DISTRIBUTED REAL-TIME CONTROL VIA THE INTERNET A Thesis by ABHINAV SRIVASTAVA

129 Pages·2003·0.51 MB·English

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DISTRIBUTED REAL-TIME CONTROL VIA THE INTERNET

A Thesis
by
ABHINAV SRIVASTAVA

Submitted to the Office of Graduate Studies of
Texas A&M University
in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

May 2003

Major Subject: Mechanical Engineering
DISTRIBUTED REAL-TIME CONTROL VIA THE INTERNET

A Thesis

by

ABHINAV SRIVASTAVA

Submitted to Texas A&M University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Approved as to style and content by:

Won-jong Kim Suhada Jayasuriya
(Chair of Committee) (Member)

Richard A. Volz John Weese
(Member) (Interim Head of Department)

May 2003

Major Subject: Mechanical Engineering
iii

ABSTRACT

Distributed Real-Time Control via the Internet. (May 2003)
Abhinav Srivastava, B.E., Motilal Nehru Regional Engineering College,
Allahabad, India
Chair of Advisory Committee: Dr. Won-jong Kim

The objective of this research is to demonstrate experimentally the feasibility of
using the Internet for a Distributed Control System (DCS). An algorithm has been
designed and implemented to ensure stability of the system in the presence of upper
bounded time-varying delays. A single actuator magnetic ball levitation system has been
used as a test bed to validate the proposed algorithm. Experiments were performed to
obtain the round-trip time delay between the host PC and the client PC under varying
network loads and at different times. A digital real-time lead-lag controller was
implemented for the magnetic levitation system. Upper bounds for the artificial and
experimental round-trip time delay that can be accommodated in the control loop for the
maglev system were estimated. The artificial time delay was based on various
probabilistic distributions and was generated through MATLAB. To accommodate
sporadic surges in time delays that are more than these upper bounds, a timeout algorithm
with sensor data prediction was developed. Experiments were performed to validate the
satisfactory performance of this algorithm in the presence of the bonded sporadic
excessive time delays.

DEDICATION
iv

To my father and mother.
v

ACKNOWLEDGMENTS

I would like to express my sincere gratitude to my thesis advisor, Professor Won-
jong Kim, for his support and fruitful discussions during my course of study at Texas
A&M University. It was a great opportunity for me to conduct the experiments. His
ability to solve basic engineering problems and practical knowledge in dealing with the
networked control systems motivated and guided me throughout my research activities.
I would also like to extend my thanks to my graduate committee members Dr.
Suhada Jayasuriya and Dr. Richard A. Volz for their interest and valuable guidance
during the research.
My thanks are due to Mr. S. C. Paschall, II for developing the single-actuator ball
levitation system that was used as a test bed for the experiments. My thanks are also due
to Mr. A. Ambike for his help in conducting the experiments for supervisory control via
the Internet. I would also like to thank Mr. A. Bhattacharya and Mr. P. P. Harihara along
with others for their cooperation throughout my research.
I am thankful to my parents, Mr. Arvind Kumar Srivastava and Mrs. Sadhna
Srivastava for their immeasurable support throughout my life. Without their love,
patience and support, I would have never come this far.
vi

TABLE OF CONTENTS

Page
ABSTRACT...................................................................................................................iii
DEDICATION...............................................................................................................iv
ACKNOWLEDGMENTS...............................................................................................v
TABLE OF CONTENTS...............................................................................................vi
LIST OF TABLES .......................................................................................................viii
LIST OF FIGURES........................................................................................................ix
CHAPTER
I INTRODUCTION.................................................................................................1
1.1 Introduction.................................................................................................1
1.2 The Internet.................................................................................................2
1.3 Internet protocols.........................................................................................2
1.4 Real-time control via the Internet................................................................4
1.5 Goal of the thesis.........................................................................................6
1.6 Thesis overview...........................................................................................6

II PRIOR WORK AND EXPERIMENTAL SETUP...............................................8
2.1 Introduction ................................................................................................8
2.2 Related work ...............................................................................................8
2.3 Test bed and its control..............................................................................13

III MODES OF CONTROL VIA THE INTERNET...............................................19
3.1 Introduction...............................................................................................19
3.2 Software architecture.................................................................................19
3.3 Supervisory control via the Internet..........................................................22
3.4 Feedback control via the Internet..............................................................27

IV ANALYSIS OF FEEDBACK CONTROL VIA THE INTERNET...................31
4.1 Introduction................................................................................................31
4.2 Modeling of the data traffic in the Internet................................................32
4.3 Stability analysis of existing controller with delays...................................33
4.4 Experimental delay measurement for LAN................................................37
vii
CHAPTER Page
V DIGITAL CONTROLLER DESIGN.................................................................42
5.1 Introduction................................................................................................42
5.2 Designing the digital controller .................................................................42
5.3 Sensor data estimation and timeout ...........................................................50
5.4 Performance evaluation of the selected algorithm.....................................70

VI CONCLUSIONS.................................................................................................72
6.1 Conclusions .................................................................................................72
6.2 Ongoing work..............................................................................................73

REFERENCES..............................................................................................................74
APPENDIX A...............................................................................................................77
APPENDIX B................................................................................................................80
APPENDIX C................................................................................................................92
APPENDIX D...............................................................................................................93
APPENDIX E..............................................................................................................105
APPENDIX F..............................................................................................................116

VITA............................................................................................................................118
viii
LIST OF TABLES

TABLE Page

I Magnetic levitation theory nomenclature ………………………………… 15
II Round-trip time delays between PCs on different LANs …………..…….. 38
III Round-trip time delays between PCs on the same LAN……………….…. 39
IV Maximum constant time delay for different sampling frequencies ………. 47
V Mean time delay based on a Uniform PDF with respect to sampling
frequencies ……………………………………………………………..… 48

VI Mean time delay based on a Poisson PDF with respect to sampling
frequencies………………………………………………………………… 4 8
ix

LIST OF FIGURES

FIGURE Page
1. Schematic representation of use of buffers in control system via communication
medium.........................................................................................................................11

2. Block diagram of portion between sensor node and controller node...........................12

3. Single-actuator magnetic ball levitation system..........................................................14

4. Basic setup for the magnetic levitation system............................................................15

5. External forces on the levitated ball.............................................................................16

6. Software architecture for controller algorithm.............................................................20

7. Block diagram for supervisory control via the Internet...............................................22

8. Software architecture for the supervisory control of the maglev system via the
Internet.........................................................................................................................24

9. HTML Web page of the maglev system for the user interface....................................25

10. HTML output Web page of the maglev system...........................................................26

11. Maglev system response to a step input of 300 µm provided via the Internet.............27

12. Block diagram for feedback control via the Internet...................................................28

13. Software architecture for feedback control via the Internet.........................................29

14. Digital control system with the induced delays...........................................................33

15. Maximum allowable constant time delay with respect to sampling frequencies.........34

16. Mean allowable random time delay based on a Uniform PDF with respect to
sampling frequencies....................................................................................................35

17. Mean allowable random time delay based on a Poisson PDF with respect to
sampling frequencies....................................................................................................36

18. Discrete model of the plant..........................................................................................43
x

FIGURE Page

19. Root locus for feedback with a gain.............................................................................44

20. Modified root locus when the lead-lag compensator is implemented.........................45

21. Closed-loop maglev system transient response for unit step.......................................46

22. Maglev system closed-loop Bode plot.........................................................................46

23. Setup for application of timeout methodology in control system with random
time delays ...................................................................................................................50

24. Plot between the value of a and the number of iterations..........................................55
1

25. Plot between the value of a and the number of iterations..........................................56
2

26. Plot between the value of a and the number of iterations..........................................56
3

27. Plot between the value of a and the number of iterations..........................................57
4

28. Plot between the value of a and the number of iterations..........................................57
5

29. Plot between the value of a and the number of iterations with arbitrary initial
1
values of the parameters for AR model.......................................................................58

30. Plot between the value of a and the number of iterations with arbitrary initial
2
values of the parameters for AR model.......................................................................59

31. Plot between the value of a and the number of iterations with arbitrary initial
3
values of the parameters for AR model.......................................................................59

32. Plot between the value of a and the number of iterations with arbitrary initial
4
values of the parameters for AR model.......................................................................60

33. Plot between the value of a and the number of iterations with arbitrary initial
5
values of the parameters for AR model.......................................................................60

34. Plot between percentage error in using AR model for sampling frequency of
333.3 Hz and number of iterations...............................................................................62

35. Plot between the percentage error in the AR model for sampling frequency of
500 Hz and the number of iterations............................................................................63

36. Plot between the value of a and the number of iterations..........................................64
1