Deformable trailing edge flaps for modern megawatt wind turbine controllers using strain gauge sensors

Abstract

The present work contains a deformable trailing edge fl ap controller integrated in a numerically simulated modern, variablespeed, pitch-regulated megawatt (MW)-size wind turbine. The aeroservoelastic multi-body code HAWC2 acts as a component in the control loop design. At the core of the proposed controller, all unsteady loads are divided by frequency content. Blade pitching and generator moment react to low-frequency excitations, whereas fl aps deal with high-frequency excitations. The present work should be regarded as an investigation into the fatigue load reduction potential when applying trailing edge fl aps on a wind turbine blade rather than a conclusive control design with traditional issues like stability and robustness fully investigated. Recent works have shown that the fatigue load reduction by use of trailing edge fl aps may be greater than for traditional pitch control methods. By enabling the trailing edge to move independently and quickly along the spanwise position of the blade, local small fl utuations in the aerodynamic forces can be alleviated by deformation of the airfoil fl ap. Strain gauges are used as input for the fl ap controller, and the effect of placing strain gauges at various radial positions on the blade is investigated. An optimization routine minimizes blade root fatigue loads. Calculations are based on the 5 MW reference wind turbine part of the UpWind project primarily with a mean turbulent wind speed close to rated power. A fatigue load reduction of 25% in the blade root moment was obtained for a continuous 6.3 m long fl ap. 194Flaps and wind turbine controllers using strain gauge sensors P. B. Andersen et al. Wind Energ. 2010; 13:193-206 196 Flaps and wind turbine controllers using strain gauge sensors P. B. Andersen et al.

Stability investigation of an airfoil section with active flap control

“…Control System Model for instance, an ideal 5-hole Pitot's tube extending from the blade leading edge [9]. A second sensor location is also investigated, and in this case the measuring point is placed at the`typical' three quarter chord position: ε Aoa,ctrl = ε 3/4 = 0.5.…”

“…The aerodynamic forces in the simulations by Buhl et al [6] are computed employing Gaunaa's [12] potential ow model for a thin airfoil section undergoing arbitrary motion and camberline deformation. Andersen et al [8] extends the model to take into account the e ects from uid viscosity and simulations including the interaction with a wind turbine standard control system are presented in Andersen et al [9]. Here, it is concluded that by apply-2 ing an active ap control the blade apwise fatigue load would be reduced up to 48 %, with respect to an HAWT without ap-like deformable trailing edges.…”

“…At the state of the art, several studies report considerable potentials for aerodynamic control methods based either on deploying tabs [4], or on classic rotating aps [5] or on ap-like deformable trailing edges [6,7,8,9,10,11]. Unlike a classic rigid plain ap, a deformable trailing edge ap de ects the aft part of the airfoil following a non-linear deformation shape, with a smooth and continuous variation of the camberline slope, thus avoiding discontinuity points as the hinge in a classic rotating ap.…”

A smart rotor configuration with linear quadratic control of adaptive trailing edge flaps for active load alleviation

“…Most of the studies opted for control algorithms based on classic PID methods, applied either to each blade independently [13,14,15,16,17], or to the whole rotor through multi-blade coordinate transformation [18,19]; other investigations have instead applied model based control algorithms, as Linear Quadratic Regulators (LQR) [20], Model Predictive Control (MPC) [12,21], or H ∞ control [9]. The flap control actions respond to the deformation state of the rotor blades; in some cases, rotor sensors are assumed to provide direct measurements of the blade deflection and deflection rate [15,20,22,17], whereas other controllers use measurements of the blade flapwise bending moment, either at selected locations along the span [14,16], or, more simply, at the blade root [19,12,21,10].…”

“…The flap control actions respond to the deformation state of the rotor blades; in some cases, rotor sensors are assumed to provide direct measurements of the blade deflection and deflection rate [15,20,22,17], whereas other controllers use measurements of the blade flapwise bending moment, either at selected locations along the span [14,16], or, more simply, at the blade root [19,12,21,10]. Some studies have also investigated flap control algorithms where additional information on the in-flow condition along the blade are provided, for instance, by measurements performed with Pitot's tubes mounted on the blade leading edge [14,12,21].…”