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Implications on loads by up-scaling towards 20 MW size

V.A.Riziotis & S.G.Voutsinas National Technical University of Athens. H.A. Madsen & F. Rasmussen. Implications on loads by up-scaling towards 20 MW size. E.S. Politis Centre for Renewable Energy Sources. Scope of the work. - Objective of the work

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Implications on loads by up-scaling towards 20 MW size

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  1. V.A.Riziotis & S.G.Voutsinas National Technical University of Athens H.A. Madsen & F. Rasmussen Implications on loads by up-scaling towards 20 MW size E.S. Politis Centre for Renewable Energy Sources EWEA annual event, Copenhagen 16-19 April 2012

  2. Scope of the work • - Objective of the work • Assess the loads of up-scaled turbines taking into account • parameters of the control system • turbulent inflow characteristics • Analysis performed in the context of geometric similarity • simple pathway to obtain a first approximation of the critical operational and structural properties - As baseline turbine of the analysis the 5MW offshore RWT of UPWIND project is used EWEA annual event, Copenhagen 16-19 April 2012 2/17

  3. Background of geometric up-scaling • For any geometric scale factor s • the rotor speed decreases with 1/s - tip speed remains constant. • the power increases with s2 rule. • the aerodynamic loads and the rotor thrust scale up with s2 while moments scale with s3. • gravitational forces and mass follow s3 scaling while gravitational moments scale with s4 • the sectional bending stiffness follows s4 rule and section moment of resistance s3. • stresses due to aerodynamic bending loads are scale invariant - weight induced stresses scale linearly. • wind turbine natural frequencies normalized with the rotational frequency values remain unchanged - absolute values decrease with 1/s scale. EWEA annual event, Copenhagen 16-19 April 2012 3/17

  4. Controller response in up-scaled turbines tuning of controller parameters using a linear eigenvalue servoaeroelastic stability tool tuning of proportional gain A limit on tower damping is set for defining consistent Kp values EWEA annual event, Copenhagen 16-19 April 2012 4/17

  5. Controller response in up-scaled turbines 5 MW 10 MW 20 MW With up-scaling, natural frequencies decrease and come closer to controller frequencies pitch angle [deg] t/T interaction of controller modes with tower 1st fore-aft bending modes leads to unstable behaviour EWEA annual event, Copenhagen 16-19 April 2012 5/17

  6. Controller response in up-scaled turbines proportional gain of upscaled turbines P-I equation constant Proportional gain is preserved with upscaling EWEA annual event, Copenhagen 16-19 April 2012 6/17

  7. Controller response in up-scaled turbines integral gain of up-scaled turbines 5 MW Integral gain follows an 1/s scaling 20 MW EWEA annual event, Copenhagen 16-19 April 2012 7/17

  8. Effect of turbulent inflow In up-scaled turbines less coherent wind is experienced by points at the same dimensionless distance EWEA annual event, Copenhagen 16-19 April 2012 8/17

  9. Effect of turbulent inflow Effect of up-scaling on purely aerodynamic loads and power sdv Lower loads are obtained as a result of the less coherent wind over the rotor disk of bigger diameter EWEA annual event, Copenhagen 16-19 April 2012 9/17

  10. Effect of turbulent inflow Energy from the wind is concentrated to p-multiples in the rotating frame. With up-scaling, rotational frequency decreases and gets closer to the frequency range where wind spectrum contains the maximum energy EWEA annual event, Copenhagen 16-19 April 2012 10/17

  11. Effect of turbulent inflow Energy from the wind is concentrated to 3p-multiples for tower loads A more pronounced 3p peak is obtained EWEA annual event, Copenhagen 16-19 April 2012 11/17

  12. Aeroelastic loads of up-scaled turbines normalized thrust force Increase in loads as a result of slower response of pitch control. If the response of the controller is made faster interaction with tower modes will take place 1Hz equivalent load Decrease in loads as a result of spatial averaging of the wind over the rotor disk due to lower coherency EWEA annual event, Copenhagen 16-19 April 2012 12/17

  13. Aeroelastic loads of up-scaled turbines blade flapwise and edgewise moments loads variation with respect to 5MW turbine tower bottom fore-aft bending moment 1Hz equivalent load EWEA annual event, Copenhagen 16-19 April 2012 13/17

  14. Aeroelastic loads of up-scaled turbines Lower variations of power and rotor speed in the partial load region EWEA annual event, Copenhagen 16-19 April 2012 14/17

  15. Conclusions • Interaction of the control system modes with the structural modes is likely to occur as the rotor size increases which implies that a time scaling must be introduced in the control system parameters. • as the rotor size increases spatial coherency of the incoming wind, from the blade root to the blade tip decreases and as a result rotor and tower loads become lower in the partial load region • better power quality and lower rotor speed fluctuations are obtained for the up-scaled turbines • the energy of the wind concentrates mainly on multiples of the rotational frequency which indicates that the wake induced effects will have a strong variation with the azimuth EWEA annual event, Copenhagen 16-19 April 2012

  16. Acknowledgements The work has been partially financed by the EC within the FP6 UpWind project EWEA annual event, Copenhagen 16-19 April 2012

  17. Thank you for your Attention EWEA annual event, Copenhagen 16-19 April 2012

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