start takes place using the existing receiving end network and line commutated converters, and the DC line. The paper shows that the black start operation can take place fast and effectively
Use of VSC-HVDC links for power system restoration
No full textThis paper shows how a VSC-HVDC system can be profitably used as a black start unit to restart a thermal power plant, as well as to help it to follow the constrained power ramping up to its technical minimum. A frequency vs real power and voltage vs reactive power droop control is proposed for the receiving end converter of the link, including a Local Frequency Integrator function which enables the system to be easily reconnected with other units
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
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
Luenberger Observer for Lithium Battery State-of-Charge Estimation
No full textOne of the main concerns regarding energy storage systems during their normal operation is the possibility to perform an accurate state-of-charge estimation. This cannot be done by simple ampere-hour counting, unless drift correction means are put in place to avoid accumulation of measurement errors over time. In this paper, a state-of-charge estimation algorithm is widely analysed and tested on a nickel manganese cobalt oxide (NMC) lithium cell. The procedure consists of the utilisation of an equivalent electrical network battery model and the implementation of a Luenberger technique for a runtime correction, from the measure of battery’s voltage and current. Although application of Luenberger-style estimation is not new in literature for application to batteries, new expressions of battery model parameters and more detailed simulations are shown, to imply much higher estimation accuracy than in the past. After setting the model parameters, different test cycles have been considered, to evaluate the robustness of the proposed technique
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
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