Analysis and control of floating offshore wind turbines

With the continuous growing of wind energy as a clean source for electricity production there is an increasing interest in the location of wind turbines in offshore areas in which there are fewer space restrictions and less turbulent wind. This increases the interest to develop floating wind turbines, which are not mounted in the sea-bed and can be used in deep waters. For their low environmental impact, the demand for FOWTs could easily be fostered. Floating turbines are large and complex mechanical structures as a consequence it is necessary to adapt control strategies to these systems, to ensure acceptable loads in order to guarantee a long lifetime. In order to reduce fatigue loads, different design control approaches are studied. To design the control, simplified models are needed. The purpose of this thesis is to develop a simplified Floating Offshore Wind Turbine (FOWT) model considering aero-dynamical loads to assess the performance of the system. The aerodynamic forces are derived and implemented in a more accurate simulator, FAST, to evaluate the overall loads acting on a FOWT. FAST is the acronym for Fatigue-Aerodynamics-Structure-Turbulence and it gives a full analysis of wind turbine models, using a high-fidelity numerical code. The developed FAST computer program simulator is applied to investigate the reliability of simplistic wind turbine models by using MATLAB and Simulink interfaces. Studying a simplification of the turbine model means identify the dominant physical dynamics behaviour that implies a good knowledge of wind turbine dynamics. The simplified model is useful when a linear control theory is applied. Due to the non-linearity of the problem, created by wind and sea kinematics, specific values are found using an empirical approach. Results are acceptable according to the approximations done. Further developments are considered to obtain a more detailed model of wind turbine and changes to control strategy.