Validation of a wind misalignment observer using field test data

• Wind observer provides rotor-equivalent wind misalignment information, to be used for wind turbine yaw control.
• Observer uses blade loads, wind speed and rotor azimuth, all quantities typically already available on modern wind turbines.
• Model-free approach, uses field test data to build observation model.
• NREL CART3 wind turbine field data is used for model validation.
• Observed wind misalignment is better correlated with met-mast measurements than the on-board wind vane.

A previously described observer of wind misalignment is validated using field test data collected on the NREL CART3 wind turbine. The observer uses blade root bending moment 1P harmonics, computed using the transformation of Coleman and Feingold, to infer the rotor-equivalent relative wind direction. The observation model parameters are determined by a least squares fitting using recorded blade loads and met-mast measured wind direction and speed; a random sample consensus (RANSAC) algorithm is used to robustify the parameter estimation procedure while detecting outliers in the experimental samples. The observer is validated using an independent verification data set: recorded blade bending loads are fed to the observer and the estimated wind misalignment is compared to both the one provided by the met-mast vanes, assumed as the ground truth, and by an on-board nacelle-mounted wind vane. Results show that the rotor-equivalent wind misalignment estimates provided by the proposed observer are well correlated in the low frequency spectrum with the met-mast reference, and in general are in much better accordance with it than the on-board wind vane measurements.