Alireza Rezaeian
DOI Number: N/A
Conference numer: IFASD-2019-057
Stability analysis of wind turbine is increasingly becoming a design critical subject in the wind energy industry. For small wind turbines with low rated power no aeroelastic instability was observed or registered but this had an end with increasing the size of the wind turbines to produce more electric power. The work presented in this paper consists of three parts. The first part describes the mechanism of some of well-known instabilities in the rotor dynamics e.g. blade flutter, rotor whirl-flutter and the instability due to the coupling of the rotor modes with the modes of the non-rotating structure. The possibilities of formation of these instabilities for a wind turbine are discussed. Furthermore, some wind turbine specific instabilities documented in the various literatures, e.g. blade edgewise instabilities (in and outside stall area), are as well highlighted. The second part introduces a stability analysis tool for rotating systems, MAESTRoS (MesH AeroElastic Stability analysis Tool for the Rotating Systems), which has been developed by the author and can be applied for the stability analysis of wind turbines. This tool makes use of the methods known from helicopter dynamics and aeroelasticity (e.g. application of multiblade coordinate system and Floquet theory). In the final part, the selected methodology of simulation of structure and control system and calculation of aerodynamic loads for the aeroelastic stability of a wind turbine is discussed. In the scope of this methodology, a wind turbine model is created in a multidisciplinary simulation environment using MBS-tool SIMPACK and SIMULINK. Aerodynamic loads are calculated using AeroDyn v13/ v15. For the (aero)-elastic stability analysis, a generic multi-megawatt wind turbine has been considered. On this paper, the emphasis is placed on prediction of rotortower coupling instability, an instability mechanism that can be related to the ground resonance phenomenon on helicopters. Demonstratively, the generic wind turbine has been scaled up (using the scale factor 2) applying the wind turbine similarity rule. Rotor-tower coupling instability of the scaled wind turbine was investigated and compared with the reference wind turbine (scale factor 1) results. This exploration has been carried out in the joint research project “GridLoads” (0324192A/B) funded by the German Federal Ministry for Economic Affairs and Energy.