For many simple systems a PID-style controller does well enough, but for more complex systems some kind of state-based model tends to work out better, whether t

For many simple systems a PID-style controller does well enough, but for more complex systems some kind of state-based model tends to work out better, whether the model is built on knowledge of the system or by observing its behavior. For the latter, there's an entire field devoted to this problem called "system identification", one popular textbook seems to be online nowadays at http://user.it.uu.se/~ts/sysidbook.pdf http://user.it.uu.se/~ts/sysidbook.pdf