Design of Robust Feed-through Compensator via Disturbance Observer

Abstract

A feed-through compensator is a dynamic system designed for a given plant, whose output is added to the output of the plant. It is typically used in order for the zeros of the combination of the plant and the compensator (seen from the new output) to have desired properties. In particular, Isidori and Marconi (2008) utilized a robust feed-through compensator for uncertain non-minimum phase nonlinear systems, which makes the combined system become of minimum phase so that the output feedback stabilization is rather easily achieved. For the design of robust feed-through compensator, they introduced the so-called auxiliary system and showed that, if the auxiliary system admits a robust output feedback stabilizer, then the robust feed-through compensator can be systematically constructed. This paper, while restricted to linear systems, presents a constructive method for designing the robust output feedback stabilizer for the auxiliary system. For this, minimum phaseness of the auxiliary system (not the plant itself) is required. In order to overcome this restriction, we also proposed a kind of nested design for which it is enough for the second auxiliary system of the auxiliary system to have minimum phaseness.