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

Abstract

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.

Data-driven repetitive control: Wind tunnel experiments under turbulent conditions

“…For other experiments executed with this turbine, see e.g. Van Solingen et al (2014) The blades used for this experiments are designed and presented in (Navalkar et al, 2016) and is shown in on the blades, which relates directly to the out-of-plane bending moments.…”

“…For results obtained with these flaps, see e.g. Navalkar et al (2016). The experiments shown in this paper are obtained without using the piezobenders on the free-floating flaps as a control input.…”