1,720,956 research outputs found
Rotor eddy current power loss in permanent magnet synchronous generators feeding uncontrolled rectifier loads
No full textAnalytical methods and transient finite element analysis (FEA) with rotating mesh are used to calculate rotor eddy current power loss in a permanent magnet synchronous generator (PMSG) connected to an uncontrolled bridge rectifier. Two winding and rectifier topologies are considered: a 3-phase winding with a 3-phase bridge rectifier and a double 3-phase winding with a 3-phase rectifier each, connected in series. Both magnet flux tooth ripple and stator MMF harmonics are considered in the calculation of rotor loss; the harmonics are added vectorially. Good agreement is observed between analytical and FEA for constant dc link current and constant voltage loads. The machine with double 3-phase windings was found to have considerably lower rotor losses that the machine with one single 3-phase winding
Calculation of no-load rotor eddy current power loss in PM synchronous machines
Get PDFThree analytical methods, and finite element analysis (FEA), are used to calculate no-load flux harmonics travelling with respect to the rotor of a surface permanent magnet (PM) machine. Rotor eddy current losses caused by each harmonic are calculated analytically using a multilayer eddy current model of the machine, in which each harmonic is represented by an equivalent current sheet on the bore of a slotless stator. Losses are also calculated using transient time-stepping FEA coupled with the equation of motion of the rotor. Significant discrepancies are observed between the results obtained from the different methods and FEA, especially when the level of saturation in the stator core is significant. <br/
Rotor eddy loss in high-speed permanent magnet synchronous generators
No full textAnalytical and transient finite element analysis (FEA) methods are used to calculate on-load rotor eddy currentpower loss in permanent magnet machines taking into account the effect of the reaction of eddy currents. The effect of thephase advance angle between the back electromotive force, and the phase current on rotor eddy current power loss isinvestigated. Both magnet flux tooth ripple and magnetomotive force harmonics are considered in the analytical calculation of rotor loss; the harmonics of the magnet tooth ripple flux and armature reaction flux are added vectorially. Good agreement between analytical and FEA results is observed when the stator laminations are assumed to have a linear BH curve. However, a significant discrepancy is observed between the analytical and FEA solutions when a non-linear BH curve is used
Comparison of PM and hybrid excited machines for marine vessel hybrid-electric propulsion
No full textThis paper evaluates the maximum torque capability of a hybrid excited synchronous machine in comparison with a conventional PM synchronous motor. The main focus of the paper is on the study of the effect of DC excitation magnetic flux on the saturation of the stator teeth,which limits the torque production capability of the hybrid machine. Magnetostatic and transient analyses are carried out for both motors. As expected the hybrid motor air gap flux controllability comes at the expense of reducing its torque density. The torque density reduction penalty is quantified and some hidden limitations and challenges of designing such a hybrid motor are revealed based on an in-depth analysis of the flux distribution within the machine
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
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