Relay-tuned FSA control for unstable processes with deadtime

In this paper, the control of open-loop unstable processes with deadtime is considered. Astrom and Hagglund´s (1984, 1988) relay auto-tuning for PID regulators is extended to such processes. Some conditions for limit cycles under relay feedback are given. A first-order unstable rational function plus deadtime is employed to model a class of the processes with a single unstable pole and deadtime. Its parameters are extracted from a relay feedback experiment. The modified finite spectrum assignment is used to control such a process and a simple method is then developed to obtain the closed-form control law for ease of real-time implementation. It is also shown that so auto-tuned MFSA system is practically stable in the face of perturbations in process dynamics. Simulation examples are included for illustration