Floating offshore wind turbines are currently regulated by means of feedback-only controllers. Most of the effort in the control field was aimed at designing a feedback controller for achieving rotor speed regulation in high winds without compromising the stability of the system. A competing need is to impart resiliency to the external disturbances, in particular to waves. In standard feedback control strategies, the disturbance rejection performance is sacrificed for stability. Adding a feedforward controller to the standard feedback controller is an effective way of improving the resilience to wave disturbance without compromising stability.In this work, a feedforward control strategy is developed with the aim of reducing the platform pitch motion caused by waves and the associated structural fatigue loads. The control strategy is based on the inversion of a linear model of the floating wind turbine, which maps the wave elevation to the main outputs, such as rotor speed and platform motions. A real- time forecast of the wave, which is obtained from a suitable upstream measurement, is utilized to compute the feedforward control action which can be either zero-mean collective pitch or individual-pitch.The feedforward control strategy is implemented in a 10MW floating wind turbine, adding the model-inversion feedforward controller to the standard feedback controller for rotor speed regulation. Numerical simulations are carried out in FAST, for a set of realistic met- oceanic conditions. It is proved that the proposed combined feedback-feedforward effectively reduces the structural loads caused by waves. In particular, the individual-pitch logic attains a similar reduction to the collective-pitch logic, but at with a lower actuation effort.

Model-Inversion Feedforward Control for Wave Load Reduction in Floating Wind Turbines

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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