3/10/2003 1

Fault-tolerant Control System Design and Analysis

Jin Jiang

Department of Electrical and Computer Engineering

The University of Western Ontario

London, Ontario N6A 5B9

Canada

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Outline of the presentation

! Overview of two approaches to fault-tolerant control system design and analysis

! Redundancy in fault-tolerant control systems! Trade-offs among redundancy, performance and

integrity

! An example of passive fault-tolerant control design

! An example of active fault-tolerant control design

! Some open problems

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Fault-tolerant control: An overview

! Passive fault-tolerant control systems! Robust fixed structure controller! Faults have been considered at the controller design stage

! Active fault-tolerant control systems! Explicit fault detection/diagnosis schemes! Real-time decision-making and controller reconfiguration

! The key to any fault-tolerant control system ! Redundancy

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Passive fault-tolerant control systems

ControllerOutputs

Actuator System

Sensor

L-

faults

faults

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Active fault-tolerant control systems

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Features and limitations

! Passive fault-tolerant control systems! Simple to implement! Difficult to account for large number of fault scenarios! Unable to deal with unforeseen faults

! Active fault-tolerant control systems! Potentially be able to deal with a large number of fault

scenarios ! Can deal with certain number of unforeseen faults! More complex to implement! Real challenge is real-time decision-making

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Redundancies

! Actuator redundancies! Multiple physical actuators• They usually act on the system at different locations

! Sensor redundancies! Multiple physical sensors• They usually measure the same physical quality

! Analytical redundancies! Rely on mathematical models (FDI)

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Actuator redundancies

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Actuator Redundancies

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Definitions of actuator redundancies

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Sensor redundancies

A1

A2

A3

Am

SystemDynamics

S11

S12

S21

S22

S2q

Sp1

Sp2

Spq

S1q

......

....

u1

u2

u3

um

y1

y2

yp

Actuator Inputs System Inputs System Outputs

Sens

or O

utpu

ts

1

2

p

zp1

zp2

zpq

....

....

....

z21

z22

z2q2

p

z12

z11

z1q1

....

....

....

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Analytical Redundancies

System ........

Analytical model

Inpu

ts

Out

puts

Intermediate system variables

SensorsRedundant system output

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Performance trade-offs

Three main factors to consider in any fault-tolerant control system design:

System Integrity (safety requirements)Performance (design specifications)Redundancy (physical and financial constraints)

Problem: How to design a control system, under a given degree of redundancy such that the integrity of the system is guaranteed and the performance is satisfactory.

Issue 1: System integrity should always be maintainedIssue 2: Faults should result in reduction of the degree of redundancy firstIssue 3: One should consider performance degradation with available

redundancies.

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Example of passive fault-tolerant control system

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Description of system

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Control system performance

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Control system performance

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Example of active fault-tolerant control system

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Simulation results

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Simulation results

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Simulation results

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Simulation results

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Some open problems

! Reliability analysis of fault-tolerant control systems

! Stability analysis of fault-tolerant control systems

! Graceful performance degradation! Integration of passive and active approaches! Industrial applications of fault-tolerant control

system technologies

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Thank You !