Linear quadratic regulation for a 10-MW tension leg platform floating offshore wind turbine operating under normal and extreme turbulence model conditions

New concepts of floaters have been developed for multimegawatt wind turbines aiming to reduce the cost of renewable energy generation in deep waters. This paper presents the preliminary design and tuning of a linear quadratic regulator (LQR) for a floating offshore wind turbine (FOWT) constituted of the DTU 10-MW offshore reference wind turbine (RWT) and the CENTEC-TLP tension leg platform (TLP). The goal of the LQR is to improve the performance of the 10-MW CENTEC-TLP FOWT above the rated wind speed using the collective blade pitch actuator within the saturation limits. The LQR design is based on a verified control-oriented FOWT model considering the measurement of surge and pitch floater motions in addition to the rotor speed. Wind and wave disturbances are assumed to be unmeasured. The LQR performance is evaluated for two above-rated operational cases, involving normal and extreme turbulence models combined with relevant sea states. Simulation results show that the designed LQR can yield a reduction of approximately 67% in the rotor speed and power standard deviations compared with a baseline proportional-integral (PI) controller. With the baseline controller, the maximum rotor speed and maximum electrical power are about 15% higher than the rated speed and power, respectively, while this value is reduced to about 6% with the LQR controller. The designed LQR can also yield a TLP pitch reduction of approximately 21%, while keeping the surge amplitude and nacelle axial acceleration below their respective limits.