Experimental study of floating wind turbine control on a Tetra-sub floater with tower velocity feedback gain

We present an experimental study of floating wind turbine control with inclusion of tower motion feedback. The study is conducted for a 1:60 scaled-model of the DTU 10MW reference wind turbine on a design variant of the TetraSub floater. A review of control methods for floating wind turbines is provided, covering both de-tune and tower motion feedback methods. We next detail the implementation in the experimental setup that includes real-time integration and low-pass filtering of the measured tower-top acceleration. We demonstrate how the tower feedback loop is able to stabilize an otherwise unstable land-based controller. The results further show that the stability is maintained for increasing values of the feedback gain until a certain limit. For the chosen control parameters and the lab-generated wind field, which had limited low-frequency energy, we observe that the variations in rotor speed, blade pitch and platform motion are generally larger for the tower loop controller. This finding is not generalizable due to the special inflow conditions and because controller optimization is not performed. For the tower loop controller, a substantial response at the floater roll frequency is identified. This is caused by the influence of blade pitch on the aerodynamic torque in combination with the constant generator torque. Mitigation through generator torque control is proposed.