Field Testing Controls to Mitigate Fatigue Loads in the Controls Advanced Research Turbine Alan D. Wright Lee J. Fingersh National Renewable Energy Laboratory Karl A. Stol University of Auckland 28th ASME Wind Energy Symposium Orlando, Fl. January 5, 2009
Presentation Scope • Show design of region 3 generator torque and blade pitch controller. • Goals: • Region 3 speed regulation • active damping of tower side-side and fore-aft motion • Describe field implementation and tests in the Controls Advanced Research Turbine. • Compare state-space control results to baseline PID control results.
Nacelle Yaw Generator Torque Blade Pitch Control Actions Commercial Turbine Control
Region 3 Control Design • Control Actuators: Collective blade pitch, generator torque • Goals: • Collective Blade Pitch Control: • Speed regulation • Tower fore-aft damping • Generator Torque Control: • Tower side-side damping • Drive-train torsion damping • Two separate control loops: • Collective blade pitch • Generator torque
Questions • Can separate control loops be used to add active damping to two closely spaced modes? • Tower 1st fore-aft mode (0.87 Hz.) • Tower 1st side-side mode (0.88 Hz.) • Will these separate loops destabilize each other? • Two separate control loops: • Collective blade pitch • Generator torque • Will adding damping reduce tower fatigue loads?
Full State Feedback Control • Regulate rotor-speed in the presence of wind-speed disturbances and stabilize turbine modes. • Stabilize flexible modes through full state feedback. • Use state estimation to provide the controller with needed states (including wind-speed). • Account for uniform wind disturbances • 2-Multiple input/single output control loops
Rotor Collective Pitch Control Model • Perturbed structural dofs & rates: • tower f-a • rotor collective flap • generator-speed Pitch actuator states
Generator Torque Control Design Model • Perturbed structural dofs & rates: • tower s-s • drive-train torsion • generator-speed filter states
Testing Strategy • Using two separate uncoupled control loops to add active damping to two closely spaced tower modes • Will these two control loops interact and destabilize the turbine? • Test the tower f-a damping with collective pitch first. • Add tower s-s damping with generator torque.
Results Probability Density Functions:
Results Tower Bending Moments:
Results Power Spectral Densities:
Results Pitch Rate and Generator Torque:
Conclusions • Designed and performed field tests of two separate control loops: • Rotor collective pitch control • active tower f-a damping • Region 3 speed regulation • generator torque control • active tower s-s damping • active drive-train torsion damping • Field tests demonstrate 30% reduction in tower f-a and 26% reduction in tower s-s fatigue loads compared to simple PID controls. • Reasons for lack of drive-train torque load mitigation not resolved. • Results showed no undesirable interactions between these separate control loops.
Future Work • Resolve issue with drive-train torsion damping and re-test controller. • Implement and field-test independent blade pitch for shear mitigation and generator torque control. • Investigate alternative sensors for independent pitch control • look ahead Lidar • additional blade sensors • hub or shaft sensors
Acknowledgements • Dr. Michael Robinson – NREL management support • Garth Johnson, Scott Wilde – CART maintenance and support • Marshall Buhl – MCrunch data analysis scripts
Questions? Dr. Alan D. Wright 303-384-6928 email@example.com