1,721,128 research outputs found
Upgrade of Exciter for Synchronous Generators basing on the Hybrid Excitation Concept
No full textIn the classical brushless arrangement, the field current of wound-field synchronous generators (SGs) is provided by exciters through rotating diode rectifiers. The control of the SG field current is achieved indirectly by regulating the field current of the exciter, whose excitation winding is stationary. This paper investigates the possibility to equip the exciter with hybrid excitation by adding surface-mounted permanent magnets (PMs). While a hybrid PM-field winding exciter has already been proposed in a recent work, where the selected condition was the rated no-load operation of the SG, in this paper the PMs are designed to sustain the generating set (genset) operation at a suitably selected load condition. This permits to further reduce the excitation losses of the exciter and to operate the genset even in case of full failure in the exciter field system, including the related electronic controller
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
Fast Analytical-Numerical Modelling of Rotor Eccentricity for Radial Active Magnetic Bearing
No full textRadial Active Magnetic Bearings (R-AMBs) have become an attractive alternative to other type of bearings in an increasing spectrum of applications. Optimum design and fine control strategies play an important role in the overall performance of such type of electro-magneto-mechanical devices. In order to achieve a quick yet accurate estimation of the main parameters that affect the behaviour of R-AMBs, a numerical-analytical model is here proposed. The analytical expression are firstly introduced. The model is implemented in a digital environment and used to numerically evaluate the inductance matrix and its variation with respect the rotor eccentricity coordinates. The results are validated through FEM and final considerations for both electromagnetic design and control design can be drawn
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
Analysis of Current Ripple effect on Lithium batteries
No full textThis paper investigates the Lithium battery behavior and possible aging effects in presence of current ripple during the operation. In the context of a research funded project aimed at increasing the safety level of Lithium batteries for the naval propulsion, we present the results of an experimental analysis aimed at investigating the effect of current ripple on cell performances. An ad-hoc experimental setup is developed to test the batteries and the effect of current ripple on battery capacity and cell aging is discussed throughout the paper
Predictive Control for An Active Magnetic Bearing System with Sensorless Position Control
No full textActive Magnetic Bearing (AMB) technology is becoming attractive for several reasons such as friction-free suspension and high-speed operation, high reliability, and vibrations exemption. These desirable features come at the cost of an increased complexity of the system, which includes position sensors, a power electronic converter and a control system dedicated to the AMBs. This paper focus on the control system design of an AMB featuring a Wheatstone bridge winding configuration. To achieve a high-bandwidth current control able to generate the desired forces, a Finite Control Set Model Predictive Control (FCS-MPC) has been proposed in this paper. The proposed FCS-MPC includes an estimation of the AMB coils inductance, which can be used to improve the control system performance and, at the same time, provide a rotor position estimation without the need of additional sensing coils and possibly without the use of conventional position sensors. The AMB is modelled considering finite element simulation results in order to evaluate the relation between coil inductance variation and rotor position. A standard PI position control is also included in the system. Finally, the control system is validated through simulation
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