Articles | Volume 1, issue 2
Wind Energ. Sci., 1, 205–220, 2016
Wind Energ. Sci., 1, 205–220, 2016

Research article 26 Oct 2016

Research article | 26 Oct 2016

Wind tunnel tests with combined pitch and free-floating flap control: data-driven iterative feedforward controller tuning

Sachin T. Navalkar1, Lars O. Bernhammer2, Jurij Sodja3, Edwin van Solingen1, Gijs A. M. van Kuik2, and Jan-Willem van Wingerden1 Sachin T. Navalkar et al.
  • 1Delft Center for Systems and Control, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, 2628 CD Delft, the Netherlands
  • 2Wind Energy Group, Faculty of Aerospace Engineering, Delft University of Technology, 2629 HS Delft, the Netherlands
  • 3Aerospace Structures and Computational Mechanics, Faculty of Aerospace Engineering, Delft University of Technology, 2629 HS Delft, the Netherlands

Abstract. Wind turbine load alleviation has traditionally been addressed in the literature using either full-span pitch control, which has limited bandwidth, or trailing-edge flap control, which typically shows low control authority due to actuation constraints. This paper combines both methods and demonstrates the feasibility and advantages of such a combined control strategy on a scaled prototype in a series of wind tunnel tests. The pitchable blades of the test turbine are instrumented with free-floating flaps close to the tip, designed such that they aerodynamically magnify the low stroke of high-bandwidth actuators. The additional degree of freedom leads to aeroelastic coupling with the blade flexible modes. The inertia of the flaps was tuned such that instability occurs just beyond the operational envelope of the wind turbine; the system can however be stabilised using collocated closed-loop control. A feedforward controller is shown to be capable of significant reduction of the deterministic loads of the turbine. Iterative feedforward tuning, in combination with a stabilising feedback controller, is used to optimise the controller online in an automated manner, to maximise load reduction. Since the system is non-linear, the controller gains vary with wind speed; this paper also shows that iterative feedforward tuning is capable of generating the optimal gain schedule online.

Short summary
In order to reduce the cost of wind energy, it is necessary to reduce the loads that wind turbines withstand over their lifetime. The combination of blade rotation with newly designed blade shape changing actuators is demonstrated experimentally. While load reduction is achieved, the additional flexibility implies that careful control design is needed to avoid instability.