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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 3 (2016) pp 2071-2076
© Research India Publications. http://www.ripublication.com
Obliteration of Harmonics on a VSI Fed Induction Motor Drive
C. K. Shankar
PG scholar, Department of Electrical and Electronics Engineering,
Sri Ramakrishna Institute of Technology, Coimbatore, Tamilnadu, India.
A. P. Roger Rozario
Assistant Professor, Department of Electrical and Electronics Engineering,
Sri Ramakrishna Institute of Technology, Coimbatore, Tamilnadu, India.
Dr. C. Ganesh
Head of Department, Department of Electrical and Electronics Engineering,
Sri Ramakrishna Institute of Technology, Coimbatore, Tamilnadu, India.
G. Leo sekar
PG scholar, Department of Electrical and Electronics Engineering,
Sri Ramakrishna Institute of Technology, Coimbatore, Tamilnadu, India.
electrical to mechanical energy conversion is done by
induction motors. Induction machine has found a wide
acceptance in most of the industrial applications [4]. Their
rugged, simple construction, reliability at lower cost combined
with the demand for less maintenance, high efficiency and
need for a simple starting arrangement has made their deep
penetration into energy conversion process possible. Induction
motors are driven from a voltage source inverter as need for
variable power at output is needed for specific applications.
This can be achieved through pulse width modulation of
inverter which provide internal control scheme for the
variable output of inverter. Increase in use of power
converters has led to increase in harmonics hence it is
essential to reduce the harmonics to improve power quality in
the network which will also improve the performance of the
machine connected to the power system network. Voltage
source inverter fed three-phase induction motor drives have
high 3n ± 1(n = odd-order) harmonic currents. This is because
the currents, are driven by the corresponding harmonic
voltages in the inverter output and they are limited by the
stator leakage impedance, as the harmonics are absent in the
back electromotive force of the motor. To obliterate these
harmonic currents, bulk inductive harmonic filters or complex
pulse width modulation techniques have to be used. Various
pulse-width-modulation techniques have been developed in
the last decade for application in the industry for drive control
[7-22]. A few examples can be cited, Pulse width modulation
based three-phase voltage source inverters with variable
voltage magnitude and variable frequency for speed control,
harmonic elimination etc. The Sinusoidal PWM technique is
the easiest modulation scheme to implement but this
technique is unable to fully utilize the DC bus voltage
available whereas SVPWM technique can increase the
fundamental output voltage by 15.5% over the SPWM
technique. This work accentuate in designing a harmonic
obliteration scheme based on space vector pulse width
modulation.
Abstract
Usage of power electronics converters to provide a variable
power at output has increased. This need for a variable power
at the output can be obtained by chopping the inverter DC
input voltages using switching devices. This technique is
called as Pulse Width Modulation. With advancement in
power electronics, the problem of harmonics in the power
system network has also been on raising side in recent years.
Pulse width modulation techniques are not only used to get
the desired output voltage but also to reduce the harmonic
content reducing the need for a separate filter to obliterate
harmonics. Various techniques such as current hysteresis
controlled pulse width modulation, sinusoidal pulse width
modulation, space vector pulse width modulation have been in
research and implemented for harmonic obliteration. This
work accentuate on the comparative analysis of the most
commonly used Sinusoidal Pulse Width Modulation and
Space Vector Pulse Width Modulation techniques which has
found wide acceptance in motor drive application. The
comparative analysis show that the space vector Pulse width
modulation yield better harmonic obliteration compared to a
Sinusoidal Pulse Width Modulation scheme when tested with
MATLAB Simulink.
Keywords: Harmonics, Sinusoidal Pulse Width Modulation,
Space Vector Pulse Width Modulation, Total Harmonic
Distortion.
Introduction
Discharge of power from renewable energy sources along
with usage of power converter to facilitate this process has
been on a rising trend in the last three decades, which
demands the needs for power converters that consists of
power electronic components to achieve the required power
conversion; associated with the process arises the problem of
power quality [1-3]. The world’s total of 80-90% of the total
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 3 (2016) pp 2071-2076
© Research India Publications. http://www.ripublication.com
Space Vector Pulse Width Modulation
Pulse Width Modulation
Space vector pulse width modulation was first introduced in
1980 by fellow German researches. Since then they have
found wide acceptance as they showed several advantages
over the traditional pulse width modulation techniques [713][15-17][19][20][22-24]. Their wide acceptance was made
possible through more effective usage of DC voltage output
peak voltage is higher in comparison to other schemes and
unnecessary switching is eliminated ensuring less
commutation losses. Space vector pulse width modulation is a
switching scheme which is done by considering the complex
reference voltage and this eliminates the need for a separate
space modulator for each of the three phases. Space vector
pulse width modulation provides a scope to adjust the
switching frequency and also generates less harmonic
distortion in both voltage and current in the output side of the
inverter which would be fed as input to the motor drive. Even
though this scheme seems complex compared to sinusoidal
pulse width modulation it has the ease of implementation with
modern micro controllers.
Inverters usually perform the task of conversion of dc power
to ac power with controlled voltage and frequency [1] [6]. The
output waveforms depend on the switching states of the
inverter switches. There are several inverter topologies
available. The topology considered in this paper for study and
analysis is three phase inverters as they are widely used for
motor drive applications. The need for variable speed drives
and needed for control over magnitude frequency and phase
can be met with the help of inverter. The output voltage of an
inverter can be controlled by the inverter itself. This can be
achieved through varying the ON & OFF period of the
inverter switches. This is termed as pulse width modulation
[1] [6] [7]. Reasons behind adapting this method as a control
scheme to get the desired output are necessity of additional
components for control is not essential and minimization of
lower order harmonic is possible. In this paper we are going to
discuss about the commonly used and the most efficient pulse
width modulation techniques. The commonly used technique
is sinusoidal pulse width modulation. Sinusoidal pulse width
modulation is implemented for single phase and three phase
inverter topologies. Space vector pulse width modulation
provides reduced switching loss and souped-up output voltage
compared to sinusoidal Pulse Width Modulation. This
technique is discussed in this paper with three phase inverter
topology.
Space Vector Pulse Width Modulation Principle
Using a space vector pulse width modulation eight possible
switching combinations can be achieved in a three leg inverter
[6]. The upper switches ON and OFF states are inverted states
of the lower switches. The voltage corresponding to the
combinations of the states are calculated and then converted
into two phase stator reference frames this transformation
from three phase quants to two phase quantities provide eight
vectors of which six are non-zero vectors and to are zero
vectors. The vectors form the axis of the hexagon as is in
figure.
Sinusoidal Pulse Width Modulation
In sinusoidal pulse width modulation the width of the
waveform vary in a sinusoidal manner. The width of the
output voltage waveform after sinusoidal pulse width
modulation depends on the carrier and reference waveform
[8]. The carrier wave is a triangular wave and the reference or
the modulating wave is a sinusoidal wave. The sinusoidal
wave and carrier wave are compared to obtain a pulse width
modulated output waveform. If the sine wave is greater than
the carrier wave then the carrier triangular wave then the
width of the output waveform width is high, if the reference
wave is lower than the carrier wave the width of the output
wave form is low thereby consists a sinusoidal output
waveform on the whole. The three phase inverter topology
considered for implementation of sinusoidal pulse width
modulation for comparison with space vector pulse width
modulation.
β axis
(010) V3
V2 (110)
2
3
V4
(011)
(000) V0
(111)V7
4
V5
(001)
1
θ
T1
V1
(100) α axis
6
5
V6 (101)
Figure 2: switching vectors
The zero vector is at origin and separation between two nonzero vector is 60 degrees. The locus of the maximum output
voltages is formed by hexagonal envelope which is in turn
formed by the non-zero voltage space vectors.
Figure 1: Three phase voltage source inverter.
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 3 (2016) pp 2071-2076
© Research India Publications. http://www.ripublication.com
β axis
b
Table I: List of switches in ON condition each state
SVPWM
STATE
1
2
3
4
5
6
7
8
Vdc
α axis
a
Vdc
LIST OF ON SWITCHES
126
136
436
435
425
125
135
462
Applying Kirchhoff voltage law on inverter output the
following equations are derived.
Sine PWM
c
Figure 3: Locus comparison of maximum output voltage in
Sinusoidal PWM and SVPWM
The relationship between line to line voltages and switching
variable vector [a b c]t is given by
=-
Vabl +
Vabi
=-
Vbcl +
Vbci
=-
Vcal +
Vcai
By applying Kirchhoff current law to nodes a, b and c
respectively, the following current equations are derived.
=Vdc
The relationship between phase voltage and switching
variable vector [a b c]t is given by
=
Iai + Ica = Iab + Ial => Iai+ Cf
= Cf
+ Ial
Ibi + Iab = Ibc + Ibl => Ibi+ Cf
= Cf
+ Ibl
Ici + Ibc = Ica + Icl => Ici+ Cf
= Cf
+ Icl
Solving the above three equations the following voltage
equations are obtained.
The adjacent two non-zero vector Vm,Vm+60 and zero vector
should be used for calculation. The list of switches in ON
state is as follows
=
Iabi -
Iabl
=
Ibci -
Ibcl
=
Icai -
Ical
Applying Kirchhoff voltage law on load side the following
equations are derived.
=-
Iabl +
Vabl
=-
Ibcl +
Vbcl
=-
Ical +
Vcal
Equations A, B and C can be represented in matrix form as
Figure 4: Possible eight switching combinations
=-
Vl +
Vi
=
Ii -
Il
=-
Il +
Vl
The plant model can be expressed as the following continuous
state space modulation.
(t)=AX(t)+Bu(t)
Where X=
Figure 5: Circuit of inverter output to the load
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 3 (2016) pp 2071-2076
© Research India Publications. http://www.ripublication.com
The value of Tmax & T min can be found from the reference
phases. The algorithm to find the values of Tmin and Tmin are
1. Initially assume Tmax=TAS & Tmin =TAS
2. Compare with TBS & TCS
If (TBS>Tmax)
Then {Tmax=TBS}
If (TBS<Tmin)
Then {Tmin=TBS}
If (TCS>Tmax)
Then {Tmax=TCS}
If (TCS>Tmin)
Then {Tmin=TCS}
Finally to calculate the gating time of the switching devices
we need to find Toffset
A=
B=
u=
where Ii is inverter output current, Vl is load side line to line
voltage and Il is load current.
The output equation can be represented as
y=Cx+Du
where y=
Toffset = (
The duration for which the top switches are turned ON are
TS1=TAS+ Toffset
TS3=TBS+ Toffset
TS5=TCS+ Toffset
C=
x=
Simulation & Results
D=0
U=[ ]
The voltage across the load is taken as the control variable.
Model of three phase voltage source inverter fed induction
motor with SPWM control and SVPWM control is simulated
using MATLAB Simulink with the following data: Vdc=400V,
frequency=50 Hz, R= 0. 3 ohm, L= 9.55e-4 H for each phase
of the induction motor.
SVPWM is most popular and convenient technique for digital
implementation and shows reduction in THD compared to
most widely used sine pulse width modulation as shown in
Table III. Figure 6, 7 & 8 show line voltage waveforms of
space vector pulse width modulation and figure 9, 10 & 11
show line to line voltages by sinusoidal pulse width
modulation. These waveforms show an increase in
fundamental voltage level in space vector pulse width
modulation when compared with sinusoidal pulse width
modulation.
Steps Involved In Implementation of Space Vector Pulse
Width Modulation:
1.
Calculation of Vα & Vβ
2.
Estimation of T1, T2 &T0
The generalized equation for Vα & Vβ is as follows
Vα=
Vβ=
VA
(VB – VC)
The generalized equation for T1 & T2 for representation of
non-zero vectors is as follows
Table II
Value of T1 & T2 in sector
SECTOR
1
2
3
4
5
6
T1
TAS-TBS
TAS-TCS
TBS-TCS
TBS-TAS
TCS-TAS
TCS-TBS
- Tmin)
Table III:
THD values for three phase VSI fed Induction motor drive
T2
TAS-TBS
TAS-TBS
TAS-TBS
TAS-TBS
TAS-TBS
TAS-TBS
USING SPWM
0. 5051
THD LEVEL
USING SVPWM
0. 4481
where
TAS=TS * [
]
TBS=TS * [
]
TCS=TS * [
]
The value of T0 can be found from
T0=Tsample - Teffective
Teffective=Tmax-Tmin
Figure 6: Line to line voltage waveform Vabl SVPWM
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 3 (2016) pp 2071-2076
© Research India Publications. http://www.ripublication.com
Figure 7: Line to line voltage waveform Vbcl SVPWM
Figure 11: Line to line voltage waveform Vcal using SPWM
Figure 8: Line to line voltage waveform Vcal using SVPWM
Figure 12: THD for sinusoidal pulse width modulation
Figure 9: Line to line voltage waveform Vabl using SPWM
Figure 13: THD for Space vector pulse width modulation
Conclusion
This article provides an comparative assay on typical
sinusoidal pulse width modulation and space vector pulse
width modulation schemes for a three phase voltage source
inverter fed induction motor drive and divulge that the space
vector pulse width modulation scheme provide a 15% increase
in fundamental voltage with waned THD level when
compared with sinusoidal pulse width modulation scheme
with the help of MATLAB Simulink simulation results.
Figure 10: Line to line voltage waveform Vbcl using SPWM
References
[1]
[2]
2075
Dr. P. S. Bimbhra, “Power Electronics” Khanna
Publishers, New Delhi, 3rd Edition, 2003.
M. H. Rashid, “A Power Electronics Handbook”
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 3 (2016) pp 2071-2076
© Research India Publications. http://www.ripublication.com
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18] Trzynadlowski. A. M, & Legowski. S, “Minimumloss vector PWM strategy for three-phase inverters”,
IEEE Transactions on Power Electronics,9(1), 2634, 1994.
[19] Van Der Broeck. H. W, Skudelny. H. C, & Stanke,
G. V, “Analysis and realization of a pulsewidth
modulator based on voltage space vectors”, IEEE
Transactions on Industry Applications,, 24(1), 142150, 1988.
[20] Ogasawara. S, Akagi. H, & Nabae. A, “A novel
PWM scheme of voltage source inverters based on
space vector theory”, Archiv für Elektrotechnik,
74(1), 33-4, 1990.
[21] Blasko. V. (1997), “Analysis of a hybrid PWM based
on modified space-vector and triangle-comparison
methods”, Industry Applications, IEEE Transactions
on, 33(3), 756-764.
[22] Liu. Y, Wu. X, & Huang. L, “Implementation of
three-level inverter using a novel space vector
modulation algorithm”, Proceedings of IEEE
International Conference on Power System
Technology,. (Vol. 1, pp. 606-610), 2002.
[23] Seo. J. H, Choi. C. H, & Hyun. D. S, “A new
simplified space-vector PWM method for three-level
inverters”,
IEEE
Transactions
on
Power
Electronics,, 16(4), 545-550, 2001.
[24] Seixas. P. F, Mendes. M, Donoso-Garcia. P, & Lima,
A. M. N, “A space vector PWM method for threelevel voltage source inverters”. Fifteenth Annual
IEEE Applied Power Electronics Conference and
Exposition, (Vol. 1, pp. 549-555), 2000.
[25] Radhakrishnan. S & Jayapal. R, “Linear current
booster for solar FED DC pumps”, IEEE
International Conference on Circuit, Power and
Computing Technologies, (pp. 1-6), 2015.
[26] Venugopal L. V, & Jayapal. R, “Matrix converter
based energy saving for street lights”, IEEE
International Conference on Circuit, Power and
Computing Technologies, (pp. 1-6), 2015.
[27] Yuvaraj. V, Deepa. S.N, & Kumar & Et al,
“Improving grid power quality with FACTS device
on integration of wind energy system”, Fifth Asia
Modelling Symposium (AMS), (pp. 157-162), 2011.
Academic Press, 2001.
B. K. Bose “Power electronics and ac drives”
Prentice hall Inc., Englewood Cliffs, New Jersey,
1986.
Kumar, “Induction and Synchronous Machines”.
Vikas Publishing House Pvt Ltd, 2000.
http://in. mathworks. com.
http://nptel. ac. in/courses/108108077.
Holtz. J, “Pulsewidth modulation for electronic
power conversion”, Proceedings of the IEEE, 82(8),
1194-1214, 1994.
Kumar. K. V, Michael. P. A, John. J. P, & Kumar.D.
S. S, “Simulation and comparison of SPWM and
SVPWM control for three phase inverter”, ARPN
Journal of Engineering and Applied Sciences, 5(7),
61-74,2010.
Rathnakumar.D, LakshmanaPerumal.J, & Srinivasan.
T, “A new software implementation of space vector
PWM”, SoutheastCon, 2005. Proceedings. IEEE (pp.
131-136),2005.
Nisha. G. K, IAENG, U. S, & Lakaparampil. Z. V,
“Harmonic elimination of space vector modulated
three phase inverter”, Proceedings of the
International Multi conference of Engineer and
Computer Scientists,Vol. 2, 2012.
Erfidan. T, Urgun. S, Karabag. Y, & Cakir. B, “New
software implementation of the space vector
modulation”,
12th
IEEE
Mediterranean
Electrotechnical Conference, 345 E 47TH ST, NEW
YORK, NY 10017 USA, 2004.
Hariram. B, & Marimuthu. N. S, “Space vector
switching patterns for different applications-a
comparative
analysis”,
IEEE
International
Conference on Industrial Technology pp. 14441449,2005.
Ahmad. R. H, Karady. G. G, Blake. T. D, &
Pinewski. P, “Comparison of space vector
modulation techniques based on performance indexes
and hardware implementation”,23rd International
Conference on Industrial Electronics, Control and
Instrumentation, IECON 97, Vol. 2, pp. 682687),1997.
Suresh. N & Babu.R. S. R, “Review on Harmonics
and its Eliminating Strategies in Power System”,
Indian Journal of Science and Technology, 8(13),
2015.
Pal. S, & Dalapati. S, “Digital simulation of two
level inverter based on space vector pulse width
modulation”, Indian Journal of Science and
Technology, 5(4), 2557-2568, 2012.
Mondal. S. K, Bose. B. K, Oleschuk. V, & Pinto. J.
O, “Space vector pulse width modulation of threelevel inverter extending operation into over
modulation region”, IEEE Transactions on Power
Electronics, 18(2), 604-611,2003.
Zhou. K, & Wang. D, “Relationship between spacevector modulation and three-phase carrier-based
PWM: a comprehensive analysis [three-phase
inverters]”, IEEE Transactions on Industrial
Electronics,, 49(1), 186-196,( 2002.
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