Precontrol in speed controller of drive

Is 'precontrol' never or rarely used in the speed controller of a drive? Is a speed controller always a PI(D) controller?
Why no precontrol (if so)?
I suppose a position controller always has a precontrol?

I am sorry I do not understand your question.
If you are reffering to a VFD being mainly used for PID systems - for pumping or certain fan applications that can be true.
But other applications - then no.
it all depends on the application

What is pre control? I have never seen that term before.

Peter Nachtwey said:

What is pre control? I have never seen that term before.

Click to expand...

Maybe 'feed forward' is more a more common name?

Plc_User said:

Maybe 'feed forward' is more a more common name?

Click to expand...

You don't sound sure so I will only speak about feed forwards.

Feed forwards are term(s) that are added to the PID output. In motion control there is usually a velocity feed forwards and an acceleration feed forward and in our case a jerk feed forward too. This means there is an added term that is proportional to the target velocity, another proportional the the target acceleration. If the feed forwards are tuned up right on a well designed system the PID control would be barely needed. In fact in our training courses we tell the students the control output due to feed forward should be within about 5% of the actual control output. This means the PID only needs to do %5 of the work and the error will be about 1/20 of would it would have been without the feed forward.

If the feed forwards are tuned right the integrator term will not wind up. When tuning the feed forwards we sometimes plot the integrator term. If the integrator term varies from zero then we know what feed forward to tune by where the motion trajectory the integrator starts to wind up.

If you are using a VFD to control the speed of a line then position control isn't of prime importance. Neither is a quick response. It probably isn't a precision application and there is plenty of time for the integrator to wind up or wind down and over shooting a position probably isn't critical. In position control there isn't time for the integrator to wind up and wind down so the feed forwards provide the instant changes in the control output instead of waiting for errors to build up. In position control one must avoid the integrator winding up because it is the main cause of over shooting the command position.

When VFDs have been used for metal cutting applications then precise position and speed control is required and feed forwards should be used. In one rotary sheer application we even added an offset to compensate for the effects of gravity during all parts of the rotation.