Robust stabilization of interval plants using lead or lag compensators

The authors show that robust stabilization over an interval for plants using lead or lag compensation reduces to the simultaneous stabilization of the vertex plants. These results are especially attractive in the case of proportion-integral compensation. Such compensators are defined by two parameters. Hence, the existence of a robustly stabilizing compensator can be carried out through graphical techniques in the plane. The authors note several open questions that remain