Research On Variable Sampling Period Scheduling Algorithm For Networked Control System

With the development of the network and information technology, the traditional controlsystem has been taken place of the networked control system (NCS) with the networkedstructure and intelligent node. That avoided the problem with hard to extend, high cost andcomplicated structure. At the same time, the network is brought into the control system,which caused some problems, such as the induced time delay, networked jam, data drop andthe generality of networked protocols, and so on, which are the hot debate in the networkedcontrol system researched by the scientists both here and abroad. The performance of thenetworked control system is determined not only by the control structure, but also by thenetworked scheduling. Therefore, the research about the networked control system is referredto the control algorithm and networked scheduling presently. The sampling period is the linkto the control and scheduling related to the performance of NCS.This dissertation is made the main contribution to the sampling period scheduling of thenetworked control system’s schedule as follows:At the point of the control performance, the stability performance of system isdetermined by the selected period value. This paper uses the mathematic model to analysis theNCS and proposes the schedule algorithm of recurrence variable sampling period to adjust thesampling period dynamically on-line according to the factors of the transmission error,time-delay, the quality of control and the means and variances of the system outputs samples.It builds the simulation model based on the earliest deadline first (EDF) schedule algorithm,and analyses the results from the evaluation index of integral of error absolute to weigh thequality of control. That proves this algorithm can modify the stability, promote the real-time,and improve the quality of control in NCS.At the point of the network communication, the uncertainty of the sharing and usablenetworked resource is aroused by the limitation of available networked bandwidth andvariable load. And the result, it brings the problem with unpredicted time delay, shake anddrop data, and so on. To resolve the problems caused by this uncertain factor, a dynamicscheduling algorithm of multi-loop network control system based on fuzzy feedback rule isproposed. It uses the fuzzy inference to determine the priority of loops according to the errorand error rate of input and output, and uses the network utilization and transienterror proportion to account the sampling period of each loop in the network control system.Therefore, it could distribute the limited networked bandwidth resources reasonably.