Very large negative "GenPwr"

Hi All,

I am running a simulation of NREL 5MW baseline turbine with TurbSim FF binary wind inflow.
In the output, I got the electrical power output of generator, “GenPwr”, to be as low as -0.6 MW at some moment of time.
Is it considered as normal operation even if we have such large negative power output?
If it is normal operation, when we would expect negative power output, and what are the causes of the high power usage?

  • My guess is that when wind speed is lower than cut-in speed, the control system is consuming the power. If that is the case, I am really curious about how “GenPwr” is calculated in this case.

Thanks a lot!

Qiang

Dear Qiang,

This would not be considered “normal”, but it is difficult for me to guess what is causing this. A couple clarifying questions:

*What generator model or torque-control model are you using?
*Is the generator degree-of-freedom (GenDOF) enabled in your model?

Best regards,

Dear Jason,

Thank you for your quick reply. In the .fst input file, I defined generator model and generator DOF to be

2 GenModel - Generator model {1: simple, 2: Thevenin, 3: user-defined from routine UserGen} (switch) [used only when VSContrl=0]
True GenDOF - Generator DOF (flag)

Some update about the negative values of GenPwr: the negative values are not synchronous with low wind speed. They occur even when the wind speed is 13 m/s.

regards,

Qiang

Dear Qiang,

What is VSContrl set to? (GenModel is only used when VSContrl = 0.) If VSContrl = 0, meaning that you using the Thevenin-Equivalent Circuit (TEC) generator model (GenModel = 2), then how did you derive the TEC model parameters for the NREL 5-MW turbine?

Best regards,

Dear Jason,

I see, I am setting VSContrl = 2 which means that FAST is using user defined variable speed control mode rather than the TEC model.
However, I do not think I have defined any UserVSCount ( I still do not know how to do this ), which means the generator is not driven correctly.
On the other hand, NREL 5MW baseline turbine uses conventional variable-speed configuration. So if I just use the simple variable speed control and define the following parameters, would we possibly solve the problem? Please let me know if any of the parameters are wrong, thanks again!


1 VSContrl - Variable-speed control mode {0: none, 1: simple VS, 2: user-defined from routine UserVSCont, 3: user-defined from Simulink} (switch)
1173.7 VS_RtGnSp - Rated generator speed for simple variable-speed generator control (HSS side) (rpm) [used only when VSContrl=1]
43093.55 VS_RtTq - Rated generator torque/constant generator torque in Region 3 for simple variable-speed generator control (HSS side) (N-m) [used only when VSContrl=1]
0.0255764 VS_Rgn2K - Generator torque constant in Region 2 for simple variable-speed generator control (HSS side) (N-m/rpm^2) [used only when VSContrl=1]
10 VS_SlPc - Rated generator slip percentage in Region 2 1/2 for simple variable-speed generator control (%) [used only when VSContrl=1]

Best regards,

Qiang

Dear Jason,

I would like to share another update. After switched to simple variable-speed control mode, the power output looks reasonable now.
On the other hand, after a little bit research, I found that the problem that I had was caused by using user-defined variable-speed control routine without correctly compiling FAST according to the instruction given in page 6 of FAST User’s Guide.

Thanks again for pointing me to the right direction to go.

With best regards,

Qiang

Dear Qiang,

Yes, the baseline torque and pitch controller for the NREL 5-MW turbine is implemented as a GH Bladed DLL. You can find a version of FAST v7.02.00d-bjj compiled with the GH Bladed DLL interface here: wind.nrel.gov/public/jjonkman/FA … erface.exe.

Best regards,