Research On Control Strategy Of Networked Control System Based On Variable Sampling Period

Networked control system(NCS)is a distributed control system using communication network as the transmission medium,It connects the system nodes distributed in different positions through the network,reduces the complexity of the system wiring,decreases the maintenance and operation cost of the system,and has the advantages of easy expansion and management,resource sharing and so on.However,due to the uncertainty of network load,the selection of sampling period is very important for NCS.If the sampling period is too small,the high sampling rate will cause the increase of network information,lead to the network busy,bring greater delay,and result in declining the service quality of the system.If the sampling period is too large,the system's information can not get timely transmission and feedback,which will reduce the control performance of the system,and cause a waste of network resources.From the point of control strategy,this paper studies the network control system based on variable sampling period.Specific research contents are as follows:1.Analysis the generation mechanism,influencing factors,distribution regular of time delay.and a delay prediction model based on RBF neural network is proposed.Simulation results show that the learning rate is accelerated and the prediction accuracy of delay is improved effectively.2.Aiming at the randomness and uncertainty of delay,a variable sampling period delay compensation strategy based on RBF neural network is proposed.Firstly,the delay prediction model based on RBF neural network is used to predict the delay time,and the prediction delay is used as the sampling period to establish the system model.The time-varying delay is transformed into a parameter of the system,which is convenient for the system analysis;Secondly,the controller design method combining the optimal control and pole placement is given,which improves the system control performance and simplifies the process of calculating the control law.Simulation results show the effectiveness of the proposed control strategy.3.Aiming at the NCS with long time delay,packet out of order and packet loss,a variable sampling period delay compensation strategy based on switching is proposed.Firstly,the sensor selects event-driven way,which can transform the problem of packet out of order and packet loss into a delay problem;Secondly,a sampling period set is set up on the basis of the maximum and minimum delay,and the controllers are designed according to each sampling period;Finally,according to the network load,the suitable sampling period and control signal are selected to improve the control performance of the system.Simulation results show the effectiveness of the proposed control strategy.