Strange FAST GenPwr Behaviour

I am attempting some very simple modelling to reproduce the turbine power curve but I am experiencing some strange behavior of generator output power.
I have tried various different wind input files, even one with wind = 0m/s. (the graph below shows the behavior of the generator output power (y axis) with no wind present).

Using alternative input wind files still results in an observed generator starting power of roughly 5mw no matter the initial wind speed.

I believe this may have something to do with the method of turbine control used in the ServoFile. This is an area I am unfamiliar with. Any advice in choosing suitable parameters would be welcomed.
Thanks in advance,
Miles

Dear Miles,

The generator power output by FAST is based on the selected torque-control or generator model. What are VSContrl and GenModel set to you in ServoDyn input file?

Best regards,

Hi Jason

I am using:
VSContrl = 5
Genmodel = 2

This modelling was done using the 32-bit windows executable

Miles

Dear Miles,

I’m not exactly sure what you are doing, but it sounds like you are running the model of the NREL 5-MW turbine with the baseline controller (implemented as a DLL). The generator power for this model is simply computed as a the mechanical power multiplied by an electrical conversion efficiency, that is for power-producing operation: GenPwr = GenTqGenSpeedGenEff (with appropriate units applied). My guess is the sudden drop in GenPwr at the beginning of the simulation is related to a sudden drop in rotor speed (the inertia of the rotor is losing energy). I’m not sure why the torque and speed don’t drop to zero, but I guess this has something to do with other conditions you are simulating.

Best regards,