Abstract
A variable-gain higher-order sliding mode pitch control strategy is proposed for a strongly nonlinear and coupled floating offshore wind power system. The main goal of the proposed strategy is to suppress platform motion caused by random disturbances such as waves and wind speed and to reduce fatigue loads and power fluctuations. Feedback control and super-twisting second-order sliding mode algorithm were adopted to carry out collective pitch control and track the rated rotor speed, which involves the factor of platform pitch. To adaptively adjust the collective pitch control parameters according to random wave and wind speed disturbances, the barrier function method was used to conceive adaptive sliding mode control gains. For comparison purposes, the proposed control strategy and PI control were executed under different wind and wave conditions on a FAST and MATLAB/Simulink platform. Furthermore, the fatigue load was calculated by Mlife. The results demonstrate that the proposed scheme is effective and robust. Moreover, it has advantages in resisting external disturbances, especially in suppressing the platform pitch and roll, as well as reducing the power fluctuations and the fatigue load on the blade root.
Highlights
To cope with the challenges posed by energy depletion and climate change, countries around the world are vigorously turning towards renewable energy
The results indicate that this multifeedback control method reduced the power output fluctuation, platform pitch, and tower fatigue load
It should be noted that the based adaptive high-order sliding mode control strategy (BAHOSM) control strategy is effective in suppressing the loads at the blade root in both environments
Summary
To cope with the challenges posed by energy depletion and climate change, countries around the world are vigorously turning towards renewable energy. As a type of high-order sliding mode, super-twisting second-order sliding mode control has been applied for variable-speed wind turbines [29,30] Implementation of these controllers requires knowledge of the upper bound on the perturbation derivatives. The upper bound is unknown and hard to calculate in the FOWT system In this case, conservative switching gain can cause sliding mode control chattering and generator torque saturation problems. When the upper bound of the uncertainty derivative is unknown, an adaptive sliding mode control strategy should be considered for the wind turbine system [19,31,32]. A barrier function-based adaptive high-order sliding mode control strategy (BAHOSM) for the nonlinear and strongly coupled barge type FOWT is proposed.
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