Field Testing Controls to Mitigate Fatigue Loads in the Controls Advanced Research Turbine

Wind turbines are complex, nonlinear, dynamic systems forced by aerodynamic, gravitational, centrifugal, and gyroscopic loads. The aerodynamics of wind turbines is nonlinear, unsteady, and complex. Turbine rotors are subjected to a complicated 3-D turbulent wind inflow field with imbedded coherent vortices that drive fatigue loads and reduce lifetime. Design of control algorithms for wind turbines must account for multiple control objectives. Future large multi-megawatt turbines must be designed with lighter weight structures, using active controls to mitigate fatigue loads while maximizing energy capture and adding active damping to maintain stability for these dynamically active structures operating in a complex environment. Most large commercial turbines still use classical controllers based on a single input and a single output (SISO). While adequate for controlling the “stiff” machines of the past, these methods are inadequate for stabilizing and mitigating loads in future large flexible multi-megawatt turbines. Advanced adaptive control algorithms based on state-space methods are better suited to these challenges. They can meet multiple control objectives with fewer control loops, using multiple control actuators and sensors for reducing fatigue loading, stabilizing the complex structure, and maximizing power. At the National Renewable Energy Laboratory, we are designing, implementing, and testing advanced controls to maximize energy extraction and reduce structural dynamic loads. These control designs are based on a linear model of the turbine that is generated by specialized modeling software. In this paper, we show the design and simulation testing of a control algorithm to mitigate tower and drivetrain loads using advanced state-space control design methods. The controller uses rotor collective pitch to regulate the turbine’s speed in Region 3. It is also designed to add active damping to the tower’s first fore-aft mode. In addition, a separate generator torque control loop is designed to add active damping to the tower’s first side-side mode and the first drivetrain-torsion mode. This paper describes implementation and field tests of this controller in the Controls Advanced Research Turbine at the National Renewable Energy Laboratory. We compare the performance of this controller to results from a typical baseline Proportional-Integral-Derivative controller designed with just Region 3 speed regulation as the goal. Employees of the Midwest Research Institute under Contract No. DE-AC36-99GO10337 with the U.S. Dept. of Energy have authored this work. The United States Government retains, and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for the United States Government purposes † Senior Engineer, National Wind Technology Center, 1617 Cole Blvd., Mailstop 3811, AIAA member ‡ Senior Engineer, National Wind Technology Center, 1617 Cole Blvd., Mailstop 3811, AIAA nonmember € Lecturer, AIAA member 47th AIAA Aerospace Sciences Meeting Including The New Horizons Forum and Aerospace Exposition 5 8 January 2009, Orlando, Florida AIAA 2009-478 Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes. All other rights are reserved by the copyright owner.