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.