Disturbance Accommodating Control of Floating Offshore Wind Turbines

Abstract

Floating offshore wind turbines offer a feasible solution for water depths greater than 60m. However, floating wind turbines will experience additional motion induced by incident wind and waves due to the lack of rigid foundations. Therefore, the control system becomes an important component that can be used to reduce the induced motions or, if not carefully taken into consideration, could exacerbate the motions. In our previous work, we demonstrated that using state space controllers with multiple objectives resulted in improved performance with respect to a gain scheduled PI controller. Further improvements were obtained by implementing individual blade pitching through periodic control as it overcomes the limitations of collective blade pitching. However, the periodic controller destabilized un-modeled degrees of freedom (DOFs) and these DOFs had to be included in the design of the controller to ensure stability of the system. Disturbance accommodating controllers can further improve the performance by canceling or reducing the effects of persistent disturbances: incident wind and waves. Currently, only wind speed is modeled as a disturbance to reject. Simulation results show that only when the platform yaw degree of freedom is included in the controller design the performance is improved through better power and speed regulation.