In this study, an innovative solution is examined for transmission problems and frequency control for wind Turbines. Power electronics and the gear boxes are the parts which are responsible of a significant amount of failures and they are increasing the operation and maintenance cost of wind turbines. Continuously transmission (CVT) systems are investigated as an alternative for conventional gear box technologies for wind turbines in terms of frequency control and power production efficiency. Even though, it has being used in the car industry and is proven to be efficient, there are very limited amount of studies on the CVT implementation on wind turbines. Therefore, this study has also an assertion on being a useful mechanical analyse on that topic. After observing several different types of possibly suitable CVT systems for wind turbines; a blade element momentum code is written in order to calculate the torque, rotational speed and power production values of a wind turbine by using aerodynamic blade properties. Following to this, a dynamic model is created by using the values founded by the help of the blade element momentum theory code, for the wind turbine drive train both including and excluding the CVT system. Comparison of these two dynamic models is done, and possible advantages and disadvantages of using CVT systems for wind turbines are highlighted. The wind speed values, which are simulated according to measured wind speed data, are used in order to create the dynamic models, and Matlab is chosen as the software environment for modelling and calculation processes. Promising results are taken out of the simulations for both in terms of energy efficiency and frequency control. The wind turbine model, which is using the CVT system, is observed to have slightly higher energy production and more importantly, no need for power electronics for frequency control. As an outcome of this study, it is possible to say that the CVT system is a candidate of being a research topic for future developments of the wind turbine technology.

When it comes to design a wind turbine rotor, several parameters have to be taken into account. The present work focuses on the inclination of the blades with respect to the rotor plane, namely the pich angle. The main goal of the project was to design a small-scale wind turbine rotor for wind tunnel tests and in this thesis the optimization of a first prototype is presented. The characterization of the performances was carried out by coupling two different approaches: an experimental and a numerical one. For the experimental part, a proper setup was built and the wind turbine model was tested in a wind tunnel. The results were compared with a Blade Element Momentum theory code developed in Python, that involved also CFD simulations to assess the aerodynamic properties of the blade sections. The analysis characterized the performances at variable collective pitch in terms of power and thrust coefficient, showing that the intitial blade design was not the optimal one. Therefore, the optimal pitch angle that maximize the power porduction was found for variable conditions. The second part of the experiments focused on the case of pitch unbalanced and the potential risks connected to it. As a result, the analysis demonstrated that any kind of pitch unbalance generates losses in the power production and may lead to a possible increase of the thrust. To compare the results, a modified BEM code was developed by assuming an axisymmetric axial induction factor. Finally, an additional analysis on the wind turbine oscillations was made, finding a connection between lateral vibrations and rotor unbalance and revealing the resonance frequency of the structure.