Quasi-decentralized control of process systems using wireless sensor networks with scheduled sensor transmissions

This paper develops a model-based networked control and scheduling framework for plants with interconnected units and distributed control systems that exchange information using a resource-constrained wireless sensor network (WSN). The framework aims to enforce closed-loop stability while simultaneously minimizing the rate at which each node in the WSN must collect and transmit measurements so as to conserve the limited resources of the wireless devices and extend the lifetime of the network as much as possible. Initially, the exchange of information between the local control systems is reduced by embedding, within each control system, dynamic models that provide forecasts of the evolution of the plant units when measurements are not transmitted through the WSN, and updating the state of each model when communication is re-established at discrete time instances. To further reduce WSN utilization, only a subset of the deployed sensor suites are allowed to transmit their data at any given time to provide updates to their target models. By formulating the networked closed-loop plant as a combined discrete-continuous system, an explicit characterization of the maximum allowable update period is obtained in terms of the sensor transmission schedule, the transmission times of the different sensor suites, the uncertainty in the models as well as the controller design parameters. It is shown that by judicious selection of the transmission schedule and the models, it is possible to enhance the savings in WSN resource utilization over what is possible with concurrent transmission condigurations. Finally, the results are illustrated using a network of chemical reactors with recycle.