H_∞Control For Networked Control Systems With Random Delays, Packet Dropouts And Quantizations

With the development of communication technologies, networked control has be-come one of the main streams of control systems design. Network-induced time delays, packet dropouts and quantization due to the use of digital communication channels with limited bandwidth have become the research focus.The objective of the networked control is twofold:(i) to guarantee the closed-loop system to be stable and,(ii) to ensure that the closed-loop system satisfies some pre-scribed performance levels. In networked control systems (NCSs), time delays, packet dropouts will result in the degradation of the system performance or system stability, and the quantization will lead to such performance degradation. Therefore, NCSs per-formance analysis and controller design guaranteeing guaranteeing the performances are particularly important.There have been numerous investigations on stability analysis, controller design, and lots of results have been obtained. Quantization of NCSs has received increasing attention in recent years. The current emphasis mainly focuses on such problems as stability anal-ysis and controller design for NCSs. When time delay, packet dropouts and quantization are considered simultaneously, the problems of H∞control for NCSs have not been taken into full consideration.This thesis, based on prior research, considers both the effects of time delays or packet dropouts and the need for signal quantization in network communication chan-nels. This thesis presents H∞control methods and quantized control strategies via state feedback, dynamic output feedback and observer-based feedback, and the proposed meth-ods can guarantee the exponential mean-square stability and H∞performance level of the closed-loop systems. The plants studied in this thesis are linear time-invariant discrete-time systems. Network-induced time delays and packet dropouts, resulting from the sensor to the controller and the controller to the actuator communication channels, are described by random variables satisfying the Bernoulli distributed sequence, and the ran-dom consecutive packet dropouts are described by the product of these random variables. Here, the quantizers are dynamic quantizers, and are conjuncted with static quantizers via dynamic scalings.First, based on LMI technique, the H∞state feedback controller design is given for NCSs with random delays such that the closed-loop system is exponentially mean-square stable and with a prescribed H∞performance level. The H∞state feedback control problem for NCSs with random delays and simultaneous quantization is also considered. The proposed H∞controller design and the quantized H∞strategy guarantee exponen-tial mean-square stability of the closed-loop system and the prescribed H∞performance level. The obtained conditions for quantized controller design are different from the ones that consider only the network-induced random delays, which inflect the influence of quantization on design conditions.Secondly, the problems of H∞dynamic output feedback control with random delays and quantization, and H∞dynamic output feedback control with random packet dropouts and quantization. The methods of controller design are given for every problem, the non-convex problem is converted to an LMI optimization problem, and the controller solution algorithm is presented by using the SLPMM. The proposed quantized H∞strategy can guarantee the exponential mean-square stability and H∞performance level of the closed-loop system.Finally, the dynamic observer-based H∞control for systems with random delays and quantization, and dynamic observer-based H∞control for systems with random packet dropouts and quantization, are studied. The methods of the controller design are given for each problem, and the encountered non-convex problem is converted into an LMI with matrix equation constraint. The proposed quantized H∞control strategies can guarantee exponential mean-square stability and H∞performance of the closed-loop system.The details of this thesis are as follows:Chapter1summarizes the development and main research methods in time delays, packet dropouts, and quantization for NCSs.Chapter2provides preliminaries about the considered problems.Based on LMI technique, Chapter3studies the H∞state feedback control problem for NCSS with random delays and quantization. First, the H∞state feedback control problem is studied for systems with network-induced random delays, which satisfies the Bernoulli distributed white sequence. The H∞controller design is proposed such that the closed-loop system is exponentially mean-square stable and with a prescribed H^performance level. Then, the state feedback H∞control problem for systems with random delays and quantization is studied. The quantizers are dynamic ones, which are composed of static quantizers and dynamic regulation parameters. The H∞controller design and the quantized H∞strategy, which guarantee exponential mean-square stability and the H∞performance level, are presented. The obtained conditions for quantized controller design are different from the ones that consider only the network-induced random delays, which inflect the influence of quantization on design conditions.Chapter4investigates the H∞dynamic output feedback control for discrete-time NCSs with random delays and quantization, and H∞dynamic output feedback control for discrete-time NCSs with random packet dropouts and quantization. The random de-lays and random packet dropouts, which occur in the sensor-to-controller channel and controller-to-actuator channel, are considered. The random delays or packet dropouts are described by the random variables taking0or1, which satisfies the Bernoulli dis-tributed white sequence. The random consecutive packet dropouts are described by the product of random variables. The quantizers considered here are also dynamic ones. The H∞dynamic output feedback controller design for NCSs with random delays and quan-tization, and the H∞dynamic output feedback controller design for NCSs with random packet dropouts and quantization are proposed. The non-convex problem is converted to an LMI optimization problem, and the controller solution algorithm is presented by us-ing the SLPMM. The H∞controller design and the quantized H∞strategy are proposed, which guarantee that the closed-loop system is exponentially mean-square stable with the prescribed H∞performance level. The numerical examples have shown the effectiveness of the proposed approaches.Chapter5studies the dynamic observer-based H∞control for discrete-time NCSs with random delays and quantization, and the dynamic observer-based H∞control for discrete-time NCSs with random packet dropouts and quantization. The descriptions of random delays and packet dropouts during the digital transmission are based on Chapter4, and the dynamic quantizers are also used in this chapter. The non-convex problem presented for each problem is converted into an LMI with matrix equation constraint. The H∞control design and the quantized H∞strategy, which guarantee exponential mean-square stability and the H∞performance level of the closed-loop system, are presented. The numerical examples have shown the effectiveness of the proposed approaches.In Chapters6, the results of the dissertation are summarized and further research topics are suggested.