Testing Further Controls to Mitigate Loads in the Controls Advanced Research Turbine

Abstract

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. 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 describe testing of a control algorithm to mitigate blade, tower and drivetrain loads using advanced state-space control methods. The controller uses independent blade pitch to regulate the turbine’s speed in Region 3, mitigate the effects of shear across the rotor disk, and add active damping to the tower’s first fore-aft bending mode. In addition, a separate generator torque control loop is designed to add active damping to the tower’s first side-to-side mode and the first drivetrain-torsion mode. This paper describes preliminary implementation and field tests of this controller in the Controls Advanced Research Turbine at the National Renewable Energy Laboratory. We make preliminary performance comparisons of this controller to results from a typical baseline proportional-integral-derivative controller designed with just Region 3 speed regulation as the goal.