Robust Quasi-decentralized Networked Control of Process Systems

This paper presents a quasi-decentralized networked control methodology for the robust stabilization of multi-unit plants whose constituent subsystems communicate over a shared resource-constrained communication network and are subject to time-varying external disturbances. The objective is to stabilize the plant while keeping the communication requirements to a minimum in order to reduce the unnecessary utilization of network resources. Initially, a local robust feedback controller is synthesized for each unit to account for the effect of the disturbances. Then the exchange of information between the local control systems is reduced by embedding, within each control system, a set of dynamic models that provide forecasts of the evolution of the plant units when measurements are not transmitted through the shared network, and updating the state of each model when communication is re-established at discrete time instances. By analyzing the resulting combined discrete-continuous closed-loop system, a necessary and sufficient condition for robust stability of the networked closed-loop plant is obtained. The stability condition can be used to explicitly characterize the interplays between the update period, the degree of plant-model mismatch, the selection of the controller design parameters, the size of the disturbances and the size of the achievable ultimate bound on the closed-loop state. Finally, the implementation of the robust networked control structure is demonstrated through an application to a chemical plant example.