Reduction in platform motion and dynamic loads of a floating offshore wind turbine-generator system by feedforward control using wind speed preview

Abstract

To reduce both the platform motion and dynamic loads of floating offshore wind turbine-generator systems, feedforward control for high wind speed regions is developed by combining with the wind speed previewed by a nacelle-mounted lidar. First, the wind speed preview using a nacelle-mounted lidar was simulated by considering the floating platform velocity and the temporal difference of laser casting. Feedforward control, in which the blade pitch is manipulated according to the preview wind speed so as to maintain the rated generator speed, is combined with gain-scheduling feedback control of the generator speed. This feedforward control is characterized by employing the first-order lag filter with the delay compensator for the preview wind speed. The effectiveness of the developed feedforward-feedback controller is analyzed through an aero-elastic-hydro-control coupled nonlinear dynamic simulation of a 5-MW floating offshore wind turbine-generator system under turbulent wind fields and irregular wave height variations. The feedforward-feedback controller provides the stabilization of the platform pitching motion and the reduction in the dynamic load variations at the blade root and drivetrain as well as the tower base in comparison to the conventional gain-scheduling feedback control of the generator speed. Moreover, the sensitivity of the settings of the first-order lag filter and the delay compensator in the wind speed preview is clarified for their optimal design.

Keywords

• renewable energy
• wind power generation
• floating offshore wind turbine
• preview control
• feedforward control
• aero-elastic-hydro coupled simulation