La traction hybride et/ou électrique est un domaine d’application en pleine croissance présentant une forte restriction en termes d’encombrement. Cela a poussé les concepteurs à créer des structures de machine adaptées. Parmi ces topologies, nous trouvons les machines synchrones à double excitation (MSDE). Ces machines permettent de combiner les avantages d’une machine à aimants et ceux d’une machine à excitation bobinée. Le choix d’un modèle pour ces machines est un élément important dans les étapes d’analyse, d’optimisation et de pré-dimensionnement. Ce mémoire présente une contribution à la modélisation des machines synchrones à simple et à double excitation basée sur la méthode des réseaux de perméances. Trois parties sont ainsi proposées. La première partie de la thèse présente deux états de l’art- un sur les machines synchrones à double excitation et l’autre sur les méthodes de modélisation des machines électriques et principalement la modélisation par réseau de perméances. Dans la deuxième partie, nous abordons la modélisation 2D de la machine synchrone à aimants permanents à concentration de flux avec prise en compte de la rotation et de la saturation. Le but de cette partie est de trouver des méthodes permettant de combiner à la fois temps de calcul et précision. On commence par la modélisation par réseau de perméances en se basant sur un maillage de l’espace d'étude par des réluctances bidirectionnelles, ainsi qu’une comparaison entre calcul du couple par le tenseur de Maxwell et flux-FMM. La deuxième section présente un couplage entre réseaux de perméances et éléments finis. La méthode proposée consiste à résoudre les deux modèles (réluctant et éléments finis) simultanément avec un logiciel EF. Le couplage s’effectue par une équivalence entre les dimensions géométriques et les caractéristiques magnétiques des matériaux. La présentation des différents modèles dans le plan précision-temps de calcul montre l’efficacité de l’utilisation des réseaux de perméances et du couplage comparé au modèle éléments finis. La troisième partie porte sur la modélisation tridimensionnelle des machines synchrones à double excitation. Dans un premier temps, nous présentons une adaptation de la modélisation par réseau de perméances aux structures tridimensionnelles. Puis, nous appliquons ce modèle aux machines synchrones à double excitation. La machine à double excitation à concentration de flux est présentée avec une étude de l’influence du feuilletage sur la capacité de contrôle du flux. Pour améliorer le contrôle du flux d'excitation, une machine à aimants enterrés homopolaire est également étudiée avec l'approche développée. La validation du modèle est réalisée par des éléments finis et des mesures expérimentales. Dans la dernière partie, une comparaison entre configurations homopolaire et bipolaire de la structure à aimants enterrés est effectuée, puis le rotor à concentration de flux est optimisé afin de le comparer à la machine à aimants enterrés. / The electric and / or hybrid driveis are an application area growing with a strong restriction in terms of congestion. This prompted the designers to create appropriate structures. Among these topologies, we find the double-excitation synchronous machine (MSDE). These machines can combine the advantages of permanent magnets machine and those of a coils excited machine.The choice of a model for these machines is an important step in the analysis, optimization and pre-sizing. This thesis presents a contribution to the modeling by magnetic equivalent circuit (MEC) of single and double excitation synchronous machines. Three parties are offered as well. The first part of the thesis presents two states of the art: one on the double-excitation synchronous machines and the other on the modeling of electrical machines, mainly in the modeling by magnetic equivalent circuit. In the second part, we discuss the 2D modeling of flux concentration permanent magnet synchronous machine taking into account the rotation and saturation. The purpose of this section is to find ways to combine both computational time and accuracy. We start by using the magnetic equivalent circuit modeling based on a mesh of the structure and each mesh is replaced by two-way reluctances, then a torque estimation are obtened by two methods flux-FMM and Maxwell stress Tensor. The second section presents a coupling between magnetic equivalent circuit and finite element method. The proposed method is to solve the two models (reluctant and finite elements) simultaneously with software EF. The coupling is performed by an equivalence between the geometric dimensions and magnetic properties of materials. The presentation of different models in terms of time-accurate calculation shows the effectiveness of the use of MEC and coupling method compared to FEM. The third part concerns the three-dimensional modeling of double excitation synchronous machines. At first, we present an adaptation of the MEC to the three-dimensional structures. Then we apply this model to the double excitation synchronous machines (DESM). The DESM with flux concentration configuration is presented. To better control the wund flux of excitation, a buried magnet homopolar machine is also studied with the same approach. Model validation is performed by finite element and experimental measurements. In the last part, a comparison between homopolar and bipolar configurations is made, then the rotor flux concentration is optimized in order to compare it to the machine magnets buried.

Cette thèse traite de la conception et implémentationd’un langage de programmation pour les systèmes detraitement de flux en temps réel, comme l’encodagevidéo. Le modèle des réseaux de Kahn est bien adaptéà ce domaine et y est couramment utilisé. Dans cemodèle, un programme consiste en un ensemble deprocessus parallèles communicant à travers des filesmono-producteur, mono-consommateur. La force dumodèle réside en son déterminisme.Les langages synchrones fonctionnels comme Lustresont dédiés aux systèmes embarqués critiques. Un programmeLustre définit un réseau de Kahn synchronequi peut être exécuté avec des files bornées et sans blocage.Cette propriété est garantie par un système detypes dédié, le calcul d’horloge, qui établit une échellede temps globale à un programme. Cette échelle detemps globale est utilisée pour définir les horloges, sé-quences booléennes indiquant pour chaque file, et àchaque pas de temps, si un processus produit ou consommeune donnée. Cette information sert non seulementà assurer la synchronie mais également à générerdu logiciel ou matériel à état fini.Nous proposons et étudions les horloges entières, unegénéralisation des horloges booléennes autorisant desentiers naturels arbitrairement grands. Les horlogesentières décrivent la production ou consommation deplusieurs valeurs depuis une même file au cours d’uninstant. Nous les utilisons pour définir la constructiond’échelle de temps locale, qui peut masquer despas de temps cachés par un sous-programme au contexteenglobant.Ces principes sont intégrés à un calcul d’horloge pourun langage fonctionnel d’ordre supérieur. Nous étudionsses propriétés et prouvons en particulier que lesprogrammes bien typés ne bloquent pas. Nous compilonsles programmes typés vers des circuits numériquessynchrones en adaptant le schéma de générationde code dirigé par les horloges de Lustre. L’informationde typage contrôle certains compromis entre temps etespace dans les circuits générés. / This thesis addresses the design and implementationof a programming language for real-time streaming applications,such as video decoding. The model of Kahnprocess networks is a natural fit for this area and hasbeen used extensively. In this model, a program consistsin a set of parallel processes communicating via singlereader, single writer queues. The strength of the modellies in its determinism.Synchronous functional languages such as Lustre arededicated to critical embedded systems. A Lustre programdefines a synchronous Kahn process network, thatis, which can be executed using finite queues and withoutdeadlocks. This is enforced by a dedicated type system,the clock calculus, which establishes a global timescale throughout a program. The global time scale isused to define clocks: per-queue boolean sequences indicating,for each time step, whether a process producesor consumes a token in the queue. This information isused both for enforcing synchrony and for generatingfinite-state software or hardware.We propose and study integer clocks, a generalizationof boolean clocks featuring arbitrarily big natural numbers.Integer clocks model the production or consumptionof several values from the same queue in the courseof a time step. We then rely on integer clocks to definethe local time scale construction, which may hide timesteps performed by a sub-program from the surroundingcontext.These principles are integrated into a clock calculus fora higher-order functional language. We study its properties,proving among other results that well-typed programsdo not deadlock. We adjust the clock-directedcode generation scheme of Lustre to generate finite-statedigital synchronous circuits from typed programs. Thetyping information controls certain trade-offs betweentime and space in the generated circuits.

This work deals with calculation and design of synchronous salient pole generator and then the transformation from this machine into so-called hybrid synchronous machine is described. This diploma thesis is done for company Siemens Electric Machines s.r.o. in Drásov. This company provided their design of synchronous salient pole generator. The model of this generator was created in programs RMxprt and Maxwell 2D. Suggestions and models were compared, and their calculated parameters were evaluated. The created model was upgraded to so-called hybrid synchronous generator. Permanent magnets were added in the created model and influence of these additional magnets is going to be analyzed. Tasks of the work are described in more details. in the introduction. The topic of synchronous generator and hybrid synchronous generator in general is described in the theoretical part. The next part of work deals with the design of salient pole generator. In the other part of the work calculation and design of the generator model are described in Ansys program. Furthermore there are some results from program compared with the results from company. Some model parts and other graphic outputs from Ansys program are shown. After that the creation of hybrid synchronous generator is described and created models of hybrid synchronous generators are compared and evaluated.

This research work focuses on the reactive power compensation of the permanent magnet synchronous generator (PSG) in wind power plants. PSG feeds a fixed voltage dc grid through a rectifier bridge. In variable speed operation, the PSG will be able to build torque only in small speed range. This is due to the fixed magnet of the PSG. External reactive power compensation provides an attractive solution to overcome this problem. Different reactive power compensation configurations were examined. Statics synchronous series compensation and a shunt passive filter were chosen as a compensation method. Simulation and implementation of small wind power plant were performed. The wind power plant consists of the synchronous generator, inverter, rectifier, coupling transformers and shunt passive filter. The experimental results agree to the proposed theory and simulation results. / Der Schwerpunkt meiner Promotion ist die Blindleistungskompensation bei einem permanenterregten Synchrongenerator. Der Synchrongenerator speist das Gleichsspannungsnetz über ein Gleichrichter. In der Drehzahlvariablen Betriebsverhalten können Nachteile auftreten. Die Folge ist, dass bei konstanter Gleichspannung und fester Erregung durch die Permanenterregung nur ein sehr kleiner Drehzahlbereich mit vernünftiger Drehmomentausbeute bedienbar ist. Ein möglicher Ausweg wäre eine variable Kompensationsspannung. Verschiedene Kompensationsverfahren wurden untersucht. Ein Series Active Filter und ein Shunt Passive-Filter wurden als Blindleistungskompensation gewählt. Im Rahmen meiner Dissertation beschäftige ich mich mit dem Aufbau und der Simulation einer Windkraftanlage. Diese besteht aus einem permanenterregten Synchrongenerator, einem Wechselrichrter, einem Gleichrichter, drei Transformatoren und einem passiven Filter. Das Versuchsergebnis zeigt, dass die Theorie mit der Simulation übereinstimmt.

No description available.

The advent of wide band-gap semiconductors in power electronics has led to the scope of efficient power conversion being pushed further than ever before. This development has allowed for systems to operate at higher and higher voltages than previously achieved. One area of consideration during this high voltage transition is the synchronous rectifier, which is traditionally designed as an afterthought. Prior research in synchronous rectifiers have been limited to low voltage, high current converters. There is practically no research in high voltage synchronous rectification. Therefore, this dissertation focuses on discovering the unknown nuances behind high voltage synchronous rectifier design, and ultimately developing a practical, scalable solution. There are three main issues that must be addressed when designing a high voltage synchronous rectifier: (1) high voltage sensing; (2) light load effects; (3) accuracy. The first hurdle to designing a high voltage SR system is the high voltage itself. Traditional methods of synchronous rectification (SR) attempt to directly sense voltage or current, which is not possible with high voltage. Therefore, a solution must be designed to limit the voltage seen by the sensing mechanism without sacrificing accuracy. In this dissertation, a novel blocking solution is proposed, analyzed, and tested to over 1-kV. The solution is practical enough to be implemented on practically any commercial drain-source SR controller. The second hurdle is the light load effect of the SR system on the converter. A large amount of high voltage systems utilize a LLC-based DC transformers (DCX) to provide an efficient means of energy conversion. The LLC-DCX's attractive attributes of soft-switching and high efficiency allure many architects to combine it with an SR system. However, direct implementation of SR on a LLC-DCX will result in a variety of light load oscillation issues, since the rectifier circuitry can excite the resonant tank through a false load transient phenomena. A universal limiting solution is proposed and analyzed, and is validated with a commercial SR controller. The final hurdle is in optimizing the SR system itself. There is an inherent flaw with drain-source sensing, namely parasitic inductance in the drain-source sense loop. This parasitic inductance causes an error in the sensed voltage, resulting in early SR turn-off and increased losses through the parallel diode. The parasitic will always be present in the circuit, and current solutions are too complex to be implemented. Two solutions are proposed depending on the rectifier architecture: (1) multilevel gate driving for single switch rectifiers; (2) sequential parallel switching for parallel switch rectifiers. In summary, this dissertation focuses on developing a practical and reliable high voltage SR solution for LLC-DCX converters. Three main issues are addressed: (1) high voltage sensing; (2) light load effects; (3) accuracy. Novel solutions are proposed for all three issues, and validated with commercial controllers. / Doctor of Philosophy / High voltage power electronics are becoming increasing popular in the electronics industry with the help of wide band-gap semiconductors. While high voltage power electronics research is prevalent, a key component of high voltage power converters, the synchronous rectifier, remains unexplored. Conventional synchronous rectifiers are implemented on high current circuits where diode losses are high. However, high voltage power electronics operate at much lower current levels, necessitating changes in current synchronous rectifier methods. This research aims to identify and tackle issues that will be faced by both systems and IC designers when attempting to implement high voltage synchronous rectifiers on LLC-DCXs. While development takes planes on a LLC-DCX, the research is applicable to most resonant converters and applications utilizing drain-source synchronous rectifier technology. This dissertation focuses primarily on three areas of synchronous rectifier developments: (1) high voltage compatibility; (2) light load effects; (3) accuracy. The first issue opens the gate to high voltage synchronous rectifier research, by allowing high voltage sensing. The second issue explores issues that high voltage synchronous rectifiers can inadvertently influence on the LLC-DCX itself - a light load oscillation issue. The third issue explores novel methods of improving the sensing accuracy to further reduce losses for a single and parallel switch rectifier. In each of these areas, the underlying problem is root-caused, analyzed, and a solution proposed. The overarching goal of this dissertation is to develop a practical, low-cost, universal synchronous rectifier system that can be scaled for commercial use.

This thesis discusses and demonstrates the benefits of simulating and optimising a manufacturing control system in order to improve flow of production material through a system with high variety low volume output requirements. The need for and factors affecting synchronous flow are also discussed along with the consequences of poor flow and various solutions for overcoming it. A study into and comparison of various planning and control methodologies designed to promote flow of material through a manufacturing system was carried out to identify a suitable system to model. The research objectives are; • Identify the best system to model that will promote flow, • Identify the potential failure mechanisms within that system that exist and have not been yet resolved, • Produce a model that can fully resolve or reduce the probability of the identified failure mechanisms having an effect. This research led to an investigation into the main elements of a Drum-Buffer-Rope (DBR) environment in order to generate a comprehensive description of the requirements for DBR implementation and operation and attempt to improve the limitations that have been identified via the research literature. These requirements have been grouped into three areas, i.e.: a. plant layout and kanban controls, b. planning and control, and c. DBR infrastructure. A DBR model was developed combined with Genetic Algorithms with the aim of maximising the throughput level for an individual product mix. The results of the experiments have identified new knowledge on how DBR processes facilitate and impede material flow synchronisation within high variety/low volume manufacturing environments. The research results were limited to the assumptions made and constraints of the model, this research has highlighted that as such a model becomes more complex it also becomes more volatile and more difficult to control, leading to the conclusions that more research is required by extending the complexity of the model by adding more product mix and system variability to compare results with the results of this research. After which it will be expected that the model will be useful to enable a quick system response to large variations in product demand within the mixed model manufacturing industry.

Thesis (MBA)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Similar trading patterns, or so-called herding by institutional investors has interested market participants and academics for some time. Recent international research has established empirical evidence of this phenomenon. The context of this study is to observe evidence of herding by institutional investors in the South African Unit Trust Industry during the period December 1991 to September 1999. Furthermore, it investigates possible relationships between institutional herding and other topics of interest. These include risk profile of funds, market volatility, house view of management companies, size of herd, returns on hypothetical portfolios and on individual shares. Empirical results indicate evidence of herding over the period, albeit at a relatively small level. The average count herding measure of 2,4% is similar to levels recorded in the American Mutual Fund and Pension Fund Industries. A currency imbalance ratio is also used to measure herding, and indicates average levels of herding of 8,3%. This measure is deemed to reflect greater accuracy. as it measures actual currency movements (size of positions) as opposed to number of funds active in a share. On average, herding is present as often on the buy side as on the sell side of the market. Intuition would suggest that as the size of a herd increases (number of funds taking similar positions), the degree of herding increases. Evidence from this study corroborates with an American study, indicating to the contrary. There is a statistically significant negative relationship between the size of a herd and degree of herding. An observation of herding measures relative to the risk profile of funds indicates the presence of a statistically significant positive relationship. Highest levels of herding are recorded in aggressive growth funds and lowest levels in income/growth funds. This supports the rationale that aggressive growth funds, by nature of their investment objective, follow high growth firms. Analysts possess less accurate information regarding future earnings; hence the greater herding levels, for whatever reason. House views, imposed by individual management companies, may also lead to higher herding levels. There is tentative evidence of the presence of this practice, particularly in two of the seven companies observed. The relationship between herding and equity market volatility indicates an interesting phenomenon. There is the presence of a strong positive relationship between quarterly volatility estimates and levels of herding. This relationship changes materially for volatility levels in excess of 9%, indicating the clear presence of a structural breakpoint. For quarterly volatility estimates greater than 9%, the relationship weakens substantially and the slope of the relationship flattens. A quarterly time series of portfolio returns is calculated relative to levels of herding to observe trading strategies practiced by fund managers. The findings indicate weak evidence of funds following positive feedback trading strategies. Furthermore, funds trade in past winners more often than in past losers, indicating the absence of window dressing strategies. There is strong evidence of funds following profit taking strategies at quarterly intervals. The absence of return reversals indicates the absence of over reaction at quarterly intervals. / AFRIKAANSE OPSOMMING: Soortgelyke handelspatrone, of sogenaamde samedromming van institusionele beleggers, is al geruime tyd vir markdeelnemers en akademici van belang. Onlangse internasionale navorsing het empiriese bewys van hierdie fenomeen opgelewer. Hierdie studie is daarop gefokus om bewyse van samedromming deur institisionele beleggers waar te neem, binne konteks van die Suid Afrikaanse Effektetrustbedryf gedurende die periode Desember 1991 tot September 1999. Daar word verder ondersoek ingestel na 'n moontlike verhouding tussen institusionele samedromming en ander onderwerpe van belang. Ingesluit hierby is die risikoprofiel van fondse, markonbestendigheid, 'house view' van bestuursmaatkappye, grootte van die samedromming, opbrengste van hipotetiese portefeuljes en individuele aandele. Empiriese resultate dui aan dat bewyse van samedromming gedurende die relevante periode wel bestaan, alhoewel dit op 'n relatiewe klein skaal plaasvind. Die gemiddelde telling samedrommingsmaatstaf van 2,4% is soortgelyk aan die vlakke waargeneem in die Amerikaanse Mutualfonds en Pensioenfondsbedrywe. 'n Geldeenheid onewewigtigheidsverhouding word ook gebruik as maatstaf van samedromming en dui 'n gemiddelde samedrommingsvlak van 8,3% aan. Die laasgenoemde maatstaf word as meer akkuraat beskou aangesien dit werklike geldeenheidbewegings (grootte van die posisies) reflekteer, in teenstelling met die aantal fondse wat aktief betrokke is by 'n spesifieke aandele. Samedromming is oor die algemeen ewe veel teenwoordig tydens die koop en verkoop van aandele in die mark. Intuïsie dui aan dat soos die grootte van die samedromming toeneem (aantal fondse wat dieselfde posisie inneem), die intensietyd van samedromming ook toeneem. Bewyse van hierdie studie bevestig die bevindinge van 'n Amerikaanse studie wat aandui dat die teenoorgestelde waar is. Statisties gesproke is daar 'n wesenlike negatiewe verhouding tussen die grootte en intensietyd van samedromming. 'n Waarneming van samedrommingsmaatstawwe, relatief tot die risikoprofiel van fondse, dui die teenwoordigheid van 'n statistiese wesenlike positiewe verhouding aan. Die hoogste vlakke van samedromming word waargeneem by aggresiewe groeifondse en die laagste vlakke by inkomste-/groeifondse. Hierdie bevinding staaf die gedagte dat aggresiewe groeifondse, as gevolg van die aard van hul beleggingsdoelwit, hoë groei maatskappye volg. Ontleders beskik oor minder akkurate inligting ten opsigte van toekomstige opbrengs en gevolglik is daar groter samedrommingsvlakke vir watter rede ookal. 'House views', soos voorgeskryf deur individuele bestuursmaatskappye, mag ook tot hoër vlakke van samedromming lei. Voorlopige bewyse ten opsigte van die teenwoordigheid van hierdie praktyk bestaan, veral in twee van die sewe maatskappye waargeneem. Die verhouding tussen samedromming en aandelemarkonbestendigheid reflekteer 'n interessante fenomeen. 'n Sterk positiewe verhouding is teenwoordig tussen kwartaalikse onbestendigheidsskattings en vlakke van samedromming. Hierdie verhouding verander wesenlik vir onbestendigheidsvlakke groter as 9%, wat die teenwoordigheid van 'n strukturele breukpunt duidelik aantoon. 'n Kwartaallikse tydreeks van portefeulje-opbrengste word bereken relatief tot die vlak van samedromming om handelstrategië, soos deur fondsbestuurders toegepas, waar te neem. Bevindinge dui aan dat daar gebrekkige bewyse is van fondse wat positiewe terugvoerstrategië volg. Daar is ook gevind dat fondse meer gereeld handel in gewese wenners as in gewese verloorders wat 'n afwesigheid van uitstallingsstrategië aandui. Daar is besliste bewyse van fondse wat winsbejagstrategië volg met kwartaalikse tussenposes. Die afwesigheid van omgekeerde opbrengste dui die afwesigheid van oorreaksie aan met kwartaalikse tussenposes.

published_or_final_version / Electrical Engineering / Master / Master of Philosophy

<p>This thesis investigates simulation of synchronous machines using a novel Magnetic Equivalent Circuit (MEC) model. The proposed model offers sufficient detail richness for design calculations, while still keeping the simulation time acceptably short.</p><p>Different modeling methods and circuit alternatives are considered. The selected approach is a combination of several previous methods added with some new features. A detailed description of the new model is given. The flux derivative is chosen as the magnetic flow variable which enables a description with standard circuit elements. The model is implemented in dq-coordinates to reduce complexity and simulation time. A new method to reflect winding harmonics is introduced.</p><p>Extensive measurements have been made to estimate the traditional dq-model parameters. These in combination with analytical calculations are used to determine the parameters for the new MEC model.</p><p>The model is implemented using the Dymola simulation program. The results are evaluated by comparison with measurements and FEM simulations. Three different operation cases are investigated; synchronous operation, asynchronous start and inverter fed operation. The agreement with measurements and FEM simulations varies, but it is believed that it can be improved by more work on the parameter determination.</p><p>The overall conclusion is that the MEC method is a useful approach for detailed simulation of synchronous machines. It enables proper modeling of magnetic saturation, and promises sufficiently detailed results to enable accurate loss calculations. However, the experience is that the complexity of the circuits should be kept at a reasonable low level. It is believed that the practical problems with model structure, parameter determination and the simulation itself will otherwise be difficult to master.</p>