Optimal tuning of PID controllers for integral and unstable processes

Tuning formulas for PID controllers applied to integral and unstable proces ses are presented. In particular, the controller parameters are determined, based on the process model, to minimise integral performance criteria such as ISE, ITSE and ISTE. Results have been obtained by means of genetic algo rthms, in order to avoid local minima in the optimisation procedure. Both t he set-point following and the load disturbance rejection design specificat ions are addressed. The achieved results can be adopted both for tuning pur poses and fur the evaluation of the performances of a pre-existing PID cont roller.