In this paper, a new symmetric multilevel inverter is proposed. A simple structure for the cascaded multilevel inverter topology is also proposed, which produces a high number of levels with the application of few power electronic devices. The symmetric multilevel inverter can generate 2n+1 levels with a reduced number of power switches. The basic unit is composed of a single and double source unit (SDSunit). The application of this SDSunit is for reducing the number of power electronic components like insulated gate bipolar transistors, freewheeling diodes, gate driver circuits, dc voltage sources, and blocked voltages by switches. Various new algorithms are recommended to determine the magnitude of dc sources in a cascaded structure. Furthermore, the proposed topology is optimized for different goals. The proposed cascaded structure is compared with other similar topologies. For verifying the performance of the proposed basic symmetric and cascaded structure, results from a computerbased MATLAB/Simulink simulation and from experimental hardware are also discussed.
I. INTRODUCTION
The multilevel inverter is a kind of dc/ac power converter that produces a desired steppedlike sinusoidal output voltage waveform from an available dc input source
[1]
,
[2]
. In recent years, this inverter has been widely recommended for medium and high power applications
[3]
. The important advantages of multilevel inverters are high quality output voltage, low harmonic distortion, low electromagnetic interference, low switching frequency, and low voltage stress on switches
[4]
. The technical and economic aspects of multilevel inverter development include modular realization, high availability, failure management, investment, and lifecycle cost
[5]
. Some applications of multilevel inverters include industrial drives, automotive applications, Flexible AC Transmission Systems (FACTS), and traction drive applications
[6]
,
[7]
. Conventional multilevel inverters are of three types—diode clamped (NPC)
[8]
, flying capacitor (FC)
[9]
, and cascaded Hbridge (CHB) multilevel inverters
[10]
.
The CHB multilevel inverter has received special attention due to its modularity, simple control techniques, reliability, and the absence of capacitor imbalance issues
[11]
. CHB multilevel inverters are mainly classified into two groups—symmetric and asymmetric multilevel inverters
[12]
. In symmetric CHB multilevel inverters, the magnitude of all dc voltage sources are equal, requiring an increased number of Insulated Gate Bipolar Transistors (IGBTs) and power diodes, as well as separate dc sources to generate many output levels
[13]
. These features lead to an increase in installation space and in the total cost of this inverter. In the asymmetric topology, the magnitude of dc voltage sources are unequal. The magnitude of a dc voltage source can be determined using various algorithms. The major advantage of the asymmetric CHB topology is it can considerably increase the number of output voltage levels using few dc voltage sources and IGBTs; however, this topology may also require a variety of dc voltage sources, which is a significant disadvantage. Several novel topologies, along with different new algorithms, for determining the magnitude of dc source voltages have been proposed
[14]

[18]
. These topologies increase the number of output voltage levels with reduced dc sources and minimum switches. However, power electronic components required therein are high.
In this paper, a basic singlephase symmetric multilevel inverter unit is discussed, and a cascaded structure for which is recommended for its use in high power applications. A cascaded structure can generate the maximum number of output voltage levels with a reduced number of dc sources and power electronic components. For generating different levels (both even and odd levels), new algorithms are proposed to determine the magnitude of dc sources. The optimal topology is discussed in the terms of the best of the proposed algorithms. The proposed topology, with its best algorithm, is then compared with the conventional topology and other topologies in existing literature. The amount of voltage blocked by switches and the required number of power electronic components are the factors considered in these comparisons. This paper is arranged as follows: (i) Basic Unit, (ii) Recommended Cascaded Structure, (iii) Optimal Topologies, (iv) Comparison with Other Topologies, (v) Simulation and Experimental Results Verification, and (vi) Conclusion.
II. BASIC UNIT
The proposed basic symmetric multilevel inverter presented in
[19]
comprises a single and double source unit (
Fig. 1
). The single source unit consists of IGBTs in series/parallel connection, as shown in
Fig. 1
(a). The dc source
V_{1}
is connected in series with switch
S_{1} (voltage adder switch)
and parallel switch
P_{1} (voltage subtractor switch)
—this basic unit is called a single source unit
(SSUnit)
. The double source unit is composed of two dc sources, along with two IGBTs in series/parallel connection. The dc sources,
V_{1}
and
V_{2}
, are connected in series with switch
S_{1}
and in parallel with switch
P_{1}
; this unit is often referred to as a double source unit
(DSUnit)
, as shown
Fig. 1
(b). When single and double source units are combined, the result is a single and double source multilevel inverter (SDSMLI). In the proposed structure, the power switches
(S_{1}, P_{1}), (S_{2}, P_{2}), …(S_{j}, P_{j})
should not be turned on simultaneously with the dc voltage sources
(V_{1}, V_{2}, …V_{n1})
, respectively, to prevent short circuiting. The suggested basic unit is divided into the following two sections: (i) The combined single and double source sub module is called the level generator unit; (ii) The series connection of the Hbridge inverter is called the polarity changer. This topology has separate generalized structures for both odd and even sources, as shown in
Figs. 1
(c) and
1
(d), wherein
n
is the number of dc voltage sources, which are separated by seriesconnected unidirectional controlled power switches
(S_{1}, S_{2}, S_{3}, …S_{j})
and are parallel with
(P_{1}, P_{2}, P_{3}, … Pi)
switches.
(a) Basic single source unit. (b) Basic double source unit. (c) Generalized structure for odd number of sources. (d) Generalized structure for even number of sources.
The
n_{th}
dc source is represented as
V_{i}
. In this unit,
V_{i}
is not connected with any parallel switch. Presented in
Table I
are the switching pattern for
n
number of dc sources, wherein 1 and 0 represent ON and OFF switches, respectively.
GENERALIZED SWITCHING PATTERN FOR BASIC SYMMETRIC MULTILEVEL INVERTER
GENERALIZED SWITCHING PATTERN FOR BASIC SYMMETRIC MULTILEVEL INVERTER
The corresponding switches are turned on to synthesize a positive stepped waveform in the level generator; the Hbridge unit is used to create a current flow in both directions at the load terminals. The maximum output voltage
(V_{o, max})
is the sum of all dc source voltages, given as:
(1) and (2) illustrate the stepped dc/dc output voltage level waveform generated by the level generator unit.
The Hbridge unit is synthesized for both positive and negative output voltage levels at the load (
V_{out}
).
The output voltage at
(V_{out})
is expressed as follows:
where
H_{S1}
–
H_{S4}
are Hbridge switches. The number of output voltage levels
(N_{Level})
, number of IGBTs
(N_{IGBT})
, and the number of dc sources
(n)
are calculated as follows.
In the proposed topology structure, the number of odd dc sources is different from the number of even dc sources; thus, must express the number of IGBTs required for given output levels and number of dc sources, as in equation (5).
Determination of the required number of single and double source submodules is calculated on the basis of the given n of dc sources, as follows:
For even number of
n
:
For odd number of
n
:
The SDSMLI can generate high number of output voltage levels with a low number of IGBTs.
In this proposed topology, the maximum blocking voltage of level generator switches are reduced because separate dc sources are connected in series/parallel, leading to reduced voltage ratings of the protecting circuits for power devices. However, these effects do not apply in the Hbridge unit (polarity changer), which is required to withstand high voltage values. For protecting the Hbridge switches, the proposed topology may need some high voltage protecting circuits to protect the power devices. This requirement is the remarkable disadvantage of Hbridge (polarity changer) based multilevel inverters.
III. RECOMMENDED CASCADED STRUCTURE
The SDSMLI topology has a few drawbacks, discussed as follows. This proposed symmetric topology requires highblocking voltage switches at the Hbridge unit and an increased number of dc sources required to generate an increased number of output voltage levels. These requirements significantly increase the cost of the multilevel inverter. To rectify these problems, a cascaded structure of the basic symmetric multilevel inverter is proposed for high power applications. The basic symmetric multilevel inverter is only suitable for mediumpower applications. This cascaded structure can generate an increased number of output voltage levels with minimum dc sources and IGBTs. The cascaded connection of the proposed SDSMLI is discussed in this section. The novel cascaded multilevel inverter topologies presented in
[14]

[18]
, and the CHB (binary and trinary configuration), the last or the
k^{th}
submultilevel inverter unit should withstand high magnitudes of dc source voltages. Thus, the
k^{th}
submultilevel inverter unit switches of the proposed cascaded structure should have high voltage ratings. Nonetheless, the proposed topology requires minimal IGBTs, reduced dc sources, and reduced variety of dc source voltages. The cascaded connection of the basic symmetric multilevel inverter is shown in
Fig. 2
. The cascaded structure consists of submultilevel units (basic symmetric multilevel inverters) connected in series. These individual submultilevel inverters should have an equal magnitude of dc source voltages. Presented in
Table II
are the different switching patterns of the cascaded structure for generating maximum output voltage levels.
Recommended cascaded single and double source multilevel inverter topology.
VALUES OF VOUTFOR DIFFERENT STATES OF THE SWITCHES
VALUES OF V_{OUT} FOR DIFFERENT STATES OF THE SWITCHES
The individual submultilevel outputs are represented as
V_{01}
,
V_{02}
....
V_{0k}
. The sum of all submultilevel output voltages is
V_{out}
(
V_{out}
=
V_{01}
+
V_{02}
+⋯+
V_{0k}
).
For simplicity, switches in the onstate are presented in
Table II
. . A zerovoltage level at the output voltage can be generated using different switching states.
In
Table II
, one state is presented and any one of the series/parallel switches presented therein can be switched on to generate the desired output voltage. Different algorithms are discussed to determine the magnitude of the dc source voltages for each individual symmetric submultilevel inverter, as listed in
Table III
. The suggested topology is asymmetric; thus, the new algorithms produce symmetric magnitude values of dc source voltages for each submultilevel inverter.
DIFFERENT PROPOSED ALGRITHMS AND THEIR RELATED PARAMETERS
DIFFERENT PROPOSED ALGRITHMS AND THEIR RELATED PARAMETERS
In the following algorithms, the base value of
V_{dc}
is assumed. The proposed topology requires multiple dc voltage sources, which can be directly provided by a photovoltaic panel or a multiwinding transformer, as shown in
Figs. 3
(a) and
3
(b). If each individual submultilevel inverter has a different dc voltage magnitude, a different output voltage rating of photovoltaic panel or a different ratio for the secondary winding turn of the transformer may be required. This requirement may reduce the efficiency of the multilevel inverter.
Arrangement of the dc voltage source. (a) using multiwinding transformer, (b) using photovoltaic system.
In order to avoid such a problem, the individual submultilevel units should have the same dc source magnitude values. However, photovoltaic panel outputs are not constant. Thus, with regard to ensuring a constant output, the dc/dc converter and MPPT algorithms are preferred
[20]

[22]
.
Table III
describes different algorithms , their possible output voltage levels and variety of dc sources. Each submultilevel inverter may require a
k
variety of dc voltage magnitudes because each inverter has a dc source voltage magnitude equal to the other inverters. The proposed cascaded structure can generate both odd and even levels using the proposed algorithms. The maximum amount of output voltage levels can be generated using the proposed algorithms, as demonstrated in
Fig. 4
and
5
.
Number of levels against k and constant n.
Number of levels against n and constant k..
The cascaded structure consists of an
n
number of dc sources and a
k
number of submultilevel inverters connected in series. In
Fig. 4
,
n
is kept constant (
n=4
) and the number of possible output voltage levels against different
k
is compared. Several
n
with a constant
k
are shown in
Fig. 5
, wherein the number of output voltage levels against a different
n
is shown. In both approaches, Algorithm7 produces a high number of output voltage levels. The generalized equation for the total number of IGBTs is as follows:
Fig. 6
illustrates the required number of switches against output voltage levels under all the proposed algorithms. Evidently, Algorithm7 produces a high number of output voltage levels with a few switches. However, the number of dc sources and the number of IGBTs is equal between all submultilevel inverters.
Number of levels against the number of IGBTs.
In
Fig. 6
shows the required number of IGBTs for each submultilevel inverter under a constant number of dc sources. Algorithm7 produces the maximum output voltage with the minimum number of IGBTs, dc sources, and variety of dc sources. Thus, Algorithm7 is considered for the optimal topology. This topology is discussed in the following section.
IV. OPTIMAL TOPOLOGIES
As mentioned, Algorithm7 is considered for the optimal topology because it can generate the maximum number of output voltages with minimal IGBTs.
 A. Optimization of the Recommended Cascaded Topology for the Maximum Number of Voltage Steps with a Constant Number of IGBTs
The number of switches in each sub module is considered equal, that is,
In terms of IGBTs,
As shown in the preceding equation,
The number of dc sources
(n)
in each submodule must be determined. The maximum number of voltage levels can be obtained as follows:
Using Equations (13), (14), and (15), the number of voltage levels in terms of the IGBTs can be calculate as follows:
Fig. 7
shows the variation of
N_{Level}
against the number of dc sources
(n)
. The maximum number of output voltage levels can be obtained with a constant number of switches when
n
=2 and
n
=4 (an even number of dc sources can produce a maximum number of voltage levels with a minimum number of IGBTs, compared with an odd number of dc sources).
Variation of and against n
 B. Optimization of the Proposed Cascaded Topology for the Maximum Number of Levels with a Constant Number of dc Voltage Sources
As mentioned, each submodule has an equal number of dc sources, as follows:
The recommended topology cascaded series of submodule consists of
n_{i}
dc voltage sources.
The general form of the
k
submodule dc voltage sources is
N_{Source}
=
n
×
k
As clearly shown in
Fig. 8
, the maximum number of voltage steps are obtained from
n
=1. Thus, a topology that considers each unit with one dc voltage source provides the maximum number of output voltage levels with the minimum number of dc sources (i.e., the conventional cascaded multilevel inverter)
Variation of [(2n+1)^{1/n}] against n.
 C. Optimization of the Proposed Cascaded Converter for the Minimum Number of IGBTs with a Constant Number of Levels
The next objective to optimize the proposed structure to allow it to generate
N_{Level}
with the minimum number of IGBTs
(N_{IGBT}s)
.
To keep
N_{Level}
constant to express the minimum number of IGBTs; (20) and (21) express the required constant IGBTs under each level for odd and even numbers of dc sources, respectively. As illustrated in
Fig. 9
, the minimum number of IGBTs is required when number of dc sources
n
is even. (i.e.,
n
=2 and
n
=4).
Variation of
Number of Levels Vs V_{Block}.
 D. Optimization of the Recommended Cascaded Topology for the Minimum Blocking Voltage of Switches with a Constant Number of Levels
In this section, to determine the minimum value of blocking voltage for the switchesare calculated as follows .
where
V_{Switch,U}
and
V_{Switch,HB}
are the peak voltages of the
Single & Double Source Unit (Level Generator Part)
and the
Hbridge Unit
, respectively.
Single Source Unit:
Double Source Unit:
The peak voltage of the level generator part is the sum of all voltages across each switch.
The generalized formula (V_{Switch,U}) :
First unit:
k^{th} Unit:
Considering (25) and (26), define the general form for the peak voltage of the level generator unit can be written as follows:
Blocking Voltage for the H Bridge Unit:
First unit:
k^{th} Unit:
Considering (43) and (44), the general form for the peak voltage of the Hbridge unit as follows:
Therefore, the peak voltage of the proposed cascaded multilevel inverter can be calculated as
V. COMPARISON WITH OTHER TOPOLOGIES
To show the capabilities of the proposed topology, the comparison with other recommended topologies in existing literature, as shown in
Fig. 11
. The cost function (CF) of the multilevel inverter can be determined as:
Cascaded structure of the recommended topologies presented in literature; (a) presented in [14], named [R14], (b) presented in [15], named [R15], (c) presented in [16], named [R16], (d) presented in [17], named [R17], (e) presented in [18], named [R18]. All topologies consider that
The multilevel inverter cost can be evaluated by (32). The cost function consists of the following: the number of IGBTs, the number of driver circuits, the variety of dc sources and blocking voltages of switches (per unit base value), and β (weight factor of the blockedvoltage switches). In this section, each parameter of the cost function between the similar topologies and the CHB (trinary configuration) is compared.
 A. Comparison of the Required IGBTs and Freewheeling Diodes
This paper aims to reduce the number of IGBTs in multilevel inverters. In a multilevel inverter, the IGBT is one of the factors that determine total cost. An increase in IGBTs leads to an increase in cost, a large installation area, a complex switching pattern, and difficulty in controlling switches.
The recommended topologies in
[15]
and
[17]
have been used with bidirectional switches (composed of two IGBTs).
On the contrary, the proposed topology,
[14]
,
[16]
, and
[18]
are composed of one IGBT. The comparison of different topologies against the proposed topology has been presented in
Fig. 12
. An even number of dc sources synthesizes a higher number of output voltage levels than an odd number of dc sources. Clearly, the even dc source of the proposed topology and [R18] requires minimal IGBTs. In addition, [R18] requires n number of power diodes for
n
dc sources, which can lead to a poor efficiency in the multilevel inverter (e.g., voltage spikes at output voltages). A comparison of the proposed topology and the CHB trinary configuration is shown in
Fig. 13
. The proposed topology and the CHB trinary configuration requires the same number of IGBTs to generate the same output voltage level.
Comparison of number of levels and switches
Comparison of number of switches with other topologies (trinary configuration).
 B .Comparison of the Required Gate Driver Circuits
Another important comparison is that between the number of gate driver circuits. These gate driver circuits consist of low power electronics devices for producing a high current drive in high power electronic devices. The use of few gate driver circuits leads to low efficiency. Each bidirectional and unidirectional switch requires only one gate driver circuit.
Fig. 14
shows the comparison of the number of gate driver circuits against the number of levels in the proposed and in the recommended topologies.
Comparison of number of driver circuits.
In this figure, [R15] uses minimal gate driver circuits. However, the proposed topology requires less number of IGBTs than [R15].
 C. Comparison of the Blocking Voltage of Switches
The maximum blocking voltage is another criterion for finding an optimum multilevel inverter topology. The maximum number of voltage levels can be achieved with a constant number of IGBTs. In the proposed topology, each submultilevel inverter has four dc sources. Therefore, the maximum blocking voltage at the level generator switch depends on the
S_{kj}
,
V(_{max}
,
S_{kj}
) switch and can be calculated as
Since,
With consideration for
n=4
and the preceding expressions, the maximum blocked voltage by
SSunit
and
DSunit
switches are
(35) and (36) are considered single and double dc source switches, respectively. The current rating of all the switches is equal to the load current; this is not the case for voltage. In the proposed topology, both
V_{dc}
and 2
V_{dc}
voltage rating switches are required. The cost of the double voltage rating switch can be determined as
For a
β
≤2, the cost of 2
V_{dc}
switches is less than the
V_{dc}
switches. For a
β
>2, the cost of 2
V_{dc}
is higher than the
V_{dc}
. The proposed topology and that presented in
[16]
require less total blocking voltage than other topologies. To reconfirm the above statement,
Fig. 15
shows that the proposed topology requires the minimum total blocking voltage against the number of levels. In this comparison, the blocking voltage of the level generator switch of the submultilevel inverters are considered.
Comparison of maximum blocking voltages in different topologies.
The maximum blocking voltage of the Hbridge switches are equal to that in the proposed topology and that presented in
[14]

[18]
. Thus, the maximum blocking voltage of the proposed topology and of the CHB (trinary configuration) is also compared. As shown in
Fig. 16
, the maximum blocking voltage of the proposed topology and CHB trinary configuration has an equal value at odd number of dc source.
Comparison of maximum blocking voltages.
 D. Comparison of the Variety of DC Source Voltages
The variety of dc sources is another important parameter that determines the cost of multilevel inverters.
Fig. 17
shows the number of levels against the number of varieties of dc sources. The proposed topology and recommended topologies in
[14]

[18]
require the minimum variety of dc sources—less than that required by the CHB (trinary configuration). The proposed cascaded structure has less IGBTs and has the minimum of blocking voltages compared with other topologies. Based on all the aforementioned comparison, can conclude that with an even number of dc sources, the proposed topology requires few IGBTs, achieves the minimum gate driver, has low blocking voltage and low dc source variety, and achieves the maximum output voltage level.
Comparison of number of levels and number of dc source voltage varieties.
Using (31), all the parameters are compared with similar topologies and found that the cost of the proposed topology is lower than the cost of the other typologies.
VI. SIMULATION AND EXPERIMENTAL RESULTS
To analyze the performance of the recommended cascaded structures, the simulation and experimental results for a 41level topology is presented and the results are analyzed.
For both simulations (which were performed using MATLAB–Simulink) and the hardware test, load values were set at R=100 Ω and L =100 mH, with an output frequency of 50 Hz. Several modulation strategies have been introduced for multilevel inverters including the sinusoidal Pulse Width Modulation (SPWM)
[23]
,
[24]
, space vector PWM
[25]
, selective harmonic elimination
[26]
, hybrid modulation
[27]
, hysteresis modulation
[28]
, and fundamental frequency switching
[29]
. For the recommended structure, the fundamental switching method is implemented because low switching frequency (nearest level control method, or NLM) is preferable for high power applications
[30]
, as shown in
Fig. 18
. The nearest level of the constant is compared with the reference signal; and appropriate pulses are generated.
Nearest level selection. (a) Level synthesis. (b) Control diagram.
Used herein is the conventional NLM, which generates steps using the basic concept of the roundingoff technique, as shown in
Fig. 18
(b). This method is suitable for the increased number of output voltage levels. This method is easily performed using the round {} function and the integer closest to x. As an additional convention, given that this method is similar to the halfheight method, halfintegers are always roundedoff to the nearest integer numbers. The largest possible error is then limited by
Vdc/2
[31]
. To analyze the performance of any new multilevel converter, consider the major index is total harmonic distortion (THD), which can calculate the quantity of harmonics presented in the output waveform.
In general, the THD can be calculated as follows:
In (38),
h
(odd order of harmonics) =3, 5, 7, … and
V_{o1}
is the fundamental output voltage of
V_{ohn}
order harmonic; and
V_{o,rms}
is the
rms
value of the output voltage. The magnitude of
V_{o1}
and
V_{o,rms}
can be calculated using the following:
where
θ_{1}, θ_{2,}, …θ_{NLevel}
are switching angles and are calculated as
For reducing voltage spikes and for limiting
dv/dt
(voltage stress across the switches), snubber circuits are preferable. In this paper, the required voltage rating of the level generator unit switches is low because separate dc sources are connected with series/parallel switches. The Hbridge unit (polarity changer), however, should withstand the sum of the all the dc source voltages present in the level generator. Thus, in the process of designing the proposed multilevel inverter, high voltage rating of a snubber circuit to be designed. Different snubber circuits are presented in
[32]
; the basic RC snubber circuit is suitable for the level generator (in low voltage switches) because the RC dissipates much current due to the nature of the resistor, and because a RCD snubber clamp circuit is suitable for the Hbridge side (in high voltage switches). The losses in a RCD snubber clamp circuit are low, but this type of circuit may require many components. Nonetheless, the prototype model described in this paper is developed using a RC snubber circuit.
 E. 49Levels of the Proposed Cascaded Topology
Shown in
Figs. 19
and
20
are the proposed cascaded structure of a 49level inverter circuit diagram and the output results, respectively. As discussed, the maximum output voltage is generated by Algorithm7, causing this algorithm to be implemented in the hardware experiment. The control fundamental switching technique is implemented in a FPGA Spartan XE3S250E controller. To implement the 49level proposed cascaded inverter with 6 dc voltage sources, 16 IGBTs (BUP400D) and 12 IGBT drivers (HCPL316j) are used. In the present structure, each source is connected with a series/parallel switch.
49level inverter based on the proposed topology for k=2 and n=3.
Simulation and experimental results of 49level submultilevel inverter. (a) Simulation output voltage and current waveforms, respectively. (b) Experimental output voltage and current waveforms, respectively.
Parameters, like magnitudes of the dc source voltages and load values, in the simulation and in the experiment are the same. The dc source magnitudes,
4 V
for
k=1
and
28 V
for
k
=2, and these input sources are provided through stepdown transformers, along with a rectifier and a voltage regulator unit. The maximum output voltage is 96 V and the load values are
R=100
Ω and
L=100 mH
. Shown in
Figs. 20
(a) and (b) are the experimental voltage and current waveforms with THDs of 1.98% and 1.478%, respectively, which are based on the load parameters. These results are close to the simulation voltage and current waveforms (as shown in
Fig. 19
(a)) with THDs of 1.65% and 0.58%, respectively. As the number of levels increases, both voltage and current THDs are reduced using fundamental switching techniques. The high inductive load is used, acting as a filter; the load and current becomes close to a sinusoidal waveform. The blocked voltage of each switch (both
V_{dc}
and 2
V_{dc}
switches) in the level generator unit and the Hbridge unit switches are presented in
Fig. 21
; a photograph of the hardware used in the laboratory as prototype inverter model is shown in
Fig. 22
.
Experimental blocking voltage of different switches for 49level sub multilevel inverter. (a) First submultilevel inverter hbridge switches. (b) First submultilevel inverter level generator switches. (c) Second submultilevel inverter Hbridge switches.
Prototype hardware.
The switching mechanism for the unidirectional switches is shown in
Fig. 23
.
Gate driver circuit and switching mechanism for switch (S_{j} &P_{j} ).
These circuits consist of an optoisolator (for isolating the switch from the controller (FPGA)), a Schmitt trigger (used to convert analog signal to digital pulses), and a buffer. Optoisolators can work with a wide range of input signal pulse widths, but a separate, isolated power supply is required for each switching device. For isolation, either a pulse transformer or optoisolators can be used. The optoisolatorbased driver is used in this prototype model.
VII. CONCLUSION
New symmetric cascade multilevel inverter structures are proposed. The maximum number of output voltage is obtained with minimal IGBTs and reduced dc voltage sources. Various new algorithms are provided to generate even and odd stepped waveforms. The proposed topology requires few power electronics components and costs less than other topologies. The best algorithms are selected and optimized for different goals such as the maximum number of output voltage levels for the minimum number of IGBTs, gate driver circuits, blocking voltage, and reduced dc sources. The proposed symmetric cascaded structure inverter is suitable for medium and highvoltage applications. The cascaded structure is verified by simulation and experimental results. To ensure a dynamic response of the proposed topology, and to serve as future work, we shall conduct a study related to industrial drives or FACTS device applications.
BIO
Jagabar Sathik Mohd. Ali was born in Madukkur, Tamil Nadu, India, in 1979. He received an undergraduate degree in electronics and communication engineering from Madurai Kamaraj University, Madurai, India, in 2002, and a Master’s degree in power electronics and drives from Anna University, Chennai, India, in 2004. He is currently working toward a Ph.D. degree from the Faculty of Electrical Engineering, Anna University, India. In 2011, he joined the Department of Electrical and Electronics Engineering, J.J. College of Engineering and Technology, Tiruchirappalli, India. His major areas of interest include analysis and control of power electronic converters and renewable energy systems.
Ramani Kannan was born in Vedaranyam in 1982. He graduated from Bharathiar University, Coimbatore, in 2004, and postgraduated from Anna University, Chennai, in 2006. He obtained a Ph.D. degree in electrical engineering from Anna University in 2012. Since January 2006, he has worked as an associate professor at the Department of EEE, K. S. Rangasamy College of Technology, Tiruchengode. He has 56 published works in international/national conferences and journals. His research interests involve power electronics, inverters, modeling of induction motors, and optimization techniques. He currently guides undergraduate and postgraduate Students and supervises Ph.D. scholars in Anna University. He is a member of the ISTE, IETE, and IEEE and has received the CAYT award from AICTE, New Delhi. He is currently part of many editorial boards and acts as editorinchief of international journals and IEEE Conferences.
Rodriguez J.
,
Lai J.S.
,
Peng F. Z.
2002
“Multilevel inverters: A survey of topologies, controls, and applications,”
IEEE Trans. Ind. Electron
t
49
(4)
724 
738
DOI : 10.1109/TIE.2002.801052
Tolbert L. M.
,
Peng F. Z.
,
Habetler T. G.
1999
“Multilevel converters for large electric drives,”
IEEE Trans. Ind. Appl.
35
(1)
36 
44
DOI : 10.1109/28.740843
Franquelo L. G.
,
Rodriguez J.
,
Leon J. I.
,
Kouro S.
,
Portillo R.
,
Prats M. A. M.
2008
“The age of multilevel converters arrives,”
IEEE Ind. Electron. Mag.
2
(2)
28 
39
DOI : 10.1109/MIE.2008.923519
Choi N. S.
,
Cho J. G.
,
Cho G. H.
“A general circuit topology of multilevel inverter,”
Power Electronics Specialists Conference, 1991. PESC '91 Record., 22nd Annual IEEE
Jun.1991
96 
103
Tehrani K. A.
,
Rasoanarivo I.
,
Sargos F.M.
2011
“Power loss calculation in two different multilevel inverter models (2DM2),”
Electric Power Systems Research
81
(2)
297 
307
DOI : 10.1016/j.epsr.2010.09.005
Gerçk C. O.
,
Ermis M.
2014
“Elimination of coupling transformer core saturation in cascaded multilevel converterbased TSTATCOM systems,”
IEEE Trans. Power Electron.
29
(12)
6798 
6809
Bhattacharya S.
,
Mascarella D.
,
Joó G.
“Modular multilevel inverter: A study for automotive applications,”
Electrical and Computer Engineering (CCECE), 2013 26th Annual IEEE Canadian Conference on
2013
1 
6
Stala R.
2013
“A natural DClink voltage balancing of diodeclamped inverters in parallel systems,”
IEEE Trans. Ind. Electron.
60
(11)
5008 
5018
DOI : 10.1109/TIE.2012.2219839
Lai J.S.
,
Peng F. Z.
1996
“Multilevel convertersa new breed of power converters,”
IEEE Trans. Ind. Appl.
32
(3)
509 
517
DOI : 10.1109/28.502161
McGrath B. P.
,
Holmes D. G.
,
Kong W. Y.
2014
“A decentralized controller architecture for a cascaded hbridge multilevel converter,”
IEEE Trans. Ind. Electron.
61
(3)
1169 
1178
DOI : 10.1109/TIE.2013.2261032
Bose B. K.
2009
“Power electronics and motor drives recent progress and perspective,”
IEEE Trans. Ind. Electron.
56
(2)
581 
588
DOI : 10.1109/TIE.2008.2002726
Jimenez O. L.
,
Vargas R. A.
,
Aguayo J.
,
Arau J. E.
,
Vela G.
,
Claudio A.
“THD in cascade multilevel inverter symmetric and asymmetric,”
Electronics, Robotics and Automotive Mechanics Conference (CERMA)
2011
289 
295
Malinowski M.
,
Gopakumar K.
,
Rodriguez J.
,
Péez M. A.
2010
“A survey on cascaded multilevel inverters,”
IEEE Trans. Ind. Electron
57
(7)
2197 
2206
DOI : 10.1109/TIE.2009.2030767
Ebrahimi J.
,
Babaei E.
,
Gharehpetian G. B.
2011
“A new topology of cascaded multilevel converters with reduced number of components for highvoltage applications,”
IEEE Trans. Power Electron.
26
(11)
3109 
3118
DOI : 10.1109/TPEL.2011.2148177
Alishah R. S.
,
Nazarpour D.
,
Hosseini S. H.
,
Sabahi M.
2015
“Reduction of power electronic elements in multilevel converters using a new cascade structure,”
IEEE Trans. Ind. Electron.
62
(1)
256 
269
DOI : 10.1109/TIE.2014.2331012
Babaei E.
,
Dehqan A.
,
Sabahi M.
2013
“A new topology for multilevel inverter considering its optimal structures,”
Electric Power Systems Research
103
145 
156
DOI : 10.1016/j.epsr.2013.06.001
Ebrahimi J.
,
Babaei E.
,
Gharehpetian G. B.
2012
“a new multilevel converter topology with reduced number of power electronic components,”
IEEE Trans. Ind. Electron.
59
(2)
655 
667
DOI : 10.1109/TIE.2011.2151813
Alishah R. Shalchi
,
Nazarpour D.
,
Hosseini S. H.
,
Sabahi M.
2014
“Novel topologies for symmetric, asymmetric, and cascade switcheddiode multilevel converter with minimum number of power electronic components,”
IEEE Trans. Ind. Electron.
61
(10)
5300 
5310
DOI : 10.1109/TIE.2013.2297300
Ramani K.
,
Sathik M. A. J.
,
Sivakumar S.
2015
“A new symmetric multilevel inverter topology using single and double source submultilevel inverters,”
Journal of Power Electronics
15
(1)
96 
105
DOI : 10.6113/JPE.2015.15.1.96
Karuppusamy P.
,
Natarajan A. M.
2015
“An adaptive neurofuzzy model to multilevel inverter for grid connected photovoltaic system,”
Journal of Circuits, Systems and Computers
24
(5)
DOI : 10.1142/S0218126615500668
Taghvaee M. H.
,
Radzi M. A. M.
,
Moosavain S. M.
,
Hizam H.
,
Marhaban M. H.
2013
“A current and future study on nonisolated DC–DC converters for photovoltaic applications,”
Renewable and Sustainable Energy Reviews
17
216 
227
DOI : 10.1016/j.rser.2012.09.023
McGrath B. P.
,
Holmes D. G.
2002
“Multicarrier PWM strategies for multilevel inverters,”
IEEE Trans. Ind. Electron
49
(4)
858 
867
DOI : 10.1109/TIE.2002.801073
Ghias A. M. Y. M.
,
Pou J.
,
Agelidis V. G.
,
Ciobotaru M.
2014
“Voltage balancing method for a flying capacitor multilevel converter using phase disposition PWM,”
IEEE Trans. Ind. Electron.
61
(12)
6538 
6546
DOI : 10.1109/TIE.2014.2320216
Aneesh M. A. S.
,
Gopinath A.
,
Baiju M. R.
2009
“A simple space vector PWM generation scheme for any general level inverter,”
IEEE Trans. Ind. Electron.
56
(5)
1649 
1656
DOI : 10.1109/TIE.2008.2011337
Buccella C.
,
Cecati C.
,
Cimoroni M. G.
,
Razi K.
2014
“Analytical method for pattern generation in fivelevel cascaded Hbridge inverter using selective harmonic elimination,”
IEEE Trans. Ind. Electron
61
(11)
5811 
5819
DOI : 10.1109/TIE.2014.2308163
Zaragoza J.
,
Pou J.
,
Ceballos S.
,
Robles E.
,
Ibaez P.
,
Villate J. L.
2009
“A comprehensive study of a hybrid modulation technique for the neutralpointclamped converter,”
IEEE Trans. Ind. Electron
56
(2)
294 
304
DOI : 10.1109/TIE.2008.2005132
Shukla A.
,
Ghosh A.
,
Joshi A.
2011
“Hysteresis modulation of multilevel inverters,”
IEEE Trans. Power Electron.
26
(5)
1396 
1409
DOI : 10.1109/TPEL.2010.2082001
Hu P.
,
Jiang D.
2015
“A levelincreased nearest level modulation method for modular multilevel converters,”
IEEE Trans. Power Electron.
30
(4)
1836 
1842
DOI : 10.1109/TPEL.2014.2325875
Du Z.
,
Tolbert L. M.
,
Ozpineci B.
,
Chiasson J. N.
2009
“Fundamental frequency switching strategies of a sevenlevel hybrid cascaded Hbridge multilevel inverter,”
IEEE Trans. Power Electron.
24
(1)
25 
33
DOI : 10.1109/TPEL.2008.2006678
Kouro S.
,
Bernal R.
,
Miranda H.
,
Silva C. A.
,
Rodriguez J.
2007
“Highperformance torque and flux control for multilevel inverter fed induction motors,”
IEEE Trans. Power Electron.
22
(6)
2116 
2123
DOI : 10.1109/TPEL.2007.909189
Zhang Y.
,
Sobhani S.
,
Chokhawala R.
1995
Snubber Considerations for IGBT Applications
Application Note International Rectifier
1 
9