Resource-aware quasi-decentralized control of nonlinear plants over communication networks

This paper presents a quasi-decentralized nonlinear control methodology for multi-unit nonlinear plants whose constituent subsystems communicate over a shared, resource-constrained communication network. 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. To this end, an uncertain nonlinear model of the plant is initially used to design, for each unit, a stabilizing nonlinear feedback controller that requires state measurements from the neighboring units for implementation. To reduce the frequency at which the measurements are transmitted over the shared network, a copy of the stable compensated plant model is embedded in each unit to provide estimates of the states of the neighboring units when measurements are not available through the network. The state of the model is then updated at discrete time instances when communication is re-established. By analyzing the behavior of the model estimation error between updates, and exploiting the stability properties of the compensated model, a sufficient condition for practical stability of the networked closed-loop plant is obtained in terms of the update period, the plant-model mismatch and the controller design parameters. The stability condition can be used to obtain estimates of the maximum allowable update period and the size of the achievable residual set. Finally, the implementation of the networked control structure is demonstrated through an application to a chemical plant example.