Wind turbine modelling using doubly-fed induction generators is a well-known subject. However, studies have tended to focus on optimising the components of the system rather than considering the interaction between the components. This research examines the interaction of the control methods for a doubly-fed induction generator (DFIG) in a wind turbine application integrating them with the crowbar protection control and DC-link brake control to make the best use of the converter. The controls of the rotor-side and the grid-side converters of the DFIG model are both well established and have been shown to work. Typically the crowbar protection is designed in order to protect the rotor-side converter and the power electronic components of the DFIG system from high currents occurring in the rotor due to the faults. The DC-link brake-overvoltage protection is also designed to prevent the overcharging of the DC-link capacitor placed between the rotor-side converter and the grid-side converter. In order to show that these protection schemes work and with thought can co-ordinate with each other, tests consisting of a number of balanced three-, two- and one-phase voltage sags are applied to the network voltage. The main contributions of this thesis are establishing operational tuning and design limits for the controllers and system subassemblies. This is to minimise the electrical subsystem interaction while maintaining adequate performance, and have an improved DC-link control. This work also includes a full electrical system study of the wind turbine and an essential literature review on significant references in the field of the DFIG wind turbine system modelling, control and protection. Specifically this research project makes a number of novel contributions to the literature: enhanced DC voltage control including operating point sensitivity analysis and dynamic stiffness assessment, sensitivity and robustness analyses of the power loop control and control loop segmentation by appropriately tuning the controller loops.

The increasing penetration of wind power into the power system dominated by variable-speed wind turbines among the installed wind turbines will require further development of control methods. Power electronic converters are widely used to improve power quality in conjunction with the integration of variable speed wind turbines into the grid. In this thesis, a detailed model of the Predictive Current Control (PCC) method will be descripts for the purpose of control of the grid-connected converter. The injected active and reactive power to the grid will be controlled to track their reference value. The PCC model predicts the future grid current by using a discrete-time model of the system for all possible voltage vectors generated by the inverter. The voltage vector that minimizes the current error at the next sampling time will be selected and the corresponding switching state will be the optimal one. The PCC is implemented in Matlab/Simulink and simulation results are presented.

There is a trend in Sweden towards increasing the electricity production from renewable energy sources in the electric grid. The increased share of renewables could be seen as essential for Sweden to be able to meet the obligated climate goals. Integration of renewables will enable Sweden to be a progressive part in reducing greenhouse gases and decreasing the global warming. However, one issue with renewable energy sources is the inverter governed production. This, together with the decommission of larger synchronous generators, results in decreasing the inertia and increasing the instability inthe grid.  This thesis is dedicated to elaborating on frequency stability issues and investigating how Variable Speed Wind Turbines (VSWT) could contribute towards stabilized operation when included in frequency support services.  The study is generated through an extensive research process where focus areas are identified. Questions are purposed and then discussed through interviews with experienced people in the field. Estimated power production series from a wind turbine park (WTP) are applied in a constructed model to study the possibilities appearing when  including VSWTs in frequency support services. The income generated from including VSWTs in different regulation power market services is with the model compared against solely procuring the production capacity on the day ahead market. The studied frequency support services are then compared altogether to generate favorable solutions. The study examines both economic as well as technical features of the inclusion of VSWTs in frequency support services.  Results found in the study were that inclusion of wind turbines for power regulation purposes could be seen as increasingly manageable and needed in the electric grid. The maturity of technical solutions alongwith a transition in the regulation power market could be observed as leading factors. The diversification of regulation abilities and the increasing economic incentives in the regulation power market was also found to be important reasons for including wind turbines in the regulation power market. In the study, it was also found thataggregating the power production from several VSWT could increase the ability to deliver the studied services.  It was concluded that inclusion of VSWT in the frequency containment reserve during disturbed operation for down-regulation purposes as well as the fast frequency reserve was the most promising frequency support products for the inclusion of wind turbines. When including battery energy storages and to a larger part managing the durability demands for the services then the frequency contain reserve for normal operation and the frequency containment reserve for disturbed operation for upregulation purposes could be observed as preferable alternatives. Regulation abilities were concluded as achievable with the use of pitch and torque regulation techniques available in the variable speed wind turbine.

Scour is a process of removing soils around foundations by currents and waves. For the pile-supported marine structures such as the monopile-supported offshore wind turbines (OWTs) and the pile-supported bridges, scour can decrease the pile capacities and alter the dynamic responses of the structures. At present, there is not a widely accepted method to estimate pile axial or lateral capacity under scoured conditions. For example, different recommendations are used among the existing design standards for estimation of the vertical effective stress and the resulting capacities for single piles under different scour conditions. None of the existing standards or design practice has even considered the scour effects on the behavior of pile groups. Furthermore, the investigation into the responses of piles under multiple hazards of scour and earthquakes is rarely reported. To address the foregoing limitations, this study first introduces an analytical solution to determining the vertical effective stress of soils around single isolated piles under scoured conditions and uses it to examine the limitations of the existing standards in estimation of pile tensile capacity (Chapter 1). The effect of soil-pile interface friction is highlighted. Next, the study proposes new approaches to investigating the combined effects of scour and earthquakes on the lateral responses of the monopile-supported OWTs in sand (Chapter 2) and soft clay (Chapter 3). Lastly, simple and practical methods are developed based on the p-y curve framework for analyzing the lateral responses of pile groups in sand (Chapter 4) and soft clay (Chapter 5) subjected to static lateral loading. The proposed methods in this study were encoded into a series of open-source computer scripts for engineering practice. They were verified with the 3D continuum finite element (FE) analyses. Using the proposed methods, standard methods, and 3D FE method, parametric analyses were conducted to investigate the scour effects on the lateral behavior of the monopile-supported OWTs under crustal earthquakes and that of the pile groups under static loading. The factors considered in the parametric study included effects of scour-hole dimensions, soil stress history, soil density, soil-pile interface behavior, soil liquefaction potential, pile group configurations, etc. Through the parametric analyses, the standard methods were critically assessed by comparing the results to those calculated by the proposed methods and 3D FE methods, and some design-related issues were also discussed. / Graduate

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This Master’s thesis focuses on the wind turbines. It describes the basic attributes of the wind energy and the wind potential of Slovak Republic, as well as the environmental impact of this sector. Meteorological data for the selected location are processed according to the Weibull distribution and they are used for the aerodynamic design of the wind turbine blades. Aerodynamic design is processed by using two methods. The first is the blade cascade theory, which is used to design prismatic and twist blades. The second method is called the blade element momentum, which is used to design wind turbine but only twist blades are designed by using this theory. Calculated aerodynamic shapes are compared and the best economic solution for the selected location is chosen.

This work is focused on the power engineering of the Czech Republic, particularly the alternative and its subset, wind power. Introduction acquaints readers with the state of energy in the country. They're the facts of the historical development of energy in Czechoslovakia and its status today. Representation of particular sources which are involved in the so-called. "Big Energy", their description and production. Each of the resources used is briefly described and discussed basic advantages and disadvantages arising from the nature of the source. It is also outlined the possible development of energy and change in the application of these resources in the future. The conclusion is devoted to alternative energy sources. Strives to cover the positive and negative aspects. It also shows the effect of alternative energy sources to power grid stability. The conclusion of this chapter is devoted to draft measures to increase the use of alternative energy sources in the energy mix of the Czech Republic. The second part is devoted to experimental measurements on small wind turbine JPT-100 from Jetpro Technology, Inc. The beginning describes the basic mathematical methods for calculating wind power and wind turbine itself. The text is accompanied by illustrative graphs. Another part deals with the actual wind turbine JPT-100. There are mentioned its characteristics, complete description of measuring workplace and measurement results.

This master thesis concerns about problematics of wind turbines. The document summarizes basic theory based on the law of momentum conservation which is essential tool for the design and calculation of wind turbines. The theory is complemented by number of correction factors and then used in the design of wind turbine for specific parameters. The calculation is performed iteratively using Matlab software and the actual code is given in appendix. Graphs summarizing the progress of various units along the blades are presented in the document. The final section briefly describes advanced topics of aerodynamics concerning other important factors that the field of wind energy deal with in recent time.

L’objet de cette thèse est de proposer et d’identifier un modèle de comportement mécanique en fatigue écrit à l’échelle du pli ou de la couche composite élémentaire. Le modèle doit permettre de prédire l’évolution des dégradations mais également la résistance résiduelle. Les matériaux concernés par cette étude sont des composites renforcés par des tissus de fibres de verre bi ou tri axiaux. Ce travail exclue les zones de liaisons ou de reprise de pli où des contraintes hors plan engendrent des couplages forts entre endommagement intra et inter laminaires. Les principaux objectifs de la thèse sont de : - Identifier sur le matériau de l’étude les mécanismes d’endommagement et leur couplage en quasi-statique et en fatigue - Caractériser et modéliser la perte de rigidité engendrée par les mécanismes d’endommagement - Caractériser et modéliser les cinétiques d’endommagement en fatigue - Caractériser et modéliser les pertes de résistance engendrées par les mécanismes d’endommagement - Implémenter et tester le modèle proposé (ou celui retenu de la littérature et qui sera modifié si besoin) dans un code de calcul EF / The purpose of this thesis is to propose and identify a model of mechanical fatigue behavior written for the lamina level. The model would be able to predict damage evolution but also residual strength. Studied materials are bi or tri axial glass fibre reinforced plastics fabrics. This work excluded joints areas where out of plane stresses generate strong coupling between intra and inter laminar damage. The main goals of the thesis are: - Identify on the material of the study damage mechanisms and their coupling in quasi-static and fatigue - Characterize and model residual stiffness caused by damage mechanisms - Characterize and model fatigue damage - Characterize and model residual strength caused by damage mechanisms - Implement and test the proposed model (or the one chosen in the literature and changed if necessary) in a computer FE code

Title: Renewable Energy Sources as Inspiration for Physics Experiments Author: Bc. Tomáš Kopřiva Department: Department of Physics Education Supervisor: RNDr. Petr Kácovský, Ph.D. Abstrakt: This thesis deals with a current issue of renewable resources of energy. It focuses on the Sun, wind and hydrogen as energy resources.The first part of the thesis provides a theoretical explanation to these resources and is followed by a practical part with the aim to explain this issue to students by using experiments included in worksheets. The theoretical part is focused on the minimal knowledge that is needed for completing the worksheets. This part also describes suitability of these resources in the context of the Czech Republic. The second part of the thesis is exclusively experimental. It describes educational kits that can be used to demonstrate renewable resources of energy. It also includes instructions to create worksheets. The attachment, which is part of the thesis, contains a set of worksheets and a CD which, among others, contains other worksheets filled in by students. Key words: renewable resources, worksheet, experiment, solar cell, fuel cell, wind turbine, efficiency