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Floating offshore wind turbines are complex dynamical systems. The use of numerical models is an essential tool for the prediction of the fatigue life, ultimate loads and controller design. The simultaneous wind and wave loading on a non-stationary foundation with a flexible tower makes the development of numerical models difficult, the validation of these numerical models is a challenging task as the floating offshore wind turbine system is expensive and the testing of these may cause loss of the system. The validation of these numerical models is often made on scaled models of the floating offshore wind turbines, which are tested in scaled environmental conditions. In this study, an experimental validation of two numerical models for a floating offshore wind turbines will be conducted. The scaled model is a 1:35 Froude scaled 5 MW offshore wind turbine mounted on a tension-leg platform. The two numerical models are aero-hydro-servo-elastic models. The numerical models are a theoretical model developed in a MATLAB/Simulink environment by the authors, while the other model is developed in the turbine simulation tool FAST. A comparison between the numerical models and the experimental dynamics shows good agreement. Though some effects such as the periodic loading from rotor show a complexity, which is difficult to capture.

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This paper will focus on using system identification on experimental data for building a mathematical model for the platform of a floating offshore wind turbine and analyzing the behavior of the structure. The floating offshore wind turbine examined in this paper uses a scaled tension leg platform as its foundation and the wind turbine is a 1:35 scaled model of the 5 MW NREL offshore wind turbine. The mathematical model of the platform will describe the displacement of the TLP in surge when affected by an irregular wave series generated from a scaled Pierson-Moskowitz wave spectrum. To obtain such a mathematical model, an examination of the displacement of the platform due to the hydrodynamic loads will be conducted on the foundation of the floating offshore wind turbine. The height of the waves and the displacement of the floating offshore wind turbines will be measured by resistive wave gauges and OptiTrack cameras, respectively, at the offshore laboratory at Aalborg University Esbjerg. System identification is used on the data obtained from the experiments, to build multiple mathematical models with different model structures, in order to find the most appropriate model structure. It is concluded from the analysis of the different mathematical models, that the Autoregressive Moving Average and Extra input model structure is the most accurate model at describing the dynamics of the platform of a floating offshore wind turbine. The model is valid for a specific operating range of Pierson-Moskowitz waves generated with a wind speed corresponding to 2 meters per seconds.

This brief proposes a solution to the long-standing problem of designing an adaptive control for the dc-dc boost converter with unknown load and unavailable input current measurement. The difficulty lies in the parametric uncertainty of the output dynamics, which poses a manifold of equilibria in the classical adaptive observer design. This is known as the detectability obstacle that imposes a restrictive assumption on the system behavior to ensure convergence. To overcome this problem, a class of saturated dynamic controllers is designed to guarantee the asymptotic regulation of the output voltage. An immersion-and invariance-based adaptive observer is proposed, which preserves the convergence property in conjunction with the controller with no need for an extra persistent excitation condition. To evaluate the transient behavior of the proposed controller, realistic simulations are provided, and then the performance comparison with two other well-known output feedback controllers is presented. Moreover, experimental results are concluded on a prototype dc-dc boost converter to support and verify the results of theory and simulations.