High performance DSP-based servo drive control for a limited-angle torque motor

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High performance
DSP-based servo drive
control for a limited-angle
torque motor
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Additional Information:
• A Doctoral Thesis. Submitted in partial fulfillment of the requirements
for the award of Doctor of Philosophy of Loughborough University.
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Publisher: (cid:13)c Yi Zhang
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HIGH PERFORMANCE DSP-BASED SERVO DRIVE CONTROL
FOR A LIMITED-ANGLE TORQUE MOTOR
by
Yi ZHANG, B. Eng
A Doctoral Thesis
Submitted in fulfilment
the
partial of requirements
for
the
award of
Doctor Philosophy Loughborough University
the
of of
December 1997
Electrical Engineering
Department Electronics
of and
UNIVERSITY
LOUGHBOROUGH
by Yi ZHANG 1997
©
ABSTRACT
This describes design implementation high
thesis the
analysis, and of a performance
DSP-based drive for limited-angle in imaging
torque thermal
servo a motor used
applications.
A limited-angle is based Laws'
torque
the
motor an electromagnetic actuator on relay
in
from 10°
the
principle, and present application the rotation required was to
-
10° in 16 flyback 4 To
+
ms, with a period of ms. ensure good quality picture
high linearity °
reproduction, an exceptionally of ±0.02 was necessary throughout the
forward In drive
the to the the
sweep. addition, voltage exciting winding of motor
be less V drive A
than the +35 the
should ceiling of amplifier. research survey
little literature due
that to the
shows was available, probably commercial sensitivity
for
the torque
of many of applications motors.
A detailed drive, including high-order linear
the
mathematical model of motor
dynamics developed
the to
and significant nonlinear characteristics, was provide an
insight into behaviour. The
the
overall system proposed control scheme uses a multi-
linear
to the
compensator, multi-loop controller, reshape substantially motor response
to
characteristic, with a non-linear adaptive gain-scheduled controller compensate
The
for
the
effectively the nonlinear variations of motor parameters. scheme
be
demonstrates demanding
that a nonlinear control system may conveniently analyzed
frequency-domain design
that the techniques
methods, and may
and synthesized using
be to track
to systems required a repetitive
reliably applied similar electro-mechanical
waveform.
during
designed,
A drive tested the
system was constructed and course of
prototype
DSP-based digital linear
The drive
the system comprises a controller, a
research.
feedback for
the
the signal conditioning circuit necessary closed-
power amplifier and
built,
loop A
control. switch-mode amplifier was also evaluated and compared with
It linear
linear that the the
the amplifier. was shown overall performance of amplifier
for
The
the
to that of the switch-mode amplifier present application.
was superior
1
Abstract
developed
the
control software was using structured programming method, with the
digital form
continuous controller converted to using the bilinear transform. The 6-
it is
than the for high
operator was used rather z-operator, since more advantageous
The implemented by developing
speed sampling systems. gain-scheduled control was
is by DSP
a schedule table, which controlled the program to update continuously the
in
the
controller parameters synchronism with periodic scanning of the motor.
The
the
experimental results show excellent agreement with simulated results, with
linearity ° forward Although did
±0.05 throughout the this
of achieved sweep. not
demanding due limitations
the to the the
quite meet very specifications of
drive it demonstrates
the the
experimental system, clearly effectiveness of proposed
control scheme.
The discrepancies between
simulated and experimental results are analyzed and
discussed, design is detailed
the
control method reviewed, and suggestions are
for further improve drive
the
presented work which may performance.
Keywords: Limited-angle drive, DSP,
torque motor, servo gain-scheduled control,
digital linear
controller, power amplifier, stivitched-mode amplifier
11
ACKNOWLEDGENIEN'TS
I like to thank Supervisor, Mr. Gordon Kettleborough, for his
would my expert
invaluable during
the
guidance, advice and great encouragement years of my research
It is his
the this thesis. to the
and writing of owing emphasis on pragmatic approach
by the be that have been
which research should carried out satisfactory results
in both My for his
theoretical thanks
achieved and experimental work. sincere strong
for the for this I be
recommendation scholarship awarded research. will always
him for his long friendship
to time
grateful profound understanding, support and
but helped
to this to
which not only enabled me complete work, also me overcome
difficulties I have
the
enormous personal which encountered.
My deep Director Research, Professor Ivor Smith, for his
to
gratitude must go my of
for detailed discussions drafts he
the
constructive comments and on many carefully
during His dedication
the the thesis.
read process of preparing enthusiasm and
improved
to the
greatly encouraged me conclude research with an overall
My for his for for
thanks the
presentation. sincere solid support scholarship awarded
His kind be
the to throughout these
research. assistance me years will gratefully
remembered.
I Department Electronic Electrical
would express my sincere thanks to the of and
Engineering for financial for I to Mr.
the support this research. am also very grateful
S. K Jim Coercive System Ltd., Rochester, Kent, UK, for the funding the
and
and
for
torque the
motor contributed research.
discussions. My
I like Dr. Keith Gregory for his
would to thank technical advice and
Department for kind
the their
thanks to the
many should also go academic staff of
help in Dr. William Forsythe, Dr. Carl Manning, Dr. Von.
and advice, particular,
Vadher, Dr. Lionel Warnes, Mr. David Hoare Dr. Errol Tez.
and
from Department. He
I like Mr. Roy Ball, has the
to thank
retired
would also who
both
devoted hours the
technician supporting research
was a most popular and many
lab
and supervision.
iv
Acknowledgements
Thanks friends in Electrical
to the Power
must also go my many and colleagues
Research Group the Department, in Steve, Bob, Robert, Lynn, Hong.
and particular,
Mac, Derrick, Gitau Bill for help friendship.
their
and valuable and
My thanks to Professor Hongyuan Wang, the former Director
special go
of
Postgraduate Institute Huazhong University Science Technology, China, his
of of and
Menglin Cai their family, for their dedicated help
wife and great encouragement,
and
in the last two decades I them in that University. Their
constant caring since met
the life, including PhD
constructive advice and guidance at various stages of my the
Loughborough University, be
research at will always gratefully valued.
Last but least, immeasurable indebtedness Hui,
to
not my sincere goes my wife our
Chen, Jing brother-in-law Feng, love,
parents, my son my sister and whose caring,
in decade,
the
endurance, understanding, and encouragement are unparalleled past
during I from for It is
them than three this traditional
which was away more years.
family
that the to to
value and spirits gave me great strength and motivation strive
complete my research.
We hold be that they
these truths to self-evident, that all men are created equal;
--
life,
by Creator that these
endowed their with certain unalienable rights; among are
liberty, happiness
the
and pursuit of
Thomas Jefferson
-
V
To Hui,
my wife
Chen,
our parents, my son
Jing brother-in-law Feng.
my sister and
V1
TABLE OF CONTENTS
Page
Abstract
........ .....................................
Certificate Originality
of
... .... .... ..... .... ...............
Acknowledgements
iv
. .... ....... .... .... .........
.... .....
Dedication
vi
..... .......... ....... ......................
Table Contents
of
vii
.......................................
List Principal Symbols
of
xiii
..................................
CHAPTER 1 INTRODUCTION
1.1 Research Background
1
. ...... .... ........ .... .......
1.2 Research Objective
2
.... ...... .... ............... ..
1.2 Thesis Organisation
3
... ..... . ..... .... ... ..... ....
CHAPTER 2 THE LIMITED ANGLE TORQUE MOTOR
2.1 Introduction Limited-motion Actuators 6
to
........ ... .......
2.2 Laws' Relay Actuator Limited-Angle Torque Motor 7
and
........
2.2.1 Principle Operation
of
....... ......... .... . ... .7
2.2.2 Description Limited-Angle Torque Motor
of
..... ..... .8
2.2.3 Stiffness 9
. ..... ... ..... ... ........ ...... ...
2.2.4 Dynamic Characteristics 10
........................
2.3 Control Specification 10
...............................
CHAPTER 3 MOTOR SYSTEM MODELLING AND
DYNAMIC ANALYSIS
3.1 Linear Models 16
...................................
3.2 Overall Transfer Function Model Analysis 19
.................
3.3 Linear Model Time Response Analysis 21
....................
3.4 Nonlinear Static Characteristics 22
........................
3.4.1 Ideal Static Characteristics 23
........................
3.4.2 Nonlinear Static Characteristics Measurement 24
............
vii
Table Contents
of
3.4.3 Mathematical Description Nonlinear
of
Static Characteristics
24
...........................
3.5 Nonlinear Model
25
.................................
3.5.1 Frequency Response Measurement 25
...................
3.5.2 Nonlinear Dynamic Modelling 26
.....................
3.5.3 Verification Nonlinear Dynamic Model 26
of
..............
3.6 Piece-wise Linear Model 27
............................
CHAPTER 4 CONTROL ANALYSIS, DESIGN AND
SIMULATION
4.1 Analysis Control Specification 51
the
of
.....................
4.2 Design Methodology 52
...............................
4.3 Performance Specification 54
............................
4.3.1 Open-loop Frequency Response 54
....................
4.3.2 Closed-loop Frequency Response 55
...................
56
4.3.3 Time Response
...............................
4.3.4 Relationship Between Frequency Time Response 56
and
.......
57
4.4 System Compensation
..............................
57
4.4.1 General Considerations
..........................
58
4.4.2 Multi-loop Structures
...........................
59
4.4.3 Types Compensators
of
.........................
59
4.5 Linear Controller Design
............................
59
4.5.1 Current Loop Design
...........................
61
4.5.2 Position Loop Design
...........................
61
4.5.2.1 Forward Compensation
.....................
63
4.5.2.2 Feedback Lead Compensation
.................
63
4.5.3 Evaluation Two-loop Control System Performance
of
.......
4.5.4 System Robustness Analysis Nonlinear
the
under
64
Motor Model
................................
66
4.6 Adaptive Controller Design
...........................
66
4.6.1 Limitation Linear Controller
the
of
..................
67
4.6.2 Gain-scheduled Controller
........................
viii