Control can improve energy capture and reduce dynamic loads in wind turbines. In the 1970s and 1980s, wind turbines used classical control designs to regulate power and speed. The methods used, however, were not always successful. These systems often had bandwidths large enough to destabilize low-damped flexible modes leading to high dynamic load fatigue failures. Modern turbines are larger, mounted on taller towers, and more dynamically active than their predecessors. Control systems to regulate turbine power and maintain stable, closed-loop behavior in the presence of turbulent wind inflow will be critical for these designs. New, advanced control approaches and paradigms must account for low-damped flexible modes in order to reduce structural dynamic loading and achieve the 20-to 25-year operational life required of today's machines. This report applies modern state-space control design methods to a two-bladed teetering hub upwind machine at the National Wind Technology Center (NWTC), which is managed by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) in Golden, Colorado. The design objective is to regulate turbine speed and enhance damping in several low-damped flexible modes of the turbine. Starting with simple control algorithms based on linear models, complexity is added incrementally until the desired performance is firmly established. This work was funded under the U.S. Department of Energy's Wind and Hydropower Technologies Program in the Office of Energy Efficiency and Renewable Energy. v y cg distance from control axis to center of gravity, in blade section, perpendicular to chordline y elastic distance from control axis to elastic axis, in blade section, perpendicular to chordline z position along blade or tower centerline D z disturbance states ˆD z estimated disturbance state 1 D z specific disturbance states 2 D z specific disturbance states 3 D z specific disturbance states z cg distance from control axis to center of gravity, in blade section, in chordwise direction z elast distance from control axis to elastic axis, in blade section, in chordwise direction z ac distance from control axis to aerodynamic center, in blade section, in chordwise direction They are also designed to attenuate (and in some cases cancel) wind disturbances, which are uniform over the rotor disk (have no azimuthal or spatial variation). Chapter 6 describes the addition of generator torque as a control input to enhance damping of the drive-train torsion mode and relieve some of the requirements placed on the rotor collective pitch control system. Chapter 7 describes the design and performance of controls using independent blade pitch as the control input. The main emphasis in the chapter is attenuation of wind disturbance components, which vary azimuthally, such as wind shear. These controls are also shown to satisfy the main control objective, regulation of rotor speed in region 3. Chapter 8 compares results for these modern control designs with results from simple PI control for the CART. In th...

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Abstract-We review the objectives and techniques used in the control of horizontal axis wind turbines at the individual turbine level, where controls are applied to the turbine blade pitch and generator. The turbine system is modeled as a flexible structure operating in the presence of turbulent wind disturbances. Some overview of the various stages of turbine operation and control strategies used to maximize energy capture in below rated wind speeds is given, but emphasis is on control to alleviate loads when the turbine is operating at maximum power. After reviewing basic turbine control objectives, we provide an overview of the common basic linear control approaches and then describe more advanced control architectures and why they may provide significant advantages.

The method of Frobenius is used to solve for the exact frequencies and mode shapes for rotating beams in which both the flexural rigidity and the mass distribution vary linearly. Results are tabulated for a variety of situations including uniform and tapered beams, with root offset and tip mass, and for both hinged root and fixed root boundary conditions. The results obtained for the case of the uniform cantilever beam are compared with other solutions, and the results of a conventional finite-element code.

online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste SummaryWind turbines are complex, nonlinear, dynamic systems forced by gravity, stochastic wind disturbances, and gravitational, centrifugal, and gyroscopic loads. The aerodynamics of wind turbines are nonlinear, unsteady, and complex. Turbine rotors are subjected to a complicated 3-D turbulent wind inflow field, which drives fatigue loading.Wind turbine modeling is complex and challenging. Accurate models must contain many degrees of freedom to capture the most important dynamic effects. Design of control algorithms for wind turbines must account for these complexities. These algorithms must capture the most important turbine dynamics without being too complex and unwieldy.Typical large commercial wind turbines are variable speed, and control generator torque in Region 2 to maximize power and control blade pitch in Region 3 to maintain constant turbine power. Simple classical control design techniques such as proportional-integral-derivative (PID) control for pitch regulation in Region 3 are typically used to design the controls for such machines.Classical control design methods are based on a single input and single output. A disadvantage of classical control methods is that multiple control loops must be used to simultaneously damp several flexible turbine modes. If these controls are not designed with great care, these control loops interfere with each other and cause the turbine to become unstable. The potential to destabilize the turbine grows as turbines become larger and more flexible, and the degree of coupling between flexible modes increases. Using all the available turbine actuators in a single control loop to maximize load-alleviating potential is advantageous. Advanced multi-input multi-output (MIMO) multivariable control design methods, such as those based on state-space models, can be used to meet these multiple control objectives and use all the available actuators and control inputs in a single control loop.The purpose of this report is to give wind turbine engineers information and examples of the design, testing through simulation, field implementation, and field testing of advanced wind turbine controls. This report will be Part I in a two-part series of reports that detail advanced control design, implementation, and test results. Part I (this report) will highlight the control development process, from forming control objectives, to designing the controller, to testing the controller through analytical simulation, to field implementation and initial field testing. Part II (to be completed later) will give a detailed comparison of results from advanced load alleviating state-space controllers to test results from baseline controllers without load alleviation. The purpose of Part II is to demonstrate through rigorous testing the load mitigating potential of the advanced state-space controllers compared to the baseline control.