Online aerodynamic parameter estimation for a fault tolerant

103 Pages·2005·1 MB·English

by  Balbahadur Singh

ONLINE AERODYNAMIC PARAMETER ESTIMATION FOR A FAULT TOLERANT
FLIGHT CONTROL SYSTEM

A Thesis by
Balbahadur Singh
B.E., Nagpur University, 2002

Submitted to the College of Engineering
and the faculty of the Graduate School of
Wichita State University
in partial fulfillment of
the requirements for the degree of
Masters of Science

December 2005
ONLINE AERODYNAMIC PARAMETER ESTIMATION FOR A FAULT TOLERANT
FLIGHT CONTROL SYSTEM

I have examined the final copy of this Thesis for form and content and recommend that it be
accepted in partial fulfillment of the requirement for the degree of Masters of Science with a
major in Aerospace Engineering.

__________________________________
Dr. James E. Steck, Committee Chair

We have read this Thesis
and recommend its acceptance:

__________________________________
Dr. Kamran Rokhsaz, Committee Member

_________________________________
Dr. Kameshwara Rao Namuduri, Committee Member

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ACKNOWLEDGMENTS

I would like to give special thanks to my advisor Dr. James E. Steck for his years of
thoughtful, patient guidance and support. I also thank my parents and friends for their continuous
encouragement.

iii
ABSTRACT

Wichita State University (WSU) and Raytheon Aircraft Company are working toward the
development of a flight control system to reduce the workload for a pilot under normal as well as
deteriorated flight conditions. An ‘easy fly system’ for a Bonanza Raytheon NASA test-bed has
been used by WSU to develop a neural network-based adaptive flight control system. In this
thesis an online technique for aerodynamic parameter estimation is presented, which is
developed to improve the adaptation. The neural-based adaptive flight controller uses an
artificial neural network for immediate adaptation in dynamic inverse control to compensate for
modeling error or control failure. Long-term adaptation to modeling error requires a permanent
correction of the aerodynamic parameters used in the inverse controller. This method is designed
to update parameters inside the controller and to provide slow and long-term adaptation to
compliment the existing immediate adaptation provided by neural networks. The method
employs gradient descent optimization, guided by the modeling error for updating each
parameter. It also uses the linearized equations of motion where the aerodynamic forces are
represented by their coefficients and derivatives. Some convergence enhancement techniques are
also used to reduce the time required for parameter identification. The aircraft is flown for
several specific maneuver patterns to decouple the effect of each parameter on the modeling
error. This helps the algorithm identify the correct parameter changes and eliminate modeling
error for all flight conditions. In-flight adjustment of parameters also replaces the time required
for off-line data analysis used by other techniques. Other online techniques like the discrete time
Fourier transform, a frequency domain-based technique, and locally weighted regression, a time
domain based method use a computationally complex solver with matrix inversions and
multiplications that require more processing power and time. The method described in this report
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uses computationally simple and direct equations to update the parameters at each time step,
which then become part of the controller. One of the challenges arises from the dependency of
the magnitude of the modeling error on each parameter. This creates a limitation on the number
of parameters that can be estimated at the same time and also increases the number of time steps
for convergence. Introducing some level of prior knowledge into the system can solve the
problem. These techniques were developed and tested in a Matlab/Simulink environment. The
results demonstrate the ability of the techniques to find a good estimate of the parameters in a
reasonable amount of time. Some limitations apply while using each technique, which open
doors for future work.
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TABLE OF CONTENTS

Chapter Page
1. INTRODUCTION....................................................................................................................1
1.1 Neural-Based Adaptive Flight Control System...............................................................1
1.2 Online Parameter Identification for Adaptive Flight Control..........................................3
1.3 Online Parameter Estimation Using Model Reference....................................................4
2. LITERATURE SURVEY.........................................................................................................5
2.1 Time Domain Methods....................................................................................................7
2.2 Frequency Domain Method.............................................................................................8
2.3 Neural Network Methods................................................................................................9
3. NEURAL-BASED ADAPTIVE FLIGHT CONTROLLER..................................................11
3.1 Aircraft Model used for Simulations.............................................................................13
3.2 Development of Linear Inverse Control Setup..............................................................14
3.3.1 Fundamental Artificial Neural Network...........................................................20
3.3.2 Artificial Neural Network Setup.......................................................................22
4. ONLINE PARAMETER ESTIMATION...............................................................................25
4.1. Online Parameter Estimation System Setup.................................................................25
4.1.1. Model Aircraft Block.......................................................................................26
4.1.2. Parameter Estimator Block..............................................................................27
4.2. Development of Parameter Estimation Routines..........................................................35
4.2.1. Estimate One Parameter Assuming Others Correct.........................................36
4.2.2. Estimate More Than One Parameter at a Time................................................38
4.2.3. Identify the Changed Parameter and Then Update..........................................40
5. RESULTS................................................................................................................................44
5.1. Results for Estimation of Single Parameter at the Same Time.....................................44
5.1.1. Estimation of a Change in C ........................................................................46
m0
5.1.2. Estimation of a Change in C ........................................................................47
mα
5.1.3. Estimation of a Change in C ........................................................................52
mq
5.1.4. Estimation of a Change in C .......................................................................52
mδe
5.1.5. Estimation of a Change in C ........................................................................54
Lα
5.1.6. Estimation of a Change in Mass.......................................................................59
5.2. Simultaneous Estimation of Multiple Parameters........................................................59
5.2.1. Estimation of a Change in C ........................................................................61
m0
5.2.2. Estimation of a Change in C ........................................................................62
mα
5.2.3. Estimation of a Change in C ........................................................................64
Lα
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5.2.4. Estimation of a Change in Mass.......................................................................66
5.2.5. Estimation of a Change in C , C , C , and mass ....................................68
m0 mα Lα
5.3. Estimation of Parameter After Identifying the Changed Parameter.............................72
5.3.1. Estimation of a Change in C ........................................................................73
m0
5.3.2. Estimation of a Change in C ........................................................................76
mα
5.3.3. Estimation of a Change in C .......................................................................78
mδe
6. DISCUSSION.........................................................................................................................80
7. CONCLUSIONS.....................................................................................................................83
LIST OF REFERENCES...............................................................................................................85
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LIST OF FIGURES

Figure Page

3.1. Control system setup plus Matlab/Simulink aircraft model.........................................12
3.2. Aircraft used to produce model the simulation............................................................13
3.3. Processing element of artificial neural network...........................................................20
3.4. Artificial neural network, processing elements, and connections................................21
3.5. Neural network connections for velocity control.........................................................22
3.6. Neural network connections for pitch control..............................................................23
4.1. Neural-based adaptive flight controller with online parameter estimation system......26
5.1. Flight maneuver velocity time history.........................................................................44
5.1.1(a). Time history of change in C values..........................................................................48
m0
5.1.2(a). Time history of pitch acceleration and NN correction.................................................48
5.1.1(b). Zoomed in time history of change in C values........................................................49
m0
5.1.2(b). Zoomed in time history of pitch acceleration and NN correction................................49
5.1.3(a). Time history of change in C values.........................................................................50
mα
5.1.4(a). Time history of pitch acceleration and NN correction.................................................50
5.1.3(b). Zoomed in time history of change in C values........................................................51
mα
5.1.4(b). Zoomed in time history of pitch acceleration and NN correction................................51
5.1.5. Time history of change in C values.........................................................................53
mq
5.1.6(a). Time history of pitch acceleration and NN correction.................................................53
5.1.6(b). Zoomed in time history of pitch acceleration and NN correction................................54
5.1.7(a). Time history of change in C values.........................................................................55
mδe
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5.1.8(a). Time history of pitch acceleration and NN correction.................................................55
5.1.7(b). Zoomed time history of change in C values...........................................................56
mδe
5.1.8(b). Zoomed time history of pitch acceleration and NN correction....................................56
5.1.9(a). Time history of change in C values.........................................................................57
Lα
5.1.10(a). Time history of forward acceleration and NN correction...........................................57
5.1.9(b). Zoomed time history of change in C values...........................................................58
Lα
5.1.10(b). Zoomed time history of pitch acceleration and NN correction....................................58
5.1.11. Time history of change in Mass values........................................................................60
5.1.12(a). Time history of pitch acceleration and NN correction................................................60
5.1.12(b). Zoomed time history of pitch acceleration and NN correction...................................61
5.2. Velocity time history....................................................................................................61
5.2.1. C update time history...............................................................................................63
m0
5.2.2. C update time history..............................................................................................63
mα
5.2.3. NN correction time history...........................................................................................63
5.2.4. C update time history...............................................................................................65
m0
5.2.5. C update time history..............................................................................................65
mα
5.2.6. NN correction time history...........................................................................................65
5.2.7. C update time history..............................................................................................67
Lα
5.2.8. Mass update time history.............................................................................................67
5.2.9. NN correction time history...........................................................................................67
5.2.10. C update time history..............................................................................................69
Lα
5.2.11. Mass update time history.............................................................................................69
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5.2.12. NN correction time history...........................................................................................69
5.2.13. C update time history...............................................................................................70
m0
5.2.14. C update time history..............................................................................................70
mα
5.2.15. NN correction in pitch acceleration time history.........................................................70
5.2.16. C update time history..............................................................................................71
Lα
5.2.17. Mass update time history.............................................................................................71
5.2.18. NN correction in forward acceleration time history....................................................71
5.3.1. Estimation of a change in C .....................................................................................75
m0
5.3.2. Estimation of a change in C ....................................................................................77
mα
5.3.3. Estimation of a change in C ....................................................................................79
mδe
x