This document presents a new method for starting induction motors to improve transient torque pulsations. It develops a mathematical model of a 415V, 4.7A, 1435rpm induction motor in MATLAB/Simulink. The proposed method connects two phases (Y and B) at startup, with the third phase (R) delayed by 0.0133333 seconds. Simulations show this unbalanced startup reduces torque pulsations and starting current compared to normal startup. The method provides smooth motor acceleration and high starting torque with minimized transients, making it suitable for induction motor applications.

1. ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 8, February 2013
219
Abstract- In this paper a new strategy for starting of induction
motor is proposed. This scheme depends on the initial switching
instances at which each phases of motor terminals are connected
to the supply. The performance analysis of the motor has been
carried out using a d-q axis induction motor model. A
mathematical model is developed in matlab/simulink for a 415 V,
4.7A, 1435rpm, 50 Hz three phase induction motor. The method is
shown to be very effective in the elimination of transient torque
pulsations and current components during the starting. The
simulation results presented in this paper show the effectiveness of
the method developed.
Index Terms-Induction Motor, Soft Starter, Torque
Pulsations, Modeling.
NOMENCLATURE
J Moment of inertia in Kg-m2
ids, iqs 2-phase stator currents in Ampere
idr, iqr Transformed two phase rotor currents in Ampere
rs, Ls 2-phase stator resistance in ohms and inductance in
Henry
rr, Lr 2-phase stator resistance in ohms and inductance in
Henry referred to stator in ohms
Te Electromagnetic Torque in N-m
TL Load Torque in N-m
Vds, Vqs 2-phasee stator voltage in Volts
Lm mutual inductance in Henry
wr rotor speed in rad/sec
Po Number of poles
I. INTRODUCTION
Three phase induction motors have been the workhorse for
many industrial and manufacturing processes from the
capacity of several kilowatts to thousands of kilowatts as the
driving units. It is a high efficiency electrical machine when
working closed to its rated torque and speed. The starting
methods of three phase induction motor [1] are generally
classified into four basic categories: Direct on line starting,
electromechanical reduced voltage starting, solid state
reduced voltage starting and variable frequency drive starting.
DOL starting of ac motors is the cheapest way but it may
present difficulties for the motor itself and the loads supplied
from the common coupling point because of the voltage dips
in the supply during starting. An uncontrolled starting may
cause a trip in either overload or under-voltage relay,
resulting in starting failure. Furthermore the number of starts
per day is limited to a few attempts. Electromechanical
reduced starting comprises of auto transformer starting,
star-delta starting, resistance or reactor starting. All these
methods have draw backs[2][3] such as need for frequent
inspection and maintenance, non simultaneous switching of
motor phases to the supply, failures in the moving parts due to
the large number of switching etc.VFD is more expensive
than any other method mainly because of the converter and
inverter section. Reduced voltage starters or so called soft
starters are often employed as effective and low cost means of
reducing high starting currents and torque pulsations through
the use of thyristor based voltage control. These are cheap,
simple, and reliable and compact in size and are increasingly
employed in industries nowadays. This circuit is a feasible
solution to the starting problem of large ac motors in
applications where the starting torque requirement of the load
is low. An Induction motor produces severe torque pulsations
depending on the initial switching instants to all the three
phases to the supply [4]. These are often large and vary from
positive to negative values. The mechanical subsystem
determines the amount of torque pulsations in shaft at starting
instant. These may cause shocks to the driven equipment and
damage in mechanical system components such as shafts,
couplings and gears. In this paper a new control strategy is
proposed for minimizing the torque pulsations which is based
on the switching instants of each phases of motor terminals
given to the supply and a mathematical model is developed in
MATLAB/SIMULINK for a 415 V, 4.7A, 1435rpm, and 50
Hz three phase induction motor.
II. MATHEMATICAL MODEL
Starting with the mathematical model of the induction
motor in terms of abc axes quantities, all space-angle and,
hence, time varying inductances are eliminated by applying
the three phase to two phase transformations; to the d-q axis
frame fixed to the stator[5]. The dynamic equations for the
induction motor are given below.
(1)
Where σ = 1- (Lm
2
/LrLs)
Vds and Vqs are given by
A Novel Method for Starting of Induction Motor
with Improved Transient Torque Pulsations
Nithin K.S, Dr. Bos Mathew Jos, Muhammed Rafeek, Dr. Babu Paul
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2. ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 8, February 2013
220
…………… (2)
and
..…………………….. (3)
The electromagnetic torque is given by
Te = …………………… (4)
And the speed is governed by
………..……………………..(5)
Fig 1: Schematic Diagram of Starter for Induction Motor
Dedicated software is developed in matlab/simulink for
modeling the drive system. The matrix equation (1) is derived
by the proper transformations of the quantities for which the
rotor reference frame is fixed in the stator. These differential
equations are used to develop a suitable system matrix for the
entire model. Here rs, rr, Ls, Lr are the corresponding stator
and rotor resistances and inductances respectively. Matrix
voltage equations can then be written as in (2) and (3) shown
below and (2) shows the transformation to d-q axis
components. After adding the torque balance equation for
dynamic operation, the model is brought into the state space
form for simulation. Matlab function for measuring the speed
in radians as well as in rpm is also developed.
III. PROPOSED CONTROL SCHEME
Fig 1 shows the schematic of the starting circuit for
induction motor. Three switches are connected to each phase
of the supply. This scheme depends on the switching instants
of each phase of the motor terminals given to the supply. The
switching instants of all the three phases to the supply
determine the current variation and the transient torque
pulsations at the starting of induction motor. So by controlling
the switching instants of the supply the torque pulsations can
be reduced to a minimized level. Also the current can be
maintained within the acceptable limit during starting.
Extensive simulations were carried out with different
combinations of initial switching instances. It is found that
improved starting torque pulsations are obtained by giving Y
and B phases simultaneously at the starting instant t=0 and R
phase with a time delay of t1. So till the switching instant of
the third phase only two phases are available at the motor
terminals. This seems to be a two phase supply to the motor,
results a reduced voltage at the starting instant hence the
current is controlled. Gradual variation in flux also reduces
the torque pulsations. So the motor gets smooth acceleration
and high starting torque with minimized torque pulsations and
reduced starting current. This is found to be better technique
which can put a great effect on the induction motor
applications.
IV. SIMULATION RESULTS
The mathematical model and the proposed control scheme
is implemented in Matlab. Switching instants of three phases
are given as follows. Three input voltages are shown in fig 2.
Switching instants of three phases are
Y,B, phases t= 0
R phase t1=0.0133333sec
Fig .2: Three Phase Input Voltages Given To The Motor
Terminal
The simulation is started with a delay of 2 sec for better
understanding. So all the waveforms in the above figures are
started at instant 2 sec. The voltage waveforms in the new
scheme are given in fig 2. Torque profile for normal starting
scheme is given in fig 3. It is observed that starting of
induction motor with small firing angles, the torque pulsations
are severe. Also the starting current is very much large. But
the time taken to attain the steady state is less compared to
profiles with large firing angles. In the case of large firing
angles, the starting torque pulsations are lesser. But the time
taken to attain the steady state is much larger [6]. Torque
pulsations are large even for this case.
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3. ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 8, February 2013
221
Fig.3: Torque Wave Forms for Firing Angle 00
Fig.4: Torque Characteristics for the Proposed Scheme
In the proposed scheme the torque pulsations are
minimized to a large extent as shown in fig 4. The starting
current is controlled and amplitude variations are reduced to a
permissible level (fig 5). So this method is well suitable for
starting of squirrel cage induction motor.
V. CONCLUSION
In this paper a new control strategy is presented to improve
the electromagnetic torque pulsations at starting. Torque
profile is seemed to be improved with minimized torque
pulsations. In order to obtain a better torque profile, the
system is properly unbalanced by giving only two phases of
supply to the motor model at the starting instant and then third
phase is applied. So this method will efficiently minimize
torque pulsations at starting, hence avoid shocks to the driven
equipment and reduce damage in mechanical system
components such as gears, couplings and shafts. This
technique can be implement in industries for large induction
motors.
APPENDIX
Induction motor details
Three phase, 415V, 4.7A, 1435rpm, 50Hz
Stator resistance, rs= 4.5 Ω
Rotor resistance, rr=4.5 Ω
Magnetizing inductance, Lm=1.296H
Stator inductance, Ls=1.3381H
Rotor inductance, Lr=1.3385H
Moment of inertia, J=0.00605 kgm2
REFERENCES
[1] R.M. Hamouda, A.I.Alolah, M.A.Badr, M.A. Abdel- halim ,
‖A Comparative Study on the Starting Methods of Three phase
wound-rotor Induction Motor’’,IEEE Transactions on Energy
Cpnversion.Vol.14, No.4, December 1999.
[2] A. J. Williams and M. S. Griffith, ―Evaluating the effects of
motor starting on industrial and commercial power systems,‖
IEEE Trans. Ind. Applicant., vol. IA-14, pp. 292–299,
July/Aug. 1978.
[3] J. Nevelsteen and H. Aragon, ―Starting of large
motors—Methods and economics,‖ IEEE Trans. Ind.
Applicat., vol. 25, pp. 1012–1018, Nov./Dec. 1989.
[4] W.S.Wood, F. Flynn, A. Shanmugasundaram. ‖Transient
Torques in Induction motors due to Switching of the supply,’’
Proc. Inst. Elect.Eng., Vol.112, no.7, pp.1348-1354, July1965.
[5] K. Sundareswaran, Bos Mathew Jos,‖ Analysis , Simulation
and Performance Comparison of AC Voltage Controller Fed
Three wire and Four wire connected Induction Motor
Drives‖,IEEE Indicon 2005 Conference, Chennai, India, 11-13
December 2005.
[6] K Sundareswaran, Bos Mathew Jos,’’ Comprehensive Study
on Starting Performance of Thyristor Controlled Induction
Motor Drives’’, IEEE Indicon 2005 conference.
AUTHOR’S PROFILE
Nithin K.S received the B.Tech degree in electrical
and electronics engineering from Govt. Engineering
College Idukki, Mahatma Gandhi University,
Kottayam, and Kerala, INDIA in 2011. He is currently
M.Tech scholar in Power Electronics at Mar
Athanasius College of Engineering, Kothamangalam,
and Mahatma Gandhi University. His areas of interest include power
electronic applications for electric motor drives.
Dr. Bos Mathew Jos received B.Tech Degree from
Mahatma Gandhi University, Kottayam, Kerala, INDIA
in 1993 and M.Tech and Ph. D Degrees from National
Institute of Technology Tiruchirappalli, INDIA in 2004
and 2010 respectively. Since 1998, he has been with
Mar Athanasius College of Engineering
Kothamangalam, Kerala. Currently, he is an Associate Professor of
Electrical and Electronics Engineering Department. His research interests
are Power Electronics and Drives.
Muhammed Rafeek has received the B.Tech degree
in electrical and electronics engineering from College of
Engineering Munnar, Cochin University of Science and
Technology, Kalamassery, Kochi, Kerala, INDIA in
2010. He is currently M.Tech scholar in Power
Electronics at Mar Athanasius College of Engineering,
Kothamangalam, and Mahatma Gandhi University. His
areas of interest include power electronic applications
for electric motor drives.
Dr. Babu Paul received B.Tech Degree from Mahatma
Gandhi University, Kottayam, Kerala, INDIA in 1990
and M.Tech from Govt. Engineering College Thrissur in
2003 and Ph.D from IIT Bombay in 2011. Since 1998, he
has been with Mar Athanasius College of Engineering
Kothamangalam, Kerala. Currently, he is an Associate
Professor of Electrical and Electronics Engineering Department.