Restricted structure control of multiple model systems with Series 2 DOF tracking and feedforward action

The solution of a scalar optimal control problem is discussed where the fee dback, series tracking and feedforward controllers are chosen to have a ver y simple. Each controller term may be chosen to be of reduced order, lead/l ag, or PID forms, and the controller is required to minimize an LQG cost-in dex. The optimization is based upon a cost-function which also allows separ ate costing of the terms due to the feedback, tracking and feedforward cont rollers, The system model can be uncertain and can be represented by a set of models over which the optimization is performed. This provides a form of robust optimal control that might even be applied to non-linear systems th at can be approximated by a set of linearized models. The theoretical problem considered is to obtain the causal, stabilizing, fe edback, series-tracking and feedforward controllers, of a prespecified form , that minimize an LQG criterion over the set of possible linear plant mode ls. The underlying practical problem of importance is to obtain a simple me thod of tuning low-order controllers, given only an approximate model of th e process. The results are illustrated in a power generation control proble m for a system represented by 12 different linearized plant models. The sin gle feedback controller that is obtained has a simple form and stabilizes t he full set of models. Copyright (C) 2001 John Wiley & Sons, Ltd.