14-04-2014, 11:51 AM
SIMULATION OF NETWORKED CONTROL SYSTEMS VIA TRUETIME
NETWORKED CONTROL SYSTEMS.pdf (Size: 1.26 MB / Downloads: 37)
Abstract
Distributed control systems have been one of the most studied and challenging areas
in control. Networked Control Systems (NCSs) are one type of distributed control
systems where sensors, actuators and controllers are interconnected by
communication networks. Integrating computer networks into control systems to
replace the traditional point-to-point wiring has enormous advantages but on the
other hand NCSs bring several issues like network-induced delays or packet
dropouts. We need to know the behavior and characteristics of networked control
systems for designing better and robust control systems. In this paper we simulate
networked control system using TrueTime. TrueTime is a Matlab/Simulink-based
simulator for real-time control systems. We are focused on simulation and testing
modern communication standard CAN and also wireless standard ZigBee.
Introduction
Nowadays we can observe the trend of passing from the traditional centralized control to
distributed control systems. The vast progress in network technology over the past decade is bringing
an advancing trend to control system, where point-to-point cables are replaced by communication
networks. The control systems where sensors, actuators and controllers are interconnected by
communication network are called Networked control systems (NCSs). There are many advantages in
NCSs, such as low cost, reduced weight and power requirements, simple installation and maintenance,
and high reliability. It leads to great application potential of NCSs in industry [1,2].
However, application of communication networks brings new problems into the feedback loop,
such as time-varying delays and the potential loss of information, which makes the analysis and design
of NCSs complicated. Many authors interested in topics of NCSs study these problems. To choose
effective approach for NCSs how to accommodate the effects of network-induced delays and packet
dropouts is very important to know the network characteristics. As a result of NCSs characteristics, the
conventional control theories must be re-evaluated before applying to NCSs [2,3,4].
Networked Control Systems
The idea of remote controlled operation leads to changing of the usual design approaches to the
control systems. We can talk about distributed control systems (DCSs). Networked control systems
(NCSs) are spatially distributed systems for which the communication between sensors, actuators, and
controllers is supported by a shared communication network [1].
Commmuncation channels
The NCSs can be designed using two different types of communication network. Wired
communication channels and their communication protocols are the most common, most reliable and
most secure way of connecting nodes communicating over an industrial network. In last few years also
the wireless communication networks have became very popular. There are several technologies for
usage in industrial applications. The main differences are in the transfer rates and the communication
protocols [7].
In this chapter we describe the basic features and characteristics of CAN and ZigBee
communication technology which are used for NCS simulation using TrueTime.
Controller Area Network (CAN)
CAN, which is the short of Controller Area Network, is the most mature and developable bus
technology. It’s a serial communicational network efficiently supports distributed control and real-
time control. CAN was originally developed for car industry. Because of its effectiveness CAN bus
has also spread into others fields of industry.
CAN bus is reliable, fast and cost effective communication channel for multi master and real-
time applications. It is ideally suites applications requiring high number of short messages for multi
recipients and system-wide data consistency is mandatory in a short period of time with high
reliability in rugged operating environments [8,9].
Conclusion
Recently, the progress in network technology over the past decade is bringing an advancing
trend to control system, where communication networks replace point-to-point cables. This paper has
introduced the fundamental characteristics of NCSs and communication network CAN and ZigBee.
We also described simulator for NCSs. TrueTime simulator is very useful and Matlab/Simulink based
tool.
We designed two networked control systems. The first one was designed with wired and the
second one with wireless communication network. We focused on three problems of NCSs that are
sampling period, network overload and packet dropout. For each of these systems we did the same
experiments and proved that performance of NCSs can be effect by bringing already mentioned tree
issues in.