Dynamic Characterization of Operational Wind Turbines using Operational Modal Analysis (bn0919)

Experimental dynamic characterization of a wind turbine, operating under variety of conditions, is a desired task as it provides useful insights that can be used for number of tasks including design optimization, validation and verification of aeroelastic and finite element codes and development of an optimal control system. However, current state of art experimental techniques are insufficient to overcome the challenges posed by a wind turbine structure. Operational Modal Analysis (OMA) is a recent technique that aims at estimating the dynamic characteristics of a structure on the basis of measured responses of the structure to ambient excitations. OMA emerges from the needs in the application field of civil infrastructure and though its ability to characterize huge and complex structures (like bridges, stadiums, buildings etc.) makes it extremely attractive for application to wind turbines as well, there are certain issues which prevent its straightforward application to wind turbines. These issues include time variant nature of the wind turbine, presence of considerable aeroelastic effects in the excitation, presence of harmonic components in the excitation etc. The goal of this paper is to address these issues in order to make OMA more applicable and suitable for wind turbines. The paper first shows the application of OMA to a parked turbine and then subsequently shows its application to operational wind turbine. It is demonstrated how incorporating techniques like Coleman transformation and proper test planning, OMA can act as a viable tool for characterizing the dynamics of an operational wind turbine.