Frequency-Shaped Penalty Functions for Robust Control Design

Modern Control Laws are based on the optimization of a certain performance Index. These control laws behave well for the nominal plant parameters but the performance can be very sensitive to small errors in the plant model. Recently considerable work has been done to evaluate robustness of modern control laws in the presence of plant transfer function uncertainties. This work indicates poor robustness particularly when state estimation is used to derive variables for feedback. This paper discusses an approach to synthesize multivariable control laws which are robust with respect to system errors. The approach is based on the frequency shaping of penalty functionals, and combines good features of modern and classical control approaches.