Adaptive Fault-tolerant Control for Time-delay Systems with
Saturation Nonlinearity and L
2
-disturbances
Wei Guan
1
,LingGuo
1
1. School of Automation, Shenyang Aerospace University, Shenyang, 110136, China.
E-mail: guanweihaha@163.com
Abstract: This paper studies the problem of designing adaptive fault-tolerant H
∞
controllers for linear time-delay
systems with actuator saturation. The disturbance tolerance ability of the closed-loop system is measured by an optimal
index. A notion of adaptive H
∞
performance index is proposed to describe the disturbance attenuation performances
of closed-loop systems. New methods for designing indirect adaptive fault-tolerant controllers via state feedback are
presented for actuator fault compensations. Based on the on-line estimation of eventual faults, the adaptive fault-tolerant
controller parameters are updating automatically to compensate the fault effects on systems. The designs are developed
in the framework of linear matrix inequality (LMI) approach, which can guarantee the disturbance tolerance ability and
adaptive H
∞
performances of closed-loop systems in the cases of actuator saturation and actuator failures. An example
is given to illustrate the efficiency of the design method.
Key W ords: Actuator Saturation; Adaptive Control; Fault-tolerant Control; Disturbance Tolerance; H
∞
Control; Time-
Delay
1 INTRODUCTION
Control systems with actuator saturation and Time − delays are
often encountered in many practical systems such as chemical
processes, electrical heaters and long transmission lines in pneu-
matic, hydraulic and rolling mill systems. Since the existence of
a delay and actuator saturation in a physical system often induces
instability of poor performance, research on time-delay systems
with actuator saturation is a topic of great practical and theoretical
importance. The problem of disturbance rejection for linear sys-
tems subject to actuator saturation has been addressed by many
authors ( [1]- [11]). Under the boundedness assumption on the
magnitude of the disturbances and in the absence of initial condi-
tion, the L
2
gain analysis and minimization in the context of both
state and output feedback were carried out in [4], [5]. The work
of [2] proposed a method for analysis and maximization of an
ellipsoid which is invariant under magnitude bounded, but persis-
tent disturbances. The works of ( [1], [3], [6], [7], [8]) all consider
the situation where disturbance are bounded in energy. The works
of ( [1], [6], [7]) formulated and solved the problem of stability
analysis and design as optimization problems with LMI or BMI
constraints. In ( [9], [10]), authors presented LMI-based synthesis
tools for regional stability and performance of linear anti-windup
compensators for linear control systems. [12] presents a method
for the analysis and control design of linear systems in the pres-
ence of actuator saturation and L
2
disturbances.
On the other hand, fault-tolerant design approach can be broadly
classified into two types: Passive approach [13]- [17] and Active
approach [18]- [23]. In the passive approach, the same controller
is used throughout normal case as well as fault cases such that this
passive fault tolerant controller is easily implemented. Some ap-
proaches to the design of passive fault-tolerant controllers have
This work was supported in part by Program for the Funds of National
Science of China (Grant Nos. 61203087, 61074090), the Liaoning Educa-
tion Department Plan Project of China (No. L2010426), and the Liaoning
Students Innovation Training Plan Project of China (Nos. 201210143012,
2012106).
been addressed by several authors (see [13]- [17] and the ref-
erences therein). An active fault-tolerant control system com-
pensates for faults either by selecting a pre-computed control
law or by synthesizing a new control strategy on-line. Some of
these methods include a strategy involving a fast subsystem for
Fault Detection and Isolation (FDI), and a supervisory system
that chooses the corresponding controller for a particular type of
fault. The adaptive approach is very important in active FTC,
which relys on the potential of the adjustments of parameters to
assure reliability of closed-loop systems in the presence of a wide
range of unknown faults. Most of the results in adaptive fault-
tolerant control are based on model reference adaptive control
(MRAC) [24]- [26], but the disturbance attenuation performances
of systems have not been addressed yet within the MRAC frame-
work.
As we all know, actuator saturation and actuator faults always
happen at the same time for time-delay systems. However, noting
all above results, there is no work that deals with this problem.
Motivated by the above observations, this paper studies the prob-
lem of designing adaptive fault-tolerant H
∞
controllers for linear
time-invariant systems with actuator saturation. A general actua-
tor fault model is considered, which covers the outage cases and
the possibility of partial faults. The disturbance tolerance ability
of the closed-loop system is measured by an optimal index. A
notion of adaptive H
∞
performance index is proposed to describe
the disturbance attenuation performances of closed-loop systems.
Based on the on-line estimation of eventual faults, the adaptive
fault-tolerant controller parameters are updating automatically to
compensate the fault effects on systems. The designs are de-
veloped in the framework of linear matrix inequality (LMI) ap-
proach, which can guarantee the disturbance tolerance ability and
adaptive H
∞
performances of closed-loop systems in the cases of
actuator saturation and actuator failures. The difference between
this paper and some existing results is that in this paper, the fault-
tolerant and saturation are considered at same time.
The paper is organized as follows. Problem statement is given in
450
978-1-4673-5532-2
c
2013 IEEE