Controlling Platform Motions and Reducing Blade Loads for Floating Wind Turbines

Offshore sites hold great promise for the growth of wind energy. To tap the vast resource in deep water sites, new support structures, such as those that float, are needed. For floating structures to succeed, they must withstand the offshore wind and wave environment. Two new methods for controlling a floating turbine and reducing the platform and blade loads are presented. The first is a method for controlling collective blade pitch and reducing platform pitch motion, a significant problem for floating structures. The rated generator speed is made a function of the platform pitch velocity. When the platform is pitching upwind, the set point generator speed is set to a larger value, and vice versa. For constant generator torque, this approach essentially makes the rated power a variable that depends on the platform pitch velocity. Fundamentally, this control approach trades power variability for platform pitch variability. The results will show substantial reductions in platform pitch motion but minor increases in power variability. Second, an individual blade pitch controller (IPC) designed to reduce blade fatigue loads is implemented for a floating turbine. The IPC approach is commonly utilized for reducing the 1P fatigue loads on the blades. The goal of implementing this IPC approach is to investigate how traditional load reduction control, which is successful for onshore turbines, integrates and performs with floating turbines. The results will demonstrate the unique challenge of reducing blade loads on a floating turbine.