One of the unique capabilities of the FAST observer is that it can lock on even if the motor is already spinning. This is very common in fan applications and is also quite useful in starter generators where you need to match synchronization before you take control. This is often called flying start, anti-wind, or matched speed.
If the motor is spinning and you enable the drive (with Rs Recal disabled), FAST will immediately attempt to lock on, take control, and drive it to the correct torque or speed. But this method can be a little harsh as the speed reference starts at 0 so you get an immediate torque command to compensate.
For a very smooth start you can do the following:
- Enable InstaSPIN-FOC/FAST but disable the PWM outputs. This allows FAST to continue to track the fan movement.
- Initialize the all PI Integrators to 0
- Get the estimated speed from FAST
- Set the speed reference to this estimated speed
- Enable the PWM output: this will allow FAST to seamlessly take control of the fan at the existing speed
- Now set the new speed & acceleration command
