This paper deals with linear parameter-varying (LPV) modeling and output H∞ control design with constrained gain for an offshore wind turbine. The controller objectives are to mitigate oscillations in the structure and drive train, to smooth power/torque output in addition to keeping the overall system stable, by means of individual pitching of the blades. A traditional procedure for designing a controller for such a system is to choose an operating point and assume it works in a suitable way under the influence of turbulent wind. In this paper, the wind turbine model is obtained from the software FAST. To design the controller, the model is linearized about several operating points. The degrees of freedom in the linearized model are chosen according to the controller objectives. The linear models are valid within the span of operating points. The constrained gain controller is obtained based on a parameter-dependent Lyapunov function and formulated in terms of linear matrix inequalities (LMIs). Finally, the controller is tested on the fully nonlinear system under the influence of turbulent wind. The closed loop system is compared with the baseline controller included in the FAST package along with a controller design based on a single linearized model.

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