Control Considerations for Very Large Floating Wind Turbines

Abstract

Increasingly large floating wind turbines (FWTs) are being introduced to access the offshore wind resource over deep water at lower cost. In connection with designing a 25 MW semi-submersible wind turbine, we examine the scaling trends associated with the dynamic performance of the generator torque and blade pitch controllers and highlight the challenges that may be encountered for such devices. The increased rotor inertia, reduced blade pitch rates, longer platform pitch and surge natural periods, and flexible modes of the tower, platform, and rotor all affect the ability of the controller to track the desired rotor speed. The effects of control design and tuning choices on the FWT behavior in representative wind and wave conditions are shown.