1,720,979 research outputs found
Reduction of electromagnetic noise and vibrations in synchronous machines using passive damper winding
No full textCette thèse de doctorat présente une méthode passive de réduction des bruits et vibrations dans les machines synchrones à aimants permanents (MSAP), utilisant un enroulement amortisseur connecté à des condensateurs. Le principe est d'ajouter un enroulement auxiliaire dans les encoches du stator, court-circuité via des condensateurs externes. L'objectif du système amortisseur passif est de réduire les composantes harmoniques d’induction dans l'entrefer, réduisant ainsi les bruits et vibrations d’origine magnétique, en particulier les composantes aux hautes fréquences induites par la MLI. Tout d'abord, la thèse présente les origines du bruit et des vibrations ainsi que les méthodes existantes de réduction dans les machines électriques. En analysant des scénarios d'application complexes, la thèse met en évidence les avantages du système amortisseur passif. Deuxièmement, le modèle analytique des MSAP avec un système amortisseur est établi et des circuits électriques équivalents sont proposés dans le repère dq0. Troisièmement, des calculs analytiques basés sur des circuits électriques sont effectués et comparés aux simulations numériques par éléments finis pour étudier l'impact du système amortisseur dans les MSAP. Les résultats expérimentaux confirment l'efficacité du système et valident les études théoriques. Le niveau de bruit est réduit d'environ 6 à 14dB sous différentes conditions de fonctionnement. Il est constaté que le système amortisseur a un impact négatif sur le rendement de la machine et que l'enroulement amortisseur occupe inévitablement de l'espace dans les encoches du stator. Une étude d'optimisation paramétrique est ensuite réalisée pour étudier l'impact des différents facteurs sur le système amortisseur et sa performance sur la réduction du bruit et des vibrations. Une optimisation multi-objectifs basée sur le modèle analytique est finalement proposée pour équilibrer le volume de cuivre de l'amortisseur, l'effet de réduction du bruit et les pertes supplémentaires dues au système amortisseur, ce qui peut étendre l'application du système.This Ph.D. dissertation introduces a passive method for noise and vibration reduction in Permanent Magnet Synchronous Machines (PMSMs), using a damper winding connected to capacitors. The principle is to add an auxiliary winding into stator slots, short-circuited via external capacitors. The objective of the passive damper system is to reduce harmonic components in the air gap flux density, thus reducing electromagnetic noise and vibrations, especially PWM-induced high frequency components. First, the dissertation introduces the origins of noise and vibrations as well as existing NVH reduction methods in electrical machines. By analyzing complex application scenarios, the dissertation highlights the advantages of the passive damper system. Secondly, the analytical model of PMSMs with a damper system is established and equivalent electrical circuits are proposed in the dq0 frame. Thirdly, analytical computations based on electrical circuits are performed and compared to numerical FEM simulations to investigate the impact of damper system in PMSMs. Experimental results confirm the effectiveness of damper system and validate theoretical studies. The noise level is reduced by about 6 to 14dB under different operating conditions. It is found that the damper system has an impact on machine efficiency and damper winding slightly takes up stator slot space. A parametric optimization study is performed to investigate the impact of different factors on damper system and its NVH reduction performance. A multi-objective optimization based on the analytical model is finally proposed to balance damper copper volume, NVH reduction effect and additional machine losses due to damper system, which can further extend the application of passive damper system
Réduction active du bruit magnétique des machines asynchrones directement connectées au réseau
No full textThis work allows, on the one hand, to better understand the study of induction machine magnetic noise and, on the other hand, to present a method to reduce it by injecting a small current harmonic.The first part explains the phenomenon, gives the known mechanical and acoustic relations and compare them to practical experimentations.The second part presents a method which allows to calculate the flux density harmonics in the airgap; they create Maxwell forces and noise. The determined relations can be used with a cage or a wound rotor and allow to know the stator and rotor current harmonics. They are compared to those given by other authors who neglect many terms.The numerical applications show the importance of a phenomenon called slotting resonance; it is responsible of important rotor current harmonics and magnetic noise. They show the validity of the theory by comparison with practical readings.The last part explains the magnetic noise active reduction method. It consists to inject a small current harmonic in order to create a force which must be in opposed to this responsible of the noise. Many implementations are described which permit to inject a supplementary current in a receiver directly connected to the network. The experimentations confirm the validity of the method.Ce travail permet, d'une part, de mieux appréhender l'étude du bruit magnétique des machines asynchrones et, d'autre part, de présenter une méthode permettant de le réduire en injectant un faible courant harmonique.Le premier chapitre expose le phénomène, fait une synthèse des relations mécaniques et acoustiques existantes et les confronte avec des expériences pratiques.Une méthode de calcul des harmoniques d'induction présents dans l'entrefer est développée dans le deuxième chapitre, ils sont responsables des forces de Maxwell à l'origine du bruit. Les relations obtenues sont valables pour un moteur à rotor bobiné ou à cage et permettent la détermination des harmoniques de courant rotorique et statorique. Elles sont comparées à celles données par d'autres auteurs qui négligent certains termes.Les applications numériques présentées dans le troisième chapitre soulignent l'importance d'un phénomène qualifié de résonance de denture, responsable de courants rotoriques harmoniques importants et de bruit magnétique. Elles montrent également la validité de la théorie en comparant les résultats aux relevés pratiques.Le dernier chapitre expose le principe de réduction active du bruit magnétique. Il consiste à injecter un faible courant harmonique créant une force qui s'oppose à celle à l'origine du bruit. Plusieurs montages sont proposés, permettant l'injection d'un courant supplémentaire dans une machine alimentée par le réseau. L'étude expérimentale permet de valider le procédé
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
Energy Transition
No full textInternational audienceThis book presents both the importance of energy transition and its associated difficulties. Providing an explanation of the physical concepts of energy and power, the book reviews global energy consumption and our dependence on energy. It discusses the links between the economy and energy. It explains the drawbacks and dangers of different energy sources and tries to compare them.Reviewing future energy resources, it evaluates several transition scenarios.It shows that the laws of physics prevent the emergence of simple and pleasant solutions.It proposes potential solutions and encourages the reader to develop better processes, from energy sources to production, to consumption.The book will be of interest to engineers and undergraduate and graduate students studying and working in various fields of energy, producers of fossil, gas, oil, coal, electric, renewable and nuclear energy, as well as all the curious people who are interested in better understanding these fundamental problems for our future.Features•Discusses the current issues with energy transition•Covers several energy transition scenarios and associated difficulties•Presents the links between economy and energy•Highlights the importance of a global discussion of energy•Encourages the development of better, improved processes in energy sources, from production to consumption
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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