Analysis and Design of the Time-delay Compensation for Networked
Control Systems with Random Communication Delay
LIU Ting, JIANG Shun, PAN Feng
Key Laboratory of Advanced Process Control for Light Industry (Ministry of Education), Jiangnan University, Wuxi, 214122
Email: liuting_jndx@163.com
Abstract: Aiming at the compensation issues of the random communication delay in networked control systems, this paper
proposes a method to design the time-delay compensation controller based on generalized predictive control. The compensation
controller consists of the network predictor and the time-delay compensator, which is used to make up for the delay with different
characteristics. Different from the traditional determination method, the control parameters depend on the random delay is given
in this paper, which can improve the system performance. Furthermore, the stability conditions of the closed-loop control system
are also constructed. Using TrueTime toolbox to simulate the real network communication, both of fixed delay and stochastic
delay in networked environment are considered to analyze the compensating performance, and the corresponding effect of
different control parameters. The simulated results illustrate a better performance of the varying-parameter compensation
controller than the fixed one.
Key Words: networked control systems, generalized predictive control, random delay, varying parameters, stability
1 Introduction
In recent years, the industrial field goes through great
changes. It requires not only to implement completely
decentralized control and resource share inside, but also to
connect to the Internet to realize remote control externally.
Networked control systems provide a feasible control mode
and become one of the current international frontier in the
field of network communication and control theory
[1,2]
.
In networked control systems, spatially decentralized
control nodes are connected by the communication network,
of which the introduction leads to characteristics different
from the traditional control. The basic problems are grouped
as network communication, control strategy and
collaborative design
[3]
. Among them, control strategy aims to
achieve controllers tolerating communication delay,
sequential disorder and packet loss.
The communication delay enables the system
performance to get worse, even leads to instability.
Influenced by communication protocol, transmission rate
and packet size, it is shown to be fixed, random, bounded or
unbounded. The difficulties of research are the uncertainty of
random delay and the serious lag caused by long delay. So
far, various control strategies are considered, including
deterministic control
[4]
, random control
[5,6]
, intelligent
control
[7]
, robust control
[8,9]
, networked predictive
control
[10-12]
, etc. The networked predictive control achieves
stability and reliability and significantly improves the system
performance. However, too many assumptions are made to
the delay to conform to the real characteristics. In [10], the
networked round-trip delay is substituted for the delay in the
feedback and the forward channel, which is not a simple
addition. In [11], communication delay is estimated through
storage queue online, but it increases the delay artificially.
In this paper, different compensation mechanisms are
designed for the delay in the feedback and the forward
*
This work is supported by National Natural Science Foundation (NNSF)
of China under Grant 61403168.
channel. Generalized predictive control is adopted, which
possesses strong environmental adaptability and robustness.
TrueTime toolbox is used here to simulate the real network.
The main contributions of this paper can be highlighted as
follows: 1) the control parameters are discussed and a
determination method is given for the networked control
strategy; 2) a comparison is made between the compensating
performance of these two different delays; and 3) the
stability conditions of closed system are concluded as well.
2 Structure of networked control systems with
random communication delay
The characteristic analysis divides the communication
delay into four parts: send-processing delay
send
T
, waiting
delay
wait
T
, transmission delay
ts
T
and receive-processing
delay
rev
T
. The specific distribution as is shown in Fig.1.
Application
layer
Link layer
Physical layer
Node A
Application
layer
Link layer
Physical layer
Node B
Fig.1 Specific distribution of the communication delay
send
T
and
rev
T
depend on the software and the hardware
performance of source equipment and destination equipment
respectively and turn to be certain.
wait
T
is determined by the
protocol in MAC layer, connection type and network load,
etc.
ts
T
lies on the network bandwidth and the transmission
distance, which is determinate. Thus, the communication
delay is composed of the determinate part and the uncertain
part, and the uncertainty mainly comes from
wait
T
. To sum
up, networked control systems inevitably possess random,
time-variant, or uncertain communication delay because of
the limited network carrying capacity.
Proceedings of the 35th Chinese Control Conference
Jul
27-29, 2016, Chen
du, China
7234