Accuracy improvement on fatigue test of megawatt wind turbine blades by adaptive fuzzy control

A single-point fatigue loading system of wind turbine blade driven by an unbalanced shaft was designed. To determine whether the vibrating performance of the loading system satisfied the fatigue test demanding, the blade was driven by different frequency under open-loop control mode in on-site flapwise fatigue test. The results showed that the more the driven frequency close to the blade's natural frequency, the more the amplitude of the blade increase. In resonance mode, the amplitude of the blade can reach the maximum value certainly. However, the peak values of the vibration have some fluctuation, which will influence the accuracy of fatigue test. To solve the unstable problem of blade's amplitude, the amplitude of blade's loading point obtained by laser range meter was taken as the control index, the deviation of the amplitude and its variation tendency were taken as the input and the loading frequency as the output, then an adaptive fuzzy control system based on multistage network was built to realize blade's constant amplitude vibrating. The on-site test showed the adaptive fuzzy control algorithm put forward in this paper could maintain the error of the peak value of vibration less than 5 mm, which satisfied the fatigue test requirement.