Effectiveness of individual pitch control on a 5 MW downwind turbine

Abstract

A novel experimental study of individual pitch control on downwind turbines is conducted. The experiment is accomplished using a sub-scale model of a 5 MW downwind turbine. It is shown that individual pitch control based on sinusoidal/cosinusoidal pitching schemes that are locked to the phase of the rotor rotation further improves the power output, yaw stability and mitigates the unsteady loads of a downwind turbine through the intelligent control system. The optimum pitching amplitude is observed to be insensitive to yaw angle. Furthermore, a negative sinusoidal pitching amplitude improves power and reduces overall unsteadiness at zero yaw angle. In the case of positive yaw; a positive cosinusoidal pitching amplitude improves power, reduces overall unsteadiness and improves yaw stability. In the case of negative yaw; when a positive sinusoidal pitching amplitude alleviates overall unsteadiness, improves yaw stability but reduces power while a positive cosinusoidal pitching amplitude increases power coefficient, alleviates overall unsteadiness but reduces yaw stability. Moreover, positive rotor yaw angle which is more stable than negative can be used to alleviate loads on downwind turbines during operation because overall unsteadiness is observed larger when the nacelle has a negative yaw angle, compared to when nacelle has a positive yaw angle.