Combined feedback–feedforward tracking control for networked control systems with probabilistic delays

In this paper, we investigate the combined feedback–feedforward tracking control problem for networked control systems (NCSs) under the discrete-time framework. Network-induced delays, both on the network links from the sensor to the controller (S–C) and from the controller to the actuator (C–A), are considered. It is assumed that the probability for the occurrence of each delay is known within a set. We apply a predictive scheme to compensate for the C–A delay, and propose to design a controller for each network-induced delay. Using the augmentation technique twice, the tracking problem of the NCS is converted to a feedback control problem for delay-free stochastic systems. The stochastic stability and the H ∞ performance of the obtained closed-loop stochastic system are analyzed in terms of a linear matrix inequality and a linear matrix equality. Then, we propose the controller design method by solving a nonlinear trace minimization problem. Finally, an example on the control of a helicopter is given to illustrate the proposed design approach.