Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-05-10T13:29:13Z No. of bitstreams: 1 leticiavasconcellosdesouza.pdf: 334599 bytes, checksum: ecaf1358f31b66f2a2e8740f4db33535 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-06-15T13:12:10Z (GMT) No. of bitstreams: 1 leticiavasconcellosdesouza.pdf: 334599 bytes, checksum: ecaf1358f31b66f2a2e8740f4db33535 (MD5) / Made available in DSpace on 2016-06-15T13:12:10Z (GMT). No. of bitstreams: 1 leticiavasconcellosdesouza.pdf: 334599 bytes, checksum: ecaf1358f31b66f2a2e8740f4db33535 (MD5) Previous issue date: 2015-08-14 / Este trabalho é voltado para professores que atuam nas séries finais do Ensino Fundamental. Tem como objetivo mostrar que é possível introduzir o estudo de Congruência Modular nesse segmento de ensino, buscando facilitar a resolução de diversas situações-problema. A motivação para escolha desse tema é que há a possibilidade de tornar mais simples a resolução de muitos exercícios trabalhados nessa etapa de ensino e que são inclusive cobrados em provas de admissão à escolas militares e em olimpíadas de Matemática para esse nível de escolaridade. Inicialmente é feita uma breve síntese do conjunto dos Números Inteiros, com suas operações básicas, relembrando também o conceito de números primos, onde é apresentado o crivo de Eratóstenes; o mmc (mínimo múltiplo comum) e o mdc (máximo divisor comum), juntamente com o Algoritmo de Euclides. Apresenta-se alguns exemplos de situações-problema e exercícios resolvidos envolvendo restos deixados por uma divisão para então, em seguida, ser dada a definição de congruência modular. Finalmente, são apresentadas sugestões de exercícios para serem trabalhados em sala de aula, com uma breve resolução. / The aims of this work is teachers working in the final grades of elementary school. It aspires to show that it is possible to introduce the study of Modular congruence this educational segment, seeking to facilitate the resolution of numerous problem situations. The motivation for choosing this theme is that there is the possibility to make it simpler to solve many problems worked at this stage of education and are even requested for admittance exams to military schools and mathematical Olympiads for that level of education. We begin with a brief summary about integer numbers, their basic operations, also recalling the concept of prime numbers, where the sieve of Eratosthenes is presented; the lcm (least common multiple) and the gcd (greatest common divisor), along with the Euclidean algorithm. We present some examples of problem situations and solved exercises involving debris left by a division and then, we give the definition of modular congruence . Finally , we present suggestions for exercises to be worked in the classroom, with a short resolution.

Composite materials are multifunctional materials having unique mechanical and physical properties that can be tailored to meet the requirements of a particular application. Aluminium based Metal Matrix Composites (MMC) always draw the attention of researchers due to its unique characteristics such as better strength to weight ratio, low wear rate and lower thermal expansion coefficient. There are various methods for manufacturing of MMC that can be grouped into two major categories: (a) Solid sate method such as powder metallurgy, co-extrusion and (b) Liquid state method such as stir casting. All of these methods for production of composites have their own advantages and disadvantages. Porosity, and poor wettabilty of dispersoids with matrix are few common problems in solid state route. Formations of undesirable phases, and segregation of dispersoids are common problems in liquid state processing route. Friction Stir Processing (FSP) technique, a derivative technique of Friction Stir Welding (FSW) has emerged as a major solid state technique to produce composites. However, there are several challenges associated with it. Most of the past work has been on limited volume of material. Researchers have tried to combine FSP technique with powder metallurgy technique to overcome aforementioned challenges associated with these techniques. Where on one hand, powder metallurgy ensures the uniform dispersion of dispersoids in the matrix, on the other hand FSP on sintered billet removes the pores and other defects. The combination of these two techniques leads to a more controlled and uniform properties. However, at the same time, it can be noted that the combination of these processes is tedious and time consuming. In this study, an attempt is made to achieve bulk dispersion of a second phase into an aluminium matrix using FSP technique. A 5 mm thickness composite is attempted in this work. To achieve this objective proper and uniform mixing of the particles is required. To achieve this, new tools and processing steps are to be designed and analyzed for a better understanding of material flow around the tool pin and the effect of different tool pin geometries on the material flow. Keeping this objective, a detailed study is carried out on material flow during FSW process using aluminium as base metal. A marker material technique is employed to understand the material flow. A strip of copper is selected as the marker material. Material flow can be qualitatively predicted during the process by observing the distribution of marker material in the weld nugget. Three different kinds of tools, each with an additional feature are designed for this purpose (a) Plain frustum shape pin (b) threaded frustum shape pin and, (c) Triflute pin . The material flow due to the plain pin tool can be considered as primary flow during the FSP. Three different kinds of flow zones are observed in the weld nugget in the case of plain tool. It is found that higher numbers of geometrical features (threads and flutes) not only enhance the material flow but also lead to the additional flow currents and more thorough and uniform mixing. A closer study of the weld nugget revealed that the copper marker particles and the matrix were diffusion bonded. Based on the reaction time available and temperature in the weld nugget a diffusion layer thickness of 4 nm is expected between copper and aluminium. However, the diffusion layer thickness was found to be 3.5 μm, which is nearly three orders of magnitude higher. This can be attributed to the enhancement of diffusion due to simultaneous application of strain and temperature. As copper is soluble in the aluminium, an insoluble marker material tin was used for study of flow in the weld nugget. However, the effect of insolubility and lower melting point had some unexpected effect on the processing loads. The normal load during steady state tool traverse in conventional butt-welding is found to be around 2.7 KN while it attains an average value of 14.7 KN when a thin strip of tin is sandwiched between these plates. However, a drop in the torque of around 13.12 NM is observed when tin was sandwiched between the plates as compared to the case when no insert was present. On closer examination of the flow behavior, it is seen that the tin melted, squeezed out and formed a lubricious layer between the tool and the work piece. This reduced the torque significantly and a concomitant drop in temperature was observed. The interaction between the tool and the colder aluminium work piece would thus result in much larger normal and transverse load Based on the expected and unexpected results of flow pattern in the weld nugget, a new FSP tool and processing steps were developed to manufacture MMC. Tungsten, which is the highest melting point metal is chosen as the dispersing phase. Further, as tungsten has high melting point, the kinetics of intermetallics formation would be low for the given FSP processing time at the processing temperature. This would lead to tungsten acting as a more ductile strengthening particle, which is expected to should give some unique characteristics to the MMC. Tungsten powder with an average diameter of 414 nm was dispersed in aluminum matrix with three different proportions after optimizing all the process parameters. It is noted that the mechanical properties are significantly influenced as the tungsten content in the matrix increases. In practice, MMC shows relatively low ductility compared to the parent metal. However in this case the composite exhibited even better ductility than the as received aluminium plates (rolled sheets). The composite showed around 129 MPa of yield strength along with 21% ductility when tungsten content is 3.8 at.%. It is also found that the reaction between aluminum and tungsten occurs during the processing and form the Al12W intermetallic phase. Though the formation of this intermetallic phase was unlikely due to the low temperature and short time available during the process, the reaction kinetics between aluminium and tungsten would have been enhanced due to the simultaneous application of strain and temperature. Given that the metal-metal, tungsten-aluminium composite produced by FSP had unique properties and also formed intermetallics, a study on incorporation of a highly insoluble material, graphite was carried out. Further graphite with its own unique properties and very low wettability with aluminium could possibly impart completely different properties to the system. Past work on graphite aluminium composites produced by other methods did not show promise. As FSP imposes high strains at relatively high flow stresses on the processed material, it was seen that the graphite got sheared to form multi-layer graphene composites with the aluminium. The graphene sheets are formed by mechanical exfoliation of graphite particles during its incorporation in the matrix. The formation of graphene was confirmed after separating the graphite from the processed zone and TEM studies of the composite. It is seen that most of the graphite got converted into multilayer graphene. This aluminium-graphene composite exhibited enhanced ductility and UTS. As received aluminium plates exhibited only 11% ductility and around 100 MPa of UTS while this composite exhibited around 26 % ductility and 147 MPa of UTS. However, there is only a slight improvement in yield strength of this composite.

Die Anforderungen, in vielen Bereichen des Maschinen- und Anlagenbaus immer mehr Leichtbaumaßnahmen zu realisieren, steigen ständig weiter an. Die Umsetzung von Leichtbaukonzepten wird durch den Einsatz neu entwickelter Werkstoffe und Werkstoffsubstitution realisiert. Es steht fest, dass die herkömmlichen Technologien eine weitere Steigerung der Leichtbaupotentiale nicht mehr gewährleisten können. In der vorliegenden Arbeit wurden neue innovative Fertigungstechnologien zur Herstellung von hohlen, MMC und damit massereduzierten Bauteilen entwickelt, die in der Kraftfahrzeugtechnik, Wärmetechnik und Medizin sowie im Maschinenbau Anwendung finden können. Die neuen Gießverfahren beinhalten Fertigungsmethoden auf der Basis des bekannten Niederdruckgießens durch gesteuerte Formfüllung und definierte Abkühlungsbedingungen.

The main circuit equipment in an HVDC station must be rated for continuous operation as well as for stresses during ground faults and other short circuits. The component impedances are thus selected for proper operation during both continuous operation and short circuit events. Normally, Electromagnetic Transient (EMT) simulations are performed for the short circuit current ratings, which can leadto time consuming iterations for the optimization of impedance values. Hence, sufficiently correct and handy formulas are useful. For that reason, in this research work, firstly, a thorough literature study is done to gain a deep understanding of the modular multilevel converter (MMC) and its behaviour after aDC pole-to-pole short circuit fault. Two associated simulation models are designed in PSCAD/EMTDC simulation software. The focus of this thesis is on DC pole-topoleshort circuit in Symmetric Monopole HVDC VSC Modular Multilevel Converter (MMC). The desired analytical expression for the steady state fault current is determined byusing mesh analysis and also by applying KCL and it is verified by doing a set of simulations in PSCAD. A detailed sensitivity study has been done in the PSCAD simulation software to understand the influence of the AC converter reactor inductance and the DC smoothing reactor inductance on the steady state as well as peak fault current respectively. From the sensitivity study, the simulated values of peak factor have been obtained. By means of the ratio in between DC side inductance (L_DC) and AC side inductance (L_AC), and by performing a number of calculations, the desired expression for the peak factor is derived. As a result, the peak fault current can be calculated. The calculated value of the peak fault current from the derived formula is compared to the simulated value and validated. An over-estimation is considered for the rating of the equipment. Along with that, the analysis of the effect of impedances of equipment and systems are done and also verified, to better judge the accuracy of the result. In the result, it is found that, the error margin obtained from the derived analytical expression for the steady state value is within 2% of the PSCAD simulated value, which means the error can be safely ignored. Similarly, the value obtained from the derived formula for the peak fault current is within 4% over-estimation margin of the PSCAD simulated value, which is quite good in terms of cost estimation for the rating of the components.

Gegenstand der Arbeit sind die Modulation, die Modellbildung und die Energiesymmetrierung von modularen Mehrpunktstromrichtern sowie der Aufbau einer Niederspannungs-Modellanlage zum Test von Regelungsverfahren. Die entwickelten Modulationsalgorithmen zeichnen sich durch niedrige Schaltfrequenz, geringe Spannungsunsymmetrie der Submodulspannungen, schnelle Berechnung und verbesserte eingeprägte Spannungen aus -- dank einer dynamisch bevorzugten versetzten Taktung. Zur Klassifizierung von Modulationsverfahren wird hier die Unterscheidung von später und früher Submodulauswahl vorgeschlagen. Der vertiefend betrachtete Fall niedriger Submodulzahlen (n<20) erfordert Verfahren mit früher Submodulauswahl, von diesen werden im weiteren fünf Algorithmen entwickelt, implementiert und experimentell erprobt. Eines der entwickelten Modulationsverfahren nutzt den Freiheitsgrad, der durch Aufteilung der Schaltflanken auf zwei Submodule entsteht, zur Verbesserung der eingeprägten Spannung. Die dabei durchgeführte Analyse unsymmetrischer Submodulspannungen erlaubt die sichere Ausnutzung dieses Freiheitsgrads im gesamten Betriebsbereich auch für andere Modulationsverfahren. Ein bei der Modellbildung der Zweigenergien neu eingenommener Standpunkt führt auf ein Stromrichtermodell, in welchem der Laststrom die Rolle eines zeitabhängigen Parameters annimmt. Das gestattet die getrennte Betrachtung von Stromrichter und Last, was sich vor allem bei der späteren (algebraischen) Parametrierung der Systemgrößen für die planungsbasierte Energieregelung auszahlt. Das Symmetrierungsproblem der Energieregelung wird mit Hilfe des zuvor hergeleiteten Energiemodells aufgegriffen. Im Unterschied zu bekannten Verfahren werden die Fehlerverstärkungen der Energiefehler-Rückführung unter Berücksichtigung der Kopplungen eingestellt, welche durch gemeinsame Nutzung des Kreisstroms entstehen, was die 10-Prozent-Abklingzeit der Energiefehler um 67 Prozent verringert. Für den Fall ohne Aussteuerung der Gleichtaktspannung konnte außerdem die zeitvariante Fehlerdynamik der Energiefehler-Rückführung in eine zeitinvariante Darstellung transformiert werden und erlaubt damit erstmals globale Stabilitätsaussagen und eine effiziente Optimierung der Polkonstellation. Eine neuartige planungsbasierte Energieregelung verbessert die Symmetrierung mit Hilfe einer Vorsteuerung, die schon während der Überführungen zu neuen Arbeitsregimes eine Verringerung der Kondensatorspannungsschwankungen erreicht. Der Aufwand der Steuerungsberechnung konnte deutlich reduziert werden, und zwar zum einen durch Aufnahme der vertikalen Energiedifferenz in die vorgegebenen Energien, und zum anderen durch die Konstruktion von Überführungen, deren Parameter vorteilhaft voneinander unabhängige Rollen einnehmen. Bei dieser Aufgabe erlaubt das hergeleitete Stromrichtermodell die bequeme Vorgabe von vier der sechs Stromrichterenergien, sodass nur zwei durch Integration bestimmt werden brauchen, was der bisher niedrigsten bekannten Ordnung für dieses Problem entspricht. Die entwickelte Steuerung reduziert die Kondensatorspannungsschwankungen und entlastet die Energiefehler-Rückführung von der Überführungsaufgabe, wie die für die Messung durchgeführte Implementierung zeigt. Ein Parametervergleich der aufgebauten Modellanlage mit typischen Mittelspannungs-M2Cs belegt die besonders gute Nachbildung der für die Energieregelung relevanten Verhältnisse im Vergleich zu anderen Modellanlagen.:I Untersuchungen zum M2C 1 Einleitung 2 Modulationsverfahren 2.1 Einleitung 2.2 Modulationsverfahren der Modellanlage 2.2.1 Eigenschaften der Modulation der Modellanlage 2.2.2 Algorithmus 1 2.2.3 Algorithmus 2 2.2.4 Algorithmus 3 2.2.5 Algorithmus 4 2.2.6 Besonderheiten bei Modulation mit zwei taktenden Modulen 2.2.7 Algorithmus 5 2.3 Vergleich der Algorithmen 2.3.1 Schaltfrequenz 2.3.2 Symmetrierung 2.3.3 Eingeprägte Spannung 2.3.4 Spektrum der Gleich- und Wechselspannung 2.3.5 Rechenzeit 2.4 Zusammenfassung 3 Modellbildung 3.1 Modellierung der Submodule und deren Reihenschaltung 3.2 Simulationsmodell zur Berücksichtigung eines unsymmetrischen Aufbaus 3.3 Modellbildung für den Regelungsentwurf 3.3.1 Anwendung von Ersatzsubmodulen für den Regelungsentwurf 3.3.2 Überblick zum weiteren Vorgehen 3.3.3 Vereinfachungen bei symmetrischem Aufbau 3.3.4 Dreiphasige und einphasige Betrachtung mittels Stromquellenlast 3.3.5 Transformation in Summe und Differenzen 3.3.6 Transformation in Energien 3.3.7 Energiegrößen für die dreiphasige Schaltung 3.4 Stationäre Lösungen der dreiphasigen Schaltung 3.4.1 Kreisstromfreier Betrieb ohne Gleichtaktspannung 3.4.2 Kreisstromfreier Betrieb mit triplen harmonic injection 3.4.3 Betrieb mit zweiter Harmonischer im Kreisstrom 3.4.4 Betrieb ohne Auslenkung der komplexen Summenenergie 3.4.5 Vergleich zweier Kreisstromformen zur Reduktion der Spannungsschwankung 3.5 Zusammenfassung der Eigenschaften des Modells und der Herleitung 4 Beiträge zur Regelung eines M2Cs 4.1 Überblick über Symmetrierungslösungen 4.2 Rückführung der Energiefehler auf den Kreisstrom 4.2.1 Fehlerdynamik 4.2.2 Einstellung der Fehlerverstärkungen bei vernachlässigter Kopplung 4.2.3 Simulation der Fehlerdynamik und des gesamten Stromrichters 4.2.4 Einstellung der Fehlerverstärkungen anhand von Eigenwerten 4.2.5 Einstellung der Fehlerverstärkungen bei Aussteuerung der Gleichtaktspannung 4.2.6 Anpassung der Einstellungen an veränderte Parameter 4.2.7 Zusammenfassung der untersuchten Einstellungen 4.3 Planungsbasierte Optimierung der Symmetrierung 4.3.1 Grundidee 4.3.2 Berechnung der Systemgrößen 4.3.3 Trajektorienplanung für die Last 4.3.4 Trajektorienplanung für den M2C 4.3.5 Berechnung des verbleibenden Parameters 4.3.6 Verbesserung des Verlaufs der Gleichtaktspannung 4.3.7 Messergebnisse 4.3.8 Zusammenfassung 5 Zusammenfassung des ersten Teils II Modellanlage mit M2C 6 Eigenschaften der Modellanlage 6.1 Besonderheiten beim Test von Regelungsverfahren 6.2 Schutzfunktionen 6.3 Dimensionierung der Komponenten 6.3.1 Berechnung des Energiehubs der Kondensatoren 6.3.2 Einfluss der Induktivität der Zweigdrossel 6.3.3 Dimensionierung der Zweigdrossel 6.3.4 Abschätzung und Simulation der ohmschen Verluste und der Halbleiterverluste 6.3.5 Verluste der Submodulkondensatoren 6.3.6 Entwärmung der Leistungshalbleiter 6.3.7 Berechnung der mindestens notwendigen Gleichspannung 6.3.8 Berechnung der maximal bereitzustellenden Zweigspannung 6.4 Vergleich von Modellanlagen mit Mittelspannungs-M2Cs 7 Zusammenfassung des zweiten Teils / The thesis deals with the modulation, the modeling and the energy balancing of modular multilevel converters as well as the construction of a low-voltage test bench for the experimental evaluation. The proposed modulation algorithms offer low switching frequency, small cell voltage imbalance, fast calculation, and improved injected voltages thanks to the idea of inherited polarity. In order to classify modular multilevel converter modulation schemes a distinction between early and late cell selection is proposed. The further investigation focuses on modulation for a small number of cells per arm (n<20) for which early selection is advantageous. Five such methods are developed, implemented and tested experimentally on a test bench. The injected voltage was improved by exploiting a degree of freedom that arises when the positive and negative edges are assigned to two cells instead of one cell. A corresponding analysis of the inherent deviations between the cell voltages enables reliable exploitation of the degree of freedom without endangering correct termination of the algorithm. The proposed arm energy modeling results in a converter model that incorporates the load current as time varying parameter and enables a beneficial separation of converter model and load model that eases trajectory planning for both. The energy balancing problem of modular multilevel converters is tackled by means of the derived arm energy model. In comparison to known approaches, the tuning scheme takes into account the coupling caused by the different circulating current frequency components and reduces the 10 percent decay-time by 67 percent. In case of zero common mode voltage a transformation of the time-variant error dynamics of the energy balancing feedback into a time-invariant form enables global stability proof and efficient eigenvalue optimization. A novel energy balancing approach based on trajectory planning and feed-forward circulating current enables a balanced operation even during transfers between operating regimes. In contrast to the classic approach of specifying circulating current components and common-mode voltage, four out of six (transformed) arm energies are specified in order to identify balanced transfers between operating regimes. The calculation cost for obtaining consistent energy references has been reduced by specifying candidate trajectories even for the vertical difference energy, and by using candidate trajectories whose parameters are responsible for independent tasks. Thus, only two energies remain that need to be determined via integration during the planning procedure. This is the lowest known order of the system to be integrated. As a benefit of this approach, no balancing error remains, i.e. the task of the balancing feedback is reduced to compensating parameter uncertainties and disturbances. The proposed energy references improve the cell voltage balance and relieves the feedback based energy balancing from the large signal transfer task. The LC-circuit of the cell capacitors and the arm inductor of the low-voltage test bench features a similar resonant frequency as reported for typical medium-voltage designs as a survey of other low-voltage test benches reveal.:I Untersuchungen zum M2C 1 Einleitung 2 Modulationsverfahren 2.1 Einleitung 2.2 Modulationsverfahren der Modellanlage 2.2.1 Eigenschaften der Modulation der Modellanlage 2.2.2 Algorithmus 1 2.2.3 Algorithmus 2 2.2.4 Algorithmus 3 2.2.5 Algorithmus 4 2.2.6 Besonderheiten bei Modulation mit zwei taktenden Modulen 2.2.7 Algorithmus 5 2.3 Vergleich der Algorithmen 2.3.1 Schaltfrequenz 2.3.2 Symmetrierung 2.3.3 Eingeprägte Spannung 2.3.4 Spektrum der Gleich- und Wechselspannung 2.3.5 Rechenzeit 2.4 Zusammenfassung 3 Modellbildung 3.1 Modellierung der Submodule und deren Reihenschaltung 3.2 Simulationsmodell zur Berücksichtigung eines unsymmetrischen Aufbaus 3.3 Modellbildung für den Regelungsentwurf 3.3.1 Anwendung von Ersatzsubmodulen für den Regelungsentwurf 3.3.2 Überblick zum weiteren Vorgehen 3.3.3 Vereinfachungen bei symmetrischem Aufbau 3.3.4 Dreiphasige und einphasige Betrachtung mittels Stromquellenlast 3.3.5 Transformation in Summe und Differenzen 3.3.6 Transformation in Energien 3.3.7 Energiegrößen für die dreiphasige Schaltung 3.4 Stationäre Lösungen der dreiphasigen Schaltung 3.4.1 Kreisstromfreier Betrieb ohne Gleichtaktspannung 3.4.2 Kreisstromfreier Betrieb mit triplen harmonic injection 3.4.3 Betrieb mit zweiter Harmonischer im Kreisstrom 3.4.4 Betrieb ohne Auslenkung der komplexen Summenenergie 3.4.5 Vergleich zweier Kreisstromformen zur Reduktion der Spannungsschwankung 3.5 Zusammenfassung der Eigenschaften des Modells und der Herleitung 4 Beiträge zur Regelung eines M2Cs 4.1 Überblick über Symmetrierungslösungen 4.2 Rückführung der Energiefehler auf den Kreisstrom 4.2.1 Fehlerdynamik 4.2.2 Einstellung der Fehlerverstärkungen bei vernachlässigter Kopplung 4.2.3 Simulation der Fehlerdynamik und des gesamten Stromrichters 4.2.4 Einstellung der Fehlerverstärkungen anhand von Eigenwerten 4.2.5 Einstellung der Fehlerverstärkungen bei Aussteuerung der Gleichtaktspannung 4.2.6 Anpassung der Einstellungen an veränderte Parameter 4.2.7 Zusammenfassung der untersuchten Einstellungen 4.3 Planungsbasierte Optimierung der Symmetrierung 4.3.1 Grundidee 4.3.2 Berechnung der Systemgrößen 4.3.3 Trajektorienplanung für die Last 4.3.4 Trajektorienplanung für den M2C 4.3.5 Berechnung des verbleibenden Parameters 4.3.6 Verbesserung des Verlaufs der Gleichtaktspannung 4.3.7 Messergebnisse 4.3.8 Zusammenfassung 5 Zusammenfassung des ersten Teils II Modellanlage mit M2C 6 Eigenschaften der Modellanlage 6.1 Besonderheiten beim Test von Regelungsverfahren 6.2 Schutzfunktionen 6.3 Dimensionierung der Komponenten 6.3.1 Berechnung des Energiehubs der Kondensatoren 6.3.2 Einfluss der Induktivität der Zweigdrossel 6.3.3 Dimensionierung der Zweigdrossel 6.3.4 Abschätzung und Simulation der ohmschen Verluste und der Halbleiterverluste 6.3.5 Verluste der Submodulkondensatoren 6.3.6 Entwärmung der Leistungshalbleiter 6.3.7 Berechnung der mindestens notwendigen Gleichspannung 6.3.8 Berechnung der maximal bereitzustellenden Zweigspannung 6.4 Vergleich von Modellanlagen mit Mittelspannungs-M2Cs 7 Zusammenfassung des zweiten Teils

The Modular Multilevel Converter (MMC) is one of the most commonly used active converters in the high-/medium-voltage sector due to its many advantages such as high scalability, high efficiency, modularity and low harmonic contents. However, in low-voltage and high-current applications, classical MMC designs are not very economical. Recently there has been interest in a new design of modular multilevel converter with interleaved submodules (ISM-MMC) capable of using lower cost, lower current switches. The aim of this study is to compare several different design configurations for a given ISM-MMC topology including classical MMC and to give the best design approach taking into account the efficiency and energy density of the system. The power loss of ISM-MMC influence the final efficiency. The loss studied in this thesis mainly consists of conduction losses and switching losses in the semiconductor devices and inductor losses. An analytical calculation method is summarized and validated by the simulation result. The simulation result is carried out in PLECS model with different system components. Power density is determined by the output power and the converter dimension. The volume of semiconductor devices and passive components determine the general dimension of the converter. This thesis discusses the selection of semiconductor devices, inductor and capacitor in the system, with semiconductor devices constraining interleaved leg current and submodule voltage, inductor constraining output current ripple and capacitor constraining capacitor voltage fluctuation. After the specific components are designed, their dimensions are evaluated, and thus the power density of different configurations can be compared. / Den modulära multinivåomvandlaren (modular multilevel converter, MMC) är en av de mest använda aktiva omvandlarna inom hög-/mellanspänningssektorn på grund av dess många fördelar som hög skalbarhet, hög verkningsgrad, modularitet och lågt övertonsinnehåll. Men i lågspännings- och högströmsapplikationer är konventionella MMC-konstruktioner inte särskilt ekonomiska. Nyligen har det funnits intresse för en ny design av modulär flernivåomvandlare med interfolierade submoduler (ISM-MMC) som kan uppnå lägre kostnad, och använda mindre halvledarelement. Syftet med denna studie är att jämföra flera olika designkonfigurationer för en given ISM-MMC-topologi inklusive konventionell MMC och att ge den bästa designmetoden med hänsyn till systemets verkningsgrad och energitäthet. Effektförlusten för ISM-MMC påverkar den slutliga verkningsgraden. Förluster som studeras i denna avhandling består huvudsakligen av ledningsförluster och kopplingsförluster i halvledarenheterna och induktorförluster. En analytisk beräkningsmetod sammanfattas och valideras av simuleringsresultatet. Simuleringsresultatet utförs men en PLECS-modell med olika systemkomponenter. Effekttätheten bestäms av uteffekten och omvandlardimensionen. Volymen av halvledarenheter och passiva komponenter bestämmer omvandlarens allmänna dimension. Denna avhandling diskuterar valet av halvledarenheter, induktor och kondensator i systemet, med halvledarenheter som begränsar interfolierad benström och submodulspänning, induktor som begränsar utströmsrippel och kondensatorbegränsande kondensatorspänningsfluktuationer. Efter att de specifika komponenterna har valts utvärderas deras storlek, och därmed kan effekttätheten för olika konfigurationer jämföras.

[pt] O objetivo deste estudo foi desenvolver compósitos à base de uma liga de AlSi (Alumix-231) com adição de 5 a 20 vol. por cento de sílica fundida, no intuito de reduzir o coeficiente de expansão térmica (CET), com relação ao da matriz, e manter as propriedades físicas do compósito, tais como densidade e dureza, ao menos no nível da matriz. Os compósitos foram desenvolvidos pela metalurgia do pó, primeiramente, prensados a 700 MPa e depois sinterizados em temperaturas entre 565 e 575 graus C por 90 min (condição T1). Os melhores resultados, em termos de redução da expansão térmica, foram alcançados após a sinterização a 565 graus C. Os compósitos com adição de 15 e 20 vol.por cento de sílica fundida exibiram coeficientes de expansão térmica tão baixos quanto 13,70 e 12,73 x 10(-6) graus C(-1) (entre 25 e 400 graus C), uma redução de 29,9 por cento e 34,8 por cento, respectivamente, em comparação com Alumix231 pura. Além disso, a densidade e a dureza desses compósitos não foram muito afetadas negativamente, pois sofreram apenas uma pequena diminuição, não superior a 6 por cento e 5 por cento, respectivamente. Em seguida, amostras sinterizadas a 565 graus C foram envelhecidas artificialmente a 160 graus C por 8 h (condição T6) e os Compósitos de Matriz Metálica (CMMs) com 15 e 20 vol. por cento de sílica fundida exibiram um aumento da dureza, cerca de 94,12 por cento e 64,71 por cento, respectivamente, em relação às amostras análogas na condição T1. Com relação à expansão térmica, houve redução dos CETs, em comparação com a liga pura envelhecida, de 27 por cento e de 32 por cento, respectivamente. Alumix-231 é uma nova e promissora liga e a sílica fundida, que nunca foi usada antes com o objetivo de reduzir sua expansão térmica, demonstrou ser uma cerâmica com aplicações promissoras como carga em compósitos de matrizes à base de Alumix-231 devido à sua expansão térmica próxima de zero e à sua baixa densidade. Como tal, os resultados obtidos mostraram que os compósitos de Alumix-231/sílica fundida são materiais potencialmente promissores para aplicações automotivas, candidatos a substituírem o ferro fundido (alta densidade, de 7,3 a 7,9 g cm(-3) , e CET de 13 x 10(-6) graus C(-1)). / [en] The goal of this study was to develop composites based on an Al-Si alloy (Alumix-231) with the addition of 5 to 20 vol. percent of fused silica, to reduce the coefficient of thermal expansion (CTE) in comparison to that of the matrix (Alumix-231), keeping the composite light and without impairing its physical properties, such as density and hardness. The composites were developed by powder metallurgy, first pressed at 700 MPa, and then sintered at temperatures between 565 and 575 degrees C for 90 min (T1 condition). The best results, in terms of reduced thermal expansion, were achieved after liquiq-phase sintering at 565 degrees C. Composites with the addition of 15 and 20 vol. percent of fused silica exhibited CTEs, as low as, 13.70 and 12.73 x 10(-6) degrees C(-1) (between 25 and 400 degrees C), a reduction of 29.9 percent and 34.8 percent, respectively, compared to neat Alumix-231. Furthermore, the density and hardness of these composites were not negatively affected, as these properties presented only a small decrease, not exceeding 6 percent and 5 percent, respectively. Then, samples sintered at 565 degrees C were artificially aged at 160 degrees C for 8 h (T6 condition), and MMCs-15 and 20 vol. percent exhibited an increase in hardness of about 94,12, percent and 64,71 percent, compared to T1 samples. Regarding thermal expansion, there was a reduction of CTEs, compared to the aged neat alloy, of 27 percent and 32 percent, respectively. Alumix-231 is a promising new alloy and fused silica, which has never been used before to reduce its thermal expansion, has shown to be a ceramic with promising applications as a filler in Alumix-231-based matrix composites, due to its thermal expansion close to zero. As such, the results obtained showed that Alumix231/fused silica composites are promising materials for automotive applications and new candidates to replace heavy cast iron components.

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This thesis provides insight into state-of-the-art Modular Multilevel Converters (MMC) for medium and high voltage applications. Modular Multilevel Converters have increased in interest in many industrial applications, as they offer the following advantages: modularity, scalability, reliability, distributed location of capacitors, etc. In this study, the modeling, control and design considerations of modular based multilevel converters, with an emphasis on the reliability of the converter, is carried out. Both modular multilevel converters with half-bridge and full-bridge sub-modules are evaluated in order to provide a complete analysis of the converter. From among the family of modular based hybrid multilevel converters, the newly released Alternate Arm Converter (AAC) is considered for further assessment in this study. Thus, the modular multilevel converter with half-bridge and full-bridge power cells and the Alternate Arm Converter as a commercialized hybrid structure of this family are the main areas of study in this thesis. Finally, the DC fault analysis as one of the main issues related to conventional VSC converters is assessed for Modular Multilevel Converters (MMC) and the DC fault ride-through capability and DC fault current blocking ability is illustrated in both the Modular Multilevel Converter with Full-Bridge (FB) power cells and in the Alternate Arm Converter (AAC). Accordingly, the DC fault control scheme employed in the converter and the operation of the converter under the fault control scheme are explained. The main contributions of this study are as follows: The new D-Q model for the MMC is proposed for use in the design of the inner and outer loop control. The extended control scheme from the modular multilevel converter is employed to control the Alternate Arm Converters. A practical reliability-oriented sub-module capacitor bank design is described based on different reliability modeling tools. A Zero Current Switching (ZCS) scheme of the Alternate Arm Converter is presented in order to reduce the switching losses of the Director Switches (DS) and, accordingly, to implement the ZCS, a design procedure for the Arm inductor in the AAC is proposed. The capacitor voltage waveform is extracted analytically in different load power factors and the waveforms are verified by simulation results. A reliability-oriented switching frequency analysis for the modular multilevel converters is carried out to evaluate the effect of the switching frequency on the MMC's operation. For the latter, a DC fault analysis for the MMC with Full-Bridge (FB) power cells and the AAC is performed and a DC fault control scheme is employed to provide the capacitor voltage control and DC fault current limit, and is illustrated herein. / Master of Science