Control of a wind turbine with a hydrostatic transmission — An extended linearisation approach

In this paper, a simplified model of the NREL 5MW wind turbine with a hydrostatic transmission is derived. A suitable control scheme is described, and the steady state operating points of the system are calculated. The system is given in extended linearised form, and this form is used to design a gain scheduled linear quadratic regulator (LQR), with wind speed and difference pressure as scheduling parameters. Steady state operating points are used as desired values for feedforward control, and disturbance compensation is implemented to minimise the influence of rotor torque variations. Wind turbines operate in different control modes, with different control objectives which are dependent on wind speed. The developed controller is designed to operate for the entire operational range of the wind turbine. The controller is validated through simulation over a range of wind speeds.