Stabilization And Tracking Control Of Networked Systems With Delays And Packet Dropouts

In recent years,the study of networked control systems has attracted much attention from scholars at home and abroad in the control area.Compared with the traditional point-to-point control systems,NCSs can be potentially designed into large-scale systems and widely used in many fields due to the simplicity in installation and maintenance,convenient layout and high flexibility.However,the integration of communication networks into feedback control loops inevitably leads to non-ideal network quality of services,e.g.,network induced delays,data packet dropouts and disordering,which make the analysis and design of NCSs more complex than those for traditional control systems.So far,enormous attentions have been paid to the issues of stability analysis and stabilization controller design.Therefore,based on previous works of others,this thesis investigates the stabilization and tracking control of NCSs with time delays and packet dropouts,and the main contributions of this thesis are summarized as follows.1)The stabilization control problems of NCSs with network induced delays has been investigated.In order to reduce the conservatism of the design,the maximum possible value of the network induced delays is partitioned into multi-equal intervals.Furthermore,in the stochastic analysis method,the time delay is described as a stochastic process based on the finite state Markov chain according to the jump characteristics of the delay in each interval,and the discrete-time jump model with parameter uncertainties is established.Considering the condition that the elements of the transition probability matrix are partly unknown(even all of them are unknown),the time-varying controller meeting the requirement of system stability is designed based on the theories of Lyapunov stability and stochastic process.Because it is difficult to obtain the jump probability of the delay,a deterministic switching control method is proposed.In this method,a discrete-time switched closed-loop system with uncertain parameters is modeled by partitioning the range of time-varying delay into multi-equal intervals and using the method of augmented matrix.Then the condition meeting the exponential stability in the closed-loop system is presented,and the quantitative relation between the number of delay intervals and the exponential decay rate is established based on the approach of average dwell time.The proposed design method can decrease the conservatism of the system design and shorten the convergence time to some degree.2)The problem of NCSs stabilization with network induced delays and packet dropouts is researched.In the stochastic system analysis method,the stochastic characteristic of packet dropouts is described as the Markov process,and the Markov jump systems with uncertain parameters are modeled by using the method of system augmented matrix.Then under the conditions that some elements of Markov chain transition probability matrix are partly unknown or even completely unknown,the necessary and suffi cient criteria of stabilization are obtained based on the theories of Lyapunov stability and stochastic process,and the time varying controller is designed to guarantee the system stochastic mean square stability.Similarly,it is difficult to obtain the probability of packet dropouts,so a deterministic switching control method is proposed.In this method,a discrete-time switched system with uncertain parameters is firstly modeled by adopting the method of system augmented matrix for NCSs with delays and packet dropouts,and then the condition satisfying exponential stability of system is obtained by using the approach of switched system based on model-dependent average dwell time.The quantitative relation between the rates of exponential decay and the packet dropouts is further established by the obtained conditions.3)For the uncertain NCSs with time-varying delays,the modelling and control of mixed event-triggered mechanism(ETM)are addressed.So far,most NCS mechanisms are based on time-triggered communications,and the execution periods are often designed according to the worst case of the system.Therefore,all sampled-data need to be transmitted over the communication networks at a fixed interval and without considering the influence of the state change of the controlled plant.Obviously,the time triggered communication mechanism can not make full use of the limited network resources,even aggravate the network burden and destroy the performance of the NCSs.Therefore,this section studies the NCSs with uncertain parameters from the perspective of saving network resources and ensuring system control performance.Firstly,an event-triggered threshold is set by using both state and state-independent information in the mixed ETM.Then the event-triggered NCSs with network induced time-varying delays,which exist in both sensor-to-controller and controller-to-actuator channels,are modeled as a general time-delay system.Based on the piecewise differentiable characteristic of the time-varying delay and by using the approach of free weighting matrix and reciprocally convex,a less conservative criterion to be globally uniformly ultimately bounded(GUUB)stability and a controller design method are derived.4)The networked output tracking control problem is investigated.In the robust H_?control method,the reference model and the augmented state space model are used to unify the network induced delays,data packet dropouts,and parameter uncertainties in the time-delay system model.Then the output tracking problem is transformed into the robust H_?control problem.Therefore,a robust state feedback controller is designed to ensure the output tracking performance in a robust H_?sense.Due to the inherent advantages of PID algorithm,the tracking output error can be eliminated.Therefore,based on the previous research,the guaranteed performance PID control method is proposed.Aiming at the second-order processes in practical engineering and industrial process,the parameter selection of PID tracking controller is reduced to the solution of linear matrix inequalities.The proposed method has realized the networked PID tracking control,and achieved the tracking control performances,i.e.,fast response and without static error.According to the proposed research conclusions,a number of illustrative simulations or experiments are carried out to verify their effectiveness.Finally,the results of the dissertation are summarized and the future work are pointed out.