Structural Health Monitoring of Wind Turbine Systems: Data-based Lifetime Models Development for Integration into Control Systems

Technical systems experience different changes due to damage increase and the change of system parameters over service lifetime. These changes are caused by system exposure to different loading profiles, leading to decreased reliability and ultimately to the loss of functionality. Concerning inevitable aging of the system, it is important to examine effects with highest impact to reducing reliability and to predict the remaining or consumed lifetime of the system so that appropriate actions can be performed in accordance with actual State-of-Health (SoH). This thesis concerns the establishment of an efficient approach for determining the SoH and lifetime prognosis of particular components of recuperative and alternative power generation systems. Concretely, Wind Turbine (WT) systems are considered. The adaption of operation conditions in accordance to estimated current State-of-Health as well as extension of the lifetime through adapted control strategy is therefore an important part. The main aim of the thesis is modeling of functionality of technical systems through the establishment of lifetime models, which are prerequisite for the development of suitable control strategy. Such control concept is known as Safety and Reliability Control Engineering (SRCE) concept and is firstly introduced and published in 1996. Aforementioned concept enables affecting system’s reliability and the extension of the lifetime by integrating the knowledge about current SoH into the control strategy. To establish lifetime model, the measurements from Structural Health Monitoring (SHM) systems and their correlation to the degradation is necessary. In accordance with this, special emphasis in this thesis is given to SHM of wind turbine components, especially those SHM methods applicable to rotor blades, bearings and gearboxes, as well as energy storage devices. In this sense, not only an examination of the component itself but also an examination of its constituent materials, are taken in consideration (composite materials, metallic structures). Implementation of adapted control strategy illustrating simultaneously the possibilities for lifetime extension and power regulation are discussed using simulation model of wind turbine. In accordance with prerequisites for adapted control strategy implementation, wind turbine fatigue load is examined and integrated into the model. Controller design in this case is conditioned by the knowledge about examined fatigue load and predicted remaining useful lifetime. Reliability-oriented control strategy proposed in the thesis affects system’s reliability through adapted control actions in accordance with current SoH. Additionally, the development of three new lifetime modeling approaches taking in consideration SHM data from tribological system are presented in this thesis. Beside lifetime model establishment concerning tribological system, an examination of damage mechanisms and lifetime modeling approaches related to Lithium-Ion Batteries (LIBs) using experimental data from LIB test rig is illustrated and discussed. Main contribution of this thesis lies in the development of new lifetime modeling approaches and in proved possibility of adapted reliability-oriented control strategy to avoid premature failures of the system, increased operation and maintenance costs, as well as critical events leading to high economical and human resource losses. Obtained results concerning proposed lifetime models with regards to prediction accuracy are satisfying for all three proposed models. The number of model parameters, model complexity, prediction accuracy, and requirements set on experimental data sets used for model training vary. These four criterion are discussed in terms of model evaluation and determination of model applicability to real systems. By tracking structural loads and effect of induced mechanical stresses on system’s reliability, it is illustrated that structural loads, primarily flap-wise bending moments of rotor blades, are decreased through adapted control strategy providing extension of remaining useful lifetime. The discrepancy between desired and obtained generator power is held as less as possible. According to the results, control objectives related to power generation are slightly sacrificed, but only when the level of structural load is excessive and the system is close to its end of life. Presented results are obtained using simulation model of wind turbine.