Aeroelastic Stability and Control of Large Wind Turbines

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Aeroelastic Stability and Control of Large Wind
Turbines
STABCON
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STABCON Aero-Servo-Elasticity of wind turbines
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PRVS and ASR turbines NM80 prototype in Tjæreborg
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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

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Effect of edgewise/flapwise whirling coupling
PRVS
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Effect of edgewise/flapwise whirling coupling
ASR
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Effect of large flapwise deflection PRVS
downwind pre-bend
upwind pre-bend
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Effect of large flapwise deflection ASR
downwind pre-bend
upwind pre-bend
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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

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Cyclic pitch actions reduce flapwise blade loads
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Cyclic pitch actions reduce tilt/yaw shaft and
tower loads
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Cyclic pitch actions affect the damping of tower
modes
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Active tower damping and cyclic pitch can be
combined
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Guidelines available from www.risoe.dk
R-1575
R-1577