Analysis of Distributed Real-Time Control Systems with Shared Network Infrastructures

Abstract

Distributed control applications are considered where the control functions are implemented by software of a centralized controller and where system state information and control commands are communicated through a shared communication infrastructure. Through the shared communication infrastructure the control functionalities of the individual control loops may influence each other and can have an affect on Service Level Objectives (SLO) to be guaranteed for each individual control application. In this contribution a novel approach is suggested for an enhanced CSMA/CD local area network infrastructure where the application control layer is directly put on an enhanced Media Access Control (MAC) layer of the communication infrastructure to minimize control delays. A comprehensive model is derived for the resulting network with all competing applications and protocol functions for safe communications. The performance of the MAC layer request is analyzed exactly by a stochastic phase TC representing its aggregated behavior. The delay performance of the individual control applications is analyzed by means of a queuing model of type GI/G/1 where GI represents the total control request arrival process and G a virtual service time TC from which the aggregated network delay parameters are derived. The distributed network control system (NCS) model with the shared infrastructure is analyzed exactly by methods of Control Theory by computational algorithms and MATLAB Simulink tool support.