ISSN 2319-8885
Vol.04,Issue.24,
July-2015,
Pages:4607-4612
www.ijsetr.com
Design and Simulation of Multilevel Inverter with Less Number of Switches
for Induction Motor Drive Application
B. NARENDER1, CH. VINAY KUMAR2, D. VIJAYA3
1
PG Scholar, Dept of EEE, SSJ Engineering College, Vattinagulapally, Hyderabad, TS, India.
Associate Professor & HOD, Dept of EEE, SSJ Engineering College, Vattinagulapally, Hyderabad, TS, India.
3
Assistant Professor, Dept of EEE, SSJ Engineering College, Vattinagulapally, Hyderabad, TS, India.
2
Abstract: This paper proposes a new Multilevel Inverter for Induction Motor Drive. The Inverter presented gives a seven level
output voltage. This inverter uses very less number of switches when compared with the other type of multi inventers like diode
clamped, flying capacitor, cascaded inventers. This topology requires very less number of carrier signals and gate drivers,
especially when used for higher levels. The above discussed inverter is fed to a induction motor drive and the performance of the
motor is analyzed. Simulation results obtained from MATLAB / SIMULINK shows the speed, torque characteristics of the motor
and seven level output voltage of inverter.
Keywords: Multilevel Inverter, PWM, Induction Motor, Total Harmonic Distortion.
I. INTRODUCTION
DC motors have been used during the last century in
industries for variable speed control applications, because its
flux and torque can be controlled easily changing the field and
armature currents respectively. But, they have the inherent
disadvantage of Commutator and mechanical brushes, which
undergo wear and tear with the passage of time. In most cases,
AC motors are preferred to DC motors, in particular, an
induction motor due to its low cost, low maintenance, lower
weight, higher efficiency, improved ruggedness and
reliability. All these features make the use of induction motors
a mandatory in many areas of industrial applications[1].
Furthermore, four quadrant operation of induction motor was
also achieved. Induction motor is popularly used in industries
due to ruggedness and robustness. The induction motors were
mainly used for essentially constant speed applications
because of the unavailability of the variable-frequency voltage
supply. The advancement of power electronics has made it
possible to vary the frequency of the voltage[2]. Thus, it has
extended the use of induction motor in variable speed drive
applications. The advancement in Power electronics and
semiconductor technology has triggered the development of
high power and high speed semiconductor devices in order to
achieve a smooth, continuous and step less variation in motor
speed.
Applications of solid state converters/inverters for
adjustable speed induction motor drive are wide spread in
electromechanical systems for a large spectrum of industrial
systems. The inverters are either Current Source Inverter
(CSIs) or Voltage Source Inverters (VSIs). Current source
inverters are widely used for the implementation of fully
generative induction machine variable speed drives. An
important and attractive feature of CSI is its good fault
protection capability and the inherent regeneration capability.
However, a CSI-fed induction motor suffers from severe
torque pulsations, especially at low speeds, which manifest
themselves in cogging of the shaft. The usual technique of
overcoming such problems in Voltage Source Inverters (VSIs)
is to pulse width modulate the input voltage waveforms. Pulse
width modulated voltage source inverters are invariably used
for AC/DC/AC conversion to provide a variable ac voltages to
the induction motor[1-2]. However, inverter fed induction
motor suffers from the presence of significant amount of
harmonics which causes undesired motor heating, torque
pulsation and EMI. The reduction in harmonics calls for large
sized filters, resulting in increased size and cost of the system.
However, the advancements in the field of power electronics
and microelectronics made it possible to reduce the magnitude
of harmonics with multilevel inverters, in which the number
of levels of the inverters are increased rather than increasing
the size of the filters.
II. MULTILEVEL INVERTER
A voltage level of three is considered to be the smallest
number in multilevel converter topologies. Due to the bidirectional switches, the multilevel VSC can work in both
rectifier and Inverter modes. This is why most of the time it is
referred to as a converter instead of an inverter in this
dissertation[1]. As the number of levels reaches infinity, the
output THD approaches zero. The number of the achievable
voltage levels, however, is limited by voltage-imbalance
problems, voltage clamping requirements, circuit layout and
packaging constraints complexity of the controller, and, of
Copyright @ 2015 IJSETR. All rights reserved.
B. NARENDER, CH. VINAY KUMAR, D. VIJAYA
course, capital and maintenance costs[3]. Three different
range so this can also be called as symmetrical multilevel
major multilevel converter structures have been applied in
inverter. The number of carrier waves used are also very less
industrial applications: cascaded H-bridges converter with
in this topology. For a conventional seven level inverter
separate dc sources, diode clamped, and flying capacitors. The
using SPWM uses six carrier waves but the proposed uses
concept of multilevel converters has been introduced since
only three carrir waves. The proposed topology can be easily
1975. Separate DC-sourced full-bridge cells are placed in
extended to three phase system also. The switch S6 used in
series to synthesize a staircase AC output voltage. The term
the inverter can be duplicated and can be extended for any
multilevel began with the three-level converter. In 1981,
levels of voltage. In the proposed inverter topology the full
diode-clamped multilevel inverter also called the Neutralbridge is used to decide the polarity of the levels and the
Point Clamped (NPC) inverter schemes were proposed. In
remaining part of the inverter is the reason for the level
1992, capacitor-clamped (or flying capacitor) multilevel
generation. The switching sequence for the proposed
inverters, and in 1996, cascaded multilevel inverters were
converter to generate seven level output voltage is shown
proposed. Although the cascade multilevel inverter was
below. In the proposed topology total ten switches are used
invented earlier, its application did not prevail until the mid
per phase.
1990s.
 +3Vdc:- The switches used for obtaining the voltage
of
3Vdc are S1, S5, S7, S10.
The advantages of cascade multilevel inverters were
 +2Vdc:- The switches used for obtaining the voltage
prominent for motor drives and utility applications. The
of 2Vdc are S2, S6, S5, S7, S10.
cascade inverter has drawn great interest due to the great
 +Vdc: - The switches used for obtaining the voltage
demand of medium-voltage high-power inverters[4]. The
of Vdc are S2, S3, S5, S7, S10.
cascade inverter is also used in regenerative-type motor drive
 0:- The switches used for obtaining the voltage of 0
applications. Recently, some new topologies of multilevel
are S2, S3, S4, S7, S10.
inverters have emerged. This includes generalized multilevel
 -3Vdc:- The switches used for obtaining the voltage
inverters, mixed multilevel, inverters, hybrid multilevel
of -3Vdc are S1, S5, S8, S9.
inverters and soft-switched multilevel inverters . These
 -2Vdc:- :- The switches used for obtaining the
multilevel inverters can extend rated inverter voltage and
voltage of -2Vdc are S2, S6, S5, S8, S9.
power by increasing the number of voltage levels. They can
 -Vdc:- :- The switches used for obtaining the
also increase equivalent switching frequency without the
voltage of --Vdc are S2, S3, S5,S8, S9 .
increase of actual switching frequency, thus reducing ripple
component of inverter output voltage and electromagnetic
interference effects.
III. PROPOSED MULTILEVEL TOPOLOGY
The PWM control strategy used for the proposed inverter
topology is Sinusoidal pulse width Modulation(SPWM) with
single reference and three carrier wave forms. The below
fig.2 shows the PWM strategy of the proposed inverter.
Fig.1.Proposed Seven Level Inverter.
The circuit of the proposed multilevel inverter is shown
in Fig.1. The inverter designed gives seven level of output
voltage. A total of ten switches are used which are
IGBT/Diodes. Six switches are used for level generation and
4 switches are used for polarity generation. Three sources are
used for generating levels. Each voltage source is of same
Fig.2.PWM strategy for proposed Inverter.
The proposed converter can be extended to any level of
inverter by adding the appropriate switches and the DC
voltage sources.Fig.3 and Fig.4 shows the nine level and
eleven level inverter topologies based on the proposed
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.24, July-2015, Pages: 4607-4612
Design and Simulation of Multilevel Inverter with Less Number of Switches for Induction Motor Drive Application
concept. For a nine level inverter the number of switches
very low efficiencies at lower speeds. The most efficient
used are 12 and for eleven level inverter 14 switches are
scheme for speed control of induction motor is by varying
used. The designed circuits are simulated on both
supply frequency. This not only results in scheme with wide
MATLAB/SIMULINK as well as PLECS software packages
speed range but also improves the starting performance.
and the results are presented.
Synchronous speed of Induction Motor is directly
proportional to the supply frequency. Hence, by changing the
frequency, the synchronous speed and the motor speed can be
controlled below and above the normal full load speed. If the
machine is operating at speed below base speed, then v/f ratio
is to be kept constant so that flux remains constant. This
retains the torque capability of the machine at the same value.
But at lower frequencies, the torque capability decrease and
this drop in torque has to be compensated for increasing the
applied voltage[5]. Any reduction in the supply frequency
without a change in the terminal voltage causes an increase in
the air gap flux[4]. Induction motors are designed to operate
at the knee point of the magnetization characteristic to make
full use of the magnetic material. Therefore the increase in
flux will saturate the motor.
Fig.3. proposed circuit for 9 level.
Fig.5.Proposed Three Phase Inverter Fed to Induction
Motor Drive.
Fig.4. proposed circuit for 11 level.
IV. VARIABLE FREQUENCY CONTROL OF
INDUCTION MOTOR
The induction motor speed variation can be easily
achieved for a short range by either stator voltage control or
rotor resistance control. But both of these schemes result in
This will increase the magnetizing current, distort the line
current and voltage, increase the core loss and the stator
copper loss, and produce a high pitch acoustic noise. While
any increase in flux beyond rated value is undesirable from
the consideration of saturation effects, a decrease in flux is
also avoided to retain the torque capability of the moto[4]r.
Therefore, the variable frequency control below the rated
frequency is generally carried out by reducing the machine
phase voltage, V, along with the frequency in such a manner
that the flux is maintained constant. Above the rated
frequency, the motor is operated at a constant voltage
because of the limitation imposed by stator insulation or by
supply voltage limitations. The below table I shows the
comparison of the number of switches for the three
conventional Multilevel Inverters and the proposed
Multilevel Inverter.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.24, July-2015, Pages: 4607-4612
B. NARENDER, CH. VINAY KUMAR, D. VIJAYA
TABLE I: Number of Components for Three-Phase
Inverters
Fig .8.The simulation 11 level output wave form of
inverter.
From the table it is clear that for a cascaded Multilevel
Inverter needs 12 switches for seven level but proposed
requires only ten switches, so 2 switches for single phase and
6 switches for three phase system are saved which also saves
the gate driver circuits also. Fig.5 shows the graphical view
of comparison of different multilevel inverters and the
number of components used.
V. MATLAB/SIMULINK RESULTS
In this section the simulation results obtained for seven,
nine and eleven level inverters are presented. The output
voltage waveforms as well as the THD analysis is also
discussed. Finally the Induction motor characteristics fed by
a three phase seven level inverter is also presents. The below
figs.6 to 11 shows the different level output voltage of the
proposed inverter
Fig.9. THD analysis for 7 level.
Fig.6.The simulation 7 level output wave form of inverter.
Fig.10. THD analysis for 9 level.
Fig.7.The simulation 9 level output wave form of inverter.
Fig.11. THD analysis for 11 level.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.24, July-2015, Pages: 4607-4612
Design and Simulation of Multilevel Inverter with Less Number of Switches for Induction Motor Drive Application
The below fig.12 shows the speed characteristics of the
Industry Applications, vol.35, no. 1, Jan. /Feb. 1999, pp. 36induction motor drive. The motor is designed to run at
44.
1500rpm.
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VI. CONCLUSION
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B. NARENDER, CH. VINAY KUMAR, D. VIJAYA
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Author’s Profile:
B.Narender received B.Tech degree in
Electrical and Electronics Engineering
from K.G. Reddy college of engineering
and technology, JNTUH University, in
2012.He is currently pursuing M.Tech
degree in Power Electronics from SSJ
College, JNTUH.
Ch.Vinay Kumar, Obtained his B.TECH
(EEE) degree from ST.MARTINS ENGG
COLLEGE, HYD, M.Tech. (Power
Electronics) from JNTU Hyderabad.
Currently he is working as Assoc. Prof.&
HOD in SSJ Engineering college,
Hyderabad. His areas of interest include
Power Electronics & Drives, Power
systems and Facts. He is having 8 years of teaching
experience.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.24, July-2015, Pages: 4607-4612