Some Studies On Smith Predictor Based Networked Control System

Abstract

An Networked Control System (NCS) uses real time communication network for closed loop control of systems. It is a class of distributed control system involving information sharing among sensors, actuators, controllers through a communication network. The present work deals with the study and analysis of network delay, packet loss and their effects across the communication channel of an NCS. An User Datagram Protocol (UDP) has been used to establish the communication channel between the two computers in the real time, and hence the network delay and packet loss between them is studied. An UDP although unreliable due to non retransmission of the lost packets, is still preferred for control system applications because of the rate of data transmission in UDP is faster. The adverse effect of network induced delay is reduced by using the classical Smith Predictor Compensator. Study on Smith Predictor performance along with a filter is made to reduce the disturbance introduced by the network. Further, the different combinations of the Smith Predictor, PI controller and Low Pass Filter (LPF) has been studied for its effect on the network delay and packet loss. The experiment was performed on the developed networked DC Servo Motor control system and the designed P-I controller based on the relay Ziegler- Nicholas tuning for the speed control of the DC Servo Motor. The experimental results were in the good agreement with the simulation result.