Robust blade pitch control of semi-submersible floating offshore wind turbines based on the modified super-twisting sliding-mode algorithm

In this paper, a novel robust collective blade pitch controller (CBPC) is proposed for the semi-submersible floating offshore wind turbine (FOWT) above the rated wind speed. The proposed CBPC is based on the modified super-twisting sliding-mode (MSTSM) algorithm. Firstly, based on a control-oriented model of the semi-submersible FOWT, the dynamics of the rotor speed and the platform pitch rate considering the lumped disturbances, which consist of external disturbances, parametric uncertainties and unmodeled dynamics, are derived. Afterward, the MSTSM algorithm-based CBPC (MSTSM-CBPC) is designed for regulating the generator power to its rated value and reducing the platform pitching motion. Comparative co-simulation tests among the gain-scheduling proportional-integral CBPC, the standard STSM algorithm-based CBPC and the proposed MSTSM-CBPC are performed. Simulation results validate the effectiveness and the superiority of the proposed MSTSM-CBPC.