# Drivetrain Dynamic Model

Greetings to the forum.

For the purposes of my research work, I need to apply Kalman filter to estimate the rotor speed and rotor torque for the FAST 5MW NREL, v8. For this purpose, I use the Drivetrain model from Estimation of rotor effective wind speed: a comparison, MN Soltani et al. The schematic representation of the drivetrain along with the equations of motion are given in the attachment. In order to apply the Kalman filter theory I need to use the correct values of Br, Bg, Ktheta, Btheta which correspond to the friction of the rotor, friction of the generator, stiffness of the drivetrain and damping of the drivetrain, respectively.

By looking at the ElastoDyn.dat, I compute Ktheta (DTTorSpr)=8.67637E+08 and Btheta (DTTorDmp)=6.215E+06, but I am unable to find the values for Bg, Br (I assume they might be lumped into Btheta, Ktheta and thus are equal to 0 but I am not sure). Could you please help me? Thank you in advance for your actions responses.

Bart

Dear Bart,

I don’t see that you’ve added an attachment. But from my understanding, Br in your model represents the aerodynamic damping (i.e. the change in aerodynamic torque with rotor speed) and Bg in your model represents the generator damping (i.e. the slope of the generator torque-speed curve). You can get both through a FAST linearization analysis.

Best regards,

Dear Jason,

thank you so much for your replies. In the forum linked as http://forums.nrel.gov/t/resistant-moment-of-the-rotor-and-of-the-electric-generator/408/1 you replied to another user that the equation of the drivetrain is

T_Aero – J_RotorAlpha = DTTorSpr(Azimuth-LSSGagPxs) + DTTorDmp*( RotSpeed- LSSGagVxs).

I was expecting a term Br (aerodynamic damping) to model viscous friction to appear in the equations i.e.

T_Aero – J_RotorAlpha = DTTorSpr(Azimuth-LSSGagPxs) + DTTorDmp*( RotSpeed- LSSGagVxs) +Br*RotSpeed.

Can you tell me please why viscous friction losses are not incorporated in the model? Thank you in advance for your responses!

Bart

Dear Bart,

Actually, aerodynamic damping and aerodynamic stiffness are included in the model because T_Aero itself depends on Azimuth and RotSpeed (though this function is nonlinear). When linearized, you could you write T_Aero = T_Aero_op + ( pT_Aero/pAzimuth )_op dAzimuth + ( pT_Aero/pRotSpeed )_opdRotSpeed, where “p” indicates partial, _op identifies an evaluation at the linearization operating point, and “d” indicates perturbations about the operating point. This will result in your expression, plus the inclusion of the aerodynamic stiffness. However, FAST does not linearize the aerodynamics during its nonlinear time-domain solution.

Best regards,

Hello everyone,

I am new to FAST and currently trying to simulate a small wind turbine model towed in a water tank.
I had a discussion with my supervisor about aerodynamic damping on wind turbine blades (since it is about 2 to 10 times bigger than structural damping according to him). Reading this and several other posts on this forum, I can see that it is included via the dependency on T_Aero on Azimuth and Rotspeed.
Now my question is:
In the paper AERODYNAMIC DAMPING OF NONLINEARILY WIND-EXCITED WIND TURBINE BLADES (P. van der Male, K.N. van Dalen, A.V. Metrikine) aerodynmaic damping is described as force reduction due to structural feedback velocity.
How does FAST account this effect?
I am using FAST v8 and AeroDyn15.

Kind regards
Joel Purtschert

Dear Joel,

Aerodynamic damping is calculated by FAST as a result of the coupling between the structural module (ElastoDyn or BeamDyn) and the aerodynamic module (AeroDyn). That is, the aerodynamic loads calculated by AeroDyn and sent to structural module depend on the structural motions (position/orientation and velocity of the various analysis nodes) sent from the structural module to AeroDyn.

Best regards,

Dear Jason,

Thank you for your quick response.

Kind regards
Joel Purtschert

Dear Jason,

Recently I am doing research in drivetrain model. I met some problem, so want to ask you for help.
Read the appendix of " Simulation for Wind Turbine Generators—With FAST and MATLAB-Simulink Modules" for learning how to use simscape to build the drivetrain model. It is detailed in every step with exception of the parameter setting.

So I want to ask where I can get these parameters of the model shown in the figure,such as stiffness, ratio an inertia. It is the model from the appendix. With these, I can verify whether I grasp the theory of this model by comparing my result to the report.

Dear FuHang,

These detailed properties of the drivetrain will depend on the wind turbine you are simulating. I’m not aware that such properties have been specified for any of the reference/baseline wind turbines publicly released by NREL.

Best regards,

Dear Jason,