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Coordinated Control Design for Wind Turbine Control Systems

Coordinated Control Design for Wind Turbine Control Systems

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Coordinated Control Design for Wind Turbine Control Systems

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  1. Coordinated Control Design for Wind Turbine Control Systems W.E. Leithead and S. Dominguez University of Strathclyde

  2. CCD for WT Control Systems Outline • Background • Models and Dynamics • Performance Requirements • Design and Performance • Conclusion

  3. CCD for WT Control Systems Background • Over the last 20 years there has been an almost exponential growth in the size of wind turbines. • In offshore machines, the trend is towards bigger machines with taller towers. • New demands are being placed on the control system.

  4. CCD for WT Control Systems Background • Control systems are now being required to regulate some fatigue related dynamic loads • Of prime interest is the tower loads. • The larger the wind turbine the greater the requirement. • Must be achieved without increasing pitch activity.

  5. CCD for WT Control Systems Background • Normal approach is to add an outer loop to the generator speed loop aimed at reducing the tower fore-aft movement.

  6. CCD for WT Control Systems Background • Interaction of the two feedback loops causes some degradation of performance of the main generator loop. • The CCD approach entails a redesign of the generator speed loop accounting for the tower speed loop. • Greater reduction of tower fatigue is achieved without increasing pitch activity.

  7. CCD for WT Control Systems Models and Dynamics • The design is based on linear models that include all the dynamic components required for control design and performance assessment. • The dynamics include: • 2 modes for the tower • 2 modes for the blades • Drive-train

  8. CCD for WT Control Systems Models and Dynamics • Dynamics from pitch demand to generator speed for a multi-megawatt machine.

  9. CCD for WT Control Systems Models and Dynamics • Dynamics from pitch demand to tower speed

  10. CCD for WT Control Systems Models and Dynamics • The models have been validated against both measured data and FLEX data

  11. CCD for WT Control Systems Performance Requirements • Above rated wind speed to regulate: • Torque via power converter • Generator speed via blade pitch • Tower speed via blade pitch • Design issue: • Nonlinear aerodynamics • Minimise pitch activity • Accommodate transmission zeros

  12. V V h(V) p Actuator T(p,W,V) p Actuator T(p,W) W W CCD for WT Control Systems Aerodynamic nonlinearity • The aerodynamics are separable . • So wind speed is an additive disturbance.

  13. CCD for WT Control Systems Aerodynamic nonlinearity • Global scheduling to linearise plant is possible • Since rotor speed is low the feedback of dW/dt can be ignored.

  14. CCD for WT Control Systems Actuator activity • The most important measures are actuator speed and acceleration. • They are subject to saturation constraints. • Most sensitive to intermediate frequency components.

  15. CCD for WT Control Systems Actuator activity • Relative sensitivity to speed and acceleration is clear

  16. CCD for WT Control Systems Transmission zeros • Zeros impair control performance • Zeros become more prominent as size of machine increases

  17. CCD for WT Control Systems Design of generator speed loop • CCD is based on a parallel plant structure

  18. CCD for WT Control Systems Design of generator speed loop • CCD enables the zeros of the tower to be counteracted

  19. CCD for WT Control Systems Design of generator speed loop • CCD reduces the pitch actuator activity

  20. CCD for WT Control Systems Design of generator speed loop Actuator acceleration

  21. CCD for WT Control Systems Design of generator speed loop • Tower base moments are reduced by modification to generator speed loop control

  22. CCD for WT Control Systems Tower feedback loop • Further reduction in the tower loads is obtained by addition of a tower feedback loop. • The interaction with the generator speed loop is kept to a minimum.

  23. CCD for WT Control Systems Tower feedback loop • Tower base moments for standard generator controller, CCD and CCD+TFL.

  24. CCD for WT Control Systems Generator speed control • Speed and power fluctuations are not degraded Speed Power

  25. CCD for WT Control Systems Performance • Llifetime reduction in equivalent fatigue loads are • CCD 13% • CCD and TFL 18%

  26. CCD for WT Control Systems Conclusion • A new controller is discussed • Not subject to size-related constraints • Designed using well-validated models • Easily tuned • Lifetime tower fatigue load reduction of 18%