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INVESTIGATIONS ON VECTOR
CONTROLLED INDUCTION MOTOR DRIVE
by
B. N. SINGH
Department of Electrical Engineering
THESIS SUBMITTED
IN FULFILMENT OF THE REQUIREMENTS FOR
THE DEGREE OF
DOCTOR OF PHILOSOPHY
to the
INDIAN INSTITUTE OF TECHNOLOGY, DELHI
INDIA
DECEMBER, 1885
DEDICATED
TO
MY PARENTS
CERTIFICATE
Certified that the thesis entitled "Investigations on Vector
Controlled Induction Motor Drive" which is being submitted by Mr.
B. N. SINGH for the award of the Degree of Doctor of Philosophy
in the Department of Electrical Engineering of the Indian
Institute of Technology Delhi, is a record of the student's own
work carried out by him under our joint supervision and guidance.
The matter embodied in this thesis has not been submitted for the
award of any other degree or diploma.
(Dr. BHIM SINGH)
Associate Professor
Department of Electrical
Engineering
I. I. T. Delhi
New Delhi-110 016 (INDIA)
(Prof. B. P. SINGH)
Department of Electrical
Engineering
I. I. T. Delhi
New Delhi-110 016 (INDIA)
ACKNOWLEDGMENTS
The author wishes to express his profound gratitude to Dr.
Bhim Singh and Prof. B. P. Singh, for their invaluable guidance
and inspiration in carrying out the work and their immense help
in the preparation of this thesis.
The author thankfully acknowledges Prof. S. S. Murthy for
his generous help and providing facilities during this work.
The author is also thankful to the authorities of the IIT
Delhi, for providing research facilities. Special thanks are due
to Messers R.P.Sharma, R.N.Singh, Meharban Singh, Arjun Singh,
Deep Chand and G.S.Negi, of the Department Workshop and Post
Graduate Machines and Drives Laboratory for their sustained help
and cooperation during the stay of the author in the institute.
The author extends his thanks to his colleagues Messers. Dr.
L.Shridhar, C.L.Putta Swamy, K.R.Rajgopal, L.B.Shilpkar, Ms.
Anuradha Srivastava, V.K.Sharma, M.Srinivas Rao, Amit Khare, Amit
Jain, Sanjeet Gupta, Mukesh Pathak and M.O. Vaishya for their
help and cooperation.
The author appreciates the ready cooperation, help and
encouragement received from his friends Messers Man Mohan
Agarwal, K.C.Agarwal, Ramesh Garg, Dilip Kumar, Ravindra Singh,
Rajesh Kumar Singh, Vijay Gupta, Rakesh Chaudhary, Akhilesh
Kumar Tiwari, Sanjeev Gupta and Pravin Kumar Singh.
The author also wishes to thank to his hostel mates
Messers C.D.Singh, Pravin Singh, Arvind Kumar Tomar, Veer Singh,
D.K.Singh, Yashveer Singh, B.K.Pradhan, Sujeet Chaudhary,
Mahaveer Jain and Suneel Khizwania for their encouragement at the
critical time of need.
The author wishes to record his appreciation for the
responsibilty shared by his younger and elder brothers Santos1
Kumar Singh and H.N.Singh at home, during the course of this
project.
New Delhi - 110016
14th December, 1995
B. N. SINGE
SUMMARY
The induction motor, ever since its development, has been
used as the main work-horse in applications requiring constant
speed operation. This is so because the cage motor has the
advantage of simpler but robust construction, maintenance free
operation and higher torque/weight ratio. Numerous attempts have
been made in the past to extend its use in variable speed mode
also, which used to be the exclusive domain of dc motors. In all
these efforts, the main objective has been to marry the inherent
structural advantages of former with the flexible characteristics
of latter. Advances in solid-state devices had paved the way for
the development of controllers which have made it possible to
provide the induction motor with some of the desirable features
of dc motors and consequently the cage motor drives are
increasingly being used and are in the process of replacing dc
drives in many applications. Since, the induction motor with a
variable frequency solid-state controller results in a highly
non-linear multivariable control plant, no standard solution has
so far emerged which could facilitate the straight forward
control of an induction motor. Field oriented control goes a long
way in providing answer to this problem. This helps in using the
cage motor in applications requiring faster dynamic response both
during starting and speed reversal, apart from the ability to
regenerate.
The cage induction motor drive with vector or field oriented
control offers a high level of dynamic performance and the
(xvi)
closed loop control associated with this drive provides the longterm stability of the system. The vector control is also called
as an independent or decoupled control wherein the torque and
flux current vectors are controlled in a manner similar to what
is done in a fully compensated separately excited dc motor.
Hence, the control plant of the cage motor drive is linearized
and it behaves like a fully compensated separately excited dc
motor.
In this investigation an indirect vector control scheme with
rotor flux orientation is used and current controlled voltage
source inverter is used as a source of excitation. The major
contribution of present investigation is summarized as follows.
(1) The main thrust of this work addresses to a comprehensive
analysis of a vector controlled induction motor drive (VCIMD)
system using real variables (currents and voltages) of the motor
in place of field variables (reference currents and voltages).
The analysis carried out is helpful for the design of vector
controlled induction motor drive. To simulate the performance of
the closed loop drive a dynamic model of the system is developed.
The model of the drive system uses speed controller and field
weakening block. Below the base speed, the rated flux in the
motor is maintained to achieve the characteristics of drive
similar to that of a separately excited dc motor, while beyond
the base speed, the flux weakening is considered. It is found
that the dynamic response of drive is fairly dependent upon the
regulation of the torque component (igs) of stator current vector
is. The current iqs (real torque component of stator current
vector) is pegged with the reference current iqs* (field current)
derived from reference torque T* , (output of speed controller
after a limiter) which is given as input to the vector control
structure. Therefore, the dynamic response of the drive is fairly
dependent upon the type of speed controller being used. In this
investigation the controllers used are namely, PI (proportional
plus integral), PID (proportional, integral plus derivative), SMC
(sliding mode controller), Adaptive SMC (ASMC), Fuzzy SMC (FSMC)
and Fuzzy PID.
The very reason of using these many speed
controllers is to verify the viability and versatility of the
developed model. Among the speed controllers being used in this
investigation PI, PID and SMC are conventional type while ASMC,
Fuzzy PID and Fuzzy SMC are advanced type. Mathematical models of
all type of speed controllers are developed.
With the help of developed model of VCIMD (vector controlled
induction motor drive) system, a comprehensive performance
analysis of the drive system is made. It is observed that the
existing drive has enough scope of improvements in its
performance in terms of energy conservation, reactive power
management and suppression of harmonics in ac mains by having an
arrangement of current controlled converter-inverter to feed
power to the motor. Apart from this, the cost of drive can be
appreciably reduced by replacing the speed sensor with the flux
model and reducing the number of current and voltage sensors
being used.
(2) The vector controlled cage induction motor drive is normally
fed from a diode bridge rectifier-current controlled voltage
(xviii)
source inverter link. The diode bridge rectifier is known t
inject harmonics into the ac mains and has low power factor
Apart from this, the regeneration of energy is not possible wit
this arrangement. As a solution to all these problems, the diod
bridge rectifier is replaced by a current controlled converter
The current controlled converter is switched at a high frequency
therefore, it draws sinusoidal current at its input whil
maintaining the power factor at unity. In addition to this, us
of current controlled converter provides the inherent capabilit
of regeneration to the drive system. Moreover, it results in a
ideal constant voltage dc link even under the condition when th
voltage and frequency of input ac mains are found to fluctuate
Therefore, the current controlled converter-inverter link give
rise to the four-quadrant operation of the drive with th
facility of energy conservation and reactive power management
The comprehensive analysis of CC-CONY-INV fed vector controlle
drive is carried out. In the current controlled converter (fron
end converter) a feedforward control of dc link power is als
incorporated along with the dc link voltage feedback. It is show
that as a result of feedforward control of the dc link power, th
input ac currents to the converter are made fast changing durin
transients and these currents are therefore, controlle
instantaneously. This helps in maintaining a close
correspondence between converter input currents and inverte
output currents. The feedforward control of the dc link powe
makes the currents input to the converter closer to sinusoida
during transients while maintaining the sinusoidal shape durin
(xix)
the steady state. It is also observed that the feedforward
control of converter improves the response of the system and
therefore, the regenerated energy is quickly pumped back to the
ac mains, which is considered as a highly desirable feature from
the energy conservation point of view.
(3) In the vector control of an induction motor, fast dynamic
performance is accomplished through quick regulation of the rotor
flux vector. The regulation of the rotor flux vector is possible
by quick control of the stator currents whichrequires an
accurate knowledge of the position of the rotor flux vector. In
the indirect vector control of cage induction motor, the rotor
flux position is ipdirectly estimated. For this accurate
estimation of the rotor flux vector position a high resolution
speed sensor is required. The speed sensor is a costly component
and its use causes an increase in the cost of drive system.
Therefore, an attempt is made towards the elimination of
mechanical speed sensor. For this purpose, a hybrid vector
control scheme, which uses the flux model of the direct vector
control and the slip frequency control of the indirect vector
control, is proposed. The flux model uses motor terminal
conditions in terms of currents and voltages and it estimates the
rotor speed which is used as a feedback signal in the indirect
vector control scheme. The estimated speed of the rotor is added
with the slip speed computed in vector control structure and this
yields the speed of rotor flux vector. From this the position of
the rotor flux vector is obtained. After knowing the position of
the rotor flux vector the stator currents of the motor can be
controlled in accordance with the requirements of the vector
control. The validity of developed flux model has been examined.
In addition to this, algorithms are developed which help in
reducing the number of current and voltage sensors used. This
further reduces the cost of the system and makes it simpler.
(4)
In order to ensure validity and viability of algorithms
developed for the purpose of performance simulation of vector
controlled induction motor drive (VCIMD) system, an experimental
verification of some of the algorithms is carried out. For this
purpose, a laboratory prototype of VCIMD system is developed
which uses 80486 processor based digital data control system.
Once, a scheme is verified practically it could be easily
extended to other control algorithms which vary in terms of speed
controller and the type of the source being used to feed power tc
the motor.
CONTENTS
Page No
LIST OF SYMBOLS
X
LIST OF FIGURES
XV
SUMMARY
CHAPTER IINTRODUCTION
1.1 General
1.2 Concept of Vector Control in Cage
Induction Motor Drive
1.3 Classification of Vector Control
Technique
1.4 High Performance Drives
1.5 Excitation Sources and Controllers for
Vector Controlled Drives
1
1.5.1 Emerging Trends in Converter
Technology
1
1.5.2 Controllers
1
1.6 Some Important Aspects of This
Investigation
1
1.7 Chapter Outlines
2
CHAPTER IILITERATURE REVIEW
2.1 General
2
2
2.2 Significant Development in VCIMD2
2.3 General Review of Literature on VCIMD3
2.4 New Trends in VCIMD
4
2.5 Conclusions
4
CHAPTER IIIDESCRIPTION OF VECTOR CONTROLLED CAGE MOTOR
DRIVE SYSTEM
3.1 General
4
4
3.2 Vector Control Method 4
3.2.1 DC Motor Analogy4
3.2.2 Basic Model of the Drive System4
3.3 Classification of Vector Control Schemes4
3.3.1 Direct Vector Control Method4
(i)
3.3.2 Indirect Vector Control Method
3.3.3 Use of Reference Frame
3.4 Proposed Vector Controlled Drive System
3.4.1 Control Strategy
3.4.2 Basic Equations of Vector Control
3.4.3 Derivation of the Equations Used
in Vector Control Structure
3.4.4 Realization of Proposed Drive
System and its Working
3.5 Conclusions
CHAPTER IVMODELING AND SIMULATION OF VECTOR CONTROLLED
CAGE MOTOR DRIVE
4.1 General
4.2 Working of Proposed Vector Controlled
Drive System
4.3 Description of a VCIMD System
4.4 Modeling of the Drive System
4.4.1
Speed Controllers
4.4.2 Modeling of the Field Weakening
Control
4.4.3
4.4.4
4.4.5
Modeling of Drive Control
Structure
8
Modeling of Current Controller and
Current Controlled Inverter
8
Modeling of the Induction Motor
8
4.5
Simulation of the Drive Performance
8
4.6
Results and Discussion
8
4.6.1
Response of the 0.75 kW Drive
8
4.6.2
Response of the 22.0 kW Drive
9
4.7
4.6.3 Sliding Mode Contour ofthe 22.0
kW Drive
9
4.6.4
Response Under Field Weakening
9
4.6.5 Response Under Disturbancein
Input Supply
10
Conclusions
10
(i)
CHAPTER V
PERFORMANCE WITH IMPROVED EXCITATION SOURCE107
107
5.1 General
5.2 Advantages of CC-CONV-INV Fed VCIMD108
5.3 Principle of Operation of UPF Converter
5.4 Modeling of CC-CONV-INV Fed Drive System 112
5.4.1 Converter Side Modeling112
5.4.2 InVerter Side Modeling117
5.5 Simulation of CC-CONV-INV Fed Vector
Controlled Drive
117
5.6 Results and Discussion118
5.6.1 Motor Starting 118
5.6.2 Speed Reversal Response of the
Drive System
120
5.6.3 System Response During Load
Perturbation
121
5.6.4 System Response to Supply Side
Disturbances
123
5.6.5 Suitability for Four Quadrant
Operation
127
5.6.6 Effectiveness of Feedforward
Control Loop
128
5.7 Conclusions
129
CHAPTER VISENSOR REDUCTION IN VCIMD SYSTEM132
6.1 General
132
6.2 Requirement of Sensors in VCIMD132
6.3 Elimination/Reduction of Sensors133
6.3.1 Elimination of Speed Sensor136
6.3.2 Reduction of Voltage Sensors139
6.3.3 Reduction of Current Sensors141
6.4 Modeling of Drive System144
6.4.1 Modeling of Cage Induction Motor145
6.4.2 Flux Model
145
6.4.3 Speed Estimator146
6.5 Simulation of VCIMD With Reduced Number
(iii)
of Sensors
147
6.6 Results and Discussion148
6.6.1 Response of VCIMD148
6.6.2 Response of Estimators149
6.7 Conclusions
CHAPTER VII
153
PRACTICAL IMPLEMENTATION OF VCIMD154
7.1 General
154
7.2 Description of Hardware of VCIMD System 154
7.2.1 Control Circuit155
7.2.2 Power Circuit 157
7.3 Software of VCIMD
158
7.4 Testing of the VCIMD 163
7.4.1 Testing of Power Circuit163
7.4.2 Testing of Control Circuit164
7.4.3 Testing of the Algorithm164
7.5 Performance of VCIMD System166
7.5.1 Response of Drive System167
7.5.2 Speed Reversal Response of Drive
System at Different Valuesof'
Reference Speeds169
7.5.3 Response of PWM Current Controller 171
7.6 Conclusions
CHAPTER VIII MAIN CONCLUSIONS AND SUGGESTIONS FOR FURTHER
WORK
173
174
8.1 General
174
8. Main Conclusions
174
8.3 Suggestions for Further Work178
BIBLIOGRAPHY
APPENDICES
181
LIST OF PUBLICATIONS
204
(iv)
196