FAULT TOLERANT SYSTEMS

awfulcorrieAI and Robotics

Oct 29, 2013 (3 years and 11 months ago)

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FAULT TOLERANT SYSTEMS


A dual
-
loop scheme for fault
-
tolerance and early fault detection

An effective control system is typically expected to possess the capability of maintaining

specified
system performance despite changes in system parameters (faults).
In some design strategies, this
implies that the ‘faults’ are automatically ‘tolerated’ without being explicitly detected.

On the other
hand, early fault detection is a basic requirement of a fault diagnosis system, which is

necessary for
the long
-
term rel
iability of engineering systems. In order to achieve both effective

control and long
-
term reliability, we propose a combined strategy, using separate loops for

control and fault
detection. A simulation example shows the effectiveness of the pro
posed scheme.


A FTC
S
trategy for Quadrotor UAVs based on

T
rajectory
L
inearization
M
ethod

Fault tolerant control on quadrotors has recently gained more and more attention. A proper fault
tolerant control strategy can improve the vehicle's performance in th
e presence of benign faults, and
even save the vehicle and valuable payload in case of severe faults. This paper presents a new fault
tolerant control strategy based on Trajectory Linearization Control approach with a special method of
transformation from
quadrotor mode to tri
-
rotor mode, and an introduction of extra control DOF.
Meanwhile, control command saturation is considered in the proposed fault tolerant control
strategy. The maximum fault tolerant capacity for the nominal controller is estimated and

specific
control strategies are presented according to fault classification. Simulations in the
SIMULINK/MATLAB environment are presented to verify the control strategy.


A New Approach in Mobile Robot Fault Tolerant Control. Minimizing Co
sts and Extendin
g
Functionality

Today’s trends in control engineering and robotics are blending gradually into a slightly challenging
area, the development of fault tolerant real
-
time applications. Hence, applications should timely
deliver synchronized data
-
sets, minimize

latency in their response and meet their performance
specifications in the presence of disturbances and faults. The fault tolerant behavior in mobile robots
refers to the possibility to autonomously detect and identify faults as well as the capability to
c
ontinue operating after a fault occurred. This paper introduces a real
-
time distributed control
application with fault tolerance capabilities for differential wheeled mobile robots. ARTEMIC
combines the power and flexibility of real
-
time open
-
source softwar
e, the robustness of nonlinear
control schemes, the efficiency of Kalman filtering and the extensibility of high
-
level programming
languages for hardware interfacing. Specific design, development and implementation details will be
provided in this paper.

Key

Words: Mobile Robotics, Fault Tolerant Control, Sliding Mode Control, Extended Kalman Filter,
Real Time Linux, Distributed Control, Grafcet


A New Approach in Mobile Robot Fault Tolerant Control Minimizing Costs and Extending
Functionality

Today’s trends i
n control engineering and robotics are blending gradua
lly into a slightly challenging
area, the development of fault tolerant real
-
time applications. Hence, application
s should timely
deliver synchro
nized data
-
sets, minimize latency in their response and m
eet their performance
specifications in the presence of

disturbances and faults. The fault tolerant behavior in mobile robots
refers to the

possibility to autonomously de
tect and identify faults as well as the capability to
continue operating after a fault
occurred. This paper introduces

a real
-
time distributed control
application with fault tolerance capabilities for differential wheeled mobile robots.

ARTEMIC
combines the power and flexibility of real
-
time open
-
source software,
the robustness of nonlinear
c
on
trol schemes, the efficiency of Kalman filtering and the extensibility of high
-
level programming
languages for

hardware interfacing. Specific design, development and implementation details will be
provided in this paper.

Key

Words: Mobile Robotics, Fault To
lerant Control, Sliding Mode Control, Extended Kalman Filter,
Real Time

Linux, Distributed Control, Grafcet


A New Fault Tolerant Control Strategy for Aircraft Systems Under Adverse Flying
Conditions

This paper describes a new fault tolerant control strategy for
aircraft systems under adverse
flying
conditions. In the proposed architecture, passive and active approaches are merged together for the
best achievable performance. The proposed F
TC approach: 1) utilizes robust control as the first line
of defense to failures/parameter variations, 2) triggers a reconfigurable controller in case of severe
impairments. Depending on the magnitude of the failure signature and the impairment severity, o
ne
controller will be switched over.


Actuator Fault Tolerant Control Desıgn Based

o
n
a

Reconfıgurable Reference Input

The prospective work reported in this paper explores a new approach to enhance the performance of
an active fault tolerant

control syste
m. The proposed
technique is based on a modified
r
ecovery/trajectory control system in which a reconfigurable

reference input is considered when
performance degradation occurs in the system due to faults in actuator dynamics. An

added value of
this work is
to reduce the energy spent to achieve the desired closed
-
loop performance. This work is
justified

by the need of maintaining a reliable system in a dynamical way in order to achieve a
mission by an autonomous system,

e.g., a launcher, a satellite, a submari
ne, etc. The effectiveness is
illustrated using a three
-
tank system for slowly varying

reference inputs corrupted by actuators
faults.


Keywords: fault tolerant control (FTC), actuator fault accommo
dation, reconfigurable reference
input.


Actuator Fault
-
To
lerant Control based on Set Separation

In this report an actuator fault
-
tolerant control (FTC) strategy

based on set separation is
presented. The proposed scheme employs a bank of observers

which match the different fault
situations that can o
ccur in the plant. Each of these observers has

an associated estimation error
with a distinctive behaviour when a estimator matches the curren
t fault situation of the plant.
With
this information from each observer, a fault diagnosis and isolation (FDI)
module is able

to
r
econfigure the control loop by selecting the appropriate sta
bilising controller from a bank
of
precomputed control laws, each of them related to one of th
e considered fault models. The
control
law consists of a reference feedforward term

and a feed
back gain multiplying the state
estimate
provided by the matching observer. The decision criteria of the FDI is based on the

computation of
sets towards which the output estimation errors related to each fault scenario

and for each control
confi
guration converge. Conditions for the design of the FDI module and for

fault tolerant closed
-
loop stability are given, and the effectiveness of the approach is illustrated

by means of a numerical
example.


Adaptive reconfiguration scheme for flight control
systems

This paper presents a framework for actuator fault accommodation using a multiple
-
model
-
based
direct adaptive control approach that does not include explicit fault detection and isolation. This
approach does not require exact information about the
controlled system and persistent input
excitations. The method can increase robustness and provides stable adaptation of unknown faults.
Asymptotic model following conditions and adaptive rules are derived and system stability is
guaranteed, while appropri
ate switching of the multiple models ensures asymptotic tracking for
system outputs. An aircraft model is given to illustrate the efficiency of the proposed method.

Keywords: actuator fault, direct adaptive reconfiguration control, multiple model, flight c
ontrol
systems


Analysis and detection of incipient faults in post
-
fault systems subject to adaptive fault
-
tolerant
control

This paper presents an effective scheme for detecting incipient faults in post
-
fault systems (PFSs)
subject to adaptive fault
-
tolera
nt control (AFTC). Through a survey of existing techniques, it is shown
that the adaptivity of the AFTC counteracts the effect of an incipient fault in the PFS. This makes
some of the conventional fault
-
detection strategies, such as Beard

Jones detection fi
lters and
adaptive observers, ineffective in this situation. It is shown that the unknown input observer (UIO) is
an effective tool; hence, the UIO is designed to decouple the incipient fault from the AFTC such that
the fault
-
detection residual is sensitiv
e only to the incipient fault. Extensive simulation study is
presented using an aircraft example to test three fault
-
detection approaches; it is demonstrated that
the UIO is the most effective tool in detecting the incipient fault in a PFS subject to AFTC.


KEY WORDS: adaptive fault
-
tolerant control; post
-
fault systems; detection of incipient faults;
unknown input observers.


Control reconfiguration after actuator failures by Markov parameter matching

Two novel linear control reconfiguration methods for pl
ants subject to actuator failures are
described. The common idea is to place a reconfiguration block between the faulty plant and the
nominal controller in order to re
-
route the signals around the broken actuator. The first method
uses a computationally sim
ple static reconfiguration block. It recovers the nominal plant
input/output behaviour by assigning the faulty plant the same Markov parameters as the faultless
plant. The second method concerns the design of the feedforward part in the virtual actuator usi
ng
the idea and results of the first approach. The virtual actuator is a dynamical reconfiguration block.
Existence conditions and solution algorithms are provided, and it is shown that both approaches
guarantee the closed
-
loop stability if the existe
nce conditions are met. An experimental study
demonstrates the practical usability of the proposed approaches.

Keywords: control reconfiguration; fault
-
tolerant control; virtual actuator; Markov parameters.


Fault Estimation and Accommodation for Line
ar MIMO Discrete
-
Time Systems

In this brief, a methodology for detection and accommodation of actuator faults for a class of multi
-
input

multi
-
output (MIMO) stochastic systems is presented. First, a new real
-
time fault estimation
module that estimates the
actuator effectiveness is developed. The actuator fault diagnosis is based
on the estimation of the state vector. Under some conditions, the stochastic system is transformed
into two separate subsystems. One of them is not affected by actuator faults, so a

reduced order
Kalman filter can be used to estimate its states. The other, whose states are measurable, is affected
by the faults. Then, the output of the nominal controller is reconfigured to compensate for the loss of
actuator effectiveness in the system.

Simulation results of a helicopter in vertical plane is presented
to demonstrate the performance of the proposed fault
-
tolerant control scheme.

Index Terms

Fault accommodation, fault estimation, flight control, linear stochastic systems,
uncertainty.


Faul
t
-
tolerant control for a shıp propulsıon system

The application of a new fault
-
tolerant control methodology to a well
-
known benchmark is
considered. The benchmark is the model of a propulsion system for a marine vehicle developed by
the Control Engineerin
g Department of Aalborg University. After a brief description of the system, a
fault analysis is carried out leading to a set of possible faults and remedial actions. Then the fault
detection and identification method, and the reconfiguration algorithm are d
escribed. Simulations on
the model illustrate the performance of the fault tolerant system for some selected fault scenarios.

Keywords: Fault Tolerant Control, Process Control, Quantitative and Qualitative Methods of Fault
Diagnosis, Marine Systems, Observ
ers.


Fault Tolerant Control of Wind Turbines


a benchmark model

The installed energy generation capacity of wind turbines is increasing dramatically on a global scale;
this means that reliability of wind turbines is of higher importance. A part of this
task is to improve
fault detection and accommodation schemes of the wind turbine. This paper presents a benchmark
model for simulation of fault detection and accommodation schemes. This benchmark model deals
with the wind turbine on a system level containi
ng sensors, actuators and systems faults in the pitch
system, drive train, generator and converter system.


From mission planning to flight control of unmanned aerial vehicles:

Strategies and
implemen
tation
tools

This paper reviews aspects of unmanned
aerial vehicle (UA
V) autonomy as suggested by the
Autonomous Control Logic chart of the U.S.

DoD UAV autonomy roadmap; levels of vehicle
autonomy addressed through intelligent control practices and a hierarchical/intelligent

control
architecture are presen
ted for UAVs. Basic modules of the control hierarchy and their enabling
technologies are reviewed; of special

interest, from an intelligent control perspective, are the middle
and high echelons of the hierarchy. Here, mission planning, trajectory

generatio
n and vehicle
navigation routines are proposed for the highest level. At the middle level, the control role is
portrayed by mode

transitioning, envelope protection, real
-
time adaptation and fault
detection/control reconfiguration algorithms which are intend
ed to safeguard

the UAV’s integrity in
the event of component failures, extreme operating conditions or external disturbances. The UAV
thus exhibits

attributes of robustness and operational reliability assuring a satisfactory degree of
autonomy. The contro
l technologies are demonstrated

through flight testing results.

Keywords: Intelligent control; Autonomous vehicle; Flight control; Adaptive control; Fault detection;
Fault tolerant control
.