Automatic track and balance of wind turbine rotors

This paper presents a new method that, by using the rotor harmonic response in the fixed frame, first detects imbalances due to pitch misalignment and then automatically corrects for them. Since a balanced rotor acts like a filter, quantities measured in a fixed frame of reference only contain frequencies equal to multiples of the number of blades: Therefore, a 1 per revolution (1P) frequency in the fixed frame is a symptom of rotor imbalance. The phase of the 1P signal is uniquely associated to the misaligned blade, while its amplitude is related to the severity of the misalignment. This allows for the formulation of a simple linear model relating 1P harmonic components to pitch misalignment angles. Given the linearity of the model, if a persistent 1P is detected, it is only necessary to further misalign the faulty blade once to allow for the identification of the model. When this has been obtained, one can readily compute the pitch angle that, applied to the faulty blade, will rebalance the rotor. The performance of the novel track and balance approach is demonstrated in the paper, with particular attention to its robustness in the face of uncertainties in the model and the operating conditions.