Nowadays, the majority of wind turbine blades are produced from composite materials which are subject to severe operational loadings. Thus, the composite material's behavior against in-service loadings is a great concern for wind turbine blade designers. This dictates the need for an experimental set-up for conducting real part experiments as similar as possible to in-service loadings. This research proposes a cost effective blade testing machine which is capable of conducting ultimate static and fatigue tests according to wind turbine blade standards. A new control unit is designed and implemented to track fatigue block loading in the frequency range of 1e3 Hz. The main focus is on designing a controller to perform desired block loading fatigue tests. The open loop transfer function is identified and the system uncertainty is calculated. PI, robust feedback and Two-Degree-of-Freedom robust controllers are designed and analyzed. Due to the poor robust performance, an adaptive feed forward controller is proposed based on the gain scheduling algorithm. Experimental results of the newly developed controller indicate a performance robustness. The proposed controller could be implemented for systems with large low frequency uncertainty at its operational frequency range, for example applications that the stiffness is variable during operation.

Keywords