Application of diagnosis and prognosis to wind turbine system based on fatigue load

Fatigue damage in wind turbine structures is mainly induced by fluctuating loads strongly affecting the structural response of the system. The examination of fatigue damage, classification of the system state, prediction of remaining lifetime as well as the extension of maintenance interval become a challenge in structural health monitoring of wind turbine systems mainly due to offshore application. This contribution focuses on the structural load analysis in terms of maintenance intervals as well as service lifetime extensions. To postpone the point in time at which the system becomes nonfunctional, the structural load has to be mitigated while the energy production is retained as close as possible to the desired value. As fatigue damage is strongly influenced by the inflow parameters, a suitable control strategy is adopted to reduce the bending moments in the blades as one typical example. The contribution discusses the case when the damage accumulation is suddenly increased due to an unexpected situation (for instance high crack propagation rate) targeting to show that even if it happens, it is possible to retain the planned service lifetime through an suitably adopted control strategy. Influencing factors on the fatigue damage progression are pointed out. Flap-wise, edge-wise blade bending moments, fore-aft and side-to-side tower bending moments time series data simulated using FAST model developed by NREL are used for these purposes. Furthermore, the system state determination based on accumulated fatigue damage is done using the diagnosis-based data-filtering algorithm, and is represented in form of traffic-light-like coding. Here each color describes a specific system state.