1. Aeroelastic Stability and Control of Large Wind Turbines
STABCON

2. STABCON: Aero-Servo-Elasticity of wind turbines
Part 2
Part 1

3. PRVS and ASR turbines: NM80 prototype in Tjæreborg

4. Investigated topics for passive instability suppression
Effect of airfoil aerodynamics
Smooth stall characteristics increases the damping
Effect of flapwise – edgewise frequency coincidence
Coincidence creates a flapwise – edgewise whirling coupling
Effect of flapwise – edgewise whirling coupling
Coupled whirling modes ”share” aeroelastic damping
Effect of torsional blade stiffness
Low torsional blade stiffness may lead to flutter
Can whirl flutter happen on a wind turbine?
Yes for extremely low tilt/yaw stiffness of nacelle support
Edgewise/torsion coupling for large flapwise deflections
Downwind flapwise bending may increase edgewise damping
Effect of yaw error on damping from wake
The destabilizing effect of dynamic inflow changes slightly by yaw errors
Effect of generator dynamics
Damping effects depend on generator type and control strategy

5. Effect of edgewise/flapwise whirling coupling – PRVS

6. Effect of edgewise/flapwise whirling coupling – ASR

7. Effect of large flapwise deflection – PRVS
downwind pre-bend
upwind pre-bend

8. Effect of large flapwise deflection – ASR
downwind pre-bend
upwind pre-bend

9. Investigated topics for integrated aeroelastic control
Power/speed controller issues
Speed controller frequency placed away from aeroelatic frequencies
Active drivetrain damping by feedback to generator torque
Drivetrain loads reduced by up to 10 %
Active drivetrain damping reduces pitch activity
Active tower damping by feedback to collective pitch
Efficiency depend on the aeroelastic damping of the tower modes
Cyclic pitch for flapwise blade and tilt/yaw load reductions
Efficiency depend on the ratio of stochastic and deterministic loading
most relative efficiency for low turbulence
Too high feedback gains may lead to whirl-flutter-like instability
Are there conflicting objectives of combined controllers?
No, if there is a sufficient frequency separation of control actions

10. Cyclic pitch actions reduce flapwise blade loads

11. Cyclic pitch actions reduce tilt/yaw shaft and tower loads

12. Cyclic pitch actions affect the damping of tower modes

13. Active tower damping and cyclic pitch can be combined

14. Guidelines available from www.risoe.dk