Research On Output Feedback Control And Fault Diagnosis For Networked Control Systems

In many complex and distributed control systems, communication networks are usu-ally used to interconnect remotely located sensors, controllers, filters, actuators and othersystems components into closed-loop control systems, which are often referred to as net-worked control systems. A typical feature in these systems is that time division multiplexedcomputer networks are employed for exchanging information between spatially distributedplant components. Compared with the conventional control systems whose componentsare connected via point-by-point cables, the new network-based systems possesses manyadvantages including increased reliability, enhanced resource utilization, reduced wiring,eased installation and maintenance. Therefore, networked control systems have receivedconsiderable research attention in recent years, and the successful application can be foundin a wide range of areas. However, the insertion of communication networks into feedbackcontrol loops has also given rise to some interesting and challenging issues due to the in-herent network-limited bandwidth, for example, network-induced delays, packet dropouts,and signal quantization, which all might be potential causes for the performance deteriora-tion or even the instability of networked control systems. Thus, traditional control theoriesand analysis methods must be reevaluated before they can be applied to networked controlsystems.This dissertation is concerned with the output feedback control and fault diagnosisproblems for networked control systems in non-ideal networked environment. The maincontents of the dissertation include the problem of quantized output feedback stabilization,the problem of output feedback H_∞control, the problem of robust fault detection, the prob-lem of reliable fault detection and the problem of fault estimation for networked controlsystems. More specifically, the following problems classified in three aspects are fully in-vestigated.First of all, the problem of output feedback control is studied for networked control sys-tems. In view of the status that only one network-induced effect is often considered whenthe control problem is addressed for networked control systems in the most of the existingliterature. So we comprehensively consider multiple network-induced effects in the disser- tation when proceeding with the stability analysis and the controller design. In Chapter2,a novel control law model is proposed to take the time delays, packet dropouts and signalquantization into consideration when the problem of quantized output feedback stabilizationis studied. In the derivation of the stability, by constructing proper Lyapunov functional andusing free-weight matrix technique, a less conservative stability condition is derived. Thestability condition depends on the lower and upper bounds of time delays, the probabilityof the packet dropouts and the quantization density. By using similar approach, under theconsideration of the packet-dropout compensation, the output feedback H_∞control is con-cerned for networked control systems with time delays and packet dropouts in Chapter3.Under the action of the designed controller, the resulted closed-loop system is mean-squareexponentially stable and satisfies the prescribed H_∞performance.Second, the problem of fault detection is investigated for networked control systems.It is assumed that the measured outputs are transmitted to the remote fault detection equip-ments via shared communication networks. In Chapter4, the robust fault detection is ad-dressed for networked control systems, where the time delays, packet dropouts and quan-tization are simultaneously considered. By designing fault detection filter, the system faultis detected according the residual evaluation strategy. Moreover, in light of the commonadoption of single-packet transmission in the existing literature, a multi-packet transmis-sion mechanism is adopted in Chapter5when the problem of the reliable fault detection isstudied.Then, the problem of the fault estimation is investigated for a class of nonlinear net-worked control systems with time delays and packet dropouts in view of the excessive em-phasis on the fault detection in the fault diagnosis. The time delays and packet dropouts aresimultaneously taken into account when we design the fault estimation filter. The systemfault is effectively estimated via the fault estimation filter.Finally, the main results of the thesis are summarized in detail, and some interestingissues to be studied in our future work are also discussed.