Proportional-Integral-Derivative tuning for servo/regulation control operation for unstable and integrating processes

The control of stable processes using PI/PID controllers is by now a well established and understood problem (even if new methods and approaches are continuously appearing). However, when the process has integrating or unstable characteristics the problem becomes much more difficult to manage. Several proposals have appeared in the literature presenting different approaches to tackle the problem. The procedures that have been proposed heavily concentrate on tunings for servo or regulation operation. A common drawback of such approaches is the high loss of performance when the other operation mode is used. In this paper, an approach for providing a unique tuning is presented. It combines tunings for both operation modes in such a way that the performance degradation is traded-off.