Quasi-decentralized Scheduled Output Feedback Control of Process Systems Using Wireless Sensor Networks*

AbstractThis paper presents a quasi-decentralized output feedback control structure for multi-unit plants with limited state measurements and distributed control systems that exchange information over a resource-constrained wireless sensor network (WSN). The networked control structure brings together model-based feedback control, state estimation and sensor scheduling to enforce closed-loop stability while simultaneously minimizing the rate of communication over the WSN. Initially, an observer-based output feedback controller is designed for each unit. To conserve the resources of the wireless devices, communication between the local control systems is suspended periodically for extended time periods during which each control system relies on models of the plant units to generate the necessary control action. Communication is then re-established at discrete time instances according to a certain schedule that determines the order and times at which the wireless sensor suites transmit the state estimates needed to update the states of the models embedded in the target units. By analyzing the combined discrete-continuous behavior of the scheduled closed-loop plant, we explicitly characterize the stability of the networked closed-loop system in terms of the communication rate, the sensor transmission schedule, the accuracy of the models, as well as the controller and observer design parameters. The results are illustrated using a chemical plant example where it is shown that by judicious management of the interplays between the control, communication and scheduling design parameters, it is possible to stabilize the plant while simultaneously enhancing the savings in WSN resources beyond what is possible with concurrent transmission configurations.