Research On Fault Toleran Control Of Networked Control Systems

Networked control systems are feedback control systems which are formed through network.In this kind of systems,the information transfers are carried out via public network platform.This kind of control mode has some advantages such as simple wiring,convenient maintenance,easy to expand,high reliability and resource sharing etc.there are also inevitable shortcomings such as delay,packet loss and sequence data disorder etc.Network control does not only consider the control process alone,but concern on the network characteristics and look the whole system as control object.Networked control system is more complicated than local control systems and it put forward higher requirement on safety of the system.In this paper,we research on the fault-tolerant control of networked control systems control object oriented from the viewpoint of control theory.The main research results in this paper are shown as follows:Firstly,the problem of stability control of networked control system with time-varing delay is studied in this paper and the method of variable sampling period is proposed in control algorithm designing.For networked control systems with time-varying delay,Time delay of networked control system is determined by the network protocol,the network working situation,the transmission distance of the data packet and other factors.Different time delay has different influence on the system.We select sampling period according to the size of time delay of the system,and limit time delay within a sampling period.In this way,we can simplify the system model when the time delay of NCS is too long,and the designing of control algorithm will be more simple,on the other hand,we can adjust control gain when time delay changes,thus the stability control of the system are ensured and the conservatism of the system is reduced when time delay is too long.Secondly,the fault tolerant control of a kind of networked control system with time-varying delay is studied following the research on stability control of the system.For computer technology and network technology has reached a very high level,only the fault of sensors and actuators are considered and Variable Sampling Period Integrity Control Algorithm is proposed.Selecting the sampling period with the rules mentioned above,and describing the fault of the sensors and actuators by the parameter matrix,we set up the synthesis model of the closed loop control system,and take this model as controlled object,construct Lyapunov stability condition of the system,and represent it in the form of linear matrix inequality.By solving matrix inequality,we can get the fault tolerant control algorithm.Thirdly,the fault tolerant control of NCS is studied considering the influence of the packet loss.A kind of integrity of fault-tolerant control algorithm based on packet loss rate is proposed for the packet loss occurs random in networked control system.Assume that packet loss occurs in Bernoulli process,we describe the process of packet loss with random variable parameters,and set up a synthesis model of the whole system,and establish the stability condition of the system in mean square based on this synthesis model.Packet loss is another basic characteristic of the networked control systems,it occurs random,but for a certain networked control system,when it works at certain period of time and work condition,the packet loss rate is measurable.Finally,the simulation results show that the research result is feasible.Forthly,the stability and fault tolerant control of nonlinear networked control system is studied.We concern on two kinds of nonlinear NCS which can be linearized.For fixed point control system,we linearize the model at the equilibrium of the system.The equilibrium of the Constant value control system depends on reference input,reference input changes,the equilibrium state changes too.This paper adopts the method of gain matching to adjust control gain when reference input change.For nonlinear NCS that can be linearized with feedback linearization,if packet loss can be neglected,to compensate for the influence of time delay,we use the predictive controller to forecast the state of the system,and construct dynamic controller to realize the linearization of the closed-loop system.By inserting fault parameters of sensors and actuators into linearization model of the system,we gain the synthesis linear model of the whole system,and base on this model construct system stability condition,realizes the integrity of the control system.Finally,through the simulation,the feasibility of the control algorithm is verified.Linearization control is limited in application,but it has good real-time performance and can meet the requirement of fault tolerance control well.Lastly,based the research mentioned above,we have given the research prospect of this subject with our own viewpoint.