Hi Mehdi,
I think the references provided by Paul give quite a good picture of the complexities that play a role in system identification of wind turbines.
Maybe one more reference that might be interesting in the context of floating wind turbines is:
Control of floating wind turbines
G.J. van der Veen, LJ. Couchman, and R.O. Bowyer
2012 American Control Conference
This paper goes into the added complexity of the dynamics of floating turbines, showing that these dynamics are varying with the wind speed for example.
Pieter Gebraad
PhD student
Delft Center for Systems and Control
Delft University of Technology