An L-infinity extension of transmission-zero and robust-design notions to global tracking in uncertain nonlinear systems

The author considers robust multitracking controllers for uncertain nonlinear systems, namely, controllers that generate prescribed tracking behavior in multivariable systems with uncertain parameters, nonlinear characteristics, and external disturbances. The approach used is based on operator formulations in special Banach spaces isomorphic to L_∞, spaces whose norms provide both precise and natural measures of global tracking. With these spaces, system equations are reformulated as fixed-point operator equations, and design criteria are realized as fixed-point inequality conditions under which tracking errors satisfy prescribed norm constraints. Among the results are explicit design parameters relating to both the time and frequency domains