Research On Robust Analysis And Event-Triggered Control Of Uncertain Networked Control Systems

In the last decade, with the rapid development of network technique, more and more network technologies have been applied to control systems. Now, networked control system (NCS) has become a hot field of research directions. Different parts of a control system can share information with each other by network, which saves wiring costs, enhances the flexibility and reliability of the system. However, some new problems such as network-induced delays, data packets disordering and dropouts are also introduced, which may degrade the performance of the system, and may even destabilize the system especially under the limited communication channel capacity. Although there have been frutitful results on both the theoretical research and the application research of NCSs, there are still some issues which need further investigation, such as the robust analysis of networked control systems with limited bandwidth, and the problems on effective utilization of network resources by using event-triggered control.This dissertation studies system modelling, robust analysis, event-triggered communication and control co-design problems for a class of uncertain networked control systems with limited bandwidth. In detail, the dissertation mainly includes the following contents:1. A time delay system for networked control system with interval time-varying delays and limited consecutive packet dropouts is obtained by using the input delay approach, which can take network-induced delays, packet dropouts and time-varying sampling intervals into consideration. A delay-dependent robust stability criterion consists of linear matrix inequalities (LMIs) is derived by using Wirtinger’s inequality, the reciprocally convex approach and a variable delay-fractioning method. Then the state feedback controller designing methods are developed. For taking into account of the delay interval information and the feature of the sawtooth delay induced by sample-and-hold, less conservative results can be obtained by using the proposed method. Moreover, less matrix variables are introduced without using the free weighting matrices. Numerical examples are given to illustrate effectiveness and less conservativeness of the proposed methods.2. The robust guaranteed cost control for networked control systems with nonzero time delay lower bound and packet dropouts is investigated. By transforming the NCS model into a time delay system, a new delay-dependent stability criterion is derived by using Wirtinger’s inequality, the reciprocally convex approach and the delay-fractioning method, which leads to a sufficient condition for the existence of a robust guaranteed cost controller, then a sub-optimal robust guaranteed cost controller is obtained by using the improved cone complementary linearization (ICCL) algorithm. The proposed method can lead to less conservative results especially for large delay lower bound because of both the feature of the sawtooth delay and the further information of the delay lower bound being taken into consideration. Numerical examples are given to illustrate effectiveness and less conservativeness of the proposed methods.3. Considering the external disturbance effects, the networked control systems are modeled as systems with interval time-varying delays. A sufficient condition in the form of LMIs for the existence of a robust H∞controller is derived by using Wirtinger’s inequality, the reciprocally convex approach, then a sub-optimal robust H∞controller is developed by using the ICCL algorithm. A numerical example demonstrates that the designed controller can not only stabilize the closed-loop NCS, but also guarantees a lower disturbance attenuation level.4. Considering effects of network-induced delays and external disturbance, the output feedback event-triggered control for a class of uncertain linear networked control systems is investigated. An observer-based discrete event-triggered scheme is presented, and a time delay system with augmented state is derived by using a new input delay approach, which can take into account of the network-induced delays, sampling intervals and the feature of the event-triggerec scheme. The robust H∞peformance analysis method is presented by using Jensen’s inquality, the reciprocally convex approach and the delay-fractioning method, then a co-design approach for the controller, the observer and the event-triggered condition is developed. A numerical example demonstrates that the closed-loop NCS with the observer based event-triggered scheme and the robust H∞controller can not only satisfy the given robust H∞performance, but also saves a large amount of network resources.5. The event-triggered robust H∞output tracking control and optimization for a class of uncertain linear networked systems is investigated. First, an event-triggered scheme is designed based on both the reference model state and the observer state. Then an augmented time delay system including the reference model state, the observer state and the observer error is derived by using the piecewise input delay approach. The co-design problem for the controller, the observer and the event-triggered condition is also investigated by using the time delay system analysis method, and a new PSO algorithm is proposed to search for the minimum Hx tracking performance index and the corresponding parameters. A numerical example is given to illustrate effectiveness of the proposed methods.