This paper deals with gain scheduling and output feedback H∞ control design for an offshore floating wind turbine. The controller objective is to mitigate oscillations in the structure and drive train in addition to smoothening the power/torque output, by means of collective pitching of the blades. In this paper, the wind turbine model is obtained by using the software FAST. Inside the FAST package there are routines to obtain linear models at several operating points by considering the most critical degrees of freedom. The degrees of freedom in the linearized model are chosen according to the controller objective. These models are valid within the span of operating points. A family of controllers is designed based on a Lyapunov function and are formulated in terms of linear matrix inequality (LMI) techniques. The LMIs are solved using YALMIP interfaced with MATLAB. Then, the controller is tested on the fully nonlinear system, and compared with the baseline controller included in the FAST package.
Wind energy is a fast growing business, and it is nowadays one of the most promising sources for renewable energy. The growth in the wind power industry has been tremendous over the last decade. Since the early 1990s wind power has enjoyed a renewed interest, particularly in the European Union where the annual growth rate is about 20%. In order to sustain such growth, wind turbine performance must continue to be improved. The wind turbines are getting bigger and bigger which in turn leads to larger torques and loads on critical parts of the structure. This calls for a multi objective control approach, because we want to maximize the power output while mitigating the unwanted oscillations in the drive train and tower structure. In this paper we will focus on the above rated wind speed conditions, i.e. the control focus is on mitigating oscillations in critical parts and keeping the torque/power output as smooth as possible.
