Convex gain-scheduled control of an LFT model

This paper deals with an extension of the convex closed loop design technique, initially proposed by Boyd and co-workers for the case of a linear plant, to the scheduled case. The issue is to synthesize an LFT controller for an open loop LFT model, describing a continuum of time invariant linearizations (typically computed at the trim points of a nonlinear plant). The LFT controller and open loop plant share the same (scheduling) parameters, supposed to be measured. Modal and H_∞ specifications on the continuum of linearizations are directly introduced in the design procedure: first, a scheduled Youla parameterization is computed on the basis of an initial observed state-feedback LFT controller, designed to satisfy modal spec. Second, a Youla parameter is computed to satisfy I/O spec. In both cases the principle is to combine a multi-model design technique with a validation on the continuum using μ analysis. A nonlinear missile example illustrates the feasibility of the approach.