Abstract
This paper describes the characteristics of overturning moments and a method for estimating external forces on a prestressed concrete tower for a propeller-type wind turbine with three blades (Hub height: 50m, Rated power: 600kW). The overturning moments based on field measurements were investigated using strain-gauge data. It was found that the static overturning moment in the along-wind direction was affected by teh thrust of the wind turbine control. Furthermore, the standard deviation of the overturning moment increased in the ranges from 5m/s to 10m/s. This is because the first natural frequency of the wind turbine tower corresponds to the blade-passing frequency, i.e. the 3P frequency. In addition, the fluctuation of external forces acting on the wind turbine tower was estimated by inverse analysis based on the model frequency transfer function, using field measurement data. As a result, the relationship between the fluctuation of external force and the rotor speed was derived and a pitch control method was found.
