Robust PI compensators design for FOPDT systems with large uncertainty

This work presents a control design method to determine the parameters of a proportional integral (PI) compensator satisfying desired specifications on the gain and phase margins or, alternatively, an upper bound on the sensitivity transfer function, for an uncertain plant. The process under consideration can be modeled by a first order plus dead time (FOPDT) model having interval parametric uncertainty, therefore a set of plants is considered. The proposed approach is based on the translation of the desired specifications into the compensator parameter space, obtaining in such a way a feasible region where design specifications are met for each of the plant considered. This feasible region is obtained by using a fractional-order system which is representative of the uncertain plant, instead of using each plant belonging to the set. To conclude, an example is given to illustrate the proposed method, this example is motivated from a real process.