# Wind Turbine Modeling

Hi,all.
I have a question about the sliding mode power control of 5MW turbine.
I would like to use the single lumped mass mode of the drive train as
JtdOmega_r/dt = Ta − KtOmega_r − Btθr − Tg
Kt=Kr+GB
GBKg
Bt=Br+GB
GB*Bg
where Kr is the rotor external damping; tau is the generator external damping; Br is the rotor external stiffness;and Bg is the generator external stiffness.

Could anyone tell me how to determine the value of Kt and Bt for such a reference wind turbine?

Thanks in advance.

Best regards
Ankang.Cao

Dear Ankang,

A few comments/questions:

• I’m assuming when you refer to tau, you mean Kg?
• What is the physical meaning of a generator stiffness Bg? I’ve not seen that before.
• A FAST linearization analysis with only the generator DOF enabled will give you a linear first-order model in terms of theta_r and omega_r, so, you should be able to derive your coefficients from that. Of course, the coefficients will depend on the operating point you linearize about (rotor speed, pitch angle, wind speed) and what generator model you’re using.

I hope that helps.

Best regards,

Dear Jason,
Thank you very much for your kindness.
1.Sorry, tau is a typo and it is Kg.
2.Stiffness refers to the ability of a material or structure to resist elastic deformation when stressed.Mostly it is very low,only exist in some papers,and can be ignored.
3.I knew coefficient depend on the operating point. And I thought the rotor external damping and generator external damping is located in Gearbox,and they are parameters,whick is can be detected sometimes.I don’t konw how to measure it.In this http://forums.nrel.gov/t/relation-between-stifness-and-inertia/1646/2 told him the value of rotor inertia.
If Kg and Kt must be detected by FAST, tell me how to do it,please.
Best regards,
Ankang.Cao

Dear Ankang,

I’m sorry, but I don’t really understand your question.

Best regards,

Dear Jason,
Thank you and sorry for bothering you.
In 5MW turbine,Kr is the rotor external damping and Kg is the generator external damping.I want these parameters,and i find the drivetrain torsional damper is 6215000(N-m/(rad/s)).I may think like this ‘Kr+GBGBKg=6215000’?
Best regards,
Ankang.Cao

Dear Ankang,

I don’t agree.

In a one DOF model with only the rigid-body generator rotation DOF enabled, then there is not drivetrain torsion and the 6215000 N-m/(rad/s) drivetrain damping of the NREL 5-MW turbine is not used.

Instead, Kr in your model represents the aerodynamic damping (i.e. the change in aerodynamic torque with rotor speed) and Kg 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 very much for your answer.I will keep working till get a suitable result.
Best regards