Download International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726

International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.1, pp. 1716-1726
ISSN 2078-2365
http://www.ieejournal.com/
Performance and Analysis of Direct
Torque Control Induction Motor FED
PWM Inverter Drives
Khadim Moin Siddiqui, Kuldeep Sahay, V.K.Giri
[email protected]

Abstract— AC asynchronous electrical motors especially
squirrel cage induction motor presents the greater advantages
on cost and energy efficiency as compared with other industrial
solutions for varying speed applications. The force-commutated
power electronics switches (GTOs, MOSFETs, and IGBTs etc)
based inverters are widely employed these days in the
conversion of constant speed into variable speed induction
motors. Due to the invention of these advanced power
electronics switches (GTOs, MOSFETs, IGBTs etc) with
improved characteristics, the PWM inverter fed induction
motors are widely replacing DC motors and thyrister bridges
day by day in the industries. The torque control or field control
method may be used with PWM inverter fed induction motors
jointly and can achieve the same flexibility in speed and torque
control as with DC motors. In this present paper, an IGBT
inverter fed squirrel cage induction motor with torque control
technique is developed and simulated in the recent
MATLAB/Simulink environment and observed the transient
characteristics of the used motor. Many motor parameters have
been used for induction motor analysis purpose. Further, V/f
control and Total Harmonics Distortion (THD) analysis has
also been carried out. Though, the stator current parameter of
the motor has been widely used from last three decades with
Motor Current Signature Analysis (MCSA) technique.
Therefore, in the THD analysis, only stator current motor
parameter has been analysed.
Index Terms— Squirrel cage induction motor
Induction Motor (IM), Pulse width modulation
Insulated Gate Bipolar Transistor (IGBT), Time
Analysis, Direct Torque Control (DTC), V/f
MATLAB/Simulink
(SCIM),
(PWM),
Domain
Control,
I. INTRODUCTION
Earlier, the DC motors were widely employed in industries
to achieve variable speed for many applications by changing
the field and armature current. Consequently, its flux and
torque controlled efficiently. But this method requires
frequent maintenance, high cost, unable to use in the
explosive environment. By using DC motors, large variation
in the motor’s speed is not possible. Therefore, for wide range
of speed control purpose induction motor fed PWM inverter
is preferred these days. Nowadays, induction motor has
become the heart of industries with modern power electronics
devices. By using this combination, IM can control the wide
range of speed with very competitive pricing. Therefore, the
induction motor has become the “workhorse” of the motion
industry [1-4,13].
In the past, the induction motors were widely employed in
constant speed applications because of the unavailability of
the variable- frequency voltage supply. The variablefrequency voltage can achieve by the advanced power
electronics semiconductor devices based inverters. These
inverters widely called Pulse Width Modulation (PWM)
Inverters. These inverters provide us capability to vary the
frequency of the voltage supplies in the relatively easy way.
As a result, the induction motor can be used in the variable
speed drive applications. The PWM inverter may control the
large amount of speed of the induction motor[1,4,7,13].
The PWM inverters covered many applications in the
electrical engineering field such as UPS, AC electric drives,
HVDC reactive power compensators in power systems and
communications to power control and conversion. In the
present time, the PWM inverter fed asynchronous motor
drives are widely used in the industries because it provides
more variable and offer in a wide range of speed control with
better efficiency and higher performance compared to
constant frequency motor drives[4-6,14].
The induction motor with advanced power electronics
inverters not only controls the motor speed but can also pick
up motor’s dynamic as well as steady state characteristics.
Subsequently, these devices can reduce the system's average
power consumption and noise generation of the induction
motor [1,7].
The three phase Squirrel Cage Induction Motor (SCIM) is
simple, efficient and robust asynchronous motor and often a
natural choice as a drive for industries with a very competitive
pricing. Squirrel Cage Induction motors (SCIM) are the most
1716
Siddiqui et. al.,
Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.1, pp. 1716-1726
ISSN 2078-2365
http://www.ieejournal.com/
extensively used electric motors for appliances, industrial
control, automation and transportation. The SCIM widely
employed these days as variable speed induction motor with
PWM inverters and replacing DC motors and thyristor
bridges in industries [1, 3, 5].
It has been seen that many researchers proposed various IM
models with different power electronics devices based
inverters and control the speed of the IM. But harmonics
always creates problems in the currents, voltage and
developed electromagnetic torque. Therefore, the modeling
of such motors is still being the challenging task [1, 8-12,14].
The IM with PWM inverters has been delivering
challenging competition with D.C motors these days and
given the cause for replacement of D.C. motors from very fast
speed in the industries. This technique is cheap and safe to
achieve variable speed efficiently with less power
consumption and minimum maintenance. Consequently save
many dollars for industries. The IM cost per KVA is
approximately one fifty than DC motors. Therefore, it seizes
higher appropriateness in antagonistic atmosphere [1-3].
In the present paper, we have proposed and developed an
SCIM fed PWM inverter model in the recent
MATLAB/Simulink environment. We have used IGBT
inverter and torque control method with induction motor
jointly for better results with reduced harmonics. The V/f
control has also been carried out for the proposed model. The
transient behavior of the induction motor has been deeply
observed. In future, this model may be used in the various
power electronics and drive applications.
II. MATHEMATICAL MODELLING of INDUCTION
MOTOR
The traditional per-phase equivalent circuit is used for
induction motor mathematical modelling purpose. The basic
diagram of per phase equivalent circuit for q and d-axis is as
shown in Fig. 1. The equations are derived in the Clarke or αβ
(stationary) reference frame by d and q variables. The d-q
transformation is widely used because it reduces three AC
quantities into two imaginary DC quantities for balanced
circuits. The simplified calculations may be carried out on
these two imaginary DC quantities for recovering the actual
three-phase AC results by performing inverse transformation.
(a)
(b)
Fig. 1 Per- Phase Equivalent Diagram of IM, (a) q-axis, (b) d-axis
The stator circuit voltage equations in the Clarke or αβ
(stationary) reference frame transformation is as follows:
V s qs  Rsi s qs  p s qs
(1)
d
dt
s
 Rsi ds  p s ds
(2)
Where,
V s ds
p
The stator voltage equations involved in the conversion of
rotating reference into stationary reference frame are as
follows:
V s qs  cos 
 s 
V ds  sin 
 sin  
 cos  
Vqs 
 
Vds 
(3)
The variable stationary reference and variable rotating
reference frame expressed by the following equations (4 & 5):
V s qs  Vm cos 
Where,   t  
V s ds  Vm sin 
(4)
(5)
The q-axis and d-axis stator voltage equations are as follows:
Vqs  Rsiqs  pqs  ds
(6)
Vds  Rsids  pds  qs
(7)
The q-axis and d-axis rotor voltage equations are as follows:
V  qr  R r i qr  p  qr    dr
Where,
(8)
    r
1717
Siddiqui et. al.,
Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.1, pp. 1716-1726
ISSN 2078-2365
http://www.ieejournal.com/
V  dr  R r i dr  p  dr    qr
(9)
For simulation of an open loop model, following flux linkage
equations (10 to 13) would be considered.
(10)
qs  Lsiqs  Lmi qr
ds  Lsids  Lmi dr
 qr  L r i qr  Lmiqs
 dr  L r i dr  Lmids
(11)
(12)
ds   (Vds  Rsids )dt
(14)
qs   (Vqs  Rsiqs )dt
(15)
(13)
In our case, for closed loop model following flux linkage
equations (14 to 16) will be considered.

s  ( 2 ds  2 qs )  tan 1 ( qs )
 ds
(16)
The total stator and rotor inductances may be expressed by the
following equations:
Ls  L1s  Lm
(17)
L r  L 1r  Lm
(18)
The developed electromagnetic torque may be written by the
following equation:
Te 
3P
( ds iqs  qs ids )
2
(19)
The rotor acceleration equation may be expressed by the
following equations:
pm   (Te    Tm )
(20)
1
Where,  
,   Fm and m  p m
2H
The abc to dq reference frame transformations in the
phase-to-phase voltage may be expressed by the following
equations. The q-axis transformed stator voltage equation is
as follows:
1
Vqs  (21Vabs   2Vbcs )
3
Where, 1  cos  ,  2  cos   3 sin 
(21)
(22)
The q-axis transformed rotor voltage equation is as follows:
1
V  qr  (2 1V  abr   2V  bcr )
3
 cos  ,  2  cos   3 sin 
The d-axis transformed rotor voltage equation is as follows:
1
V  dr  (21V  abr  2V  bcr )
3
Where, 1  sin  , 2  sin   3 cos 
(24)
In the preceding equations, θ is the angular position of the
reference frame, while δ= θ - θr is the difference between the
position of the reference frame and the position (electrical) of
the rotor. Because the machine windings are connected in a
three-wire Y configuration, there is no homopolar (0)
component. This also justifies the fact that two line-to-line
input voltages are used inside the model instead of three
line-to-neutral voltages.
The dq to abc reference frame transformations applied for the
phase currents may be expressed by following equations:
The phase a current in the stator side may be expressed by the
following equation:
ias  1iqs   2ids
(25)
Where, k1
 cos  , k2  sin 
The phase b current in the stator side may be expressed by the
following equation:
ibs  3iqs   4ids
(26)
Where,
k3 
 cos   3 sin 
 3 cos   sin 
, k4 
2
2
The phase a current in the rotor side may be expressed by the
following equation:
ii ar  1i qr  2i dr
Where, 1
(27)
 cos  , 2  sin 
The phase b current in the rotor side may be expressed by the
following equation:
ii br  3i qr  4i dr
(28)
Where,
The d-axis transformed stator voltage equation is as follows:
1
Vds  (21Vabs   2Vbcs )
3
Where, 1  sin  , 2  sin   3 cos 
Where, 1
(23)
3 
 cos   3 sin 
 3 cos   sin 
, 4 
2
2
The phase c current in the stator side may be expressed by the
following equation:
ics  ias  ibs
(29)
The phase c current in the rotor side may be expressed by the
following equation:
i cr  i ar  i br
(30)
1718
Siddiqui et. al.,
Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.1, pp. 1716-1726
ISSN 2078-2365
http://www.ieejournal.com/
The complete mathematical modelling of the used induction
motor may be understood by equations (1 to 30).
III. PROPOSED DIRECT TORQUE CONTROL INDUCTION
MOTOR FED PWM INVERTER
The force-commutated electronic switches are widely
employed these days to convert constant speed asynchronous
motors into variable speed asynchronous motors. Power
electronics switches such as MOSFETs, GTOs and IGBTs
efficiently controls the induction motor. The Pulse Width
Modulation (PWM) voltage source(VSC)
inverter-fed
induction motor are widely used these days and gradually
replacing DC motors and thyristor bridges. With PWM
inverter, combined with advanced control strategies such as
field-oriented control or direct torque control, we can achieve
the same flexibility in speed and torque control as with DC
machines. Since, it has been observed that the IGBTs inverter
fed into induction motor give better results rather than other
power electronics switches based inverters fed induction
motor in many power applications with reduced harmonics.
Therefore, in the present work, the torque control simulation
model has been developed in the MATLAB with PWM
inverter fed induction motor. The Insulated Gate Bipolar
Transistor (IGBT) inverter has been used in the conversion of
DC voltage into AC voltage.
The proposed inverter fed induction motor simulation
model is as shown in Fig. 2. The positive load torque ought to
be applied on the shaft, if electric motor operates in the
motoring mode or negative for generating mode. The nominal
full load positive torque is applied on the machine’s shaft is
15 Nm for motoring mode. The SCIM block available in the
MATLAB/Simulink having three inputs and one output. The
three phase supply would be given in the three inputs and
output side one bus selector has been used. The bus selector
de-multiplexes many outputs of induction motor. There are 21
motor signatures are hidden in induction motor’s one output.
We can de-multiplex these signals as per our requirement. In
our case, we have been de-multiplexed only maximum six
parameters for analysis purpose.
Fig. 2 Proposed DTC Control SCIM Fed PWM Inverter Simulation Model
In the present paper, a three-phase SCIM rated 3 HP, 220
V, 1430 RPM is fed by a sinusoidal PWM inverter has been
considered for analysis purpose. The sinusoidal reference
wave base frequency is used 50 Hz while the triangular carrier
wave's frequency is calculated and set to 1650 Hz. The
modulation factor is 33 and ought to be choose as high as
possible for better results. Therefore, the triangular carrier
wave's frequency corresponding to the given modulation
factor is 50×33=1650 Hz. Since, the switching frequency
(1650 Hz) is relatively high. Therefore, maximum time step is
restricted to 10 µs. This high switching frequency (1650 Hz)
is required for the inverter. It is recommended in [2-3] that the
modulation factor (mf) ought to be an odd multiple of three
and that value has to be as high as possible.
The machine's rotor is short-circuited for SCIM. The
smoothing reactor has also been placed between the inverter
and the electric machine for simulating the effect of a
smoothing reactor. Consequently, we have set the stator
leakage inductance twice to its actual value. If we use PWM
inverter then noise will be introduced in the electromagnetic
torque, voltage and currents but the motor's inertia will
prevents the noise from appearing in the motor's speed.
The Clarke or αβ transformation (stationary reference
frame) is used in this work. The reference frame is required
for the conversion of input voltages (abc reference frame) into
the output currents (dq reference frame). If we are interested
to do park transformation then the rotor reference frame ought
to be choose.
In the stationary reference frame, the rotor angle value is
set to 0 and the value of δ is set to -θr. The reference frame
affects the simulation speed, waveforms of all dq variables
and in some certain cases the accuracy of the obtained results.
The brief descriptions of the used SCIM block parameters are
given in appendix (Table I).
1719
Siddiqui et. al.,
Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.1, pp. 1716-1726
ISSN 2078-2365
http://www.ieejournal.com/
Magnetic Field (RMF) 1430 RPM after 0.4 sec. At the
starting, the magnitude of the 50 Hz stator current reaches 96
A peak( 68 A RMS) whereas its steady state value is attained
12.25 A( 8.66 A RMS).
The developed electromagnetic torque waveform reveals
that the stable condition is achieved after 0.4 sec. the strong
oscillations have been observed in the electromagnetic torque
waveform at starting. If it is zoomed, the noisy torque will be
observed with a mean value of 15 N.m.
100
80
<Stator current is_a (A)>
60
40
20
0
-20
-40
-60
-80
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
1
0.7
0.8
0.9
1
(a)
100
80
60
<Rotor current ir_a (A)>
The snubber circuit is essential with IGBT and provided
inbuilt in the MATLAB/Simulink Library. In the used IGBT
block, we have set the value of snubber capacitor infinite
(short- circuit). It means the purely resistive snubber has been
used. Generally, the Insulated Gate Bipolar Junction
Transistor (IGBT) do not use snubbers but every non-linear
elements are used in the MATLAB/Simulink is modeled as a
current source. Consequently, we need to provide a parallel
path across each IGBT to allow connection to an inductive
circuit (stator of an induction motor). But, the circuit
performance would not be affected by choosing high value of
the snubber. A pulse generator is employed to control the
inverter bridge.
In the present work, the torque control method has been
used for induction motor controlling purpose with PWM
inverter. Since, the field or vector control method is a pretty
attractive control method but due to some serious drawbacks
is not used in this present work. The field control method
relies deeply on accurate acquaintance of the motor
signatures. The rotor time constant is particularly hard to
measure accurately, and to make matter very inferior because
it varies with temperature. The torque control method
proficiently controls the IM than field control method. It
estimates the stator flux and electric torque by Clarke or αβ
transformation and terminal measurements. The mathematical
equation of torque control has already been discussed. The
approximated stator flux and electric torque are directly
controlled by comparing them with their relevant demanded
values by using hysteresis comparators. The two
comparator’s output will then be used as input signals of an
elective switching table. The value of the direct torque control
feedback constant k has been computed 6.693
.
IV. RESULTS in SYMMETRICAL CONDITION
(HEALTHY STANDSTILL CONDITION)
40
20
0
-20
-40
-60
-80
-100
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
(b)
1600
1400
1200
Rotor Speed(RPM)
The simulation result in symmetrical condition or healthy
standstill condition of the motor is as shown in Fig. 3. Six
motor parameters of the induction motor have been used for
performance and analysis purpose. These are stator current,
rotor current, rotor speed, developed electromagnetic torque,
q-axis stator/rotor flux. In the standstill condition of the
motor, the load torque and slip set at 15 and 1 respectively.
The obtained results show that all the considered motor
parameters have been reached in the steady state condition
after 0.4 seconds. In the starting of the motor, the first
transient peak of the stator current and electromagnetic torque
waveforms having highest amplitude when it is decreased and
reached in the stable condition. The proposed simulation
model is simulated only for 1 sec for clear visualization of
transient
characteristics.
Therefore,
the
transient
characteristic of the motor is clearly visualized.
The squirrel cage induction motor starts and reached in the
steady state condition after 0.4 sec and attained Rotating
1000
800
600
400
200
0
-200
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
1
(c)
1720
Siddiqui et. al.,
Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.1, pp. 1716-1726
ISSN 2078-2365
http://www.ieejournal.com/
140
100
100
80
80
<Stator current is_a (A)>
<Electromagnetic torque Te (N*m)>
120
60
40
20
60
40
20
0
0
-20
-40
-20
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
0
0.1
0.2
0.3
1
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
1
0.7
0.8
0.9
1
0.7
0.8
0.9
1
0.7
0.8
0.9
1
(a)
(d)
80
1
0.8
60
<Rotor current ir_a (A)>
<Stator flux phis_q (V s)>
0.6
0.4
0.2
0
-0.2
40
20
0
-20
-0.4
-0.6
-40
-0.8
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
0
0.1
0.2
0.3
1
0.4
0.5
0.6
Time (seconds)
(b)
(e)
1440
0.6
1420
1400
Rotor Speed(RPM)
<Rotor flux phir_q (V s)>
0.4
0.2
0
1380
1360
1340
-0.2
1320
-0.4
1300
0
0.1
0.2
0.3
-0.6
0.4
0.5
0.6
Time (seconds)
(c)
60
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
1
(f)
Fig. 3 Motor Parameters in Symmetrical Condition(Healthy Standstill
Condition), (a) Stator Current, (b) Rotor Current, (c) Rotor Speed, (d)
Electromagnetic Torque, (e) q-axis Stator Flux, (f) d-axis Rotor Flux
If we zoomed stator and rotor current waveforms, the
harmonics will be displayed multiple of the 1650 Hz
switching frequency. This is filtered by stator inductance.
Therefore, we can say that the 50 Hz frequency component is
dominant. Similarly, q-axis stator and rotor flux is also
attained steady state condition after 0.4 sec. After passing
transient time, perfectly sinusoidal signal can be observed.
Therefore, finally we can say that the proposed simulation
model given expected correct results.
Second healthy running condition has also been considered
and observed due to the clear revelation of the transient
characteristics. In the healthy running condition mode the slip
is set at 0.04. At this slip, we can get 1430 RPM rotor speed
on full load nominal torque. This is our nominal speed of the
40
<Electromagnetic torque Te (N*m)>
-0.8
20
0
-20
-40
-60
-80
-100
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
(d)
1721
Siddiqui et. al.,
Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.1, pp. 1716-1726
ISSN 2078-2365
http://www.ieejournal.com/
1
0.8
0.4
0.2
0
-0.2
-0.4
-0.6
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
1
(e)
0.6
<Rotor flux phir_q (V s)>
0.4
0.2
0
80
-0.2
60
40
-0.4
-0.6
-0.8
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
1
<Rotor current ir_a (A)>
<Stator flux phis_q (V s)>
0.6
When IGBT inverter frequency is increased or decreased
compared to the rated frequency, the large variation in the
rotor speed has been achieved. The inverter frequency
variation has been considered from 70 Hz to 6 Hz. It may be
observed from Table III, that the inverter frequency is able to
control the speed up to 1825 RPM to 238 RPM. Therefore, we
can say that a wide range of speed control is possible through
this proposed inverter fed induction motor with torque control
technique by the V/f control strategy efficiently. In the similar
way, if we change the power, the same speed variation will be
taken place. It has been observed that the motor power will be
varied from 2.95 HP to 0.15 HP. Hence, we can say that an
efficient V/f control has been successfully implemented in
this model.
20
0
-20
-40
(f)
Fig. 4 Motor Parameters in Symmetrical Condition(Healthy Running
Condition), (a) Stator Current, (b) Rotor Current, (c) Rotor Speed, (d)
Electromagnetic Torque, (e) q-axis Stator Flux, (f) d-axis Rotor Flux
-60
-80
0
0.2
0.4
0.6
0.8
1
1.2
Time (seconds)
1.4
1.6
1.8
1.4
1.6
1.8
1.4
1.6
1.8
1.4
1.6
1.8
2
(a)
100
The SCIM fed PWM inverter with torque control can
control the large amount of speed of the motor. The used
induction motor (3 HP, 4 Pole, 50Hz) motor's speed can be
controlled efficiently by the V/f control method. The speed
can vary from 1825 RPM to 238 RPM by changing the
frequency of the inverter.
The rotor current, stator current, rotor speed, and
electromagnetic torque for various frequencies have been
carried out. It may be observed from Fig. 5 and Fig. 6. If we
observe only rotor speed waveform for 70 Hz and 30 Hz in
Fig. 5 and Fig. 6. The large variation in the rotor speed has
been taken place by the inverter frequency. It has been
observed from the Fig. 3 that when the motor frequency is 50
Hz then the rated rotor speed is achieved i.e. 1430 RPM.
<Stator current is_a (A)>
60
40
20
0
-20
-40
-60
-80
0
0.2
0.4
0.6
0.8
1
1.2
Time (seconds)
2
(b)
2000
1500
Rotor Speed(RPM)
V. V/f CONTROL by PROPOSED SIMULATION
MODEL
80
1000
500
0
-500
0
0.2
0.4
0.6
0.8
1
1.2
Time (seconds)
2
(c)
70
60
<Electromagnetic torque Te (N*m)>
motor. In this mode, we may observe that the transient time
has been decreased and flux waveforms give perfectly
sinusoidal flux. Therefore, we can say that the motor is given
excellent results in the healthy running condition also.
The transient variation in the motor parameters is given in
the appendix(Table II) for different loading conditions. From
Table II, we may observe that how our used induction motor
works in the different loading conditions. In the standstill
healthy mode, the slip is set at 1. Consequently, the rotor
speed is zero but RMF value is shown in the Table II i.e. 1430
RPM for clear comparison purpose.
50
40
30
20
10
0
-10
-20
-30
0
0.2
0.4
0.6
0.8
1
1.2
Time (seconds)
2
(d)
1722
Siddiqui et. al.,
Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.1, pp. 1716-1726
ISSN 2078-2365
http://www.ieejournal.com/
Fig. 5 Motor Parameters in Symmetrical Condition for Inverter
Frequency f=70 Hz, (a) Stator Current, (b) Rotor Current, (c) Rotor
Speed, (d) Electromagnetic Torque
150
<Rotor current ir_a (A)>
100
50
0
increased or decreased, the motor signatures will be varied
correspondingly, as shown in Table III. When the frequency
of the inverter is 50 Hz then the stator current, rotor speed and
electromagnetic torque are 95.46A, 1430 RPM and 128.17
N-m respectively. These are high values in the first transient
peak because of high switching frequency of the inverter. For
other frequencies, the variations in the induction motor
parameters are as shown in the Table III.
-50
300
250
-150
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
1
(a)
120
100
<Stator current is_a (A)>
80
60
40
<Electromagnetic torque Te (N*m)>
-100
200
150
100
50
0
-50
-100
20
-150
0
-200
-20
0
0.1
0.2
0.3
-40
0.8
0.9
1
250
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
1
200
<Electromagnetic torque Te (N*m)>
(b)
1000
800
Rotor Speed(RPM)
0.7
Fig. 7 Electromagnetic Torque vs. Time for f=22 Hz
-60
-80
0.4
0.5
0.6
Time (seconds)
600
400
200
150
100
50
0
-50
-100
-150
-200
0
-250
-200
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
1
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
1
Fig. 8 Electromagnetic Torque vs. Time for f=15 Hz
(c)
300
<Electromagnetic torque Te (N*m)>
250
200
150
100
50
0
-50
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (seconds)
0.7
0.8
0.9
1
(d)
Fig. 6 Motor Parameters in Symmetrical Condition for Inverter Frequency
f=30 Hz, (a) Stator Current, (b) Rotor Current, (c) Rotor Speed, (d)
Electromagnetic Torque
The transient variations in the motor parameters are as
shown in Table III(appendix). In the transient analysis only
first transient peak has been observed. The transient analysis
has been carried out for three motor parameters. These
parameters are stator current, rotor speed and electromagnetic
torque. When frequency is 50 Hz, we have been achieved
rated values of the motor. When the inverter frequency is
It has clearly been observed in the Table III, that upto 22
Hz frequency, the electromagnetic torque first transient peak
is being increased upto 281.39 N-m. If we further decreases
the frequency, the maximum peak electromagnetic torque is
being decreased as can observe from Table III and Fig. 7 and
Fig. 8. The electromagnetic torque waveform has been shown
for 22 and 15 Hz frequency respectively for clear revelation
purpose. These Figs (7 and 8) show that the first maximum
transient peak is being decreased if frequency is decreased.
Therefore, we can say that the induction motor parameter
variations in the transient conditions are completely
controllable by this proposed simulation model.
VI. TOTAL HARMONIC DISTORTION (THD) ANALYSIS
The harmonic analysis of this proposed simulation model
has also been carried in this section for its stator current and
line to- line voltage. The stator current waveforms for 1 KHz
and 5 KHz maximum frequencies are as shown in Fig. 9 and
Fig. 10 and observed small harmonics (1.11 % & 2.26%).
1723
Siddiqui et. al.,
Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.1, pp. 1716-1726
ISSN 2078-2365
http://www.ieejournal.com/
THD variation with maximum frequency is as shown in
Table IV(appendix). It has been observed from the Table IV
when the maximum frequency is being increased then the
THD will also be getting increased. Therefore, in the
proposed simulation model, we ought to choose the accurate
maximum frequency for obtaining the maximum efficiency of
the motor.
Fig. 12 THD in Input Voltage when Max. Frequency is 5 KHz
Fig. 9 THD in Stator Current for Closed Loop when Max. Frequency is 1
KHz
Fig. 10 THD in Stator Current for Closed Loop When Max. Frequency is 5
KHz
The THD for various maximum frequencies is as shown in
Table IV. The fundamental frequency is set at 50 Hz for
various maximum frequencies.
The THD in the Line-to-Line Input Voltage (LLIV) for 1
KHz maximum frequency is very small. It is because of the
reality that IGBT based inverter efficiently control the
induction motor upto 1 KHz frequency in spite of disturbance
occur in the supply due to inverter. When the maximum
frequency again increased, the THD in the LLIV will be
increased, but the THD in stator current will be less. It has
been clearly observed in the previous recent researches that
the THD value obtained relatively high in the LLIV as well as
stator current [13]. Therefore, we can say that if upcoming
researchers will use IGBT inverter fed induction motor model
in the upcoming researches. They may achieve maximum
efficiency of the induction motor in various applications.
The magnitude of the fundamental frequency is as shown in
the spectrum window i.e. 311 V (Fig. 11 & Fig. 12). This
inverter voltage 311 V is compared well with the obtained
theoretical value 311 V for modulation index m=0.9. This
inverter voltage may be find out from the following equation.
VLLrms 
Fig. 11 THD in Input Voltage when Max. Frequency is 1 KHz.
m
3
 Vdc = m  0.612 Vdc
2
2
(31)
The harmonics are displayed in the LLIV in percent of the
fundamental component. The harmonics has been observed as
multiples of carrier frequency (n×33± k). The 30% highest
harmonics visualized at 31st harmonic and 35th harmonic
(33+2). These values we already expected. It can be clearly
observed in Fig. 10. The THD value in the LLIV has been
obtained 1.70 to 62.27 % for 0 to 5000 Hz maximum
frequency range.
VII. CONCLUSIONS
In the present paper, it has been observed that the squirrel
cage induction motor with a power electronics device based
inverter presents the greater advantages on cost and energy
1724
Siddiqui et. al.,
Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.1, pp. 1716-1726
ISSN 2078-2365
http://www.ieejournal.com/
efficiency, compared with other industrial solutions for
varying speed applications. The induction motor fed PWM
inverter with torque control has been proposed and
implemented in the recent Matlab/Simulink environment.
From proposed simulation model, the transient performance
of the used induction motor has been analysed. It has been
observed that the simulation model has been given excellent
results with reduced harmonics. The extensive simulation has
been performed for 3HP, 4 pole, 50 Hz induction motor with
IGBT inverter and torque control technique jointly. The
obtained simulation results have given ultimate solution for
the wide range of speed control with lower harmonics. Since,
the rapid improvement in the power electronics
semiconductor devices based inverters enable us to control
large speed with reduced harmonics with the care of the
induction motor safety also. The V/f control method has also
been successfully discussed efficiently. The transient
behavior of the motor has been discussed and observed that
the maximum transient peak is completely controllable with
varying inverter frequency. In future, this simulation model
may be employed in various applications and may be
diagnosed different motor faults by suitable Digital Signal
Processing (DSP) techniques.
Appendix
Table I Motor Description and Equivalent Parameters
Rotor Type: Squirrel Cage
Reference Frame: Stationary
Motor: 3HP
Rotor Speed: 1430 RPM
Frequency: 50 Hz
No. of Poles:4
DC Voltage: 400 V
Stator Resistance: 0.435 ohm
S.No.
1
2
3
4
5
6
7
LT
MPTSC
MPTRC
RS
MPTEMT
(A)
(A)
(RPM)
(N-m)
1
95.46
87.12
1430
(RMF)
128.17
15
0.04
86.76
79.81
1430
54.06
15/2
0.02
87.47
81.81
48.53
N-L
0
1
95.46
87.20
1470
1500
(RMF)
N-LR-N
0
0.04
86.97
80.33
1500
50.28
H-YR-N
H-L
70
50
30
22
21
10
6
MPTEMT
(N-m)
(RPM)
80.86
95.46
116.98
127.11
127.13
120.04
142.38
1825
1430
903
792
773
457
238
66.18
128.17
261.39
281.39
279.25
175.48
105.79
Table IV THD Variation with Maximum Frequency
S.No.
1
2
3
4
5
5
Fundamental
Frequency
Maximum
Frequency
(Hz)
(KHz)
50
50
50
50
50
50
1
2
3
4
5
5
THD (%)
LLIV
SC
1.70
42.52
42.55
58.73
62.27
62.27
1.11
2.08
2.09
2.24
2.26
2.26
ACKNOWLEDGMENT
Authors acknowledge Technical Education Quality
Improvement Program Phase-II, Electrical Engineering
Department, Institute of Engineering & Technology,
Lucknow for providing financial assistantship to carry out the
research work.
[1]
[2]
[3]
15
H-Y
(A)
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Slip
(N-m)
Rotor
speed
MPTSC
(Hz)
Table II Transient Variation in Motor Parameters
MC
Inverter
frequency
128.17
MC: Motor Condition, H-Y: Healthy, H-Y-R-N: Healthy Running, H-L:
Half- Load, N-L: No-Load, N-L-R-N: No-Load Running, LT: Load Torque,
MPTSC: Maximum Peak Transient Stator Current, MPTRC: Maximum
Peak Transient Rotor Current, MPTEMT: Maximum Peak Transient
Electromagnetic Torque, RS: Rotor Speed
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Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.1, pp. 1716-1726
ISSN 2078-2365
http://www.ieejournal.com/
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Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives