Analysis and Synthesis of Networked Control Systems with Limited Communication Capacity


Student thesis: Doctoral Thesis

View graph of relations


  • Fei HAN


Awarding Institution
Award date19 May 2014


With the rapid development of modern industry, control systems are becoming larger in scope and more decentralized in location, and are thus difficult to be implemented in a traditional directly-connected way. Consequently, networked control systems(NCSs) have attracted considerable research attention in recent decades, where the various components of control systems are connected through communication networks with benefits such as easy maintenance and low cost. However, the introduction of communication networks intro control systems will bring several challenging issues due to limited communication capacity, such as packet dropouts, network-induced delays, quantization, data rate and media access constraints. Due to these network-induced issues, the performance of NCSs will be much degraded and control systems can even become unstable. Therefore, it is of both theoretical and practical significance to develop novel approaches to analysis and synthesis of NCSs in order to reduce the adverse effects of these network-induced issues. In particular, this thesis will concentrate on the control and estimation problems of NCSs with limited communication capacity.

At first, a novel output feedback controller design method for a class of discretetime linear NCSs is presented, where the issues of network-induced delays, packet dropouts and quantization in both sensor-to-controller (S/C) and controller-to-actuator (C/A) channels are addressed simultaneously. The packet dropouts and network-induced delays are modeled together as the bounded time-delays in the buffer of the receiving node. A new asynchronous quantization scheme is proposed, where the dynamic quantization parameters at each node are updated locally so that the synchronized quantization parameters between sending and receiving nodes are not needed. The corresponding quantization errors are converted into the bounded system uncertainties. By constructing a Lyapunov-Krasovskii functional, a sufficient condition for the asymptotical stability of the closed-loop NCSs is derived in terms of a set of linear matrix inequalities. Moreover, the corresponding dynamic output feedback controller gains are obtained by an algorithm based on the cone complementarity linearization.

Then we study the H∞ state feedback control problem for a class of networked nonlinear systems with packet dropouts and network-induced delays, where the nonlinear systems are represented by T-S fuzzy dynamic models. The packet dropouts and network-induced delays are modeled together as the time-delays at receiving node governed by a transition probability matrix. A piecewise compensator is designed to estimate the lost or delayed packet throughout the transmission in order to obtain the better H∞ performance of the closed-loop NCSs. Based on a piecewise Lyapunov functional, the piecewise compensator and controller parameters are derived by introducing some slack matrices and solving a set of linear matrix inequalities.

We also investigate the network-based filter design method for a class of nonlinear systems represented by T-S fuzzy dynamic models. A unified framework is proposed to model the networked nonlinear filtering systems with network-induced delays, packet dropouts and quantization. Dynamic quantizers are utilized to solve the saturation and dead zone problems in comparison to traditional static quantizers, and the delays and packet loss are modeled together as the time-delays in the buffer at the receiving node. The attention is focused on the design of a piecewise filter so that the overall filtering error system is asymptotically stable with a guaranteed H∞ performance. The corresponding filter parameters are determined by linear matrix inequality techniques based on a piecewise Lyapunov functional.

Finally, the modeling and control of a network-based nonlinear quadrotor is presented. The network-based nonlinear quadrotor is approximated by a T-S fuzzy dynamic model. Both the network-induced delays and packet dropouts in S/C and C/A channels are addressed. Based on a common Lyapunov functional, a fuzzy controller is designed by solving a set of linear matrix inequalities so that the resulting closed-loop quadrotor system is asymptotically stable with a guaranteed H∞ performance. Simulation results are provided to illustrate the effectiveness of the proposed methods.