Page 53 - IJEEE-2022-Vol18-ISSUE-1

Al-Jrew, Mahmood & Ali
inverter was the need for many separate DC sources to
supply the inverter.
In (2014), R. Nagarajan and M. Saravanan developed a 9
level cascaded multilevel inverter with reduced switching
components, carrier signals and gate drivers. It included
hybrid structure of two portions, the first one generate the
level voltage using high-frequency switches. The other part
generate the polarity of the output voltage using low
frequency switches. That topology required eleven switches
and four separated sources are required. The findings clearly
indicated that the suggested architecture might function as a
multilayer inverter with fewer switches and carriers [7].
In (2015), N. Prabaharan and K. Palanisamy investigated
15 level inverter with asymmetric DC source and different
types of multicarrier PWM signals. Comparison had been
done among the suggested reduced switches topology and
the classical topologies (Diode clamped, Flying Capacitor
and Cascade H-Bridge). The suggested configuration
consisted of eight switches (two of them were connecting
with DC sources), that arrangement had been utilized to
double the output level of voltage based on the values of DC
sources [8].
V. Rajkumar and T. Nadu introduced a model of a 21-
asymmetric cascade MLI with a lower number of switches.
The inverter used in that study employs just 11 switches, 3
diodes, and 4 asymmetrical sources with multicarrier PWM
to generate the required output voltage. For the reverse
current flow problem, anti-parallel diodes utilized, allowing
several levels to be achieved at the outputs. The simulation
shows that even if one of the switches fails, the system can
still produce numerous voltage levels without shunting down
the entire system. The used topology in this study employs a
lower number of power semiconductor components and
minimizes overall cost [9].
A. I. M. Ali et al. created an arrangement for a single-
phase, five-level inverter with load voltage control via PWM
in (2018).The basic construction of that inverter consists of
two parts. The first one is a full H-bridge inverter, which is
responsible for the polarity of the output voltage. The second
part (consisting of two cells) is responsible for adjusting the unidirectional switches, 2 bidirectional switches, and 2
output level of voltage. The two cells connected in series.
The first one contains a single DC-source in series with a
switch, and this series combination connected in parallel
with the diode, while the second one consists only of a DC
source. A PI controller utilized in a closed loop circuit to
manage and regulate sinusoidal load voltage. Even though
the developed arrangement used fewer switches and lower
harmonic content, the experimental results show lower
efficiency than expected [10].
In a separate study [11], two topologies for multilevel
output voltage inverters were presented. The first
configuration synthesizes (15 levels) at the output. It
consisted of three DC voltage sources and ten
unidirectional and bidirectional switches. The second
configuration consisted of four DC voltage sources and 12
switches to create 25 levels at the output, which is an
expansion of the first topology. Both topologies
implemented with lower voltage rated across the switches.
The experimental findings demonstrate the feasibility of
these topologies with various types of loading combinations
| 49
and various modulation indexes. Even though the two
topologies required fewer number of switches, the drawback
is the needed to separated DC voltage supplies which
increase the inverters cost.
In (2020), V. Anand and V. Singh created a modular
inverter with a basic unit that can be extended in series to
achieve the required output level voltage. The designed basic
unit consisted of four bidirectional and unidirectional
switches, and two DC sources. To create a symmetrical 7-
level inverter, nine unidirectional and bidirectional switches,
and three DC voltage sources are required. Using the same
components, it can be generates 15 level with asymmetrical
DC voltage sources. When two basic unit connected in
series, a maximum of 27 level were formed. Comparison had
been made for the developed inverter using five algorithms
for asymmetrical multilevel inverter in term of the number
of DC sources, stresses on each switch and efficiency. As a
result, the developed modular inverter employed fewer ON-
state switches and has a lower block voltage across switches.
The drawback of that configuration is that the efficiency
decreases as the over and under modulation as RMS as well
as THD both increases [12].
In (2021), M. S. Bin Arif et al. suggested basic module
which operated with symmetrical and asymmetrical DC
sources using nearest level control technique. It can generate
15 level at the output with eight switches, and 4 DC sources
and it can be generalized to generate more number of levels.
When compared with the basic topology, which requires ten
switches to produce the same output level voltage. Analysis
reveals that the suggested system required lower rated
switches and overall block voltage. The findings were
achieved for unity power factor loads, as well as with
changing modulation index. The results show that with the
increasing in output power rating, the efficiency of the
designed 15-level inverter reduced [13].
B. Hosseini Montazer, J. Olamaei, M. Hosseinpour, and
B. Mozafari, introduced the bidirectional MLI topology to
feed low power factor RL loads with symmetrical and
asymmetrical DC sources. In the symmetric topology, the
suggested unit includes 5 separate DC sources with 9
diodes that may yield 11 levels, while the conventional
architectures require 12 switches or more to create 11 levels
at the output. The asymmetric topology generates 19 levels
in the output using the same components. The problem of
reverse current and voltage spikes had been studied. The
suggested topology analysis has been validated by the
experimental laboratory results [14].
In (2021), A. Abdali, A. Abdulabbas, and H. Nekad
conducted a comparison between conventional and non-
conventional topologies. The non-conventional topologies
used in the study were 3-phase 9 and 17 output voltage
levels. The 9-levels topology required (11 switches/ phase)
and 4 DC sources, while the 17-levels topology required (32
switches/phase) and 8 DC sources. The developed topologies
require fewer switches to produce the same output voltage
level using the conventional topologies and can be extended
to produce a high number of levels [15].