- About
-
The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
provided by the
Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
Search results
Showing 1 to 5 of 5 (0.079 seconds)Spelling suggestions: "subject:"harmonic reduction"" "subject:"armonic reduction""
| 1 |
Programmed harmonic reduction in inverters and controlled rectifiersDeib, Deib Ali January 1993 (has links)
No description available.
|
| 2 |
Harmonic currents generated by personal computers, their effects on the power system and methods of harmonic reductionAintablian, Hrair January 1994 (has links)
No description available.
|
| 3 |
Real-time torque ripple compensationfor PMSMs in robotics applicationsJieqiong, Wang January 2024 (has links)
The Permanent Magnet Synchronous Motors (PMSM) have wide application in the robotics field due to its efficiency and reliability. As a servo system, it demands high precision in different control applications. Torque ripple is a critical issue resulting in mechanical vibrations and shortening the life of PMSMs, especially at low speeds. Because the magnitude of speed harmonics is proportional to the magnitude of the torque harmonics of the same order, methods to reduce speed harmonics can be utilized for torque ripple minimization. This thesis work proposes three methods for torque ripple reduction. One method is based on harmonic speed control (HSC) and harmonic current control (HCC). Another method uses the fuzzy to adjust PI parameters based on HSC-HCC. The third method utilizes torque ripple estimation (TRE) and HCC. In the proposed methods, torque ripples are estimated using a torque ripple model (TRM). At low speeds, speed harmonics and current harmonics are obtained based on an adaptive linear neural-based filter. The errors between the optimal harmonic current reference from HSC or TRE and the harmonic current from extraction are used to generate harmonic voltage in HCC. This harmonic voltage is fed back to compensate and reduce torque ripple. Furthermore, a feedforward compensation method is proposed to minimize torque ripple across a range of speeds based on the feedback compensation results. Finally, simulations and experiments are carried out to demonstrate the validity and performance of the proposed torque ripple reduction methods.
|
| 4 |
Tissue harmonic reduction : application to ultrasound contrast harmonic imaging / Imagerie ultrasonore non linéaire : réduction des harmoniques tissulaire en imagerie de contrastePašović, Mirza 11 May 2010 (has links)
Les agents de contraste sont de petites bulles qui répondent non linéairement lorsqu’ils sont exposés à ultrasons. La réponse non-linéaire donne la possibilité d’images échographiques harmoniques qui a beaucoup d’avantages sur l’imagerie fondamentale. Toutefois, afin d’accroître l’échographie de contraste d’imagerie harmonique de performance nous devons d’abord comprendre la propagation non linéaire d’ultrasons. La non-linéarité du milieu déforme l’onde qui se propage, tels que les harmoniques commencent à se développer. La théorie qui a été prévue est la mise en œuvre, qui a permis une nouvelle méthode de modélisation de propagation des ultrasons non-linéaire. La connaissance acquise au cours de ce processus a été utilisée pour construire un deuxième signal à composantes multiples pour la réduction des harmoniques générées en raison des non-linéarités des tissus. En conséquence, la détection d’agents de contraste ultrasonore aux harmoniques a été augmentée. Une puissante technique d’imagerie échographique (Pulse inversion) a été renforcée avec le deuxième signal pour la réduction des harmoniques. Qu’est-ce qui a été appris pendant l’investigation : le pulse inversion technique a donné une nouvelle phase codée, appelée inversion de seconde harmonique. En outre, il a été noté que pour différents types de médias le niveau de distorsion de l’impulsion à ultrasons est différent. Cela dépend en grande partie du paramètre non linéaire B / A. Les travaux sur ce paramètre n’a pas été fini, mais il est quand même important de continuer dans cette direction puisque B / A imagerie avec des agents de contraste ultrasonore a beaucoup de potentiel. / Ultrasound contrast agents are small micro bubbles that respond nonlinearly when exposed to ultrasound wave. The nonlinear response gives possibility of harmonic ultrasound images which has many advantages over fundamental imaging. However, to increase ultrasound contrast harmonic imaging performance we must first understand nonlinear propagation of ultrasound wave. Nonlinear propagation distorts the propagating wave such that higher harmonics appear as the wave is propagating. The theory that was laid down, was allowed implementing a new method of modelling nonlinear ultrasound propagation. The knowledge obtained during this process was used to construct a multiple component second harmonic reduction signal for reduction of their harmonics generated due to the tissue nonlinearities. As a consequence detection of ultrasound contrast agents at higher harmonics was increased. Further more, a powerful ultrasound imaging technique called Pulse Inversion, was further enhanced with multiple component second harmonic reduction signal. What was learned during investigation of the Pulse Inversion, technique lead to a new phase coded ultrasound contrast harmonic method called second harmonic inversion;. Also it was noted that for different type of media the level of distortion of ultrasound pulse is different. It depends largely on the nonlinear parameter B / A. Although the work on this parameter has not been finished it is very important to continue in this direction since B / A imaging with ultrasound contrast agents has a lot of potential.
|
| 5 |
Les cantates de Nicolaus Bruhns (1665-1697) / The cantatas of Nicolaus Bruhns (1665-1697)Fructus, Michel 03 December 2009 (has links)
Nicolaus Bruhns (1665-1697) fut organiste à la Marienkirche de Husum (Schleswig-Holstein), et Kapellmeister au service des ducs de Schleswig-Holstein-Gottorf. Si nous ne possédons aujourd’hui qu’une poignée de ses pièces pour orgue (quatre praeludia et un choral-fantaisie), nous pouvons apprécier l’ingéniosité de cet auteur à travers sa production d’œuvres sacrées, douze cantates où règne une énergie comparable à celle de son professeur Dietrich Buxtehude.Soucieux de mieux cerner les enjeux de l’identité créatrice, nous proposerons une approche contradictoire, fondée sur deux conceptions opposées de l’œuvre d’art : elle est par voie de conséquence le produit d’une culture (parce qu’elle est liée au contexte artistique qui la précède, au regard des éléments qui la constituent et qui sont facilement identifiables dans les œuvres du passé, toute œuvre peut être perçue et pensée comme une synthèse de différents modèles, une forme d’aboutissement culturel), mais aussi le fruit d’une individualité (une œuvre d’art est une élaboration unique, indépendante de toute autre production, au regard des facteurs d’unité qui la structurent ; toute œuvre peut alors être perçue et pensée comme une entité autonome).Cette étude nous permettra de mettre à jour un soubassement de l’activité psychique : l’estimation de la distance entre le fixe et le muable. / Nicolaus Bruhns (1665-1697) was an organist at the Marienkirche in Husum (Schleswig-Holstein), and Kapellmeister to the dukes of Schleswig-Holstein-Gottorf. If we own today only a handful of his pieces for organ (four praeludia and a chorale-fantasia), we can appreciate the cleverness of this author through his production of sacred works, twelve cantatas where the energy which appears is similar to that of his professor Dietrich Buxtehude.With the concern to better define the stakes of creative identity, we shall put forward a contradictory approach based on two opposite conceptions of the work of art : it is in essence the product of a culture (since it is linked to the artistic context which precedes it, according to the elements which constitute it and which are easily identifiable in the works of the past, any work can be perceived and thought as a synthesis of various models, a form of cultural achievement), but also the result of individuality (a work of art is a unique construction, independent from any other production according to the factors of unity which structure it ; any work may then be perceived and thought as an autonomous entity).This study will enable us to bring to light a basis of the psychic activity : the appraisal of the distance between the fixed and the changing.
|
Page generated in 0.0883 seconds