Speed funnel control with disturbance observer for wind turbine systems with elastic shaft

The results from [1] and [2] are combined and extended to speed funnel control with simplified disturbance observer for wind turbine systems (WTS) with elastic shaft where active damping is necessary but only generator-side speed measurement is available. It is shown that (i) WTS with elastic shaft and disturbance observer have relative degree one, bounded-input bounded-output (BIBO) stable zero-dynamics and known sign of the high-frequency gain, (ii) active damping by the disturbance observer is feasible and (iii) funnel control guarantees “speed tracking with prescribed transient accuracy” and, so, achieves maximum power point tracking (MPPT). Control and damping performance of two funnel speed controllers with and without disturbance observer are compared in simulations.