Closed Loop Control Strategies Definition

This report represents Deliverable D6.4 “Closed Loop Control Strategies Definition v2” of Work Package 6, “Integrity Management and Control Strategies”, of the EU H2020 project Mooring Sense.
The purpose of this deliverable is to describe the closed-loop control strategies that have been designed and implemented within the project. Two control loops are proposed and integrated into IKERLAN’s OpenDiscon open-source wind turbine controller code. The first control loop implements a method from the literature introducing torque demand variations to reduce blade pitch oscillations around rated wind speed. The second control loop makes use of a thrust force observer and the feedback of the smart sensor designed for the MooringSense project (platform and turbine position and attitude) to limit the thrust force in the turbine.
The mentioned observer description and validation is also provided in this document showing good correlation values between the estimated values and the values obtained from the simulation tools for different test cases.
Similarly, the control algorithms are explained, and their performance is validated using the platform and turbine modelled in SIMA software. Finally, it is shown that both proposed strategies help to mitigate the loads in the mooring lines and the FOWT (tower, blades, etc.) in terms of magnitude and cyclic loading, increasing the fatigue life expectation. However, generator torque variations are increased for turbulent wind conditions and power production must be the reduced if the thrust limitation strategy is enabled.