Presentations

Abstract

Fatigue plays a pivotal role in the design considerations for large offshore wind turbines installed on monopiles. This phenomenon is primarily caused by the wind and wave actions, resulting in undesirable vibrations of the support structure. In contrast to the fore-aft direction, where the presence of blades offers additional aerodynamic damping, the lateral or sideways direction experiences relatively less damping. The majority of contemporary wind turbines integrate control algorithms specifically designed to mitigate sideways vibrations and reduce fatigue on the support structure. In most of modern offshore turbines, a specific control algorithm, so called active sideway tower damper, is developed to control the side-side support structure oscillations by modulating the either of generator torque or individual blades pitching depending on the operational conditions. Adjusting the generator torque or pitching the blades induces a counterforce to moderate lateral oscillations of the support structure and consequently, improves the fatigue life of the support structure. The active tower damper employs sinusoidal modulation of the rotor torque or blade pitches, synchronized with the natural frequency of the turbine. Typically, this damper power regulation exhibits amplitudes ranging between 100 kW to 500 kW. It is important to note that these deliberate sinusoidal power variations become discernible on the transmission grid, posing potential risks to grid stability. A crucial equilibrium must be struck between the amplitude of these variations and the overall lifetime of the foundation. Presently, the European Association for the Coordination of Transmission System Operators (ENTSO-E) is actively formulating European standards aimed at limiting the permissible levels of forced power variations. This paper outlines the findings of an extensive measurement campaign and subsequent data analysis conducted on three instrumented turbines. The objective is to quantify the extent of lifetime consumption resulting from a regulating the active tower damper amplitude.