Combined individual pitch and trailing edge flap control for structural load alleviation of wind turbines

Ungurán, Róbert; Kühn, Martin

doi:10.1109/acc.2016.7525262

Cited by 11 publications

(11 citation statements)

References 15 publications

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“…In aero-elastic simulations, fatigue load reductions up to approximately 30 % have been found for a trailing edge flap covering up to 25 % of the blade span of a 5 MW turbine (Barlas et al, 2012a). In most of the numerical studies the aerodynamic loading was computed by blade element momentum (BEM) codes (e.g., Bernhammer et al, 2016;Chen et al, 2017;Ungurán and Kühn, 2016), which have been extended with different engineering models to account for the unsteady flow (e.g., Bergami and Gaunaa, 2012). As viscous and unsteady aerodynamics have a great influence on dynamically deflected flaps (Leishman, 1994), it is, however, important to also apply higher-fidelity models and gain knowledge of the flow physics.…”

Section: Introductionmentioning

confidence: 99%

An investigation of unsteady 3-D effects on trailing edge flaps

et al. 2017

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Abstract. The present study investigates the impact of unsteady 3-D aerodynamic effects on a wind turbine blade with trailing edge flap by means of computational fluid dynamics (CFD). Harmonic oscillations are simulated on the DTU 10 MW rotor with a morphing flap of 10 % chord extent ranging from 70 to 80 % blade radius. The deflection frequency is varied in the range between 1 and 6 p. To quantify 3-D effects, rotor simulations are compared to 2-D airfoil computations and the 2-D theory by Theodorsen. It was found that the deflection of the flap on the 3-D rotor causes a complex wake development and induction which influences the loads over large parts of the blade. In particular, the rotor near wake with its trailing and shed vortex structures revealed a great impact. Trailing vorticity, a 3-D phenomenon, is caused by the gradient of bound circulation along the blade span. Shed vorticity originates from the temporal bound circulation gradient and is thus also apparent in 2-D. Both lead to an amplitude reduction and shed vorticity additionally to a hysteresis of the lift response with regard to the deflection signal in the flap section. A greater amplitude reduction and a less pronounced hysteresis is observed on the 3-D rotor compared to the 2-D airfoil case. Blade sections neighboring the flap experience, however, an opposing impact and hence partly compensate for the negative effect of trailing vortices in the flap section with respect to integral loads. Comparisons to steady flap deflections at the 3-D rotor revealed the high influence of dynamic inflow effects.

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Section: Introductionmentioning

confidence: 99%

An investigation of unsteady 3-D effects on trailing edge flaps

et al. 2017

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“…For an analysis of the induction zone effect, we set the range of the focus distance and telescope position along the blade radius at F ∈ [10, 40 m] and R ∈ [20, 60 m], based on a previous investigation (Ungurán et al, 2018). The range of the other input variables are determined by the results of simulations with laminar inflow and power law wind shear with coefficients of 0.1, 0.2, and 0.3.…”

Section: Simulation Set-upmentioning

confidence: 99%

“…stant, and that Taylor's frozen turbulence hypothesis (Taylor, 1938) holds (Ungurán et al, 2018). We perform large-eddy simulation (LES) in the subsequent sections to examine the usefulness and limitations of these assumptions and further analyse the uncertainties in the blade-mounted lidar measurement as well as the measurement sensitivity with respect to lidar and telescope parameter changes.…”

Section: Case Conditionsmentioning

confidence: 99%

“…The blade-mounted lidar system is a novel technique that enables us to sample the wind component parallel to the rotor shaft axis around the swept area (Bossanyi, 2013) and has been demonstrated to be technologically viable (Mikkelsen et al, 2012). Such a feature of the system enables addressing the mitigation of higher-harmonic dynamic blade loads through feedback-feedforward individual pitch and trailing edge flap controllers (Ungurán et al, 2018(Ungurán et al, , 2019, while simultaneously posing challenges with the presence of the induction zone. The closer the lidar measurement is taken to the rotor plane, the higher the deficit between the measured inflow and free flow wind speeds.…”

Section: Introductionmentioning

confidence: 99%

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Uncertainty identification of blade-mounted lidar-based inflow wind speed measurements for robust feedback–feedforward control synthesis

et al. 2019

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Abstract. The current trend toward larger wind turbine rotors leads to high periodic loads across the components due to the non-uniformity of inflow across the rotor. To address this, we introduce a blade-mounted lidar on each blade to provide a preview of inflow wind speed that can be used as a feedforward control input for the mitigation of such periodic blade loads. We present a method to easily determine blade-mounted lidar parameters, such as focus distance, telescope position, and orientation on the blade. However, such a method is accompanied by uncertainties in the inflow wind speed measurement, which may also be due to the induction zone, wind evolution, “cyclops dilemma”, unidentified misalignment in the telescope orientation, and the blade segment orientation sensor. Identification of these uncertainties allows their inclusion in the feedback–feedforward controller development for load mitigation. We perform large-eddy simulations, in which we simulate the blade-mounted lidar including the dynamic behaviour and the induction zone of one reference wind turbine for one above-rated inflow wind speed. Our calculation approach provides a good trade-off between a fast and simple determination of the telescope parameters and an accurate inflow wind speed measurement. We identify and model the uncertainties, which can then be directly included in the feedback–feedforward controller design and analysis. The rotor induction effect increases the preview time, which needs to be considered in the controller development and implementation.

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“…The reduction of higher frequency loads was also achieved in Barlas et al . and Unguran and Kühn by employing additional trailing edge flaps and in Larsen et al . by using additional flow measurement sensors.…”

Section: Introductionmentioning

confidence: 99%

Load reduction on a clipper liberty wind turbine with linear parameter‐varying individual blade pitch control

2017

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The increasing size of modern wind turbines also increases the structural loads caused by effects such as turbulence or asymmetries in the inflowing wind field. Consequently, the use of advanced control algorithms for active load reduction has become a relevant part of current wind turbine control systems. In this paper, an individual blade pitch control law is designed using multivariable linear parameter-varying control techniques. It reduces the structural loads both on the rotating and non-rotating parts of the turbine. Classical individual blade pitch control strategies rely on single-control loops with low bandwidth. The proposed approach makes it possible to use a higher bandwidth since it accounts for coupling at higher frequencies. A controller is designed for the utility-scale 2.5 MW Liberty research turbine operated by the University of Minnesota. Stability and performance are verified using the high-fidelity nonlinear simulation and baseline controllers that were directly obtained from the manufacturer. pitch control algorithm should not change the thrust and the torque of the turbine in order to maintain the power output at its desired level.Sophisticated, model-based state space control approaches also became possible by transforming the whole periodic system into the non-rotating frame. 7 Multivariable control designs were investigated in Bossanyi 2 on the basis of a linear quadratic regulator and in Geyler and Caselitz 8 and Vali et al. 9 on the basis of H 1 -norm optimal control. Adaptive control techniques for individual blade pitch control are presented in Magar et al. 10 Periodic control for load reduction using individual blade-pitch control was developed and tested in Stol et al. 11 These controllers aimed at the once-per-revolution (1P) blade loads and were shown to yield similar results as the classical two-SISO-loops control strategy. A direct extension of this control strategy to target loads at higher frequencies is addressed in van Engelen 12 and Petrović et al. 13 additionally using complex, higher-order transformations of the sensor data. Successful field test results of such controllers for two-bladed and three-bladed turbines is presented in Bossanyi et al. 14 However, in this case, a linear analysis of the closed-loop model to verify robustness and performance is not straightforward anymore. Further, it also requires several design steps instead of a single one. This is also true for the feedforward filters added in each of the two SISO loops to cope with the 3P loads on the nacelle proposed in Bossanyi. 15 The feedforward filters are designed using a constrained numerical optimizations technique. Because of these reasons, the classical two-SISO-loops control strategy serves for comparison in this paper. The reduction of higher frequency loads was also achieved in Barlas et al. 16 and Unguran and Kühn 17 by employing additional trailing edge flaps and in Larsen et al. 18 by using additional flow measurement sensors. The disturbance accommodation techniques that are presented in W...

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Combined individual pitch and trailing edge flap control for structural load alleviation of wind turbines

Cited by 11 publications

References 15 publications

An investigation of unsteady 3-D effects on trailing edge flaps

An investigation of unsteady 3-D effects on trailing edge flaps

Uncertainty identification of blade-mounted lidar-based inflow wind speed measurements for robust feedback–feedforward control synthesis

Load reduction on a clipper liberty wind turbine with linear parameter‐varying individual blade pitch control

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