A UK registered company, AADcontrol, Ltd. announced that it has successfully tested a process to damp away unwanted tower vibration to a one megawatt wind turbine located on the coast near Rotterdam, Netherlands.
The proprietary process, called Active Aerodynamic Damping (AAD) provides the forces needed to damp tower motions inherent in “soft tower” wind turbines, without adding weight to the system or compromising performance. The test wind turbine has a 62 meter rotor diameter and an operational rotor speed of about 27 rpm. In an effort to reduce costs, it was fitted with a so-called “soft tower” when it was designed and installed in 1999. One of the difficulties in designing a soft tower, however, is that the damping inherent in the steel tower structure is very low. This means that if a tower should begin to vibrate, the tower motion can persist and even come into resonance with the tower’s natural vibration frequency. Initial operation of the turbine revealed serious vibration problems. At wind speeds near rated power a once per revolution tower vibration would initiate and build to a point where the tower top was swaying back and forth on the order of two to three meters. Active Aerodynamic Damping, for which the patent process has been initiated, can offer a cost effective means of controlling unwanted tower motion and can lead to substantially reducing tower cost and risk.