State-Space Control of Tower Motion for Deepwater Floating Offshore Wind Turbines

Abstract

The offshore wind energy potential is huge and to capture that energy, turbines have to be placed further offshore. Floating wind turbines offer a solution for deep waters. However, a floating wind turbine has extra motions that will affect the turbine in power production and structural loads. Therefore, the turbine control system has to be able to regulate power production and maintain safe operation of the turbine under incident wind and wave conditions. The work presented here discusses the application of state-space optimal controllers to regulate rotor speed and platform pitch above rated wind speed. A gain scheduled PI controller is used as a baseline to gauge the performance of the new controllers developed. A collective pitch linear quadratic regulator, designed to only regulate rotor speed and platform pitch, improves system performance but this improvement is thought to be due to better controller tuning as both controllers use the same mechanism to restore platform pitch and regulate speed. Individual blade pitch control using periodic control theory is applied because it uses a different mechanism to regulate platform pitch. Preliminary simulation results show that individual blade pitch control has platform pitch regulation over collective pitch controllers. However, unintended excitation of platform roll indicate that a more complicated controller may be required to ensure closed loop stability of the entire floating turbine.