This paper presents a quantitative analysis of the fatigue loads in a down wind, yaw-controlled, fixed pitch, two-bladed teetered-rotor wind turbine using proportional-integral, full-state optimal, and fuzzy logic controllers. Time-domain simulation data is generated using the EASY5x/WT software developed at the University of Texas at El Paso. The simulation data reveal that the choice of controller type, or the controller dynamics, can play a very important role in the fatigue life of a wind turbine and should be considered early in the design process of the wind turbine. In summary, the fuzzy logic controller is the most robust controller under a wide regime of wind conditions. It provides the best overall performance in terms of power regulation capability and minimum fatigue loads. The optimal controller with a full-state Kalman filter observer provides a satisfactory performance interms of power regulation capability and loads when the operating condition is close to the design point at which the controller was optimized. It fails to regulate the power output when the actual operating point deviated too far, about 30 percent in our computer simulations, from the designed operating point. The PI controller provided satisfactory performance in power regulation. However, it produced the worst fatigue loads to the wind turbine among the three controllers.

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