FAST_SFunc

Good morning,

I’m working with a FAST-Simulink model. The first input of the Wind Turbine block demands electrical generator torque and electrical power (according to FAST’s User Guide).
I think that the electrical power is in the generator output, but I have doubts: could it be in the grid?
Thank you

Dear Ana,

The electrical power refers to the power output of the generator. The electrical power is an indirect input to the FAST S-Function because it is used only for output purposes. It does not directly impact the equations of motion–like the generator torque does–but can be passed as output to be used for controls feedback. You don’t need to calculate it if you don’t need to output it because it will not impact any other result of FAST.

I hope that helps.

Best regards,

Hi again,

I’m doing some tests to make sure which torque is being demanded by Wind Turbine block:

  • Setting:
    - VSContrl=3
    - GenModel=1
    - GBoxEff=80%
    - GenEff=90%
    - GBRatio=16.9
    - DrTrDOF=False

I use Constant blocks to supply electrical generator torque and electrical power demands to the FAST wind turbine block: Te=1300Nm, Pe=100kW

Wind Turbine block’s Outputs:

   - Powers: all results are consistent

         RotPwr=146kW;     HSShftPwr=117kW=(GBoxEff/100)*RotPwr   OK;     GenPwr=100kW (equal to the input Pe)  OK

   -Torques: ???

         RotTorq=27500Nm;    HSShftTq=1300Nm=(GBoxEff/(100*GBRatio))*RotTorq     OK;         GenTq=1300Nm   ??????      GenTq=HSShftTq?

I understand: HSShftTq without electrical losses (generator input ), GenTq with electrical losses (generator output). If I’m right should be GenTq=(GenEff/100)*HSShftTq=1171.5Nm but I have GenTq=1300Nm, thus GenEff isn’t being used, isn’t it?
Does it occur because VSContrl=3 (but GenModel=1)? Thus I think that Wind Turbine block demands generator torque without electrical losses.

Thank,

Best Regard,

Ana

Dear Ana,

For clarification of how the drivetrain model in FAST works, please see the following forum post: http://forums.nrel.gov/t/resistant-moment-of-the-rotor-and-of-the-electric-generator/408/1. Please note that following nomenclature differneces between that post and your post:

Your Post → Linked Post
GenTq → T_Gen
RotTorq → LSShftTq
RotPwr → LSShftTqRotSpeed
HSShftPwr → HSShftTq
GenSpeed

To clarify, the electrical torque (GenTq = T_Gen) is the torque applied to the generator rotor (or high-speed shaft (HSS)) from the generator stator. This should equal the mechnical torque within the HSS, HSShftTq, if the HSS is not accelerating or decelerating. It is the generator electrical power, GenPwr, that is influenced by the generator efficiency – see point 3 in the post linked above. Also, GenModel is only used when VSContrl = 0.

I hope that helps.

Best regards,