An H∞-almost disturbance decoupling problem for nonstrictly proper systems-A singular perturbation approach

The authors consider the almost disturbance decoupling problem with internal stability for a general class of nonstrictly proper systems. Under a set of solvability conditions, the state feedback and the observer-based measurement feedback controllers are explicitly constructed. All the developed controllers guarantee the asymptotic stability of the closed-loop system in the absence of the disturbances. Furthermore, they maintain disturbance quenching in the H_∞ sense. The controllers are parameterized in terms of a tuning parameter through which the desired degree of decoupling can be achieved