AN ANTIWINDUP DESIGN FOR LINEAR-SYSTEMS WITH INPUT SATURATION

An anti-windup design problem is posed and it is shown that all ''obse rver-based'' anti-windup modifications solve this problem at least loc ally. Sufficient conditions for an observer-based anti-windup modifica tion to solve the global version of this problem are presented. A nove l observer-based anti-windup design is then proposed such that the ant i-windup problem can be interpreted in terms of a reduced-order system . In particular, the proposed anti-windup design induces an invariant subspace for the dynamic behavior of the mismatch between the constrai ned and unconstrained closed-loops. The dynamics in this invariant sub space are identical to the behavior of the plant with input saturation starting at the origin, stabilized by linear state feedback and drive n by the mismatch between the unconstrained input and this input passe d through a saturation function. The second part of the paper shows ho w the original dynamic compensator can be modified, while retaining th ose dynamic features that produce a desirable closed-loop steady-state response. to ensure that the requisite invariant subspace exists and it is reasonably tuned for input saturation. Two case studies are carr ied out on systems that have been investigated in the literature. (C) 1998 Elsevier Science Ltd. All rights reserved.