RotorTorque, FAST interfaced with simulink


I’d like to know how does FAST compute the torque of the rotor.
I also have a problem when FAST is interfaced with simulink.I am working on my master thesis as an electrical engineer on wind energy. I made the model of the yaw control and variable speed control in simulink and it worked fine, but when I insert FAST in order to simulate the wind turbine the simulation is very slow. For example a simulation of 20s may take up to 45 minutes! In the beginning I thought that maybe it has to do with the sample time. I use in my simulink model a sample time of 10^-5 and in FAST a DT of 0.004. I put a rate transition block before and after the FAST block, but nothing changed. Have you any idea, of the cause of this problem?

Thank you in advance,


Dear George,

For information on how the rotor torque is computed in FAST, please see the forum post found here:

Regarding your long run times, I’m not sure I understand what you mean when you say, “I use in my simulink model a sample time of 10^-5.” Regardless, have you chosen time steps that are appropriate to your model? There are many good topics on this forum explaining how to choose a proper time step (DT) for FAST. But basically, the highest natural frequency in your model determines the required DT. Algebraic loops in a Simulink model are also known to cause long run times. More information and suggetions on how to resolve a problem regarding algebraic loops are availalable in the Simulink documentation and in the forum post found here:

Best regards,