Research On Control And Scheduling Methods For Networked Control Systems With Resource Constraints

Feedback control systems wherein the control system components(sensors, controller, actuator, etc)are closed through a real-time network are called networked control systems(NCS),which are fully spatially distributed systems. A great deal of attention has been focused on this class of control systems in recent years. Compared with conventional point to point control systems, NCS have advantages of less wires, high reliability, good flexibility and share of information resources, etc.Bacause of these distinctive benefits,typical application of these systems ranges over various fields,such as automotive,mobile robotics,advanced aircraft,and so on. However, in real networked control systems, there often exist various of network restrictions such as limited bandwidth resource, network communication protocol etc, which result to incur some new issues such as network-induced time delay,multiple-packet transimission and dropping network packets,network communication constraints,network scheduling etc. This new problems make the analysis and design of NCS complex.In this dissertation, we focus on the networked control systems suffering to bandwidth constraints or communication protocol constraints. Due to this class of research plants, some aspects such as system modeling and control, co-design of network scheduling and control are studied. The main achievements are as follows:Firstly, for the networked control system with communication constraints, the notion of communication sequence is employed. At the same time, considering the influence of uncertain short time delay, the NCS is modeled as a discrete switching system with uncertainty, which integrates information scheduling and control. The schedulability conditions and asymptotic stability results of this closed loop system are discussed in detail. The solution of control law is also given under a certain periodic communication sequence by means of linear matrix inequalities(LMI) approach.Secondly, for the networked control systems with multi-packet transmission and uncertain short time delay, system modeling and control problem is studied on the condition that data packet transmission using dynamic scheduling strategy. In the first place, supposing that the packet transmission process has the Markov characteristic which also contains the case of data dropouts, the synthetic model which considering the issuses of time delay, data dropouts and multiple-packet transmission is constructed. The stochastic stability condition and controller design method are also obtained. In the second place, for the case of uncertain packet transmission sequence, a compensator is introduced to compensate the effect of part of data dropouts in the process of multiple-packet transmission. Based on this, the NCS is modeled as a discrete stochastic switching system, and the stability of the system is also analyzed.Thirdly, due to the information rate constraints problem in the networked control system, a deterministic communication scheduling strategy is proposed to control data transmission of network nodes and is applied in the MB-NCS, the model of MB-NCS with communication scheduling role is constructed. Furthermore, the stability of the system is analyzed and the stability region of the plant states is provided. Simulation result shows that under obtaining good system performance, the introduced communication scheduling strategy reduces the data transmission times obviously,which lightens the effects of bandwidth constraints on system performance effectively.Fourthly, the modeling and control problem is studied for the networked control system with time-varying bounded sampling period and time delay, it is modeled as a class of discrete dynamic interval system. Based on this, we study the problems of system stability, guaranteed cost control and H_∞control, each controller design method is also given. The proposed method provides a good theory guide for the research of time-varying period scheduling.Finally, for the networked control system with limited bandwidth and flexible workload, a dynamic feedback scheduling strategy is proposed. The available bandwidth is predicted by using LS_SVM approach, the performance indices of the control loops are proposed based on fuzzy logic control technique. And the predicted network bandwidth is dynamically allocated by the bandwidth manager and priority assigner in terms of the control performance indices. By comparing to the error-based bandwidth and priority allocation method, the results of simulation highlight that the proposed algorithm can optimize the performance of control loop and has more flexible in uncertain running conditions.