  Based on a reduced-order, dynamic nonlinear wind turbine model in
Takagi-Sugeno (TS) model structure, a TS state observer is designed as a
disturbance observer to estimate the unknown effective wind speed. The TS
observer model is an exact representation of the underlying nonlinear model,
obtained by means of the sector-nonlinearity approach. The observer gain
matrices are obtained by means of a linear matrix inequality (LMI) design
approach for optimal fuzzy control, where weighting matrices for the individual
system states and outputs are included. The observer is tested in simulations
with the aero-elastic code FAST for the NREL 5 MW reference turbine, where it
shows a stable behaviour both for IEC wind gusts and turbulent wind input.
