Abstract
A novel strategy to reduce unwanted swings and motions in floating wind turbines is presented. At above rated wind speeds, the platform, on which the wind turbine is mounted, causes the generator speed control loop to become unstable. The proposed strategy assures stability of the control loop by an additive adjustment of the measured generator speed using tower fictitious forces. The developed strategy is independent of the platform and wave dynamics.
Highlights
For onshore wind turbines, the interaction between the drive-train dynamics and the tower dynamics introduces zeroes in the transmittance between pitch demand and generator speed
When a wind turbine is mounted on a non-stiff structure such as a floating platform, the drive-train dynamics interact with the dynamics of the floating platform through the tower
The right half plane zeroes arising from the interaction between the drive-train dynamics and the tower, at above rated wind speeds and at frequencies close to the tower frequency, can be removed by a control scheme called power coordinated control (PCC) [7], see Figure 3
Summary
The interaction between the drive-train dynamics and the tower dynamics introduces zeroes in the transmittance between pitch demand and generator speed. E.g. nacelle fore-aft accelerations/velocities to demanded pitch angle or to demanded generator torque, to provide active tower damping has been used with both land-based and floating wind turbines The impact of this strategy on rotor speed regulation and drive-train loads has to be carefully balanced. Adding such forces to the measured generator speed decouples the nacelle dynamics from the tower/platform dynamics at low frequencies and standard controllers for land-based wind turbines can be used in offshore floating applications without retuning This decoupling approach is robust since it does not depend on dynamic models of the wind turbine, only on the relative acceleration of the reference frames. The term in depends on wind speed and pitch angle but is weakly nonlinear such that, at above rated, the gain scheduling can handle its implementation
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