Optimal PID controllers for unstable and resonant plants

This paper presents some results for robust tuning of PID controllers for different kinds of plants. The design method is based on a constrained optimization procedure. For stable non-oscillating plants a set of auto-tuning rules is given, which leads to almost optimal controllers. It is also noted that remarkably good results can be obtained for integral, highly resonant, and even unstable plants with poles not too far in the right half-plane