Hybrid Systems in Process Control

Modeling and control of hybrid systems, with particular emphasis on process control applications, are considered in this article. Based on a number of observations on typical mixed discrete and continuous features for such applications, a fairly general model structure for hybrid systems is proposed. This model structure, which clearly separates the open loop plant from the closed loop system, is suitable for analysis and synthesis of hybrid control systems. To illustrate this, three di erent approaches for control-law synthesis based on continuous and discrete speci cations are discussed. In the rst one, the hybrid plant model is replaced by a purely discrete event model, related to the continuous speci cation, and a supervisor is synthesized applying supervisory control theory suggested by Wonham-Ramadge. The other two methods directly utilize the continuous speci cation for determination of a control event generator, where time-optimal aspects are introduced as an option in the last approach.