1,721,013 research outputs found
Improving Fault Tolerance of Multiphase LCI-Fed Synchronous Motor Drives
No full textLoad-commutated inverters (LCIs) are reliable and efficient drives to supply synchronous motors in high power industrial applications. However, inadequate attention is dedicated to this type of drive especially for higher phase numbers and in the case of faults. It is a proven fact that the fault tolerance of the voltage-source inverter (VSI)-fed multiphase machines is enhanced as the number of phases increases. However, the same principle is not necessarily applicable to the LCI-fed multiphase synchronous machine drives. As it will be shown in this paper, a thyristor failure may cause the drive instability and the situation can be more critical for higher phase numbers. In this paper, open-circuit faults and their consequences are investigated and compared for symmetrical and asymmetrical multiphase LCI-fed drives. Also, a new control strategy is proposed to restore the drive stability in the case of open-circuit faults in LCI-fed drives. Simulation results for a five-phase drive show that the control system can efficiently keep the machine synchronism in the event of phase open-circuit faults
Design of an efficient starting circuit for LCI-fed synchronous motor drives
No full textIn this paper, after going through different starting schemes used in industry and literature to accelerate LCI-fed wound-field synchronous machines (WFSMs) from standstill, an efficient forced-commutation circuit is designed based on the field-oriented control strategy in stator flux reference frame. The proposed circuit can use SCR devices with current rating much smaller than that of the main switches. A complete explanation of the circuit operation and its parameters design procedure is presented. Then, simulation studies are conducted to verify the theoretical analysis and the results are compared with those of a common starting scheme. Comparisons show the superiority of the proposed circuit especially in terms of torque pulsations
Field oriented control of LCI-fed WFSM drives in stator flux reference frame
No full textLoad-commutated inverters (LCIs) in conjunction with the wound-field synchronous motors (WFSMs) are one of the most applicable drive topologies, and in some cases the only choice, in high-power medium-voltage applications. In this paper, a novel strategy is presented for field oriented control (FOC) of these drives in stator flux coordinates. Considering rotor saliency, independent flux and speed control is carried out to achieve maximum torque to ampere ratio. Furthermore, the proposed strategy provides a simple way to design the PI controllers' parameters according to the phase-controlled DC machine and WFSM drive analogy. Simulation studies are presented to verify the performance of the total proposed control scheme. Comparisons show the superiority of the proposed method over the conventional drive technologies for LCI-fed WFSM drives
LCI-fed wound-field synchronous motors: A technology status review and new development trends
No full textLoad-Commutated Inverters (LCIs) are today one of the main converter topologies used for very-high-power drive applications, although new topologies, based on PWM technology and employing IGBT or IGCT as power switches instead of SCR's, have been recently gaining attractiveness also for increasing power ratings. The paper presents an overview of today's LCI technology and its applications, highlighting its strengths and weaknesses. Furthermore, the most promising lines of development are drawn along which LCI drive technology is being improved to overcome its major drawbacks and maintain competitiveness with Voltage-Source-Inverter (VSI) based counterparts
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
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
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