Internal Stability of Disturbance Feedback Control Loops

Abstract

This paper deals with the so-called Disturbance Feedback Control concept, which is a technique to improve the disturbance rejection capabilities of existing control loops. We perform an internal stability analysis of a generic DFC setup and identifies several stability conditions that the DFC law must satisfy in order to guarantee stable closed-loop operation, assuming all subsystem blocks are linear and time invariant. The validity of the stability conditions are illustrated on two examples, a simple scalar example that serves to illustrate instability in case of an open-loop unstable plant model, and a more involved example concerning a DFC design for a gantry crane considered in earlier publications.