Research Of Networked Control System With Disturbance Based On Real-time Wavelet Filtering

Networked control system(NCS) is a special distributed feedback control system wherein the control loops are closed through real-time network.In the NCS,controller,sensor and actuator nodes exchange information through a shared network.Integrating computer technology,communication technology and control theory,NCS is an emerging technology and becoming future trend of modern industry.Although NCS has the advantages of resources share,reduced system cost,increased system agility and ease of system maintenances,network transfer causes the time delays and data package dropout.That not only makes it difficult to analyze the system,but also can't apply conventional control theories to NCS directly.Networked control system with time delay and data package dropout is studied in this dissertation.Main achievements are as follows:Firstly,modeling of networked control system with time delay and data package dropout are presented.Considering the disturbances,the mathematic models of networked control system with short time delay and long time delay are established,and the discrete-time models of NCS with time delay are given.Considering data packet loss,the discrete-time models of NCS with state feedback and output feedback are given.Secondly,PID controller based on real-time wavelet filtering is designed.On the basis of wavelet real-time filtering,wavelet filter,which is founded,is used in control system combined with PID controller.Based on specific examples,how to choose the parameter of the controller,wavelet basis function,decomposing depth,threshold selection rule,sizes of moving window and compensation window is discussed.Finally,compensation control of networked control system is studied.In order to resolve the disadvantage of network-induced delay and packet loss uncertainty in NCS,applying a real-time queuing protocol,the network-induced delay is limited in a control period,and three model-free strategies for control packet dropout compensation,namely,PD,PD2 and PD3 are developed.Based on wavelet filter,an improve wavelet filter is given,and both of them are used in NCS with disturbance.