Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Exponential growth of the global wind turbine market has led to a significant increase in the capacity of wind turbine generators. Modern turbines require higher support structures as higher wind speeds combined with longer blades are necessary to increase their generating capacity. The standard 80-90 m tower is thus not economically viable anymore. Transportation logistics of large steel towers has led to concrete towers becoming a viable option. There are currently no design codes dealing exclusively with the design of concrete wind turbine towers. The aim of this project is to investigate and highlight important aspects of the design process of a normally reinforced high strength concrete wind turbine tower. The tower was designed using nonlinear finite element modelling as a design tool to accurately design the tower for various loads and load cases. An analytical design method was developed that can be used in the preliminary design stage. Finally, the importance of the soil-structure interaction was investigated through a sensitivity analysis. It was found that the formation of cracks greatly affected the stiffness of the structure and that the reduction in stiffness increased the deflection significantly. It was also found that a structure that has sufficient strength to resist the ULS loads may not necessarily comply with the maximum deflection limit for the SLS. The concrete strength class required was not only determined by the maximum compression stress the concrete would experience, but also by the stiffness required to ensure that the tower frequency is within the turbine’s working frequency. The dynamic behaviour of the tower was also affected by the formation of cracks. The fundamental frequency of the tower was reduced by 46% after the SLS loads were applied. It was found that the soil preparation for the foundation plays a vital role in ensuring that the tower frequency is not reduced to a level where it falls outside the turbine working frequency. / AFRIKAANSE OPSOMMING: Die eksponensiële groei van die globale wind turbine mark het gelei tot ʼn beduidende toename in die opwekkingskapasiteit van wind turbine kragopwekkers. Moderne turbines benodig hoër ondersteuningstrukture om hulle opwekkingskapasiteit te verhoog en daarom is die standaard 80-90 m toring nie meer geskik nie. Die vervoer logistiek van groot staal torings het daartoe gelei dat beton torings ʼn lewensvatbare opsie geword het. Daar is huidiglik geen ontwerpkodes wat uitsluitlik handel met die ontwerp van beton wind turbine torings nie. Die doel van hierdie projek is om die ontwerp proses van ʼn bewapende hoë sterkte beton wind turbine toring te ondersoek en belangrike aspekte uit te lig. Die toring word ontwerp deur ʼn nie-liniêre eindige element model te gebruik as ʼn ontwerp hulpmiddel, om die toring akkuraat te ontwerp vir verskeie laste en lasgevalle. ʼn Analitiese ontwerpmetode is ontwikkel wat gebruik kan word in die voorlopige ontwerpfase. Laastens is die grond-struktuur interaksie ondersoek deur ʼn sensitiwiteitsanalise. Daar is gevind dat die vorming van krake die styfheid van die struktuur aansienlik beïnvloed en dat die vermindering in styfheid die defleksie beduidend vermeerder. Daar is ook gevind dat ʼn struktuur wat voldoende sterkte het om die uiterste lastoestande te weerstaan, nie noodwendig voldoen aan die maksimum defleksiegrens vir die diens lastoestande nie. Die beton sterkte klas wat benodig is, is nie net bepaal deur die maksimum druk spanning wat die beton sal ondervind nie, maar ook deur die styfheid wat vereis word om te verseker dat die toring se frekwensie binne die turbine se werksfrekwensie val. Die dinamiese gedrag van die toring is ook beïnvloed deur die vorming van krake. Die fundamentele frekwensie van die toring is verlaag met 46% nadat die diens lastoestande toegepas is. Daar is gevind dat die grond voorbereiding vir die fondasie ʼn belangrike rol speel om te verseker dat die toring se frekwensie nie verlaag word tot ʼn vlak waar dit buite die turbine se werksfrekwensie val nie.

Thesis (MScEng)--Stellenbosch University, 2012 / ENGLISH ABSTRACT: Wind energy is a very current topic, both locally and internationally. It is one of the most rapidly growing renewable energy sources with installed capacity doubling every three years. South Africa's installed wind energy currently accounts for only 10 MW of the 197 GW worldwide installed capacity. With a 10 TWh renewable energy production target set for 2013 by the South African government, renewable energy projects have gained momentum in recent years. This target, together with data from case studies and reports on resource planning and technical requirements, shows that South Africa is well positioned for the implementation of wind energy sources. All this development in the local wind generation market creates a need for local knowledge in the field of wind energy as well as a need to efficiently model and analyse wind turbine systems and grid interactions for local operating conditions. Although the relevant model topologies are well established, obtaining or deriving appropriate parameter values from first principles remains problematic. Some parameters are also dependent on operating conditions and are best determined from site measurements using parameter estimation methodologies. One of the objectives of this project is to investigate whether the system parameter values can be obtained by performing parameter estimation on the model of a wind turbine system. The models used for parameter estimation processes require fast simulation times. Therefore, basic C-code S-function models of the wind turbine system components, i.e., the wind turbine blade, gearbox and generator, were developed and compiled as a Simulink library. These library components were then used for the parameter estimation process. The developed models, as well as the complete wind turbine system model, were validated and their performance evaluated, by comparing them to existing Simulink block models. These models all proved to be accurate and all showed reductions in simulation times. The principle of performing parameter estimation on C-code S-function models is proven by case studies performed on the individual models and the complete wind turbine system. The power coefficient matrix parameter values of the individual turbine blade model estimated with 100% accuracy for the excited elements. The individual gearbox parameter values all estimated accurately with errors below 2.5%. The parameter values of the individual generator models were estimated accurately for the ABC model, with errors below 4%, and less accurately for the DQ model with errors below 13%. The estimation results obtained for the complete wind turbine system model showed that the parameter values of the gearbox model and generator model were estimated accurately when the system model was excited through a step in angular velocity and steps in amplitude of the stator voltages respectively. A final estimation showed that a combination of gearbox and generator parameter values were accurately estimated when the model was excited through both a step in angular velocity and steps in the amplitude of the stator voltages. / AFRIKAANSE OPSOMMING: Windenergie is 'n baie aktuele onderwerp beide plaaslik en internasionaal. Windenergie is een van die vinnigste groeiende hernubare energie bronne met die geïnstalleerde kapasiteit wat driejaarliks verdubbel. Suid-Afrika se geïnstalleerde windenergie maak tans slegs 10 MW uit van die wêreldwye geïnstalleerde kapasiteit van 197 GW. Die Suid-Afrikaanse regering het ’n 10 TWh hernubare-energie produksie teiken gestel vir 2013. As gevolg hiervan het hernubare-energie projekte die laaste paar jaar momentum gekry. Hierdie teiken, tesame met die data van gevallestudies en verslae oor hulpbronbeplanning en tegniese vereistes, toon dat Suid-Afrika goed geposisioneer is vir die implementering van windenergiebronne. Hierdie ontwikkelinge in die plaaslike windenergie mark skep ’n behoefte aan plaaslike kennis op die gebied van windenergie, asook die behoefte vir ’n doeltreffende wyse vir die modellering en analisering van windturbine stelsels en netwerk integrasie vir plaaslike werkskondisies. Alhoewel die betrokke model topologieë reeds goed gevestig is, is die verkryging van toepaslike parameter waardes vanuit eerste beginsels steeds problematies. Sommige parameters is ook afhanklik van die werkskondisies en kan die beste bepaal word deur gebruik te maak van parameter estimasie metodologieë vanaf terrein metings. Een van die doelwitte van die projek is om ondersoek in te stel na die moontlikheid om die stelsel parameter waardes te verkry deur parameter estimasie toe te pas op ’n windturbine stelsel. Die modelle wat gebruik word vir die parameter estimasie prosesse benodig vinnige simulasie tye. Daarom is basiese C-kode S-funksie modelle vir die komponente van windturbine stelsels, d.w.s., die wind turbine lemme, ratkas en generator, ontwikkel en saamgestel as ’n Simulink biblioteek. Die komponente in hierdie biblioteek was toe gebruik vir die parameter estimasie proses. Die ontwikkelde modelle sowel as die hele windturbine stelsel model was gevalideer en hul werksverrigting geëvalueer, deur dit te vergelyk met bestaande Simulink blok modelle. Hierdie modelle het almal getoon dat hulle akkuraat is en het almal ’n vermindering in simulasie tyd getoon. Die beginsel van parameter estimasie wat uitgevoer word op C-kode S-funksie modelle, is bewys deur gevallestudies wat op die individuele modelle en die hele windturbine stelsel model uitgevoer was. Die geperturbeerde elemente van die kragkoëffisiënt-matriks arameter van die individuele turbine lemme model se waardes het 100% akkuraatheid geëstimeer. Die individuele ratkas model se parameter waardes was almal akkuraat geëstimeer, met foute kleiner as 2.5%. Die individuele generator modelle se parameter waardes was akkuraat geëstimeer vir die ABC model, met foute kleiner as 4%, en minder akkuraat vir die DQ model, met foute kleiner as 13%. Die resultate wat verkry is van die estimasie wat uitgevoer is op die volledige windturbine stelsel model, het getoon dat die parameter waardes van die ratkas model en die generator model akkuraat geëstimeer word, wanneer die stelsel model onderskeidelik deur ’n trap in die hoeksnelheid en trappe in die amplitude van die stator spannings geperturbeer word. ’n Finale estimasie het getoon dat ’n kombinasie van ratkas en generator parameter waardes akkuraat geëstimeer kan word as die model deur beide die trap in hoeksnelheid en die trappe in die amplitude van die stator spannings geperturbeer word.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The electromagnetic and mechanical design aspects of an optimally designed double-sided rotor radial flux permanent magnet wind generator with non-overlap iron-cored stator windings are analysed in this thesis. The generator topology proposed in this study aims to reduce the strength demand on the generator structural support, caused by the magnetic attraction forces between the rotor and stator iron components, and in so doing reducing the overall generator mass. The proposed design has very good cooling properties. Compared to a conventional iron-cored permanent magnet generator and an air-cored permanent magnet generator, the double-sided rotor iron-cored topology performs the best with reference to mass and efficiency. / AFRIKAANSE OPSOMMING: Die elektro-magnetiese en meganiese ontwerp-aspekte van ‘n optimal ontwerpte tweesydige rotor radial-vloed permanente magneet windgenerator met nie-oorvleulende ysterkern statorwindings word in hierdie tesis ontleed. Met die generator topologie wat in hierdie studie voorgestel word, word beoog om die strukturele materiaal wat vir die generator benodig is te verminder. Die magnetise aantrekkingskragte tussen die yster komponente van die rotor en stator word dus aangespreek in hierdie studie, om sodoende ook die algehele massa van die permanente magneet generator te verminder. Die voorgestelde tweesydige-rotor ontwerp het baie goeie verkoelings eienskappe en het ‘n kleiner massa en hoër effektiwiteit as beide ‘n konvensionele ysterkern generator met ‘n enkelsydige-rotor en ‘n tweesydige-rotor lugkern permanente magneet generator met dieselfde drywingsvermoë.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / In this study the focus is on the implementation of a coreless axial ux permanent magnet (AFPM) generator for use in a wind generator application with direct battery charging. The wind generator power system is analysed and discussed. The common concerns with AFPM wind generators in recti er-fed direct battery charging applications, such as maximum power point matching and acoustic noise emission, are discussed. In this study the AFPM wind generator is theoretically analysed and the different winding topologies for this type of machine are evaluated. This evaluation is based on a theoretical analysis and con rmed by nite element analysis and practical measurements. It is shown that an AFPM machine equipped with nonoverlapping windings can give a similar performance to that of normal overlapping windings, while using less copper. It is shown in this thesis that the coreless AFPM generator has a relatively low internal phase synchronous inductance resulting in severe problems with regard to maximum power matching and noise. A method is proposed and in detail analysed in this thesis whereby better power point matching is achieved and near-sinusoidal current is obtained using AFPM generators in direct battery charging wind energy systems. The wind generator system's performance is verified with a SimplorerTM simulation package and practical measurements. The calculations from theoretically derived equations are in good agreement with finite element and measured results.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The electromagnetic and mechanical design aspects of optimally designed doublesided rotor radial flux permanent magnet wind generators with non-overlap aircored (iron-less) stator windings are analysed in this thesis. The wind generator is implemented in a battery charging system for use in rural settlements and farms. The optimal generator and system design is based on an accurate analytical model and is confirmed with finite element analysis. It is shown, amongst other things, that the electromagnetic design and surprisingly not the mechanical design, determines the rotor yoke dimensions and, hence, largely the mass and cost of the generator. Alternative battery charging systems are also considered and discussed. / AFRIKAANSE OPSOMMING: Die elektromagnetiese en meganiese ontwerp aspekte van optimaal ontwerpte dubbel-kant rotor radiale vloed permanente magneet windgenerators met nieoorvleuelende lug kern (sonder yster) statorwindings word in hierdie tesis ontleed. Die windgenerator word geplaas in 'n battery-laai stelsel vir gebruik in landelike nedersettings en plase. Die optimale generator en die stelsel ontwerp is gegrond op 'n akkurate analitiese model en is bevestig met eindige element analise. Daar word onder andere getoon dat die elektromagnetiese ontwerp, en nie die meganiese ontwerp, die rotor juk dimensies en dus grootliks die massa en die koste van die generator, bepaal. Alternatiewe battery-laai stelsels word ook oorweeg en bespreek.

Master of Science / Department of Electrical and Computer Engineering / Ruth Douglas Miller / This thesis presents the design of two models for permanent-magnet direct-drive wind turbines. The models are of a 10 kW and a 5 MW wind turbine, which are representative of residential scale and commercial scale turbines respectively. The models include aerodynamic and mechanical simulations through the FAST software, as well as concurrent electrical simulations through the SimPowerSystems toolbox for MATLAB/Simulink. The aim is to provide wind turbine designers and researchers with a comprehensive simulation tool that they can use to design and test many different aspects of a wind turbine. The particular novelty of these models is their high level of detail in electromechanical simulations. For each model, a generator speed controller was designed in a reference frame attached to the generator’s rotor, and was executed with a 3-phase active rectifier using space-vector pulse-width modulation. Also for each model, active and reactive power controllers were designed in a reference frame synchronous with the grid, and were executed with a 3-phase inverter using space-vector pulse-width modulation. Additionally, a blade pitch controller was designed for the 5 MW model. Validation of the models was carried out in the MATLAB/Simulink environment with satisfactory results.

L'objectif de cette thèse est de démontrer comment faire une analyse théorique de fatigue et de mécanique de la rupture d'une structure éolienne à l'axe horizontal. La chaîne des calculs nécessaires pour atteindre cet objectif s'avère être particulièrement longue pour deux raisons : d'abord, la vitesse du vent varie aléatoirement avec le temps ; deuxièmement, l'amplitude de vibration du mât est amplifié en raison des ses fréquences naturelles de vibration. Un chapitre entier est consacré à la modélisation de la vitesse du vent dans l'espace et dans le temps. Ce même chapitre démontre comment synthétiser un signal aléatoire à partir d'une fonction de densité spectrale de puissance (DSP). La force axiale du rotor est le chargement le plus important sur une structure éolienne à l'axe horizontal. Cette force a un rapport non linéaire avec la vitesse du vent. Cela implique la nécessité de déterminer la DSP de la force axiale à partir de son signal, en se servant d'une technique d'estimation spectrale. La méthode Thomson Multitaper s'est avéré la plus satisfaisante pour cette application. La DSP des déplacements du mât est déterminée en associant la réceptance du système structurel avec la DSP de la force qui représente tous les chargements. Un signal de contrainte peut finalement être synthétisé à partir de sa DSP. La technique de comptage de cycles de chargement connue sous le nom de rainflow est abordée et appliquée. Le fait que le signal de contraintes a une amplitude variable implique la nécessité d'employer une technique plus avancée de simulation de propagation de fissures. La technique choisie pour cette thèse est connue sous le nom de strip-yield (bande d'écoulement). / The objective of this thesis is to demonstrate how to do theoretical analyses of fatigue and fracture mechanics in a structure for horizontal axis wind turbine. The chain of calculations required to reach this objective is particularly long for two reasons : firstly, the wind speed varies randomly with time , secondly, the vibration amplitude of the mast is amplified due to its natural frequencies of vibration. A whole chapter is dedicated to modeling the wind speed in space and time. The same chapter shows how to synthesize a random signal by employing a power spectral density function (PSD). The axial force of the rotor is the most important loading on a structure for horizontal axis wind turbine. This force has a non linear relation with the wind speed. This implies the need to determine the PSD of the axial force from its signal, by employing a spectral estimation method. The Thomson Multitaper method revealed to be the most satisfactory for this application. The PSD of displacement of the mast is determined by associating the receptance of the structural system and the PSD of the force representing all loadings. Finally, a signal of stress can be synthesized from its PSD. The fatigue cycle counting method known as rainflow is discussed and employed. The fact that the signal of stress has a variable amplitude implies the need of a more sophisticated method to simulate a crack propagation. The method chosen in this thesis is called strip-yield.

The world is entering the future where integration of renewable energy sources within the power grid will play an important role when facing the challenge of reducing global warming. The intermittent generation characteristics associate with renewable energy sources can be handled by the implementation of microgrids. A Microgrid is a group of energy source (e.g. wind, solar etc) that are located in the same local area that can operate independently in the event of electricity outage and can also be connected to the national grid in case of energy demand exceeds than the energy produced in the same local area. The implementation of microgrid in an electrical distribution system must be well planned to avoid problems. The EU has set high goals to reduce the non-renewable energy sources by 2030. EU has started some local energy systems (microgrids) and Simris is a part of it. This study is about a microgrid project at Simris in the south-east of Sweden. The village of Simris has 140 households supplied by a wind turbine of rated power 500kW and a solar power plant of 440 kW rated power. This project is run by E. ON within the framework and collaboration of Interflux, in which several network operators within the EU participate to investigate flexibility options in local energy systems.  The aim of this study is to find different scenarios in which the Simris microgrid can be run in islanded-mode. Four different scenarios were investigated, and simulation was done in MATLab. After simulation the results were discussed in the “Analysis and Results” section and the size of the wind turbine, the solar park (PV)and the battery were suggested for each of the scenarios. A short calculation was also included between the installation cost of the suggested wind turbine and the needed battery size. The cost of battery is much higher than the cost of wind turbine, so its beneficial for the economy of the microgrid to have a wind turbine of 1000 kW rated power and battery size 35 MWh rather than using the same old wind turbine of 469 kW rated power and upgrade the battery to 462 MWh.

Actuellement, la construction d’un parc éolien nécessite une étude acoustique qui doit assurer la tranquillité des habitants aux alentours et la conformité au regard de la réglementation en vigueur. Pour ce faire, des mesures acoustiques sont réalisées sur une période d’environ deux semaines. Durant ces mesures, des cycles de marche et d’arrêt des machines sont réalisés afin de mesurer la différence de niveau sonore entre le bruit ambiant (éoliennes en fonctionnement) et le bruit résiduel (éoliennes à l’arrêt). Un plan de bridage des machines est alors calculé et fourni à l’exploitant afin de l’implémenter dans le système de contrôle local des éoliennes (SCADA). Actuellement, ce plan dépend grossièrement des conditions météorologiques et des périodes de la journée, supposées corrélées aux conditions acoustiques. En pratique, cette manière de procéder engendre fréquemment des dépassements du critère réglementaire et/ou des pertes de production électrique. Ceci est dû aux conditions acoustiques qui évoluent sans cesse, à la fois pour le bruit particulier (bruit des éoliennes seules) qui dépend finement des conditions météorologiques, et pour le bruit résiduel qui dépend de toutes les autres sources de l’environnement et qui est fondamentalement de nature stochastique. La thèse vise à proposer un algorithme de contrôle du parc éolien en temps réel basé sur un nouveau paradigme de contrôle. On y étudie la possibilité de contrôler un parc éolien à partir d’un système en boite noire d’estimation temps-réel du niveau résiduel et du niveau particulier par séparation de sources. Dans le manuscrit, on définit tout d’abord une formulation du problème dans le cadre du contrôle en identifiant les problématiques propres à ce sujet, une définition des variables du problème et en se rattachant à l’état de l’art du contrôle. Ensuite, on propose deux solutions complètes de contrôle et une évaluation expérimentale. La première est une solution déterministe, qui s’appuie sur un algorithme d’optimisation combinatoire sous contrainte, et qui s’inspire du contrôle actuel des parcs éoliens tout en tenant compte de l’estimation par séparation de sources, alors supposée exacte. On y propose en outre une étude de la capacité du système déterministe à satisfaire le critère réglementaire français qui est aujourd’hui calculé à l’aide de médianes temporelles des variables acoustiques. La seconde est une solution stochastique, qui est basée sur une représentation d’état des variables acoustiques et des incertitudes gaussiennes. Elle inclut un filtrage de Kalman non-linéaire, afin de fusionner l’incertitude sur le modèle acoustique et l’incertitude de séparation de sources, un algorithme espérance-maximisation afin de ré-estimer les incertitudes du problème qui varient d’un parc à un autre, et une adaptation robuste de l’algorithme combinatoire afin de prendre en compte les incertitudes estimées / Currently, acoustic studies are required to set wind farms up. They must ensure the tranquility of the inhabitants around the farms in accordance with current regulations. For this purpose, acoustic measurements are made during a couple of weeks. When measuring, the wind turbines are periodically stopped in order to evaluate the difference between ambient noise levels (with the turbines on) and residual noise levels (with the turbines off). A curtailment plan is then computed and sent to the wind farm owner in order to set it up in the local turbine control system (SCADA). Currently, the curtailment plan roughly depends on the weather conditions and the time of the day which are allegedly correlated to the acoustic variables. In practice, it frequently leads to violations of the acoustic constraints or electrical power loss. This is because the acoustic conditions constantly and strongly evolve over time: the wind turbine noise level finely depends on the weather conditions and the residual noise level depends on all the other acoustic sources and has therefore a stochastic nature. The goal of the thesis is to design a principled real-time control algorithm for wind farms. To do so, we investigate the use of a black-box source separation system that estimates the residual noise level and the wind turbine noise level. We first provide a theoretical formulation of the problem by accounting for specific practical issues, by defining the variables of the problem and by binding these issues to the state of the art. Then, we propose two complete control solutions and run an experimental evaluation. The first solution is a deterministic algorithm based on a constrained combinatorial optimization algorithm, which is inspired by the current approach for controlling wind farms while exploiting the source separation system. Moreover, we present a study of its ability to fulfill the French acoustic constraints that are computed as temporal medians of the acoustic variables. The second solution is stochastic and based on a state-space model defined by means of Gaussian uncertainties. It features a nonlinear Kalman filter in order to fuse the uncertainties of the model and of the source separation system, an Expectation-Maximization algorithm that computes the uncertainties for a specific farm, and a robust variant of the deterministic algorithm that takes the estimated uncertainties into account when computing the optimal command

The goal of this Thesis is to demonstrate, through experimentation, that ocean waves have a positive effect on the performance of an offshore wind turbine. A scale model wind turbine was placed into a wave tank that was completely covered and fitted with a variable speed fan to create different wind and wave conditions for testing. Through testing, different power coefficient vs. tip speed ratio graphs were created and a change in power coefficient was observed between steady operating conditions and operating conditions with waves. The results show a promising increase in power production for offshore wind turbines when allowed to operate with the induced motion caused by the amplitude and frequency of water waves created. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.