International Journal of Engineering Technology, Management and Applied Sciences
www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476
Reversing Voltage Reduced Switch Multilevel Inverter
Jithinmon Rajan Philip
Electrical & Electronics Engineering
St. Joseph’s College of Engineering & Technology
Palai
Lallumol K. Johny
Assistant Professor, Electrical & Electronics
St. Joseph’s College of Engineering & Technology
Palai
Abstract— Multilevel inverters are widely used
other topologies because it does not have any
clamping diodes and flying capacitors.
As already mentioned multilevel inverter has large
number of power switches and it normally leads to
complexity in controlling the power switches. Many
methods have been developed to decrease the
number of switches [6]. Many modulation
techniques are applied to multilevel inverters for
selective harmonic elimination [7], [8].carrier based
Pulse Width Modulation [9], [10], Space Vector
Modulation [11], [12] and Fundamental Frequency
Modulation [13], [14]. The Pulse Width Modulation
(PWM) control [15] is the best technique of
controlling the output voltage within the inverters.
This paper presents a new multilevel inverter called
Reversing Voltage Reduced Switch (RVRS)
multilevel inverter. It has reduced number of
switches as compared to conventional multilevel
inverters and also Reversing Voltage (RV) inverter.
This paper is based on a nine level inverter with
Reversing Voltage topology. Pulse Width
Modulation (PWM) signals for the switches are
generated with the help of carrier based PWM
scheme using Phase Disposition Sinusoidal Pulse
Width Modulation (PD-SPWM) method. Phase
Disposition Sinusoidal Pulse Width Modulation use
carriers to drive the inverter and all the carrier
waveforms are in phase. The proposed topology is a
symmetrical topology since all the values of voltage
sources are equal in magnitude.
especially for high power high voltage applications. It
has variety of advantages over conventional inverters
such as low harmonic distortion, less electromagnetic
interferences and high dc link voltages. It has also
certain disadvantages mainly higher number of
components and complex power control techniques. In
this paper a new topology is proposed with Reversing
Voltage component. This proposed topology has fewer
number of components as compared to former Reversing
voltage topology, Hence, it requires only fewer gate drive
and carrier signals.
Keywords- Multilevl Inverter, SPWM, Reversing
Voltage, Topology.
I. INTRODUCTION
A simple Inverter is a device which converts DC
power to AC power. The two level inverter requires
high switching frequency, it’s efficiency is less and
it’s switching losses are very high. Multilevel
inverters are introduced to overcome these
disadvantages. Multilevel inverters are able to
synthesize output voltages with reduced harmonic
distortion and lower electromagnetic interferences.
The concept of multilevel inverters has been
introduced since 1975 and the term multilevel began
with three level inverter. Multilevel inverters consist
of large number of power semiconductor switches in
order to perform the power conversion in small
voltage steps. Multilevel inverter output is a
staircase waveform and it closely resembles
sinusoidal waveform. The advantage of multilevel
inverters are improvement in staircase waveform
quality, less input current distortion, lower
electromagnetic interferences.
Many topology have been introduced for multilevel
inverter [1], [2]. Multilevel inverters are widely used
in drives, PV systems and automotive applications.
The harmonic content of the output decreases as the
number of level increases.
The multilevel inverters are mainly classified as
Cascaded multilevel inverter [3], Diode clamped
multilevel inverters [4], Flying capacitor multilevel
inverters [5]. The control method of cascaded H
bridge multilevel inverter is more convenient than
45
II. REVERSING VOLTAGE INVERTER
Figure 1. Schematic of Nine-level RV inverter.
Mr. Jithinmon Rajan Philip, Ms. Lallumol K. Johny
International Journal of Engineering Technology, Management and Applied Sciences
www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476
. In conventional Multilevel inverters switches are
combined to produce a high frequency wave form in
positive and negative polarities [18] but in actual
practice it is not required to utilize all the switches
for generating bipolar levels. This idea is put into
practice by Reversing Voltage (RV) topology. RV
topology mainly consists of two important parts.
First part is called the level generation part (left
portion of Figure 1.) and it generates output levels
only in the positive polarity. This part operates at
high frequency hence, high frequency switches are
required by this section in order to generate the
required output levels.
Second part is called Polarity generation part (
Right portion of Figure 1.) and it helps in generating
the polarity of the output voltage. This part operates
at low frequency that is line frequency. Hence, RV
topology combines the two parts (high and low
frequency) to generate multilevel output voltage. So
the level generation part generates the positive
output levels which are generated at high frequency
and these output levels are fed to H-bridge inverter
section which is the polarity generation part and this
polarity generation part generates required polarity
of the output. Therefore, extra switches required for
generating bipolar levels can be eliminated.
The RV topology in nine levels in shown in
Figure 1. Here we can see that it requires 12
switches and four isolated sources. Hence, the left
stage (level generation) generates the required
output levels without polarity and the right stage
(polarity generation) determines the polarity of
output voltages. The polarity generation part
transfers the required output levels to either positive
or negative direction in order to obtain required
output polarity that is, it reverses the voltage
direction when the voltage polarity required to be
changed for negative polarity.
This topology can be extended for any number of
levels by duplicating the section specified in Fig. 1.
RV topology shown in Figure 1. Can be also
reduced to seven level . Hence, this topology is
modular. RV topology can also be applied to three
phase application.
RV topology requires fewer components as
compared to other conventional nine level inverters.
Another advantage of this topology is that it requires
half the number of carrier signals for Sinusoidal
Pulse Width Modulation (SPWM) controller.
SPWM for nine level conventional converters
requires eight numbers of carriers but for RV
46
topology it requires only four carriers. Switching
sequences for each level is shown in TABLE I. RV
topology utilizes PD-SPWM for simplicity.
TABLE I
SWITCHING SEQUENCES FOR EACH LEVEL
III. RVRS MULTILEVEL INVERTER
A. General Description
Reversing Voltage Reduced Switch (RVRS)
topology is a similar topology as that of RV
topology. On closely watching the RV topology one
may find that certain modification can be done on
RV topology without causing or altering the output
waveform. This leads to RVRS topology. A nine
level RVRS inverter is shown in Figure 2.
Figure 2. Schematic of a nine-level RVRS inverter.
As compared to Reversing Voltage topology
presented earlier RVRS topology has fewer
components. Reversing Voltage nine-level inverter
has twelve numbers of switches whereas in RVRS
Mr. Jithinmon Rajan Philip, Ms. Lallumol K. Johny
International Journal of Engineering Technology, Management and Applied Sciences
www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476
nine-level inverter has only eight numbers of
switches while four switches of RV inverter is
replaced by four diodes. Hence, we can say that
RVRS topology has lesser number of switches and
therefore drive circuitry for this topology will be
also less.
Reversing Voltage Reduced Switch topology is also
divided into two parts. First part (left section in
Figure 2.) is the level generation part and this
section generates the output voltage levels only in
positive polarity. It consists of four numbers of
switches and four diodes. The level generation part
operates at high frequency and therefore, this part is
termed as high frequency section. The second part
(right section in Figure 2.) is called polarity
generation part and it helps in generating required
polarity for the output voltages. This section
operates at low or line frequency and therefore, this
part is referred to as low frequency section.
B. Switching Sequences
Switching sequences of RVRS inverter are easier
than it’s counter parts. It is mainly because it does
not need to generate negative pulses for negative
cycle control. Thus, there is no need for extra
conditions for controlling the negative voltage.
Instead, the reversing full bridge converter performs
this task. This topology is redundant and flexible in
switching sequence. The switching sheme for each
level is shown in TABLE II.
TABLE II
SWITCHING LEVELS FOR RVRS INVERTER
47
Mr. Jithinmon Rajan Philip, Ms. Lallumol K. Johny
International Journal of Engineering Technology, Management and Applied Sciences
www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476
These switching sequences can be implemented
using logic gates. The signal stage should be isolated
from power stage by optocouplers for control circuit
protection.
The gating signals to the output stage, which
changes the polarity of voltage is relatively simple;
the output stage is an H-bridge inverter and it has
two modes forward and reverse mode. In the
forward mode, switches 5 and 8 in Figure 2. will
conduct and hence, output voltage polarity is
positive and in reverse mode switches 6 and 7 will
conduct and hence, the output voltage polarity is
negative.
Figure 3. Switching sequences for different levels.
In TABLE II the numbers shown are according to
Figure 2. And these switches should be turned to
generate the required voltage levels. According to
the TABLE II there are five possible switching
patterns. The dc sources are externally adjustable
sources, therefore there is no need for voltage
balancing. The switching sequence here is so
selected so as to minimize the switching transition
during each transfer. This will lead to lesser
switching power dissipation. These sequences are
shown in Figure 3.
Similar to RV topology RVRS topology also
utilizes PD-SPWM. Carriers in this PWM technique
do not have any coincidence and they have a definite
offset from each other and are in phase with each
other. The modulator and four carriers for SPWM
are shown in Figure 4.
Figure 4. SPWM carrier and modulator for RVRS
topology.
The number of switches in the path of conducting
current in proposed RVRS topology is lower than
cascaded inverter and hence, it has better efficiency.
48
IV. SIMULATION RESULTS
Simulation of RVRS topology is performed using
MATLAB and the results are shown below.
Modulation techniques are used to synthesize a
controlled output voltage [19]. There are various
modulation techniques, of which Phase Disposition
Sinusoidal Pulse Width Modulation (PD-SPWM)
technique is used. Here PD-SPWM is used to drive
the switches in the level generation part and
switches in the polarity generation part are driven by
line frequency. In RVRS topology, a phase
modulation signal is compared with
carriers for
an n level inverter and all the carriers are in phase.
Since this converter works only in positive polarity,
RVRS topology half of the conventional carriers for
SPWM controller. Here PD-SPWM is used for
driving the high frequency switches and low
frequency polarity generation drive signals are
generated with the line frequency (50 Hz), and they
only changes at zero voltage crossings. MATLAB
simulation diagram of RVRS topology is shown in
Figure 5.
Figure 5. RVRS topology.
Here gating signals to the switches in the level
generation part is provided my means of logic gates
while those at polarity generation part is driven at
Mr. Jithinmon Rajan Philip, Ms. Lallumol K. Johny
International Journal of Engineering Technology, Management and Applied Sciences
www.ijetmas.com August 2015, Volume 3, Issue 8, ISSN 2349-4476
line frequency. The proposed RVRS topology
consists of eight switches and four DC sources.
Gating signals to each of the Four switches in level
generation part is shown in Figure 6.
Figure 6. Complete gate signals for level generation
part.
The output voltage thus obtained is shown in Figure
7. and Figure 8. Respectively.
V. CONCLUSION
This paper presents a modification of existing
Reversing Voltage Topology (RV) by replacing
certain switches with diodes without altering the
performance of RV topology. The new topology
proposed has superior features over conventional
multilevel inverters as it requires only fewer
switches. Hence, gate drive circuitry required can be
reduced and as compared to RV topology this new
topology has even less number of switches and
hence fewer gate drives. In this topology the
switching is divided into high and low frequency
section. This will further add up to the efficiency of
inverter and reducing the overall size and cost of
final prototype.
PD-SPWM is utilized for this topology and it has
fewer complexities since we require only positive
carriers.
The simulation results of RVRS nine level inverter
is demonstrated in this paper and output is also
obtained.
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49
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