A Structural Fatigue Monitoring Concept for Wind Turbines by Means of Digital Twins

Wind turbines are complex mechatronic systems designed to withstand high dynamic loads over a considerable period due to environmental influences. Following the guidelines from DNVGL or IEC, the design process of modern wind turbines is governed by a rather rough classification of annual mean wind speed and turbulence intensity resulting in very conservative design loads compared to the actual load conditions at the specific erection site of the wind turbine. Thus, structural reserves are very likely at the end of the turbine’s approved lifetime. Driven by this, a research collaboration between different institutions from wind industry and research facilities was initiated with the aim to exploit these structural reserves by means of continuous, model-based fatigue monitoring of individual wind turbine structures. Within this contribution, the authors present the fundamental process chain, arising challenges and first solutions employing the broad expertise of the individual project partners. Generally, the following key requirements are set for the monitoring concept: Precise estimation of the endured fatigue loads at critical spots by means of a digital twin; low sensor installation effort on the operating turbine comprising a minimal set of long-term reliable measurement hardware at accessible positions; online data processing on the turbine control system unit (SCADA). The research project comprises the design of state estimators for tower and blade structure, the definition of an optimal sensor network, the development of damage models for materials of blades and tower, concept studies on a scaled testbed of the turbine and the tests on the real wind turbine.