Robustness of the estimator As explained before the synthesis

The observer model identification phase was performed as previously explained, by subjecting a nominal wind turbine model to wind fields of different known mean speed and direction, and recording the associated blade root moments. This nominal observation model was then used for estimating wind misalignments from the response of perturbed wind turbine models, obtained by changing some of the machine parameters with respect to their nominal values. The study considered perturbations in the following model parameters:•Stiffness of foundations (up to −40% change), on account of different Z-VEID-FMK characteristics of different installations. Only reductions in the foundation stiffness of the reference virtual model were considered, as higher values did not lead to noticeable changes in the response.•Vertical inclination of the wind flow (up to ±6° with respect to the value used for the identification of the observation model), on account of orographic effects of different installation sites.•Rotor imbalance due to pitch misalignment of one of the three blades (up to ±0.9°).•Miscalibration of one blade load sensor, where bending moment m in the flapwise or edgewise direction is assumed to be sensed as ms = c + sm, c being a constant bias (up to ±0.1% of the bending moment at standstill with the blade parallel to the ground) and s a miscalibration scaling factor (considered to be comprised in the range s∈[0.9,1.1]).•Changes in the airfoil aerodynamic characteristics (up to 24% increase in drag and up to 24% reduction in lift), on account of effects such as leading edge erosion, dirt accumulation and formation of ice on the blades.