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© 2005 - 2008 JATIT. All rights reserved.
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PERFORMANCE ANALYSIS OF 18-PULSE AC-DC
CONVERTER FED VECTOR CONTROLLED INDUCTION
MOTOR DRIVE (VCIMD)
1
R.A.Gupta, 2Rajesh Kumar, 3Bharat Bhushan Jain
1
Prof. Department of Electrical Engineering, MNIT, Jaipur, India-302017
2
Reader, Department of Electrical Engineering, MNIT, Jaipur, India-302017
3
Research Scholar, Department of Electrical Engineering, MNIT, Jaipur, India-302017
E-mail: rag_mnit@rediffmail.com, rk.rlab@gmail.com, bharat_pce@rediffmail.com
ABSTRACT
In this paper, design of novel autotransformer based 18-pulse Ac-Dc Converter fed vector controlled
induction motor drive is discussed and its Matlab/Simulink model is also given. The design procedure for
proposed autotransformers shows the flexibility in the design for making it a cost effective replacement
suitable for retrofit applications, where presently a six-pulse diode bridge rectifier is used. Using the above
designs we can capable to suppress harmonics up to 13th in 18-pulse configuration of the VCIMD. Various
simulation results are given for autotransformer and VCIMD in topology C and D. THD analysis at No load
and Load is also done.
Keywords: Autotransformer, multi pulse AC-DC converter, power quality, and vector controlled induction
motor drive (VCIMD).
1. INTRODUCTION
With the proliferation of power-electronic
converters, the majority of dc drives are being
replaced by variable frequency induction motor
drives. These variable frequency induction motor
drives are generally operated in vector control [1],
as it is an elegant way of achieving highperformance control of induction motors in a way
similar to the dc motor. These vector-controlled
induction motor drives (VCIMDs) are fed by an
uncontrolled ac–dc converter which results in
injection of current harmonics into the supply
system. These current harmonics, while
propagating through the finite source impedance,
result in voltage distortion at the point of common
coupling, there by affecting the nearby consumers.
Various methods based on the principle of
increasing the number of pulses in ac–dc
converters have been reported in the literature to
mitigate current harmonics [2]–[4]. These methods
use two or more converters, where the harmonics
generated by one converter are cancelled by
another converter, by proper phase shift. The
autotransformer-based configurations [5, 6, 16-18]
861
provide the reduction in magnetics rating, as the
transformer magnetic coupling transfers only a
small portion of the total kilovolt-ampere of the
induction motor drive. These autotransformerbased schemes considerably reduce the size and
weight of the transformer. Autotransformer-based
18-pulse ac-dc converters [16-18] have been
reported for reducing the total harmonic distortion
(THD) of the ac mains current. To ensure equal
power sharing between the diode bridges and to
achieve good harmonic cancellation, this topology
needs Interphase transformers and impedancematching inductors, resulting in increased
complexity and cost. Moreover the dc-link voltage
is higher, making the scheme non applicable for
retrofit applications.
To overcome the problem of higher dc-link
voltage, Hammond [5] has proposed a new
topology, but the transformer design is very
complex. To simplify the transformer design,
Paice [6] has reported a new topology for
18pulse ac-dc Converters But this topology requires
higher rating magnetics, resulting in the
enhancement of capital cost. Bhim Singh [9, 11,
and 14] also gives various VCIMD model with
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various autotransformer connections. In this paper,
an 18-pulse Ac-Dc converter fed vector controlled
induction motor drive (VCIMD) is simulated,
which is used an novel autotransformer for 18pulse production. The presented techniques for the
design of the autotransformer provides flexibility
in design to vary the output voltages to make it
suitable for retrofit applications (where presently,
a six-pulse converter is being used, as shown in
Fig. 1) without much alterations in the system
layout. This topology results in improvement in
THD of ac mains current and power factor even
under light load conditions.
IGBT Based Inverter
isa
Zs
isb
Zs
Va = V∠0° Vb = V∠ −120° Vc = V∠120°
′
′
Va′ = V∠ + 20° Vb = V∠ − 100° Vc = V∠140°
(1)
(2)
Here Va, Vb, and Vc are the phase voltages.
Similarly″
″
″
Va = V∠ − 20 ° Vb = V∠ − 140 ° Vc = V∠100 °
(3)
Where, V is the rms value of phase voltage.
ias
Ld
A
Assume the following set of voltages:
+
ibs
B
Cd
isb
Three Phase
VCIMD
ics
–
ias
3 Phase, 415V,
50 Hz
6 Pulse diode Bridge Rectifier
PWM Current
Controller
ias* ibs*
ibs
ics*
Field Orientation and
Reference Current
Generation
Fig. 2 Winding connection diagram of the
proposed autotransformer for 18-Pulse (Topology
C)
iqs* ω2*
imr*
T
Speed Controller
ω r*
+ –
T*
Limiter
Estimator for
ids*, iqs*, ω2*
Field
weakening
ωr
Fig.1 Six-Pulse Diode Bridge Rectifier Fed Vector
Controlled Induction Motor Drive (Topology-A)
2. DESIGN OF AUTOTRANSFORMERS
FOR 18-PULSE AC-DC CONVERTER
The minimum phase shift required for proper
harmonic elimination is given by [2]Phase Shift= 600 /No. of 6 –pulse Converters
To achieve the 18-pulse rectification, the
following conditions have to be satisfieda) Three sets of balanced three-phase line
voltages are to be produced, which are ±200or
400 for 18-pulse required out of phase with
respect to each other. Here, /±200 phase shift is
used to reduce the size of the magnetics.
b) The magnitude of these line voltages should
be equal to each other to result in symmetrical
pulses and reduced ripple in output dc voltage.
Fig.2 shows the winding connection diagram of
the proposed autotransformer for achieving 18pulse rectification. The phasor diagram shown in
Fig. 3 represents the relationship among various
phase voltages.
Fig.3 Vector diagram of Phase Voltages for 18Pulse ac-dc converter (Topology C)
The phase shifted voltages for phase “a” of are ′
(4)
V a = V a + 0 . 25777 V c − 0 . 1371 V b
″
V a = V a + 0 . 25777 V b − 0 . 1371 V c
(5)
Similarly phase shifted voltages for phase “b” are′
(6)
V b = V b + 0 . 25777 V a − 0 . 1371 Vc
″
(7)
V b = V b + 0 . 25777 V c − 0 . 1371 V a
Similarly phase shifted voltages for phase “c” are-
862
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′
V c = V c + 0 . 25777 V b − 0 . 1371 V a
″
V c = V c + 0 . 25777 V a − 0 . 1371 V c
(8)
Va1 = 0.963Va' = Va + K 5Vb + K 6Vc
(9)
Va'1 = 0.963Va' = Va + K 3Vc − K 4Vb
(12)
V = 0.963V = Va + K 3Vb − K 4Vc
(13)
''
a1
Thus, the autotransformer uses two auxiliary
windings per phase. A phase-shifted voltage is
obtained. Due to the 18-pulse operation, the
average voltage at dc link is higher than that of a
six-pulse diode bridge rectifier output voltage by
about 3.7%. The proposed autotransformer design
has been modified to make it suitable for retrofit
applications (to achieve the dc link voltage same
as that of six-pulse diode bridge rectifier). Fig.4
shows the generalized arrangement of the
autotransformer windings for varying the
transformer output voltages while still maintaining
the 18-pulse operation (ensuring an angle of 200
between the transformer output voltages with
respect to the supply voltages). This can be
achieved by simply varying the tapping positions
on the windings.
Vc1"
Vc
Vc1'
C
K3
K4
K6
Va1
A
V a'1 = V a + 0 .2852 V c − 0 .09485 V b
(15)
= V a + 0 . 2852 V b − 0 .09485 V c
(16)
V
''
a1
Similarly, phase shifted voltages for phase “b” are(17)
V b 1 = V b + 0 . 0371 V a + 0 . 0371 V c
V b'1 = V b + 0 . 2852 V a − 0 .09485 V c
(18)
V b'1' = V b + 0 .2852 V c − 0 . 09485 V a
(19)
V c'1 = V c + 0 . 2852 V b − 0 . 09485 V a
(21)
V = V c + 0 . 2852 V a − 0 . 09485 V b
(22)
''
c1
Va
Va1"
Vb1"
Thus, by simply changing the transformer
winding tapping, the same dc link voltage as that
of 6-pulse diode bridge rectifier is obtained.
Vb1
Vb
By solving above equations K3, K4, K5 and K6 are
calculated. These equations result in
K3 =
0.2852, K4 = 0.09485, K5 = 0.0.0371 and K6 =
0.0371 for the desired phase shift in
autotransformer.
The phase shifted voltages for phase “a” are as(14)
V a 1 = V a + 0 . 0371 V b + 0 . 0371 V c
Similarly, phase shifted voltages for phase “c” are(20)
V c 1 = V c + 0 . 0371 V b + 0 . 0371 V a
Va1'
K3
K5
''
voltages for the retrofit arrangement of the
proposed 18-pulse ac-dc converter.
K4
Vc1
′
Where Va1 Va1 and Va1 are the reduced phase
K5
K6
''
a
(11)
B
Vb1'
Fig.4 Winding connection diagram of the
proposed autotransformer for 18-Pulse suitable
for retrofit Application (Topology D)
For achieving this, all the three-phase shifted
voltages, i.e., and are reduced by about 3.7% from
the supply voltage, for retrofit arrangement in 18pulse operation respectively asBy following the above procedure, for same dc
link voltage as that of six-pulse diode bridge
rectifier, the values of K3, K4, K5 and K6 are
calculated as shown in fig.4.4 for retrofit
arrangement as(10)
Va1 = 0.963Va' = Va + K 5Vc + K 6Vb
The kVA rating of the autotransformer is
calculated as
(23)
kVA = 0 . 5 V winding I winding
∑
Fig.5 shows the schematic diagram of proposed
autotransformer based 18 -pulse ac–dc converter
with a phase shift of +200 and −200 along with the
pulse multiplication circuit, resulting in 18-pulse
ac–dc converter, referred as Topology C and Fig. 6
shows the schematic diagram of proposed
autotransformer based 18-pulse ac–dc converter
suitable for retrofit applications, referred as
Topology D.
3. MODELING OF VCIMD
Vector-control schemes are classified according
to how the field angle is acquired. If the field angle
is calculated by using terminal voltages and
863
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currents or Hall sensors or flux-sensing winding,
then it is known as direct vector control.
Fig.5 Autotransformer based 18-pulse AC-DC Converter (with phase shift of ±200) fed VCIMD
(Topology C)
Fig.6 Autotransformer based 18-pulse AC-DC Converter fed VCIMD Suitable for Retrofit Applications
(Topology D)
The field angle can also be obtained by using rotor
position measurement and partial estimation with
only machine parameters but not any other
variables such as voltages or currents; using this
field angle leads to a class of control schemes
known as indirect vector control.
Fig.1 shows the schematic diagram of an indirect
VCIMD. In the rotor-flux-oriented reference frame
the x-component of the stator current reference
i sx∗ is obtained as –
= i mr + τ r ( Δ i mr / Δ T )
vector
864
i sx∗
(24)
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The
two
phase
currents
of
motor
namely ias and ibs and the motor speed signal
ωr are
sensed for achieving the vector control
mode of induction motor drive. The closed loop PI
speed controller compares the reference speed
(ω
∗
r
) with motor speed (ωr) and generates
∗
reference torque T (after limiting it to a suitable
value) as –
T
∗
(n)
=T
∗
( n −1 )
+ K
p
{ω
e(n)
− ω e ( n −1 )
+ K I ω e(n)
∗
}
(25)
∗
Where T(n ) and T(n −1) are the output of the PI
controller (after limiting it to a suitable value) and
ωe(n) and ωe(n−1) refer to speed error at the nth and
(n − 1)th instants. Kp and KI are the proportional
and integral gain constants.
The y-component of the stator current reference
ω 2∗ = i sy∗ /(τ r imr )
ψ ( n ) = ψ ( n −1) + (ω 2 + ω r )ΔT
(27)
(28)
k = (3 / 2)( P / 2){M /(1 + σ r )}
(29)
Where imr is the magnetizing current, ω is the
slip speed of rotor, ωr is the angular velocity of
∗
2
rotor. P, M, and
σ r = (1 − L2m / Ls Lr ) are
number of poles, mutual inductance, and rotor
leakage factor, respectively, Ψ(n) and Ψ(n−1) are the
value of rotor flux angles at nth and (n − 1)th
instants, respectively, and ΔT is the sampling time
taken as 100 μs.
∗
∗
These currents ( i sx , i sy ) are in synchronously
rotating reference frame and these are converted
into stationary reference frame three-phase
∗
∗
∗
currents ( ias , ibs , ics ) as-
vector i sy is obtained from the out put of the PI
ias∗ = −i sy∗ sinψ + i sx∗ cosψ
controller as -
ibs∗ = − cosψ + 3 sinψ isx∗ (1 / 2)
∗
i
∗
sy
= T
∗
/ ki
[
+ [sinψ +
(26)
mr
∗
∗
The x-component i sx and y-component i sy of
the stator current form the inverter current
reference vector in rotor-flux-oriented reference
frame, which is then converted to stationary
reference frame using rotor flux angle calculated
as sum of the rotor angle and the value of slip
angle as –
the
]
(30)
]
3 cosψ isy∗ (1 / 2)
ics∗ = −(ias∗ + ibs∗ )
Where
(31)
(32)
ias∗ , ibs∗ and ics∗ are the three-phase
reference currents. These three-phase reference
currents generated by the vector controller are
compared with the sensed motor currents (ias, ibs,
and ics).
1
Out1
1
In1
2
Out2
3
Out3
2
In2
4
Out4
.25777
Product
Subtract
Constant
5
Out5
Subtract1
.1371
Product1
Constant1
3
In3
Subtract2
6
Out6
.25777
Constant2
Product2
Subtract3
7
Out7
.1371
Product3
Constant3
.25777
Product4
Constant4
.1371
Subtract4
8
Out8
Product5
Constant5
Subtract5
9
Out9
Fig.7 Matlab/Simulink diagram for the autotransformer suitable for 18-pulse ac-dc converter fed VCIMD
(Topology-C)
865
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1
Out1
1
In1
.0371
Product6
Subtract6
K5/6
2
In2
4
Out4
.0371
Product7
Subtract7
2
Out2
K6
.2852
Product
Subtract
K3
.0371
5
Out5
Subtract1
Product8
Subtract8
K5
.09485
Product1
K4
3
In3
6
Out6
Subtract2
.2852
Product2
K3'
Subtract3
7
Out7
.09485
Product3
K4'
.2852
Product4
K3''
Subtract4
.09485
8
Out8
Product5
9
Out9
K4''
Subtract5
Fig.8 Matlab/Simulink diagram for the autotransformer suitable for 18-pulse ac-dc converter fed VCIMD
Suitable for Retrofit Applications (Topology D)
1
In1
2
In 2
vao*
vao
300
Constant
wr*
vqs*
vqs*
vao*
vds*
vbo*
we
vco*
vco*
wsl
ia
vbo
ib
vco
ic
Tl
Te
we
wr
vbo*
vds*
wr
vao
vbo
1
Iabc
+
Torque and Flux Control
we
Sum2
vco
-
Command Voltage
Generator
3-phase PWM Inverter
Mux6
0
Constant1
2
Torque
Induction Motor
3
Speed
Fig.9 Matlab/Simulink model of Vector Controlled Induction motor (VCIM)
The calculated current errors are866
3
Out3
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ikc = iks∗ − iks ,
where k = a, b, c
(33)
These current errors are amplified and fed to the pulse width modulation (PWM) current controller,
which controls the on and off periods of different
Out 1
In1
Out 2
Out3
In1
Vdc
A+
I n1
A-
I n2
In2
+
In3
Iabc
A
In2
Out 4
Iabc
In4
B+
I n3
Torque
B
Te
In2
Out 5
In5
In1
Speed
C
BOut 6
I n4
wr
In6
VCIMD
3_ph source
Out 7
In3
In7
Out 8
In8
Out 9
In9
C+
I n5
C-
I n6
Diode Rectifiers
-
Discrete,
Ts = 1e-005 s.
powergui
interphase transformer
Autotransformer
for topology C
Fig.10 Matlab/Simulink model of 18-pulse ac-dc converter fed VCIMD (Topology-C)
867
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Out1
In1
Out2
Vdc
In1
A+
In1
A-
In2
In2
Iabc
Out3
+
In1
In3
Iabc
A
Torque
Out4
In4
B+
Te
In3
B
In2
In2
Out5
In5
Out6
In6
Out7
In7
Speed
wr
C
B-
In4
C+
In5
C-
In6
VCIMD
3_ph source
In3
Out8
In8
Out9
In9
-
Discrete,
Ts = 1e-005 s.
Autotransformer
for topology C
powergui
Diode Rectifiers
interphase transformer
Fig.11 Matlab/Simulink model of 18-pulse ac-dc converter fed VCIMD (Topology-D)
Fig.12 shows the output of this autotransformer
i.e. combination of voltage Vaa’a’’, Vbb’b’’, Vcc’c’’,
switches in VSI. The VSI generates the PWM Vabc, Va’b’c’, Va’’b’’c’’, which is suitable for
voltages being fed to the motor to develop the topology-C.
torque for running the motor at a desired speed
under required loading conditions.
200
150
100
4. MATLAB-BASED SIMULATION
0
-50
-100
-150
-200
0
10
20
30
40
50
60
Time(msec)
70
80
90
100
Fig.12 Output voltage of autotransformer for 18Pulse Operation (Topology-C)
450
400
350
300
Voltage(Volt)
Fig.7 shows the Matlab/Simulink model of
autotransformer suitable for 18-pulse ac-dc
converter fed VCIMD Topology-C.
Fig.8 shows the Matlab/Simulink model of
autotransformer suitable for 18-pulse ac-dc
converter fed VCIMD suitable for retrofit
applications Topology-D. Fig.9 shows the
Matlab/Simulink model of Vector Controlled
Induction motor (VCIM).
Fig.10 shows the Matlab/Simulink model of 18pulse ac-dc converter fed VCIMD Topology-C and
Fig.11 shows the Matlab/Simulink model of 18pulse ac-dc converter fed VCIMD suitable for
retrofit applications Topology-D.
18 Pulse
50
250
200
150
5. SIMULATION RESULTS AND
DISCUSSION
5.1 18- Pulse Ac-Dc Converter Fed VCIMD
(Topology-C)
100
50
0
868
0
20
40
60
80
100
120
Time(msec)
140
160
180
200
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(c)Torque
Fig. 15 Matlab/Simulink Results of 18-Pulse ACDC Converter Fed VCIMD (Topology-C) - at NoLoad
10
5
Iabc(Amp)
Fig.13 Output Voltages across the Bridge
Rectifiers for 18-Pulse Operation ( Topology-C)
Fig. 13 shows the output of the diode bridge
rectifiers and Fig. 14 shows the output voltage of
Interphase transformers, which is fed to the
inverter of VCIM through filter. These wave forms
show that the output contains 18-pulses.
500
450
400
0
-5
Vdc(Volt)
350
-10
0.6
300
0.62
0.64
0.66
Time (s)
250
200
0.7
100
Mag (% of Fundamental)
150
100
50
0
0.68
0
0.2
0.4
0.6
0.8
1
Time (s)
Fig.14 Output Voltage waveform of Interphase
Transformers for 18-Pulse Operation (TopologyC)
The various results such as motor current Iabc,
Speed and Torque are obtained for different load
conditions are shown in following figures (15-18).
80
THD= 7 . 4 5 %
60
40
20
0
0
5
10
Harmonic order
15
20
Fig.16 Matlab/Simulink Results of 18-Pulse ACDC Converter Fed VCIMD (Topology-C) - Motor
Current and Harmonic Spectrum, at No-Load
40
40
30
30
20
Iabc(Amp)
Iabc(Amp)
20
10
0
10
0
-10
-10
-20
-20
-30
-30
-40
0
-40
0.2
0.4
0.6
0.8
1
Time (s)
0
0.2
0.4
0.6
0.8
1
(a)Motor Current (Iabc)
Time (s)
(a)Motor Current (Iabc)
350
350
300
300
250
Speed (rps)
Speed (rps)
250
200
150
100
150
100
50
50
0
0
-50
200
-50
0
0.2
0.4
0.6
0.8
0
0.2
0.6
0.8
1
0.8
1
Time (s)
(b)Speed
(b)Speed
140
120
140
100
Torque(Nm)
120
100
Torque(Nm)
0.4
1
Time (s)
80
80
60
60
40
40
20
20
0
0
0
0.2
0.4
0.6
Time (s)
0
0.2
0.4
0.6
0.8
1
Time (s)
869
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450
Fig. 17 Matlab/Simulink Results of 18-Pulse ACDC Converter Fed VCIMD (Topology-C) - at
Load
400
350
Voltage(Volt)
300
Iabc(Amp)
15
250
200
10
150
5
100
0
50
0
-5
0
20
40
60
80
100
120
Time9msec)
140
160
180
200
-10
-15
0.6
0.62
0.64
0.66
Time (s)
0.68
Fig.20 Output Voltages across the Bridge
Rectifiers for 18-Pulse Operation (Topology-D)
0.7
Mag (% of Fundamental)
100
TOPOLOGY - D
80
426.944
THD= 5 . 8 1 %
426.942
60
426.94
40
426.938
20
0
426.936
0
5
10
Harmonic order
15
426.934
20
426.932
Fig.18 Matlab/Simulink Results of 18-Pulse ACDC Converter Fed VCIMD (Topology-C) -Motor
Current and Harmonic Spectrum, at Load
426.93
426.928
426.926
0.02
0.025
0.03
Time (s)
0.035
0.04
Fig.21 Output Voltage waveform of Interphase
Transformers for 18-Pulse Operation (TopologyD)
5.2 18-Pulse Ac-Dc Converter Fed VCIMD
(Topology-D)
Fig.19 shows the combination of voltage
Va1a1’a1’’, Vb1b1’b1’’, Vc1c1’c1’’, Va1b1c1, Va1’b1’c1’
and Va1’’b1’’c1’’which is suitable for topology-D
VCIMD. Fig.20 shows the output of the diode
bridge rectifiers and Fig.21 shows the output
voltage of Interphase transformers.
The various results such as motor current Iabc,
Speed and Torque are obtained for different
conditions are shown in following figures (22-25).
40
30
20
150
10
Iabc(Amp)
200
100
50
0
-10
-20
0
-30
-50
-40
-100
0
0.2
-150
0.4
0.6
0.8
1
Time (s)
(a)Motor Current (Iabc)
-200
0
10
20
30
40
50
60
Time(msec)
70
80
90
100
350
Fig. 19 Output voltage of autotransformer for 18Pulse Operation (Topology-D)
300
Speed(rps)
250
200
150
100
50
0
-50
0
0.2
0.4
0.6
Time (s)
(b)Speed
870
0.8
1
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© 2005 - 2008 JATIT. All rights reserved.
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350
140
300
120
250
Speed(rps)
Torque(Nm)
100
80
60
200
150
100
50
0
40
-50
20
0
0.2
0.4
0.6
0.8
1
Time (s)
(b)Speed
0
0
0.2
0.4
0.6
0.8
1
140
Time (s)
(c)Torque
120
Torque(Nm)
100
Fig.22 Matlab/Simulink Results of 18-Pulse ACDC Converter Fed VCIMD (Topology-D) - at NoLoad
80
60
40
20
0
10
0
0.2
0.4
Iabc(Amp)
5
0.6
0.8
1
Time (s)
(c)Torque
0
-5
-10
0.4
0.45
0.5
Time (s)
0.55
Fig.24 Matlab/Simulink Results of 18-Pulse ACDC Converter Fed VCIMD (Topology-D) - at
Load
0.6
100
Mag (% of Fundamental)
15
80
10
THD= 6 .8 8 %
Iabc(Amp)
60
40
20
0
0
5
10
Harmonic order
15
0
-5
-10
20
-15
0.6
Fig.23 Matlab/Simulink Results of 18-Pulse ACDC Converter Fed VCIMD (Topology-D) - Motor
Current and Harmonic Spectrum, at No-Load
0.62
0.64
0.66
Time (s)
0.68
0.7
Mag (% of Fundamental)
100
40
30
20
Iabc(Amp)
5
10
80
40
20
0
0
-10
THD= 5 . 8 3 %
60
0
5
10
Harmonic order
15
20
-20
-30
-40
0
0.2
0.4
0.6
0.8
1
Time (s)
Fig.25 Matlab/Simulink Results of 18-Pulse ACDC Converter Fed VCIMD (Topology-D) - Motor
Current and Harmonic Spectrum, at Load
15
10
Iabc(Amp)
5
0
-5
-10
-15
0.5
0.6
0.7
0.8
0.9
Time (s)
(a)Motor Current (Iabc)
1
In both cases, as we starts motor on simulation at
t=0sec, motor draws high current (~ 40A) before
reaching the steady state. At t= 0.23sec motor
reaches at steady state where it draws the current
of the order of 6A. In Loading Condition we apply
a load of TL= 14N-m, at t = 0.5 sec and removes it
at t=0.8sec.As we apply the load, motor draws
more current for its needs of the order of 10A.
Here controller starts working, and ensures the
constant desired speed. As we removed the load
current again current settles down to no load value
i.e. 6A and speed remain constant, and controller
role is omitted again.
Table I shows the various THD of both topologies.
871
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© 2005 - 2008 JATIT. All rights reserved.
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Table I
THD ANALYSIS OF TOPOLOGY C & D
Sr.
Topology
THD at No
THD on
No.
Load
Load
1.
Topology-C
7.45%
5.81%
2.
Topology-D
6.88%
5.83%
6. CONCLUSION
The design, modeling, simulation, and
development of 18-pulse ac–dc converter fed
VCIMD has been presented for various load in two
topologies ‘C’ & ‘D’. It has been observed that the
design of the proposed autotransformer is flexible
for making it suitable for retrofit applications,
where presently a six-pulse diode bridge rectifier
is being used. The proposed 18-pulse ac–dc
converter fed VCIMD topology-‘D’ has less THD
as compared to topology-‘C’.
APPENDIX
Three-Phase Squirrel Cage Induction Motor10 HP (7.5 kW), 3-Phase, 4 Pole, Y- connected,
415 V, 50 Hz,
Rs = 1.0 Ω, Rr = 0.76 Ω,Xls = 1.1404 Ω
Xlr =1.7122 Ω, Lm = 0.114 H, J=0.1 kg·m2.
PI Controller – Kp = 10.0, KI = 0.1
DC link parameters: Ld =0.6mH,Cd = 2200μF.
Magnetics ratings – Autotransformer Rating - 2.4
KVA, Interphase Transformer-0.58 KVA
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872
Journal of Theoretical and Applied Information Technology
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www.jatit.org
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