speed control in low speed region

Hi, all
When I using the FAST simulation to simulate the torque control in low speed region. From the Fast user manual, I know that the control is
Tem=K_opt* omega_r
where K_opt is a constant, and the omega_r is the rotor speed. I have a question about the simulation result. Here is the wind speed (I using the constant wind speed (9m/s))

Here is the torque input and rotor speed

Since I using the constant speed, in time interval [0 5]s, why the rotor speed is increasing. Is this normal?


Torque should be related to rotor speed squared in your formula (see page 26 of manual), does this resolve the issue?


Dear Prof. Paul.Fleming
Thanks for your reply. From the figures, I can see that the optimal rotor speed is 17rpm when the wind speed is 9m/s. But when I set the initial rotor speed as 17 rpm, I think the rotor speed should stay around 17rmp. But when I simulate this, the rotor speed will also increase to a large value, and then back to the neighborhood of 17rpm. Why this phenomenon appear?

There could be a couple of reasons for the transient behavior. I mentioned earlier relating torque to the square of rotor speed, did you try this?

Dear Paul.Fleming.
Yes, the figures are obtained using the torque controller which the square of rotor speed. Thanks
Best wishs

In that case my guess is it is a start-up transient, usually I remove the first 30-60s from a simulation as being a period of time while the transients settle-out,

Thanks for your reply