FAST + Simulink pitch deg or rad?

I’m using FAST nonlinear WTG model inside the Simulink environment. Seems to me that the blade’s pitch angle in OutData is always measured in deg, while the pitch control I pass to the model should be in rad. Is that correct?


Hi Stefano,

Yes, you’re understanding of the FAST S-Function for Simulink is correct. The OutData array contains outputs with the conventions described in the “Output Files” section of the FAST User’s Guide (e.g., “deg” for angle and “kNm" for torque). The control inputs, however, must follow the same convention of FAST’s user-defined control routines (e.g., “rad” for angle and "Nm” for torque).

I hope that helps,

Hi all,
Using SIMULINK I could able to stabilize the speed of HSS by controlling torque and Power=torque*speed ( rad/s).
Now I am putting full featured grid model (electric grid+generator controls), for this task I am bit confused about the values that I shld pass to FAST because:

  1. Grid power will be always less than mechanical power and governed by operating conditions of the grid.
  2. Air gap torque of machine will be less than that of T_mechanical due to losses and other reasons.
    Your inputs on this will help me to stabilize the system with full featured model of the grid+converter+generator.


Dear Uday,

I’m not sure I understand your question.

The FAST S-Function block in Simulink simply needs you to specify the torque (in N-m) that the generator applies to the high-speed shaft. This torque can be derived from a simple torque-speed relationship or a much more sophisticated model depending on feedback from sensors (model output parameters) and/or including logic for electrical components. The applied aerodynamic loads, the inertia dynamics, and the mechanical losses (friction in the gearbox) are intrinsically included in the equations of motion implemented in the FAST S-Function block.

The electrical power (in watts) is an indirect input to the FAST S-Function block. It is used only for output. 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 use it for output.

I hope that helps.

Best regards,

Hi Jason,

Thank you for your prompt reply, as result I could able to solve the problem of stabilizing the output at desired value.
Recently, I moved from 32 bit O/S to 64 O/S ( Windows Xp to WIndows 7), and now I am getting error message, during the start of simulation that S Function doesn’t exit.
I think I have to recompile the S_fuction block again. Is there any easy way out ?, Also correct me if my interpretation is wrong.

Thanks & Regards

Have you tried installing the 32-bit version of MatLab on your 64-bit Win 7 box?

Hi Marshall,
Thank you for your prompt reply I re-installed matlab 32 bit version and its working fine.
But, Sure Some or the other day I have to migrate to 64 bit version.
Thank you once again for your inputs.


Hi Uday,

The FAST S-Function for Simulink that we supply in the archive of FAST v7.00.00a-bjj is compiled as a .mexw32 file. The “w32” part implies a Windows 32-bit version of MATLAB. You must recompile the FAST S-Function if you want to run it in 64-bit MATLAB. The source files necessary for recompiling the S-Function are available in the “Simulink” folder of the archive.

Best regards,