L’enseignement et l’apprentissage de l’écriture est un sujet très discuté mais on parle moins d’autres formes de représentation permettant de véhiculer aussi des savoirs. Lorsque l’individu apprend à représenter (créer et/ou se servir de la représentation) il peut s’approprier un outil indispensable pour construire une pensée critique, accéder aux savoirs institués et résoudre ses problèmes.Nous étudions le cas, à l’école maternelle, d’une mise en œuvre renouvelée de l’ingénierie didactique le « jeu des trésors » (Brousseau, 2004) au sein d’une ingénierie coopérative à l’ESPE de Bretagne.Cette étude longitudinale s’appuie notamment sur des séquences de vidéo. Nous décrivons la façon dont des élèves de cinq ans apprennent, sur une durée de huit mois , à construire et développer des pratiques de production et de déchiffrage des représentations, orales et graphiques, dans un contexte de communication, et à ajuster et à coordonner leurs actions avec celles d’autrui en vue d’aboutir à résoudre en commun le problème posé. Nous reconstruisons la généalogie didactique de leurs pratiques pour répondre à la question : « comment et dans quelles circonstances leurs pratiques ont-elles été apprises ? ». Ici, le rôle du professeur est essentiel. Il agit sur la construction d’un arrière-plan contractuel, associé au processus de représentation, donnant un cadre de repères qui façonne la perception des élèves.Nos outils sont issus du jeu didactique (dialectiques contrat didactique/milieu ; réticence/expression), et nous explorons la dimension affective de ce modèle au sein de la théorie de l’action conjointe en didactique. / Teaching and learning how to write is a heavily discussed topic but discussion is not so frequent when it comes to other forms of representation conveying knowledge as well. When individuals learn how to represent (that is, how to create and/or make use of representation), they can appropriate an essential tool to build critical thought, get into institued knowledge and solve their problems.We are studying the case of a renewed implementation of didactic engineering called « The treasure game » (Brousseau, 2004), within cooperative engineering at the ESPE in Brittany.This longitudinal study notably leans upon video sequences. We describe how pupils aged five, on an eight months period, learn to build and develop practices of production an d deciphering representations, both oral and graphic, in a context of communication. We describe also how they adjust and coordinate their actions with other pupils’, so as to solve a problem in common. We reconstruct the didactic genealogy of their practices in order to answer the following question : « How and in what circumstances have they learnt their practices ? ». There, the teacher’s part is essential. He/She will act upon the construction of a contractual background, associated with the process of representation, providing a framework meant to shape the pupils’perception.Our tools take their roots in the theoretical framework of didactic game ( dialectics didactic contract/ milieu ; reluctance/expression), and we explore the affective dimension of this framework within the Joint Action Theory in Didactics.

As the world moves towards a cleaner and greener future, electrical machines for various industrial purposes and transport applications have gained a lot of attention. Permanent magnet synchronous machines (PMSMs) are usually the solution for electric vehicle (EV) applications thanks to their high efficiency, compactness and high-power density. On the downside, although the price of rare-earth materials has recovered close to historical levels, concerns still remain and the questions on the environmental sustainability of these materials have also been raised, which has encouraged the researchers to consider rare-earth-free machines.The switched reluctance machine (SRM) is one of the competitive alternatives, thanks to the simple and robust construction, high reliability and inherent fault tolerance capability. However, it has a bad reputation when it comes to torque ripple and acoustic noise. And the highly nonlinear characteristic brings much difficulty to routine design purposes and machine optimisation.Therefore, some of the above mentioned problems are addressed - a torque-ripple-reduction, reliable and low-cost system of SRMs is presented in this thesis. Firstly from the modelling point of view, a combined magnetic equivalent circuit (MEC) and finite element (FE) model of SRMs is developed for fast characterization the nonlinear behavior. Secondly from the control point of view, various torque-ripple reduction techniques are implemented and compared. Moreover, a minimal current sensing strategy with enhanced fault-detection capability is proposed and validated experimentally. It requires two current sensors, to replace the phase current sensors, with no additional devices for fault detection, to achieve a more compact and low-cost drive. Finally from the reliability point of view, an interturn short-circuit fault detection method and a rotor position estimation approach are investigated and validated experimentally, which leads to a more reliable system. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Ce travail s'intéresse à la modélisation pour le dimensionnement de moteurs à reluctance variable. Dans une première partie, on donne notre approche du problème de dimensionnement, puis on définit les trois grands types de modèles que le concepteur en électrotechnique sera amené à rencontrer. Enfin, on présente différentes méthodes de conception de moteurs à reluctance variable qui ont été mises en œuvre. Dans une seconde partie, nous présentons une méthodologie permettant d'intégrer des modèles semi analytiques dans un processus d'optimisation de type gradient : les boites de calcul. Nous présentons celles que nous avons créées, puis un exemple de leur application au dimensionnement d'un moteur à reluctance variable de type classique. On s'intéresse dans la troisième partie à la modélisation en vue du dimensionnement d'un moteur à reluctance variable à motifs. Après une présentation de la structure d'un tel moteur, on en présente un modèle analytique, puis un modèle numérique, modulaires. Enfin, on s'appuie sur la complémentarité qui existe entre ces deux modèles pour proposer une méthode de dimensionnement.

This thesis deals with the design and implementation of a feedback control scheme for a DC Hybrid Active Power Filter used to filter harmonics from a Switched Reluctance Motor (SRM) Drive load. Power electronic systems are non-linear & dynamic [1,3,5]. Power electronic systems employ switching circuits to maximize their efficiency at the penalty that switching circuits generate electrical noise called ripple current and voltage or conducted electromagnetic interference (EMI). The ripple current drawn by the power electronic systems needs to be attenuated to an acceptable level. Filters attenuate this to an acceptable level. Traditionally filters with passive inductors and capacitors are used. Active filters contain switching elements in addition to passive inductors and capacitors which reduce overall size of passive components used. Two control approaches, full-state state space, and plain proportional feedback, are evaluated for this filter. Circuit models are simulated in SPICE and mathematical models are simulated in Matlab/Simulink for evaluating these control approaches. Proportional feedback control was chosen for implementation and the reason for this is provided in the thesis. The active filter was tested with chosen feedback control and experimental results were compared with simulation results. Inferences and scope for further work are finally presented.

Frequency response analysis (FRA) is a frequency-domain method which is used to detect mechanical faults in transformers. The frequency response of a transformer is determined by its geometry and material properties, and it can be considered as the transformer’s fingerprint. If there are any mechanical changes in the transformer, for example if the windings are moved or distorted, its fingerprint will also be changed so, theoretically, mechanical changes in the transformer can be detected with FRA. A problem with FRA is the fact that there is no general agreement about how to interpret the measurement results for detection of winding damages. For instance, the interpretation of measurement results has still not been standardized.The overall goal of this thesis is to try to enhance the understanding of the information contained in FRA measurements. This has been done in two ways: (1) by examining the FRA method for (much) higher frequencies than what is usual, and (2) by developing a new method in which FRA is combined with the ideas of Time Domain Reflectometry (TDR). As tools for carrying out the above mentioned steps, models for the magnetic core and the winding have been developed and verified by comparison to measurements.The usual upper frequency limit for FRA is around 2 MHz, which in this thesis has been extended by an order of magnitude in order to detect and interpret new phenomena that emerge at high frequencies and to investigate the potential of this high-frequency region for detection of winding deteriorations.Further, in the above-mentioned new method developed in this thesis, FRA and TDR are combined as a step towards an easier and more intuitive detection and localization of faults in transformer windings, where frequency response measurements are visualized in the time domain in order to facilitate their interpretation. / QC 20111122

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The focus of this thesis is position sensorless control of a transverse-laminated reluctance synchronous machine. Rotor position information is required for high-performance closedloop control of the reluctance synchronous machine and is conventionally supplied by unreliable hardware position resolvers. In addition a FPGA-based rapid prototyping system is completed as part of the research term for control of the machine drive system. For the first time the unified active- ux (AF) method is investigated and implemented for position sensorless control of the transverse-laminated reluctance synchronous machine in this study. The method is based on the torque equation of the machine and is basically the same for any AC machine. The estimation scheme is implemented for closed-loop position sensorless control from low- to rated speed in the entire rated load range with simulation and measured results confirming its capabilities. A number of characteristics of the machine (including generator operation) have implications for implementation of the active- ux (AF) method and are therefore investigated. Another position estimation method investigated is the arbitrary injection (AI) scheme which is derived to be completely machine parameter independent. The method simply requires a current progression at each calculation step allowing use of a smaller injection voltage. This method is implemented again on the reluctance synchronous machine and is shown to be capable of position sensorless current and speed control of the drive from standstill to rated speed with simulation and measured results. However, when the machine is operating above low speeds it is shown that this technique is only capable of position sensorless control at low loads. To deliver position sensorless control in the entire rated speed and load range a new hybrid controller scheme is designed and implemented. The hybrid scheme is speed and load dependent with hysteresis regions for stability at specific working points. The active- ux (AF) method is implemented in the low to rated speed range at medium to rated loads while the arbitrary injection (AI) method is implemented elsewhere. Measured results show that the scheme is capable of position sensorless control in the entire rated speed and load range with some limitations on dynamics. Because of the limitations on dynamics of the hybrid scheme an assisted fundamental model position estimation scheme was investigated. Simulation results show that this controller requires further investigation. / AFRIKAANSE OPSOMMING: Die fokus in hierdie tesis is die posisie-sensorlose beheer van 'n transvers-gelamineerde reluktansie sinchroonmasjien. Rotor posisie inligting word benodig vir geslote-lus beheer van die reluktansie sinchroonmasjien met ho e-werkverrigting, en word normaalweg deur onbetroubare hardeware sensors verskaf. As deel van die navorsings-termyn is 'n FPGAgebaseerde beheerstelsel vir die masjien stelsel voltooi. Die \aktiewe-vloed" posisie-afskattings metode is ondersoek en vir die eerste keer ge mplementeer vir posisie-sensorlose beheer van die transvers-gelamineerde reluktansie sinchroonmasjien. Die metode is dieselfde in konsep vir alle WS masjiene en word basseer op die vergelyking vir wringkrag van die masjien. Vollas geslote-lus posisie-sensorlose beheer van die masjien in die lae tot ho e spoedbereik is suksesvol ge mplementeer met simulasie en gemete resultate. Verkskeie inherente eienskappe van die masjien het implikasies vir gebruik van die \aktiewe-vloed" metode (insluitend generator werking) en is dus ondersoek. Die \arbitr^ere injeksie" metode wat afgelei is om onafhanklik van masjien parameters te wees is ook odersoek. Hierdie metode verlang slegs 'n stroom-afgeleide by elke tydstip en benodig dus 'n kleiner injeksie-spanning. Hierdie metode is weer ge mplementeer op die reluktansie sinchroon masjien met suksesvolle posisie-sensorlose beheer in die hele spoed bereik getoon in simulasie en praktiese resultate. Dit word egter getoon dat hierdie metode slegs onder lae-las toestande posisie sensorlose beheer bo lae-spoed kan bewerkstellig. Ten einde posisie-sensorlose beheer in die hele spoed en wringkrag bereik te verkry is 'n nuwe hibriede beheerskema ontwerp en ge mplementeer. Die skema is spoed en las afhanklik met histerese vir stabiliteit by 'n spesi eke werkpunt. Die \aktiewe-vloed" metode word gebruik bo lae spoed teen 'n minimum las terwyl die \arbitr^ere injeksie" andersins ge mplementeer word. Gemete resultate toon dat die skema posisie-sensorlose beheer van die masjien in die hele spoed en las bereik toelaat met sommige beperkings op dinamika. Met inagneming van die beperkings op die hibriede metode is 'n ondersteunde fundamentele model afskattingskema ondersoek. Simulasie resulate toon dat hierdie beheerder verdere ondersoek benodig.

L’achat d’occasion est un phénomène de consommation en plein essor. Alors que les motivations du consommateur à acheter d’occasion ont suscité de nombreuses recherches, les freins sont rarement étudiés, notamment dans le contexte de l’achat en ligne. Pourtant, une meilleure compréhension de ces freins présente des enjeux aussi bien économiques qu’environnementaux ou sociétaux. Dans ce travail, nous nous intéressons aux freins relatifs à la perception d’une contagion physique ou symbolique des produits d’occasion. En effet, ces freins – qui sont soulignés dans la littérature sur l’achat hors ligne – sont remis en question par le contexte spécifique de l’achat sur Internet. Nous mobilisons ainsi la théorie des lois de la magie sympathique pour étudier dans quelle mesure la loi de contagion et la loi de similitude peuvent influencer l’achat d’un produit d’occasion en ligne. Cette thèse repose sur un design expérimental comportant trois études empiriques. Les résultats obtenus permettent d’identifier des déterminants situationnels et individuels de la contagion physique ou symbolique des produits d’occasion vendus en ligne et d’étudier leur influence négative sur l’intention d’achat. Contrairement à l’achat hors ligne, nous montrons que la contagion physique repose alors sur un mécanisme cognitif. De plus, les résultats indiquent que la loi de similitude permet de limiter les effets de la contagion. En conclusion, cette recherche permet de proposer plusieurs solutions pour améliorer la vente des produits d’occasion en ligne. / Secondhand shopping is a growing phenomenon. While secondhand shopping motivations received a lot of attention in marketing literature, consumer reluctance to shop secondhand remains under-Researched, especially in an online context. Yet, the stakes in better understanding this reluctance are not only economic, but also environmental and societal. In this research, we focus on consumer reluctance that is related to the perception of a physical or symbolic contagion of secondhand products. Indeed, while this reluctance is highlighted in literature on secondhand shopping offline, its role is questioned in an online context. Hence, we use the theoretical framework of the laws of sympathetic magic to study to what extent the contagion or similarity laws influence the intention to shop secondhand online. We use an experimental design made of three empirical studies. Results enable us to identify several situational and individual antecedents of the physical or symbolic contagion associated to a secondhand product sold online, and to study how contagion negatively influences the intention to purchase. In opposite to offline shopping, we show that physical contagion relies on a cognitive mechanism. Moreover, results show that the similarity law can reduce the effects of contagion. To conclude with, this research suggests various solutions to improve the sales of secondhand products online.

In diesem Beitrag wird gezeigt, welche Auswirkung die Rotorform einer Reluktanzmaschine und die Ansteuerung mittels Umrichter auf den Verlusthaushalt der Maschine hat. Darüber hinaus werden die Möglichkeiten zur Verluststeuerung, welche sich durch den Betrieb von Reluktanzmaschinen ergeben, vorgestellt. / This paper shows the effect of the rotor shape of a reluctance machine and the converter control on the losses of the machine. In addition, it will be shown which possibilities for loss control will result from the operation of reluctance machines.

Indiana University-Purdue University Indianapolis (IUPUI) / The purpose of this thesis is to perform modeling from different perspectives for an airgapless motor. The airgapless motor is a proposed type of electric machine whose purpose is to replace hydraulic machines in low speed high torque applications. Because of the nature of the movement for this device, modeling of this device is atypical to the modeling done with other electric machines. This thesis will present the operating principle of the airgapless motor and take an analytical approach to modeling the torque and total energy in the device. In addition, this thesis will present the power electronics necessary to drive this device and offer recommendations to maximize the torque and minimize the torque ripple. MATLAB simulations are used to verify that the conclusion of this thesis are consistent with observations made by previous publications and prototypes.

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