Suppression of Packet Losses and Disturbances in Networked Control Systems Based on Equivalent-Input-Disturbance Approach

This article presents a method of suppressing packet losses and exogenous disturbances for a networked control system (NCS) subject to network-introduced delays. The NCS has two feedback loops: 1) a local one and 2) a main one. The local feedback loop contains a state observer, an equivalent-input-disturbance (EID) estimator, and state feedback. It is used to ensure prompt disturbance suppression. The controller in the main feedback loop contains an internal model to track a reference input. The system is divided into two subsystems for the design of controllers. The state-observer gain is designed for one subsystem using the concept of perfect regulation to ensure disturbance estimation performance. The state-feedback gains of the other subsystem are designed based on a stability condition in the form of a linear matrix inequality (LMI). A tracking specification is embedded in the LMI-based stability condition to ensure satisfactory tracking performance. A case study on a two-finger robot hand control system and a comparison with a Smith-EID and $H_{\infty }$ controller approach validate the effectiveness and superiority of the presented method.

I. Introduction

A networked control system (NCS) is a control system in which signals are converted, packed, coded, and passed through a network medium and exchanged among system components, such as controllers, actuators, and sensors. It is implemented through a communication network [1]. An NCS has many significant advantages, such as the elimination of unnecessary wiring, low cost, and high reliability [2], [3]. And it has been successfully applied in environmental monitoring, smart grids, microelectromechanical systems, and many other fields [4].