Designing PI controllers for robust stability and performance

The design of proportional-integral (PI) controllers can profitably be carried out by referring to a normalized process model and to the loci of constant stability margins and crossover frequency in the parameter space. These loci are easily obtained from linear interpolation conditions. After checking the compatibility of the specifications with the controller structure, it is shown how the above-mentioned loci can be exploited for tuning purposes and robustness analysis. Criteria for choosing the controller parameters within the admissible region are discussed with the aid of examples.