Ripple-free conditions for lifted multirate control systems

Measurements in chemical processes are often unavailable at a uniform rate due to constraints on the sampling rates of process variables. Situations s uch as these and others give rise to a set of multirate signals comprising a multirate system. Control of multirate systems is appealing and challengi ng from a theoretical and practical point of view. Multirate control design in the lifting framework consists of lifting the system and subsequently d esigning a controller for the single-rate lifted system. In this work, it i s shown that under certain conditions, intersample ripples arise in the out puts of closed-loop multirate systems, The process output can be guaranteed to be ripple-free if the controller satisfies certain constraints. Further , it is shown that the presence of an integrator in the plant aids in elimi nating these intersample ripples. Experimental evaluations are presented in support of these theoretical results. (C) 2001 Elsevier Science Ltd. All r ights reserved.