Field testing of individual pitch control on the NREL CART2 wind turbine

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Field testing of individual pitch control on the
NREL CART-2 wind turbine E. Bossanyi and A
Wright Garrad Hassan Partners Ltd., NREL
Presented at EWEC 2009, Marseille
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Context

• Work carried out as part of the EU 6th Framework
  integrated project UPWIND.
• Over many years, simulations have demonstrated
  that Individual Pitch Control (IPC) can be an
  effective means of reducing wind turbine fatigue
  loading.
• To date, no publishable field test data is
  available to prove that IPC actually lives up to
  expectations in reality.
• Using the public-domain CART-2 and CART-3
  research turbines at NREL, this project provides
  a way to achieve the field validation which is
  needed to provide the confidence to design new
  turbines which rely on the load reductions which
  IPC can provide.

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The NREL Turbines

• Two turbines available 42m diameter, 660 kW
• Although not representative of modern multi-MW
  designs, turbines are adequate for proof of
  principle
• Research turbines advantage of being very
  accessible with minimum fuss
• CART-2 2-bladed aiming for measurements in
  spring 2009
• Turbine ready and operational
• Relevant 2-Bladed turbines still a definite
  option for large offshore machines
• Uses conventional strain gauges, but very robust
  well calibrated
• Fast pitch actuator should be suitable for IPC
• CART-3 3-bladed aiming for measurements in
  spring 2010
• Turbine ready but awaiting completion of the
  control system by NREL

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Programme

• July 2008 Principles agreed
• CART-2 testing Spring 2009 (should already be
  underway)
• CART-3 testing one year later
• October - November 2008 CART-2 algorithm design
  completed and tested in simulations.
• Delay awaiting final DOE signature of
  confidentiality agreement. Once this is in
  place
• Transfer of algorithm to NREL
• Further NREL proving simulations
• Still hoping to start field tests before end of
  current wind season!
• Summer 2009 CART-3 algorithm design to start.
• Spring 2010 CART-3 field testing.

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CART-2 turbine

• Teetered rotor, but teeter will be locked with
  teeter brake. Principle is to use IPC instead of
  teetering to reduce out of plane blade hub
  loads.
• Bladed model completed.
• CART-2 control algorithm designed by GH
• Optimal power production over nominal speed range
• Speed regulation by interacting torque and
  collective pitch control
• Drive train damping filter in torque controller
• F/A tower damping by collective pitch control
• 1P individual pitch control to reduce rotating
  and non-rotating loads
• 2P individual pitch control not required
• Simulation testing completed.

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Simulation at 18 m/sTower F/A damping Tower
base bending moment (My)

• Significant reduction of fore-aft tower vibration
  and fatigue loading at 1st tower frequency.

Tower 1st fore-aft mode
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Simulation at 18 m/s IPC Blade root out of
plane bending moment (My)

• 1P out of plane loads virtually eliminated on
  rotating components.
• Teeter hinge no longer needed!

Rotation frequency (1P)
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Simulation at 18 m/s IPC Rotating hub moment
(My)

• 1P out of plane loads virtually eliminated on
  rotating components.
• Teeter hinge no longer needed!

Rotation frequency (1P)
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Simulation at 18 m/s IPC Yaw moment (Yaw
bearing Mz) non-rotating frame

• 1P (rotating) becomes 0P and 2P on non-rotating
  components.
• 0P compensates for wind shear and direction
  change reduces peak loads.
• Large reduction in 2P fatigue loading.

Blade passing frequency (2P)
Low frequency (0P)
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Simulation at 24 m/s IPC Yaw moment (Yaw
bearing Mz) non-rotating frame

• Reduction at 0P helps to reduce peak yaw nod
  moments.
• Reduced 3P also helps.
• Reduced 3P means lower fatigue loads.

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Simulation at 18 m/s Pitch activity

• IPC requires extra pitch action
• Additional pitching is concentrated at 1P

Rotation frequency (1P)
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Simulation at 18 m/s Pitch activity
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IPC 2 Blades vs 3 blades

• Control action calculated in non-rotating frame
  two axes, just the same for any number of blades.
• Number of blades is embodied in the rotational
  transformations

• For 2-blades, non-rotating fatigue loads (2P) are
  reduced.
• For 3 blades, non-rotating fatigue loads are at
  3P. Reducing these requires additional (2nd
  harmonic) IPC at 2P (rotating), to reduce
  non-rotating loads at 1P and 3P. (Higher
  harmonics are also possible, but probably
  unnecessary.)

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2nd Harmonic IPC

• The CART-3 turbine will provide the opportunity
  for field testing of both 1P and 2P IPC

• The CART-3 algorithm is not yet designed, but a
  similar algorithm has already been designed for
  the Upwind 5MW reference turbine.

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1st and 2nd Harmonic IPCUpwind 5MW reference
turbine (3 bladed)

• Rotating loads reduced at
• 1P
• 2P

• Non-rotating loads reduced at
• 0P (and 2P)
• 3P (and 1P)

1st harmonic IPC
2nd harmonic IPC
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1st and 2nd Harmonic IPCUpwind 5MW reference
turbine (3 bladed)

• Extra pitch action at
• 1P
• 2P

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Conclusions

• IPC can replace teeter hinge on 2-bladed turbine
  (reduces 1P loads in rotating components).
• IPC on 2-bladed turbine also reduces 2P fatigue
  loading on non-rotating components.
• On 3-bladed turbine, 2nd harmonic (2P) IPC is
  needed to reduce the 3P fatigue loads on
  non-rotating components.
• CART-2 field measurements to start soon, with 1P
  IPC and tower fore-aft damping.
• CART-3 field measurements next year, with 1P and
  2P IPC and tower fore-aft damping.
• 2P IPC proven in simulations for 5MW Upwind
  turbine.

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Acknowledgements

• This work has been carried out under the 6th
  Framework Integrated Project Upwind. The
  support of the European Commission is gratefully
  acknowledged.