Active tower damping for an innovative wind turbine with a hydrostatic transmission

In this paper, a decentralised control approach for an innovative 5 MW wind turbine with a hydrostatic transmission is presented that covers the whole range from low to very high wind speeds. An active damping of tower oscillations is achieved by using the pitch angle as control input. An elastic multibody system is employed to derive a control-oriented model for the first tower bending mode, which serves for the design of a stabilising control law. The active oscillation damping is combined with a multi-variable gain-scheduled PI state feedback control that allows for tracking desired trajectories for the angular velocities of both rotor and generator. The overall control performance is illustrated by realistic simulation results, which show an improved damping of tower oscillations and excellent tracking behaviour for the controlled variables.