Individual Blade Pitch Control of a Floating Offshore Wind Turbine on a Tension Leg Platform

Abstract

A disturbance accommodating controller (DAC) to reject wind speed perturbations is applied on a 5MW wind turbine mounted on a tension leg platform (TLP). Multi-blade coordinate (MBC) transformation is used to address the periodicity of the floating wind turbine system. A method to apply DAC after applying MBC transformation is developed and several implementation options are presented. Simulations were carried out to assess the fatigue loads of the system in accordance with IEC61400-3 standard design load case 1.2; however simulations were restricted to region 3 analysis due to the lack of region transition logic currently implemented for the DAC. A gain scheduled PI (GSPI) controller is used as a baseline/reference controller to compare the performance of the DAC. Simulation results show that the DAC significantly improves power and speed regulation, reduces tower fatigue loads, and maintains the fatigue loads of the blades and the shaft to a comparable level to the baseline controller applied on the TLP. This improvement is due to the use of individual blade pitching and rejecting wind speed variations. Relative to an onshore wind turbine with a GSPI controller, the DAC reduces tower side-side fatigue load and maintains the blade and shaft loads to a comparable level. Tower fore aft fatigue loads remain higher by 27% (instead of 45% increase by the baseline controller on the TLP).