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Hyung-joon Bang – One of the best experts on this subject based on the ideXlab platform.

Niels Kjolstad Poulsen – One of the best experts on this subject based on the ideXlab platform.

  • a smart rotor configuration with linear quadratic control of adaptive trailing edge flaps for Active Load alleviation
    Wind Energy, 2015
    Co-Authors: Leonardo Bergami, Niels Kjolstad Poulsen

    The paper proposes a smart rotor configuration where Adaptive Trailing Edge Flaps (ATEF) are employed for Active alleviations of the aerodynamic Loads on the blades of the NREL 5 MW reference turbine. The flaps extend for 20 % of the blade length, and are controlled by a Linear Quadratic (LQ) algorithm based on measurements of the blade root flapwise bending moment. The control algorithm includes frequency weighting to discourage flap activity at frequencies higher than 0.5 Hz. The linear model required by the LQ algorithm is obtained from subspace system identification; periodic disturbance signals described by simple functions of the blade azimuthal position are included in the identification to avoid biases from the periodic Load variations observed on a rotating blade. The LQ controller uses the same periodic disturbance signals to handle anticipation of the Loads periodic component. The effects of Active flap control are assessed with aeroelastic simulations of the turbine in normal operation conditions, as prescribed by the IEC standard. The turbine lifetime fatigue damage equivalent Loads provide a convenient summary of the results achieved with ATEF control: a 10 % reduction of the blade root flapwise bending moment is reported in the simplest control configuration, whereas reductions of approximately 14 % are achieved by including periodic Loads anticipation. The simulations also highlight impacts on the fatigue damage Loads in other parts of the structure, in particular, an increase of the blade torsion moment, and a reduction of the tower fore-aft Loads.

  • full scale test of trailing edge flaps on a vestas v27 wind turbine Active Load reduction and system identification
    Wind Energy, 2014
    Co-Authors: Damien Castaignet, Thanasis K Barlas, Thomas Buhl, Niels Kjolstad Poulsen, Jens Jakob Wedelheinen, Niels Anker Olesen, Christian Bak, Taeseong Kim

    A full-scale test was performed on a Vestas V27 wind turbturbine equipped with one Active 70 cm long trailing edge flap on one of its 13 m long blades. Active Load reduction could be observed in spite of the limited spanwise coverage of the single Active trailing edge flap. A frequency-weighted model predictive control was tested successfully on this demonstrator turbine. An average flapwise blade root Load reduction of 14% was achieved during a 38 minute test, and a reduction of 20% of the amplitude of the 1P Loads was measured. A system identification test was also performed, and an identified linear model, from trailing edge flap angle to flapwise blade root moment, was derived and compared with the linear analytical model used in the model predictive contcontrol design model. Flex5 simulations run with the same model predictive control showed a good correlation between the simulations and the measurements in terms of flapwise blade root moment spectral densities, in spite of significant differences between the identified linear model and the model predictive contcontrol design model. Copyright © 2013 John Wiley & Sons, Ltd.

Dale E Berg – One of the best experts on this subject based on the ideXlab platform.

  • an overview of Active Load control techniques for wind turbines with an emphasis on microtabs
    Wind Energy, 2010
    Co-Authors: Scott J Johnson, C P Van Dam, Jonathon P Baker, Dale E Berg

    This paper outlines the benefits and challenges of utilizing Active flow control (AFC) for wind turbturbines. The goal of AFC is to mitigate damaging Loads and control the aeroelastic response of wind turbturbine blades. This can be accomplished by sensing changes in turbine operation and activating devices to adjust the sectional lift coefficient and/or local angle of attack. Fifteen AFC devices are introduced, and four are described in more detail. Non-traditional trailing-edge flaps, plasma actuators, vortex generator jets and microtabs are examples of devices that hold promise for wind turbturbine control. The microtab system is discussed in further detail including recent experimental results demonstrating its effectiveness in a three-dimensional environment. Wind tunnel tests indicated that a nearly constant change in CL over a wide range of angles of attack is possible with microtab control. Using an angle of attack of 5 degrees as a reference, microtabs with a height of 1.5%c were capable of increasing CL by +0.21 (37%) and decreasing CL by −0.23 (−40%). The results are consistent with findings from past two-dimensional experiments and numerical efforts. Through comparisons to other Load control studies, the controllable range of this microtab system is determined to be suitable for smart blade applications. Copyright © 2009 John Wiley & Sons, Ltd.

  • Active Load control techniques for wind turbines
    , 2008
    Co-Authors: Dale E Berg, Scott J Johnson

    This report provides an overview on the current state of wind turbturbine control and introduces a number of Active techniques that could be potentially used for control of wind turbturbine blades. The focus is on research regarding Active flow control (AFC) as it applies to wind turbturbine performance and Loads. The techniques and concepts described here are often described as ‘smart structures’ or ‘smart rotor control’. This field is rapidly growing and there are numerous concepts currently being investigated around the world; some concepts already are focused on the wind energy industry and others are intended for use in other fields, but have the potential for wind turbturbine control. An AFC system can be broken into three categories: controls and sensors, actuators and devices, and the flow phenomena. This report focuses on the research involved with the actuators and devices and the generated flow phenomena caused by each device.

Jong-won Lee – One of the best experts on this subject based on the ideXlab platform.

Timothy C. Green – One of the best experts on this subject based on the ideXlab platform.

  • Dynamic stability of a microgrid with an Active Load
    IEEE Transactions on Power Electronics, 2013
    Co-Authors: Nathaniel Bottrell, Milan Prodanovic, Timothy C. Green

    Rectifiers and voltage regulators acting as constant power Loads form an important part of a microgrid‘s total Load. In simplified form, they present a negative incremental resistance and beyond that, they have control loop dynamics in a similar frequency range to the inverters that may supply a microgrid. Either of these features may lead to a degradation of small-signal damping. It is known that droop control constants need to be chosen with regard to damping, even with simple impedance Loads. Actively controlled rectifiers have been modeled in nonlinear state-space form, linearized around an operating point, and joined to network and inverter models. Participation analysis of the eigenvalues of the combined system identified that the low-frequency modes are associated with the voltage controller of the Active rectifier and the droop controllers of the inverters. The analysis also reveals that when the Active Load dc voltage controller is designed with large gains, the voltage controller of the inverter becomes unstable. This dependence has been verified by observing the response of an experimental microgrid to step changes in power demand. Achieving a well-damped response with a conservative stability margin does not compromise normal Active rectifier design, but notice should be taken of the inverter-rectifier interaction identified.