Control and robust tower oscillation damping for a wind turbine equipped with a hydrostatic drive train and a synchronous generator

In this paper, a model-based control is proposed for an innovative 5 MW wind turbine with a hydrostatic transmission and a synchronous generator. The proposed control is derived by solving Linear Matrix Inequalities (LMIs) so that given parameter uncertainties and state-dependent matrices can be considered adequately. It comprises both a SISO control for the rotor angular velocity by adjusting the hydrostatic transmission as well as an active oscillation damping of tower bending oscillations, where the pitch angle serves as control input. The control is capable to operate within the whole operating range from low to very high wind speeds. A disturbance observer is used to estimate the aerodynamic rotor torque as well as leakage effects in the hydrostatic transmission. Here, the wind speed can be reconstructed from the estimated rotor torque. The overall control performance is illustrated by realistic simulation results, which show an improved damping of tower oscillations and an excellent tracking behaviour for the controlled variables.

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