A robust control design in the parameter space

A graphical technique is proposed for design of controllers for plants with uncertain parameters. The technique is an interpretation of the Faedo-Kharitonov analysis in the space of controller parameters using the parameter mapping and the zero exclusion condition. The robust stability regions are delineated explicitly in terms of two controller parameters by plotting at most four curves in the parameter plane, regardless of the number of uncertain parameters. This allows for an effective characterization of lead and lag controllers for high-order interval plants. Multiparameter robust controller designs are accomplished with the same effort by relying on the standard dominant poles requirement.