I am studying control systems, and in my studies I have encountered the topic of control scheme of the form
and I have seen thaht this control scheme is really useful since it is possible to add a lag or lead compensator outside the closed loop, so it won't give stability problems.
At this point I was curious to know a little more and in particular I would like to know if it is possible to use a prefilter which is a delay. In such a way it would be possible to avoid the problem of stability given by a system with delay.
So, to explain better, I would have for example:
and so I could design a stable closed loop without delay, and then filter the reference with a delay, so use:
instead of using a closed loop with delay, which gives stability problems.
Do you think it would be a good idea? Or it would be impossible or conceptually wrong?