An increasing number of wind turbines implement individual blade pitch control (IPC) to reduce turbine dynamic loading, and thereby, to reduce the capital and operational costs associated with energy production. The aim of this paper is to demonstrate IPC on a wind turbine prototype, in a model-free data-driven manner and with reduced pitch activity. For this, subspace predictive repetitive control (RC) is used, which combines online system identification with the continuous implementation of RC to form a fully adaptive control law. The controller is tested on a scaled two-bladed wind turbine with active pitchable blades, placed in an open-jet wind tunnel. Substantial load reductions to an extent of 68% are observed, and strict control over actuator signal frequency content is achieved. The control law also demonstrates the ability to adjust to changes in system dynamics while maintaining a high degree of load alleviation.Index Terms-Adaptive control, individual pitch control (IPC), load alleviation, repetitive control (RC), subspace identification, wind turbine.

(2014). Subspace predictive repetitive control to mitigate periodic loads on large scale wind turbines. Mechatronics, 24(8), 916-925. DOI: 10.1016/j.mechatronics.2014 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. a b s t r a c tManufacturing and maintenance costs arising out of wind turbine dynamic loading are one of the largest bottlenecks in the roll-out of wind energy. Individual Pitch Control (IPC) is being researched for cost reduction through load alleviation; it poses a challenging mechatronic problem due to its multi-input, multi-output (MIMO) nature and actuation constraints related to the wear of pitch bearings. To address these issues, Subspace Predictive Repetitive Control (SPRC), a novel repetitive control strategy based on the subspace identification paradigm, is presented. First, the Markov parameters of the system are identified online in a recursive manner. These parameters are used to build up the lifted matrices needed to predict the output over the next period. From these matrices an adaptive repetitive control law is derived.To account for actuator limitations, the known shape of wind-induced disturbances is exploited to perform repetitive control in a reduced-dimension basis function subspace. The SPRC methodology is implemented on a high-fidelity numerical aeroelastic environment for wind turbines. Load reductions are achieved similar to those obtained with classical IPC approaches, while considerably limiting the frequency content of the actuator signals.

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An extension of the spectrum of applicability of rotors with active aerodynamic devices is presented in this paper. Besides the classical purpose of load alleviation, a secondary objective is established: optimization of power capture. As a first step, wind speed regions that contribute little to fatigue damage have been identified.In these regions, the turbine energy output can be increased by deflecting the trailing edge (TE) flap in order to track the maximum power coefficient as a function of local, instantaneous speed ratios. For this purpose, the TE flap configuration for maximum power generation has been using blade element momentum theory.As a first step, the operation in non-uniform wind field conditions was analysed. Firstly, the deterministic fluctuation in local tip speed ratio due to wind shear was evaluated. The second effect is associated with time delays in adapting the rotor speed to inflow fluctuations caused by atmospheric turbulence. The increase in power generation obtained by accounting for wind shear has been demonstrated with an increase in energy production of 1%. Finally, a control logic based on inflow wind speeds has been devised, and the potential of enhanced power generation has been shown by time-domain simulations.

Abstract. In this paper Linear Individual Pitch Control (LIPC) is applied to an experimental small-scale two-bladed wind turbine. LIPC is a recently introduced Individual Pitch Control (IPC) strategy specifically intended for two-bladed wind turbines. The LIPC approach is based on a linear coordinate transformation, with the special property that only two control loops are required to potentially reduce all periodic blade loads. In this study we apply LIPC to a control-oriented small-scale two-bladed wind turbine, equipped with, among others, two highbandwidth servomotors to regulate the blade pitch angles and strain gauges to measure the blade moments. Experimental results are presented that indicate the effectiveness of LIPC.