Control and dynamic analysis of a 10 MW floating wind turbine on a TetraSpar multi-body platform

Abstract

The role of wind turbine controllers in stabilizing floating offshore wind turbines (FOWTs) is critical in the above-rated operational regions. In this paper, three types of control methods are tested on a 10 MW FOWT mounted on a TetraSpar multi-body platform to numerically investigate the rotor and platform dynamics. A validated aero-hydro-servo-elastic coupling tool based on FAST and AQWA is used to analyse the integrated floating wind turbine model. The results show that the baseline controller designed for the onshore application yields the highest blade pitch and platform pitch fluctuations primarily due to the negative damping effect. Conversely, the detuned controller obtained by derating the control gains reduces these fluctuations and sufficiently mitigates the damping problem. It is also observed that the instabilities caused by the higher frequency baseline controller and the resulting structural penalties are reduced when the detuned controller is employed. On the other hand, the open-loop type fixed blade pitch control method resulted in the highest rotor speed and surge translation. Further analysis found that the tension responses on some of the tendons are dominated by the coupled pitch mode when implementing the detuned and the fixed blade pitch control options.