Durch Umwandlung unterschiedlichster Formen von Energie in mechanische oder elektrische Energie wird die Menschheit seit Jahrhunderten bei der Umsetzung von Arbeitsprozessen im Alltag und bei der industriellen Nutzung unterstützt. Strömende Medien wie Wasser oder Wind gelten dabei als die ältesten Energielieferanten. Im Rahmen der Dissertation wird das Konzept einer zugspannungsverankerten Plattform für Offshore Windenergieanlagen (WEA) vorgestellt, wobei neben den, für diesen Plattformtyp typischen, vertikalen auch geneigte Verankerungselemente Verwendung finden. Diese Art der Verspannung einer zugspannungsverankerten Plattform, respektive ’Tension Leg Platfrom’ (TLP) ist bisher von keiner Quelle bekannt und stellt ein Alleinstellungsmerkmal dar. Folglich sollen Untersuchungen zum dynamischen Verhalten schwimmender Gründungen für Offshore WEA, im Speziellen zu einer TLP mit vertikalen und geneigten Ankerelementen, im Rahmen dieser Arbeit erstmalig vorgestellt werden. Die Plattform ist ein modular gestaltetes Tragwerk bestehend aus großen Rohren und mit integrierten zylindrischen Auftriebskörpern. Diese erzeugen im Transportzustand der Plattform vom Hafen zum Einsatzort und im Betriebszustand innerhalb eines Windparks den nötigen Auftrieb. Infolge der speziellen Art der Verspannung werden die Bewegungen der TLP durch die, aus den Belastungen resultierenden, Seildehnungen dominiert. Damit stellte die TLP im Vergleich zu anderen schwimmenden Gründungen ein bewegungsarmes System dar. Inhalt der hier vorgelegten Arbeit sind Untersuchungen zum dynamischen Verhalten schwimmender Offshoregründungen, im speziellen einer TLP für Windenergieanlagen. Es wurden unterschiedliche Tragstrukturen für TLP-Systeme entwickelt und im Rahmen von Modellversuchen getestet. Den Kern der Arbeit bildet der Vergleich des dynamischen Tragverhaltens der unterschiedlichen Plattformen unter Berücksichtigung der geometrischen und strukturellen Randbedingungen.

The integration of dispatchable renewable energies like biomass, geothermal and reservoir hydro technologies into an electrical network present no greater challenge than the integration of conventional power technologies for which are well understood by Eskom engineers. However, renewable energies that are based on resources that fluctuate throughout the day and from season to season, like wind and solar, introduce a number of challenges that Eskom engineers have not dealt with before. It is current practice for Eskom‟s generation to follow the load in order to balance the demand and supply. Through Eskom‟s load dispatching desk at National Control, generator outputs are adjusted on an hourly basis with balancing reserves making up only a small fraction of the total generation. Through the Integrated Resource Plan for Electricity of 2010, the Department of Energy has set some targets towards integrating renewable energy, including wind and solar generation, into the South African electricity market consequently introducing variability on the supply side. With demand that varies continually, maintaining a steady balance between supply and demand is already a challenging task. When the supply also becomes variable and less certain with the introduction of non-dispatchable renewable energy, the task becomes even more challenging. The aim of this research study is to determine whether the resources that previously helped to balance the variability in demand will still be adequate to balance variability in both demand and supply. The study will only concentrate on variable or non-dispatchable renewable energies as will be added to the South African electrical network according to the first two rounds of the Department of Energy‟s Renewable Energy Independent Power Producer Procurement Programme. This research study only looks into the balancing challenge and does not go into an analysis of voltage stability or network adequacy, both of which warrant in depth analysis. / Thesis (MIng (Development and Management Engineering))--North-West University, Potchefstroom Campus, 2013.

The integration of dispatchable renewable energies like biomass, geothermal and reservoir hydro technologies into an electrical network present no greater challenge than the integration of conventional power technologies for which are well understood by Eskom engineers. However, renewable energies that are based on resources that fluctuate throughout the day and from season to season, like wind and solar, introduce a number of challenges that Eskom engineers have not dealt with before. It is current practice for Eskom‟s generation to follow the load in order to balance the demand and supply. Through Eskom‟s load dispatching desk at National Control, generator outputs are adjusted on an hourly basis with balancing reserves making up only a small fraction of the total generation. Through the Integrated Resource Plan for Electricity of 2010, the Department of Energy has set some targets towards integrating renewable energy, including wind and solar generation, into the South African electricity market consequently introducing variability on the supply side. With demand that varies continually, maintaining a steady balance between supply and demand is already a challenging task. When the supply also becomes variable and less certain with the introduction of non-dispatchable renewable energy, the task becomes even more challenging. The aim of this research study is to determine whether the resources that previously helped to balance the variability in demand will still be adequate to balance variability in both demand and supply. The study will only concentrate on variable or non-dispatchable renewable energies as will be added to the South African electrical network according to the first two rounds of the Department of Energy‟s Renewable Energy Independent Power Producer Procurement Programme. This research study only looks into the balancing challenge and does not go into an analysis of voltage stability or network adequacy, both of which warrant in depth analysis. / Thesis (MIng (Development and Management Engineering))--North-West University, Potchefstroom Campus, 2013.

Transportation and installation of offshore wind turbines (Tower, Nacelle and Rotor) is a complete process conducted over several phases, usually in sequence. There are several factors that can turn this process into a challenge. These factors can either be due to offshore site conditions or the technical limitations of the installation vessels. Each project has its own characteristic parameters and requires a unique optimum solution. This paper identifies the dynamics of the installation process and analyzes the effects of each phase on the progression of events.The challenges in wind turbine installations due to offshore environment were investigated, the effects of each were explained and their significances were stressed. Special installation vessels were examined and their technical specifications were analyzed in terms of working conditions, dimensions, service performances, and crane capacities as well as projecting future design trends. Several offshore wind farm projects were analyzed; their installation methods were specified, and compared to each other to determine advantages and disadvantages of different pre-assembly concepts. The durations of the sub-phases of the process were defined in terms of different variables such as site conditions and individual vessel performance. These definitions were used for making time estimations, and conducting further analyses regarding the effects of different site specific parameters on the overall project duration.In conclusion, this study considered the main operation parameters in an offshore wind turbine installation context: the benefits and drawbacks of different pre-assembly methods were researched and evaluated resulting in new knowledge and a productive contribution for optimizing “the offshore turbine transportation and installation process”, based on actual time usage.

Στις μέρες μας το ενεργειακό πρόβλημα αποτελεί ένα από τα σπουδαιότερα προβλήματα του πλανήτη, το οποίο μαζί με την ραγδαία κλιματική αλλαγή οδηγούν στην ανάγκη για παραγωγή ηλεκτρικής ενέργειας με όσο πιο οικονομικό αλλά και φιλικό με το περιβάλλον τρόπο. Συνεπώς οι Ανανεώσιμες Πηγές Ενέργειας και κυρίως η αιολική ενέργεια αποκτούν σπουδαίο ρόλο στο στόχο αυτό και αλλάζουν άρδην τόσο τον Ευρωπαϊκό όσο και τον Παγκόσμιο ενεργειακό χάρτη. Στην παρούσα διπλωματική εργασία μελετάμε μια διάταξη ανεμογεννήτριας, η οποία αποτελείται από μια σύγχρονη μηχανή μόνιμου μαγνήτη (PMSG), από έναν μετατροπέα συχνότητας (back-to-back converter) και από ένα R-L φίλτρο στην πλευρά του δικτύου. Επιπλέον, η απουσία μηχανικών εξαρτημάτων στην σύγχρονη μηχανή μόνιμου μαγνήτη (PMSG), όπως δακτυλίων ολισθήσεως και ψηκτρών, την κάνει, ελαφρότερη, με υψηλότερο λόγο ισχύος προς βάρος γεγονός που της προσδίδει μεγαλύτερη αποδοτικότητα και αξιοπιστία. Λόγω των προαναφερθέντων πλεονεκτημάτων, η σύγχρονη μηχανή με μόνιμο μαγνήτη (PMSG) αποτελεί μια ελκυστική λύση για τα αιολικά συστήματα. Σκοπός λοιπόν αυτής της εργασίας είναι να μελετήσουμε το πλήρες σύστημα της ανεμογεννήτριας στο d-q στρεφόμενο σύστημα κάθετων αξόνων μέσω του μετασχηματισμού Park και να εφαρμόσουμε την κατάλληλη μεθοδολογία ελέγχου ούτως ώστε να επιτύχουμε μέγιστη απομάστευση ισχύος από τον άνεμο με ταυτόχρονη ρύθμιση της τάσης της dc διασύνδεσης αλλά υπό μοναδιαίο συντελεστή ισχύος για την πλευρά του δικτύου. Τέλος, προσομοιώνουμε το πλήρες σύστημα με το Simulink του Matlab και στη συνέχεια παρουσιάζουμε τις αποκρίσεις των προσομοιώσεων και εξάγουμε συμπεράσματα. / Nowadays the energy problem is one of the most important global problems, which together with the rapid climate change lead to the need for power generation as more economical and environmentally friendly way. Therefore, the Renewable Energy Sources and especially wind power have a great role in this objective and radically change both the European and the global energy map. In this thesis we consider a wind turbine device, which comprises a permanent magnet synchronous machine (PMSG), a frequency converter (back-to-back converter) and an R-L filter on the grid side. Thus, the absence of mechanical parts in permanent magnet synchronous machine (PMSG), as sliding rings and brushes, to make, lighter, with a higher power to weight ratio which gives greater efficiency and reliability. Due to the above advantages, the permanent magnet synchronous machine (PMSG) is an attractive solution for the wind. Aim of this thesis is to study the complete wind turbine system in the d-q rotating vertical axes system through the Park transformation and to apply the appropriate control methodology in order to achieve maximum energy harvesting from the wind, with a simultaneous control of the dc link voltage under unit power factor for the grid side. Finally, we simulate the complete system with the Matlab Simulink and then we present simulations of the responses and draw conclusions.

This work presents the coupling between two different formulations applied to flow simulation and analysis of wind rotors, integral and differential formulations. First, for the integral formulation is defined a control volume where the variables problem are defined, as well as the necessaries working hypothesis, then a proposed mathematical modeling is defined. Simulations through NACA airfoils, using Computational Dynamic Fluids, are performed in order to evaluate drag and lift coefficients, to be used in the integral formulation. The Navier-Stokes equations are solved in house and the Smagorinsky turbulence model with Van Driest damping function is retained. The computational code is implemented with structured cartesian mesh, where the airfoil is modeled using the Immersed Boundary Methodology. The results of simulation through a NACA0012 airfoil are shown for several attack angles and Re = 10000. Results of energetic efficiency are presented for a horizontal axis wind turbine using the integral formulation, where the coefficients are given by differential formulations. / Este trabalho apresenta o acoplamento entre as duas formulações diferentes aplicadas à simulação do escoamento e análise de rotores eólicos, formulações integral e diferencial. Primeiramente para a formulação integral é definido um volume de controle onde as variáveis do problema são definidas, bem como as hipóteses simplificadoras necessárias, para então ser proposta uma modelagem matemática. Simulações do escoamento em aerofólios NACA, utilizando Dinâmica dos Fluidos Computacional, são realizadas a fim de determinar os coeficientes de arrasto e sustentação, os quais foram utilizados na formulação integral. As equações de Navier-Stokes são resolvidas em um código computacional e o modelo de turbulência de Smagorinsky com função de amortecimento de Van Driest é utilizado. O código computacional é implementado com uma malha cartesiana estruturada, e o aerofólio é modelado utilizando a Metodologia da Fronteira Imersa. Os resultados da simulação através de um aerofólio NACA0012 são mostrados para vários ângulos de ataque e Re = 10000. Os resultados de eficiência energética são apresentados para uma turbina eólica de eixo horizontal utilizando a formulação integral, onde os coeficientes são dados pelas formulações diferenciais. / Mestre em Engenharia Mecânica

The popularity of distributed generating (DG) sources have been increasing over the past few years. With the increasing penetration of these DGs, the concept of micro grid is becoming popular. A micro grid is a small power system network with distributed generating sources which can operate seamlessly irrespective of the presence of the utility grid. Operating the micro grid in this manner increases system reliability and reduces power interruptions. However, it introduces several control challenges. This thesis aims at analysing the behaviour of a micro grid system during the transition between grid connected mode and islanded mode of operation and address the control challenges through novel schemes. With the presence of grid, the micro grid system variables, such as voltage and frequency, are strictly regulated by the grid. The local sources follow the voltage and frequency reference set by the grid and supply constant power. With the loss of grid, that is when the system is islanded, the network variables need to be regulated by the local sources. The control structures for the inverter-based sources during the two operating modes are detailed in the present work. With the loss of grid, the system should be able to transfer seamlessly to islanded mode without any transients. Similarly, when the grid supply is restored, the micro grid should seamlessly resynchronize to the grid without any transients. This thesis proposes two novel controller schemes for achieving seamless transfer between grid-connected and islanded mode in micro grids. The rst scheme uses an output feedback topology to reduce the transitions during mode transfer. The second scheme uses a Linear Quadratic Regulator (LQR) theory based compensator to achieve seamless transfer. The performance of the proposed schemes have been validated through simulations on a benchmark micro grid network for various operating conditions. An experimental micro grid set-up is developed with a single inverter based DG source. The droop control scheme for islanded mode of operation has been validated on hardware.

The growing demand for power and increased environmental concerns gave an impetus to the growth of clean and renewable energy sources like wind, solar etc. There is a remarkable increase in the penetration of wind energy systems in the last decade and this trend is bound to increase at a much faster pace in future. This ever increasing penetration of wind power generating systems pose multi-fold challenges related to operational and stability aspects of the grid. Present day wind energy systems mostly comprise of variable speed wind generators. A large fraction of present day variable speed wind turbine generators use doubly fed induction machine (DFIM). This thesis deals with modeling and grid coordination aspects of variable speed wind gener- ators. In particular, the short coming of the existing steady state equivalent circuit of a DFIM is identified and subsequently, an accurate equivalent circuit of a DFIM is proposed. Relevant mathematical basis for the proposed model is presented. The proposed steady state equivalent circuit of a doubly fed induction machine is further validated using dynamic simulations of a standalone machine. Based on the proposed equivalent circuit, two approaches for computing the initial values of state variables of a DFIM is proposed. The first approach is a linear formulation where the losses due to resistance of the stator and rotor windings are neglected. The second approach is a non-linear formulation which takes the losses into consideration. Further, analysis is carried out on grid connected doubly fed induction generators (DFIG). A framework to incorporate DFIG based variable speed wind farms in the steady state power flow analysis is proposed. The proposed framework takes into consideration important aspects such as voltage dependent reactive power limits and mode of reactive power control of associated converters. Some of the challenges in a grid connected DFIG especially during su- persynchronous mode of operation are identified. The advantages of a non-Maximum Power Point Tracking (MPPT) mode of operation under certain operating conditions is highlighted. Finally, aspects pertaining to coordination of grid connected variable speed wind generators are studied. A trust region framework to determine the reference values to the control loops of converters in a variable speed wind generator is proposed. The proposed framework identifies the reference values considering other reactive power controllers in the grid. Moreover, the proposed framework ensures that the steady state voltage stability margin is maximized. On the computational front, trust region algorithms ensure global convergence. The mathematical models and initialization algorithms proposed in this thesis are tested on standalone systems under various control scenarios. The algorithms proposed to incorporate a grid connected DFIG in steady state analysis tools have been tested on a sample 6-bus system and a practical 418-bus equivalent system of Indian southern grid.

Lors de la phase de dimensionnement d’un générateur électrique, des choix préliminaires imposent généralement la topologie. Cette thèse a pour objectif d’apporter une aide décisionnelle au choix des structures de générateurs de fortes puissances. L’intérêt des machines à haute efficacité énergétique est porté par des objectifs environnementaux forts. En conséquence, maîtriser et comprendre l’origine des pertes dans les machines de production d’électricité est un enjeu capital. Ainsi, une méthodologie de calculs de pertes fer est développée pour des générateurs de fortes puissances.Dans les secteurs de la production et conversion d’énergie, les Machines Synchrones à Double Excitation présentent un fort potentiel pour répondre aux défis de la transition énergétique. Dès lors, il est important de quantifier l’impact de ces nouvelles structures par rapport aux solutions existantes. Cette thèse propose une modélisation par méthodes analytiques et semi-analytiques dans l’objectif de concevoir un ensemble de structures de générateurs. La modélisation est également comparée à deux prototypes de fortes puissances, dont un pour une application éolienne à attaque directe.Ensuite, cette modélisation est employée dans un processus de conception par optimisation. Les structures Pareto optimales sont comparées suivant différents cahiers des charges. Ces optimisations permettent de mettre en avant des gains significatifs par rapport aux solutions existantes notamment sur des données statistiques de fonctionnement éolien. / During the design phase of an electrical generator, the topology is generally imposed by preliminary criteria. This thesis aims at providing a decision support for the choice of high power generator structures. The interest for high efficiency machines is driven by strong environmental objectives. Consequently, understanding the origin of losses in power generation machines is a major issue. Thus, a methodology for iron loss calculation is developed for high power generators.In the energy production and conversion sectors, Hybrid Excitation Synchronous Machines have a great potential to respond to the challenges of energy transition. It is important to quantify the impact of these new structures compared with existing solutions. This thesis proposes analytical and lumped models to design a set of generator structures. The modeling approach is also compared with two high power generators, including one for a direct drive wind turbine. Then, this modeling is used in an optimization design process. The optimal Pareto structures are compared according to different specifications. These optimized designs show significant gains compared to the existing solutions, especially on wind profile from a Weibull probability density function.

Les capacités installées d’énergie éolienne continuent à croître rapidement et prennent une place de plus en plus significative dans le monde. Au fur et à mesure, les études menées sur la conception, la sureté de fonctionnement et la supervision de la chaîne éolienne ont pris progressivement de l’importance. Deux axes de recherche ont été privilégiés dans cette thèse. Le premier concerne la continuité de service d'une éolienne connectée au réseau en présence de défaut de court-circuit entre spires dans une phase du stator de la génératrice asynchrone à cage d'écureuil. L'analyse du défaut ainsi que son impact sur le système éolien et notamment sur la qualité de la puissance produite souligne l'intérêt de développement d'un algorithme de détection et d'isolation rapide, dédié par la suite à la reconfiguration de la commande. Ainsi, une commande tolérante au défaut (CTD) a été conçue de manière à éviter l'arrêt de la production, compenser l'impact de défaut et garder des performances acceptables de la qualité d'énergie produite. Le travail effectué s'est articulé sur les observateurs à mode glissant (OMG), communément connus comme outil puissant pour la supervision et la commande à la fois. Le deuxième axe porte sur la sécurité structurale et la stabilité du système éolien sous contraintes vibratoires. Les travaux se répartissent en deux parties complémentaires : L'établissement d'un modèle numérique tridimensionnel (3-D) sous un logiciel d’analyse par éléments finis (ANSYS) et la réalisation des essais vibratoires sous différentes excitations au sein d'une plateforme vibratoire (TREVISE). Dans ce cadre, un modèle numérique (3-D) d'une éolienne à axe horizontal couplée à un mât et une fondation adéquats a été développé en utilisant la méthode de volumes finis (FVM) afin d'appréhender son comportement vibratoire. Les essais vibratoires expérimentaux valident le modèle numérique et permettent l’identification de la réponse dynamique de la structure d'une manière fine. De plus, nous avons élaboré un modèle expérimental de la tenue de l’éolienne aux contraintes vibratoires de formes aléatoire, sinusoïdale et impulsionnelle. / The wind energy capacity carries on growing quickly and taking an increasingly significant place in the world. Progressively, research studies dealing with designing and supervising wind turbines have become more important. Two areas of research were developed in this thesis. The first one concerns the continuity of service of a wind turbine connected to the grid while an inter-turn short-circuit fault is present in the stator phase of the induction squirrel cage generator. The analysis of the fault as well as its impact on the wind turbine system and mainly on the quality of the produced power highlights the interest of development of a fast detection and isolation algorithm, dedicated to the reconfiguration of the control law. Hence, a fault tolerant control scheme has been established in order to avoid stopping production, compensate the fault impact and maintain acceptable performances of the quality of the produced energy. The carried out work was based on sliding mode observers, commonly known as robust tools for monitoring and controlling at the same time. The second axis concerns the structural modeling and stability checking of the wind system under vibratory stresses. The work is divided into two complementary parts: The establishment of a three-dimensional (3-D) numerical model using a finite element analysis software (ANSYS) and the realization of vibratory tests under different excitations within the platform (TREVISE). In this framework, a numerical (3-D) model of a horizontal axis wind turbine coupled to a suitable tower and foundation was developed basing on the finite volume method (FVM) in order to analyze its vibratory behavior. The experimental vibratory tests validate the numerical model and allow the identification of the dynamic response of the structure in a precise way. In addition, we have developed an experimental model of the behavior of the wind turbine under vibratory stresses of random, sinusoidal and impulse shapes.