Research On The Time Delay, Packet Dropout And Packet Disordering In Networked Control Systems

Networked control system(NCS) is a set of communication network and controlsystem in one of the fully distributed, networked real-time feedback control system,where all the information in the sensor, controller and actuator is transmitted over thenetwork. Compared with the traditional point-to-point wiring, integrating computernetwork into control systems brings about more advantages, such as lower cost,reduced weight, simpler installation and maintenance, higher reliability and flexibility.Nowadays, NCSs are increasingly being used in various contexts, transportation,aircraft, manufacturing plants, power grid etc. However, NCSs application inevitablygives rise to some new challenges such as network-induced delay, packet dropout,packet disordering. In this dissertation, for reducing the negative influence from thesenetwork issues, we apply some methodologies such as integral-inequality methodology,model-based methodology, linear estimation methodology and prediction-basedmethodology to discuss the stability and controller design for NCSs. The maincontents are as follows:(1) The stability and state-feedback controller design for a class of NCSs withtime-variant delay are discussed. Firstly, with the Newton-Leibniz formula application,the sufficient stabilization criteria and controller design for retarded system arepresented by the improved integral inequality. Furthermore, we apply the results to theNCSs with time-variant delays. Based on the different cases of time delays, we modelthe NCSs with interval time delay. And by using convex theory, the sufficient stabilization conditions and the according controller design are obtained. Finally,numerical examples demonstrate the validity and the effectiveness of the proposedtechniques.(2) The stability and state-feedback controller design for a class of NCSs withMarkovian packet loss are studied. By using the switched Lyapunov functionalapproach, the packet-loss-dependent controller is designed for the NCSs with shorttime delay and Markovian packet dropout. Moreover, we discuss the stability andcontroller design of NCSs with packet loss occurring only in the back channel. Basedon the estimation information from the model plant, we model the switched systemsaccording to different cases of packet dropouts. Thus, the sufficient criteria and theaccording controller design dependent on packet dropout for NCSs with arbitrarypacket loss and Markovian packet loss are obtained. When packet loss happens duringthe data transmission over the network, different from using the last successfullytransmitted packet by zero-order holder (ZOH), the missing data can be dynamicallycompensated by the model plant, thus the negative effects from packet dropouts arereduced.(3) The stabilization and H_∞controller design for networked controlled systemswith long time delay and packet dropout are discussed. By applying the linearestimation methodology to compensate for the network-induced delays and packetdropouts, we model the switched systems dependent on the different cases of timedelays. The sufficient stabilization conditions and the according H_∞controller designof the closed-loop NCSs are presented by using switched-Lyapunov function and conecomplementary linearization (CCL). In this paper, with all kinds of time delays(shorter than one period, shorter than two periods, shorter than three period etc) taken into consideration, by using the linear estimation methodology to compensate for themissing data, the system is stabilized and has the good H_∞interference rejectioncapability.(4) The stabilization and H_∞output tracking controller design for networkedcontrol systems with both time delay and packet disordering are discussed. We analyzethe relation between the time delay and packet disordering. By modelling theparameter-uncertain NCSs with multi-step delay, we discuss the stability and H_∞control of NCSs with packet disordering. Furthermore, with a predictor located at thecontroller node to predict the future inputs for time delay and packet disordering, theswitched system for three different cases of predition numbers is modelled. Thus, thestabilizaiton criteria and the according H_∞output tracking controller design of theclosed-loop NCSs are presented by using switched-Lyapunov function. Due to thedynamical compensation by the predictor at the controller node and rationalconsideration with the different cases of prediction numbers, the designed controller isboth delay-and packet-disordering-dependent, thus the method presented in this papercan effectively reduce the negative effects from the time delays and packet disordering,and the H_∞output tracking performance is improved accordingly.