babae i 2014
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10.1109/TIE.2014.2336601, IEEE Transactions on Industrial ElectronicsIEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS
A Single-Phase Cascaded Multilevel Inverter
Based on a New Basic Unit with Reduced
Number of Power SwitchesEbrahim Babaei, Member, IEEE , Sara Laali, Student Member, IEEE , and Zahra Bayat
Abstract — In this paper, a new single-phase cascaded
multilevel inverter is proposed. This inverter is comprisedof series connection of the proposed basic unit and is able
to generate only positive levels at the output. Therefore,an H-bridge is added to the proposed inverter. This
inverter is called developed cascaded multilevel inverter.In order to generate all voltage levels (even and odd) atthe output of the developed topology, four different
algorithms are proposed to determine the magnitude ofdc voltage sources. Reduction in the number of power
switches, driver circuits and dc voltage sources areadvantages of the developed single-phase cascadedmultilevel inverter. As a result, the installation space and
cost of the inverter are reduced. These features are
obtained by the comparison of the conventional cascadedmultilevel inverters with the proposed cascaded topology.The ability of the proposed inverter in generation all
voltage levels (even and odd) is reconfirmed by using theexperimental results of a 15-level inverter.
Keywords — Cascaded multilevel inverter; basic unit; H-
bridge; developed cascaded multilevel inverter.
I. INTRODUCTION
The demand for high voltage, high power inverters are
increasing and it is impossible to connect a powersemiconductor switch to high voltage network directly.
Therefore, the multilevel inverters had been introduced
and are developing now. There are different kinds ofarray for power switches, diodes and dc voltage
sources to generate a desired ac output in multilevelinverters. With an increasing the number of dc voltage
sources in input side, the sinusoidal like waveform can
be generated at the output. As a result, the total
harmonic distortion (THD) decreases and the outputwaveform quality of the increases, which are two mainadvantages of the multilevel inverters. In addition,
lower switching losses, lower voltage stress of dv dt
on switches; high efficiency and better electromagnetic
interference are other most important advantages of the
multilevel inverters [1-5]. These kinds of inverters are
generally divided into three main categories; neutral
point (NPC) clamped multilevel inverter, flyingcapacitor (FC) multilevel inverter and cascaded
Manuscript received July 19, 2013; revised November 24, 2013
and February 26, 2014; accepted April 23, 2014.Copyright © 2014 IEEE. Personal use of this material is permitted.
However, permission to use this material for any other purposes must
be obtained from the IEEE by sending a request to pubs- [email protected]
The authors are with the Faculty of Electrical and Computer
Engineering, University of Tabriz, Tabriz, Iran (e-mails: e- babaei@tabr izu.ac.i r; s.laali@tabri zu.ac.ir;
multilevel inverter [6-9]. There is no diode clamped or
flying capacitors in cascaded multilevel inverters.
Moreover, these inverters consist of modularity, simplicity
of control and reliability and require lowest number of power semiconductor devices to generate a particular level
[1, 10-11]. As a result, the losses and total cost of theseinverters decrease and the efficiency will increase [12].Therefore, the cascaded multilevel inverter has received
more attentions. These inverters are comprised of series
connection of basic units, which consist of different array
of power switches and dc voltage sources. Generally, these
inverters divided into two main groups; symmetriccascaded multilevel inverter with the same amplitude of dc
voltage sources and asymmetric cascaded multilevelinverter. The asymmetric cascaded multilevel inverter
generates higher number of output levels in comparison
with symmetric one by same number of power electronicdevices because of different amplitude of its dc voltage
sources. As a result, the installation space and total cost ofan asymmetric cascaded multilevel inverter is lower than
symmetric one [11-12].Up to now, different basic units and so different cascaded
multilevel inverters have been presented in literature. In
[13-18], different symmetric cascaded multilevel invertershave been presented. It is also presented another topology
with two different algorithms as symmetric and
asymmetric one in [19]. The main disadvantages of the
symmetric cascaded multilevel inverters are the high-required number of power switches, insulated gate bipolartransistors (IGBTs), power diodes and driver circuits
because of the same magnitude of dc voltage sources.These disadvantages will be higher in topologies which
bidirectional power switches from voltage point of view
have been used in them that presented in [15] and [19].
Each unidirectional switch requires an IGBT with an anti parallel diode and a driver circuit while bidirectional one
includes of two numbers of IGBTs, two anti parallel
diodes and one driver circuit if common emitterconfiguration is used. However, both unidirectional and
bidirectional power switches conduct current in bothdirections. In order to increase the number of output
levels, the different asymmetric cascaded multilevelinverters have been presented in [12, 14, 19-20]. The maindisadvantages of these inverters are the high magnitude of
dc voltage sources.Although, different symmetric and asymmetric cascaded
multilevel inverters had been presented in literature but in
order to increase the number of generated output levels byusing lower number of power electronic devices, a new
basic unit is proposed in this paper. By series connection
of several proposed basic units, a new single-phase
cascaded multilevel inverter is proposed. Then, in order togenerate all positive and negative levels at the output, a H-
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bridge will be added to this inverter because the proposed inverter only generates positive levels at the
output. This inverter called developed proposedcascaded multilevel inverter. In order to generate all
voltage levels at the output, four different algorithmsare proposed. Several comparisons are also done
between the developed cascaded multilevel inverter
and its proposed algorithms with the conventional
cascaded multilevel inverters. Based on these
comparisons, the developed cascaded inverter requiresminimum number of power switches, IGBTs, power
diodes, driver circuits and dc voltage sources. Finally,
in order to investigate the capability of the developedcascaded multilevel inverter in generation all voltage
levels, the experimental results of a 15-level inverter
are used.
II. PROPOSED TOPOLOGY
Fig. 1 shows the proposed basic unit. As shown in Fig.
1, the proposed basic unit is comprised of three dcvoltage sources and five unidirectional power switches
from voltage point of view. The used dc voltagesources are insolated ones that are supplied by
renewable sources such as fuel cell, photovoltaic etc. In
the proposed structure, the power switches of2 4
( , )S S ,
1 3 4 5( , , , )S S S S and
1 2 3 5( , , , )S S S S should not be
turned on simultaneously to prevent the short circuit of
dc voltage sources. The turn on and off states of power
switches for the proposed basic unit are shown in TableI. As shown in Table I, the proposed basic unit is able
to generate three different levels of 0,1 3
V V and
1 2 3( )V V V at the output. It is important to note that
the basic unit is only able to generate positive levels at
the output.
Fig. 1. Proposed basic unit
TABLE I.
Permitted turn on and off states for switches in the proposed basic
unit
ov
Switches statestate
5S 4S 3S 2S 1S
0onoffoffoffoff1
1 3V V offononoffon2
1 2 3V V V offoffononon3
In order to increase the number of output voltage
levels, it is possible to connect n number of basic unit
in series. As this inverter is able to generate all voltage
levels except1
V , it is necessary to use of additional dc
voltage source with the amplitude of1
V and two
unidirectional switches from voltage point of view that
are connected in series with the proposed basic units.
The proposed single-phase cascaded multilevel inverterthat is able to generate all levels is shown in Fig. 2(a). In
this inverter, the power switches of1
S and2
S and dc
voltage source of1
V have been used to produce the lowest
output level. The amplitude of this dc voltage source is
considered1 dcV V (equal to minimum output level). The
output voltage level of each unit is indicated by,1o
v ,,2o
v ,
, ,o nv and ov . The output voltage level ( )ov of the
proposed cascaded multilevel inverter is equal to:
,1 ,2 ,( ) ( ) ( ) ( ) ( )o o o o n ov t v t v t v t v t (1)
The generated output voltage levels of the proposed
inverter ( )o
v based on off and on states of switches are
shown in Table II. As mentioned before and according toTable II, the proposed inverter that is shown in Fig. 2(a) is
only able to generate positive levels at the output.
Therefore, in order to produce positive and negative levels
at the output an H-bridge with four switches of1
T to4
T is
added to the proposed topology. This inverter is called
developed cascaded multilevel inverter and shown in Fig.2(b). If the switches of
1T and
4T are turned on, the load
voltage ( ) Lv is equal to ov and if the power switches of
2T and3T are turned on, the load voltage will be
ov .
For the proposed inverter, the number of switches
( ) switch
N and dc voltage sources ( ) source
N are given by
below equations, respectively:
65 n N switch (2)
13 n N source (3)
when n is the number of series connected basic units.
As the unidirectional power switches from voltage point of
view are used in the proposed cascaded multilevel
inverter, the number of power switches is equal to thenumbers of IGBTs, power diodes and driver circuits.
(a) (b)
Fig. 2. The cascaded multilevel inverter; (a) proposed topology; (b)
developed proposed topology
The other main parameter in calculation the total cost of
the inverter is the maximum amount of blocked voltage by
the switches. If the values of the blocked voltage byswitches are reduced, the total cost of the inverter
decreases [12]. In addition, this value has most importanteffect in selection the semiconductor devices because this
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value determines the voltage rating of required powerdevices. Therefore, in order to calculate this index, it is
necessary to consider the amount of the blockedvoltage by each of the switches. According to Fig. 2(b),
the values of the blocked voltage by switch1
S and2
S
are equal to:
1 2 1,1S S V V V (4)
1, 2, 3,
1, 3,2
j j j
S j S j
V V V
V V
(5)
4, 2, 2,S j S j jV V V (6)
5, 1, 2, 3,S j j j jV V V V (7)
1 2 3 4 ,maxT T T T oV V V V V (8)
where,maxo
V is the maximum amplitude of producible
output voltage.
Therefore, the maximum amount of the blockedvoltage in the proposed cascaded multilevel inverter
( )block V is equal to:
,
1
n
block block j block block,H
j
V V V V
(9)
In (9),,block j
V ,block V and
block,H V indicate the blocked
voltage by th j basic unit, additional dc voltage sources
and the use H-bridge, respectively.In the developed inverter, the number and the maximum
amplitude of generated output levels are based on thevalue of used dc voltage sources. In order to generate all
voltage levels in the developed cascaded multilevel
inverter, four different algorithms are proposed to
determine the magnitude of dc voltage sources. These proposed algorithms and all their parameters are calculated
and shown in Table III. According to the facts that the
magnitude of all proposed algorithm except the first oneare different, the proposed cascaded multilevel inverter
based on these algorithms is considered as asymmetriccascaded multilevel inverter. In addition, based on theequations of the maximum output voltage levels and the
maximum amplitude of it, it is clear that these values in
the asymmetric cascaded multilevel inverter are more than
symmetric one with the same number of used dc voltagesources and power switches.
TABLE II.
THE GENERATED OUTPUT VOLTAGE LEVELS ( )ov BASED ON OFF AND ON STATES OF POWER SWITCHES
ov 1S
2S 1,1S
2,1S 3,1S
4,1S 5,1S
1,2S 2,2S
3,2S 4,2S
5,2S 1,nS
2,nS 3,nS
4,nS 5,nS
0 off on off off off off on off off off off on off off off off on
1V on off off off off off on off off off off on off off off off on
1,1 3,1V V off on on off on on off off off off off on off off off off on
1,1 2,1 3,1V V V off on on on on off off off off off off on off off off off on
1,2 3,2V V off on off off off off on on off on on off off off off off on
1,2 2,2 3,2V V V off on off off off off on on on on off off off off off off on
1,1 1,2 1,3
2,1 2,3
V V V
V V
off on on on on off off on off on on off
off off off off on
1,1 1,2 1,3
2,1 2,2 2,3
V V V
V V V
off on on on on off off on on on off off off off off off on
1, 2, 3,1
( )n
j j j j
V V V
off on on on on off off on on on off off off off off off on
1,1 1, 2, 3,
1
( )n
j j j
j
V V V V
on off on on on off off on on on off off off off off off on
TABLE III.
THE PROPOSED ALGORITHMS AND THEIR RELATED PARAMETERS
Proposed algorithm Magnitude of dc voltage sources level N
,maxoV
block V
First proposed algorithm1( ) P
1, 2, 3, j j j dcV V V V
1, 2, , for j n 6 3n (3 1) dcn V (21 6) dcn V
Second proposed algorithm2
( ) P
1,1 2,1 3,1 dcV V V V
1, 2, 3,2
j j j dcV V V V
2, 3, , for j n
12 3n 6 2n (40 13)dc
n V
Third proposed algorithm3( ) P
1,1 2,1 3,1 dcV V V V
2
1, 2, 3,
13
3
j
j j j dcV V V V
2, 3, , for j n
15(3 ) 4
n
15(3 ) 3
2
n
dcV
1[82(3 ) 7]n
dcV
Fourth proposed algorithm4( ) P
1
1, 2, 3,0.5 2 j
j j j dcV V V V
1, 2, , for j n
32 5n 2(2 3)n
dcV 2[7(2 ) 22]n
dcV
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III. COMPARING THE PROPOSED TOPOLOGY
WITH THE CONVENTIONAL TOPOLOGIES
The main aim of introducing the developed cascaded
multilevel inverter is to increase the number of outputvoltage levels by using minimum number of power
electronic devices. Therefore, several comparisons are done between the developed proposed topology with the
conventional cascaded multilevel inverters that have been
presented in literature. Theses comparisons are done from
the number of IGBTs, driver circuits and dc voltage sources points of view. In addition, the maximum amount of blocked voltage by power switches is also compared
between proposed cascaded multilevel inverter and other presented topologies in references because of the effect of
this value in voltage rating of used power devices in
topologies. It is important to note that the voltage rating ofselected power switches is completely depended on the
structure of used basic unit of cascaded multilevel inverters
and the considered algorithm to determine the magnitude of
dc voltage sources. For instance, there are symmetric andasymmetric states for conventional H-bridge multilevelinverters, which in symmetric condition the voltage rating
of all used semiconductor devices in all bridges are same
but in asymmetric condition, these values are directlydepended on the selected algorithm to determine the
magnitude of dc voltage sources. However, in asymmetric
H-bridge cascaded multilevel inverter, the voltage rating ofdevices that are used in each bridge are same to each other
but these values are different to the voltage rating of
devices in other bridges. In this comparison, the proposedcascaded inverter that is shown in Fig. 2(b) with its
proposed algorithms is considered by1
P to4
P ,
respectively. In [13], a symmetric cascaded multilevel
inverter has been presented that is shown by1
R in this
comparison. The conventional cascaded multilevel inverter
has been presented in [14]. This inverter that is known as
symmetric one is considered by2
R . In addition, two other
algorithms have been presented for conventional H-bridgecascaded multilevel inverter in [12] and [20] that are
considered by3
R and4
R , respectively. In [15-17] three
other symmetric cascaded multilevel inverters have been
presented. These inverters are shown by5 7
R R ,
respectively. The other cascaded multilevel inverter withtwo different algorithms has been presented in [19]. This
inverter with its algorithms is presented by8
R and9
R ,
respectively. Another symmetric cascaded multilevelinverter that has been presented in [18] is considered by
10 R in this comparison. Fig. 3 indicates all of the above-
mentioned cascaded multilevel inverters.
(a) (b) (c)
(d) (e)
(f) (g)
Fig. 3. The cascaded multilevel inverters; (a) conventional cascaded
multilevel inverter 2 R for 1 2 n dcV V V V [14], 3 R for
1 2, 2dc n dcV V V V V [12], 4 R for
1 2, 3dc n dcV V V V V [20]; (b) presented topology in [17] 7 R
for 1 2 n dcV V V V ; (c) presented topology in [19] 8 R for
1 2 n dcV V V V , 9 R for 1 2, 2dc n dcV V V V V ; (d)
presented topology in [18] ( 10 R ); (e) presented topology in [16] 6 R for
1 2 n dcV V V V ; (f) presented topology in [15] 5 R for
1 2 n dcV V V V ; (g) presented topology in [13] 1 R for
1 2 n dcV V V V
Fig. 4 compares the number of IGBTs of the proposed
topology with the other above-mentioned cascaded
multilevel inverters. As it is obvious, the proposed inverterneeds lower number of IGBTs to generate a specific level.In addition, the fourth proposed algorithm has the best
performance between all of the proposed algorithms for thedeveloped cascaded inverter. However, in this comparison
the unidirectional power switches have been used in manyof the considered cascaded multilevel inverters. As
mentioned before, the number of used IGBts is equal to thenumber of power diodes. As a result, the number of
required power diodes in the fourth proposed algorithm ofthe developed topology is lower than other above-
mentioned inverters and their proposed algorithms.
Fig. 4. Variation of IGBT N versus level N
Fig. 5 indicates the comparison of the proposed cascaded
inverter with other above-mentioned topologies from thenumber of driver circuit point of view. As each switchrequires a separate driver circuit, the number of driver
circuit is equal to the number of power switches. Therefore,
this comparison is also indicates the number of required
power switches in the cascaded multilevel inverters. Asshown in Fig. 5, the number of driver circuit based on the
fourth proposed algorithm of the developed cascadedinverter is lower than other proposed algorithms for this
0 10 20 30 0 50 0 70 80 0 1 00
2 7 8, , R R R
1 R
9 R3 5 6
, R R R1
P
2 P 4
R
4 P
3 P
200
160
120
80
40
020 60 10040 80
IGBT N
level N
10 R
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inverter and other above-mentioned cascaded multilevel
inverters.
Fig. 5. Variation ofdriver N versus
level N
Fig. 6 compares the number of dc voltage sources of the proposed topology with the other above-mentioned
cascaded multilevel inverters. As it is obvious, the numberof required dc voltage sources in the developed cascaded
multilevel inverter is less than other presented multilevel
inverters in the literature. This difference will be higher
while the fourth proposed algorithm is considered todetermine the magnitude of dc voltage sources of the
proposed topology.
Fig. 6. Variation of source
N versuslevel
N
Fig. 7 compares the maximum amount of blocked voltage by power switches in the proposed topology with the other
above-mentioned cascaded multilevel inverters. It is pointed out that in this comparison
4 1 2, 3dc n dc R for V V V V V indicates other algorithms
for H-bridge cascaded multilevel inverters that is presentedin [20]. As it is obvious, this value in the proposed inverter
is less than other presented cascaded multilevel inverters
except the H-bridge cascaded multilevel inverter and
presented topologies by7
R and10
R . However, this is the
main disadvantage of the proposed cascaded inverter butthis inverter has different advantages in comparison to H-
bridge cascaded inverter and the presented topologies by
7 R and
10 R such as its required lower number of IGBTs,
driver circuits and dc voltage sources. It is point out that all
values are considered in per unit anddcV is used as the base
value in per unit system.
Fig. 7. Variation ofblock V versus
level N
As it is obvious from above comparisons, the proposeddeveloped cascaded multilevel inverter has best
performance between all of the above-mentioned multileveltopologies. Reduction in the number of required IGBts,
power diodes, driver circuit, dc voltage sources and the
amount of blocked voltage by power switches are
remarkable advantages of the proposed inverter that
obtained from comparisons. However, the maximum
amount of blocked voltage in the H-bridge cascaded
inverter and the presented inverter as 7 R is lower than this
value in the proposed cascaded inverter. These advantageslead to reduction in the installation space and total cost of
the inverter. These features will has most influence when
the fourth proposed algorithm is used to determine the
magnitude of dc voltage sources.Therefore, this inverter could be a suitable replacement of
the conventional cascaded multilevel inverters in many
applications such as drive and control of electricalmachines, connection of renewable sources, FACTS
devices etc.
IV. EXPERIMENTAL RESULTS
In order to clarify the correct performance of the developed
proposed inverter in generation a desired output voltagelevels, the experimental results have been used. The
number of required power electronic devices in the
proposed inverter is completely based on the selected
algorithm to determine the magnitude of dc voltage sourcesin generation specific number of output levels. For instance,
in order to generate minimum 49 levels at the output, the
numbers of required power switches and dc voltage sourcesand the maximum value of blocked voltage by switches
based on the first proposed algorithm are equal to
46 switch
N , 25 source
N , and 174block
V pu , while these
values based on the second proposed algorithm are equal to
31 switch
N , 16 source
N , and 187block
V pu . The third
proposed algorithm needs 21 switch
N , 10 source
N , and
731block V pu while the fourth proposed algorithm
requires the same number of power electronic devices but
its value of blocked voltage is 202block
V pu . It is
important to note that the proposed inverter based on thefourth algorithm this inverter is able to generate 59 levels at
the output. In this section, the investigations are done on a
cascaded multilevel inverter that is shown in Fig. 8. Thisinverter consists of two proposed basic units and one
additional series connected dc voltage sources that lead touse of seven numbers of dc voltage sources and twelve
unidirectional power switches. The first proposed algorithm
is considered to determine the magnitude of dc voltage
sources. In addition, the magnitude of dc voltage source is
considered 20dcV V . According to (5), this inverter is
able to generate 15 levels (seven positive levels, seven
negative levels and one zero level) with the maximum
amplitude of 140 V at the output. It is important to note thatthe used IGBTs on the prototype are BUP306D (with an
internal anti-parallel diode). The 89C52 microcontroller by
ATMEL Company has been used to generate all switching pattern. Each switch requires an isolated driver circuit. The
isolation can be provided using either pulse transformers or
opto-isolators. Opto-isolators can work in a wide range ofsignal pulse width, but a separate isolated power supply is
required for each switching device. The opto-isolator based
gate driver circuit has been used in prototype. In order to
switching, a determined data Table is used in offline. Thisswitching Table is supplied in the EPROM memory of the
microcontroller. By addressing the rows of the Table, the
0 10 2 0 30 0 50 0 70 80 90 100-5 0
0
500
0
5 0
0
5 0
0
5 0
0
80604020
3500
2500
1500
500
0 100
8 R6 R
9 R2 4 7, R R R
11 4 ,, P P R2 P
3 P
level N
[ ]block V pu
10 R
20
2 5 6 8 1 01, , , , R R R R R P
1 7, R R
2 P 3 9
, R R4
R3
P 4
P
0 20 8060 100level N 40
60
100
20
Source N
Drive N
level N
120
60 1008020 400
40
200
80
160
5 70
20
0
60
80
2 7, R R
1 R
10 R
3 6 8, , R R R
1 P
4 R
5 R
9 R
2 P
3 P
4 P
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information of the switches states are sent to the
microcontroller port. Therefore, there is no need to
sampling and the sampling frequency is not considered but
the reading frequency of the Table’s rows could be
regulated between 20kHz to 50kHz. As a result, to send theinformation of a period (at the main frequency of 50Hz)
with the time interval such as 40 sec , the rows of the
Table will be equal to 20000/40=500. It is obvious that inorder to send the information of the Table with 500 rows to
the output port, the high numbers of rows will be repeated.
In this condition, there is no problem because of the excitedcapacitance in the microcontroller. In all process of the
experimental performance, the load is assumed as a
resistive-inductive load ( ) R L with 70 R and
55 L mH . It is important to point out that the used control
method in this inverter is the fundamental control method.The main reason to select this control method is its low
switching frequency than other control methods that leads
to reduction in switching losses. Moreover, the calculations
of optimum switching angles to eliminate the selectiveharmonics and decrease the total harmonic distortion arenot the subject of this paper.
Fig. 8. Cascaded 15-level inverter based on the proposed basic unit
Fig. 9 shows the experimental results. As it is obvious fromthese figures, this inverter is only able to generate positive
levels at the output. Fig. 9(a) shows that the added dc
voltage source generates the minimum magnitude of outputlevels that is equal to lower value of used dc voltage
sources. Fig. 9(b) and Fig. 9(c) indicate that each unit
generates the output voltage levels of zero, 40V and 60V.
By adding an H-bridge, this inverter is able to generate all positive and negative levels at the output. Fig. 10 shows the
waveforms of load voltage and current. As shown in Fig.10, this inverter generates a step waveform with 15 levels
and maximum amplitude of 140 V. By comparing the
current and voltage waveforms, it is clear that the currentwaveform is near to ideal sinusoidal waveform and consists
of a phase shift in comparison to the load voltage. These
differences are because of resistive-inductive load featurethat used for proposed inverter. The resistive- inductive
load acts as a low pass filter.As mentioned, the used power switches on the developed
cascaded multilevel inverter are as unidirectional ones fromvoltage points of view, so in order to verify this fact the
voltage on switches1
S ,1,1
S ,2,1
S ,3,1
S and4,1
S of the first
proposed unit are indicated in Fig. 11, respectively. It is
noticeable that the waveforms of voltage across2
S and
5,1S are same asov and
,1ov , respectively. As shown in
these figures, the magnitude of the blocked voltages onswitches are either positive or zero and there is any
negative amount on them. This fact reconfirms the existingof unidirectional power switches in this topology.
The frequency of the final output is not exactly 50Hz
because a little delay is happened for selecting and sending
the information of each row in EPROM memory of the
microcontroller to the output port. The total delays for 500
rows lead to small difference between the output frequencyand the main frequency of 50Hz. It is important to note that
it is possible to get exactly the desired output frequency ifthe delay time of the microcontroller is considered in
calculations.
(a) (b)
(c) (d)
Fig. 9. Output voltage waveforms of each unit; (a)ov ; (b)
,1ov ; (c),2ov ;
(d)ov
Fig. 10 Waveforms of load voltage and current
(a) (b)
(c) (d)
(e)
Fig. 11. The voltage on switches; (a)1S ; (b)
1,1S ; (c)2,1S ; (d)
3,1S ; (e)
4,1S
V. CONCLUSION
In this paper, a new basic unit for cascaded multilevel
inverter is proposed. By series connection of several basic
units, a cascaded multilevel inverter is proposed that only
generates positive levels at the output. Therefore, a H-
2.5ms
10V
2.5ms
10V
2.5ms
10V
2.5ms
10V
10V
2.5 ms
7/25/2019 Babae i 2014
http://slidepdf.com/reader/full/babae-i-2014 7/70278-0046 (c) 2013 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See
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10.1109/TIE.2014.2336601, IEEE Transactions on Industrial ElectronicsIEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS
bridge is added to the proposed inverter to generate all
voltage levels. This inverter is called developed cascaded
multilevel inverter. In order to generate even and odd
voltage levels at the output, four different algorithms are
proposed to determine the magnitude of dc voltage sources.Then, several comparisons are done between the developed
proposed single-phase cascaded inverter and its proposedalgorithms with cascaded multilevel inverters that have
been proposed in literature. According to these
comparisons, the developed proposed cascaded topology
requires less number of IGBTs, power diodes, drivercircuits and dc voltage sources than other presentedcascaded topologies in literature. These features will be
remarkable while the fourth proposed algorithm is used forthe developed cascaded inverter. For instance, in order to
generate minimum 63 levels at the output, the developed
cascaded topology based on the fourth proposed algorithmneeds 19 numbers of power diodes, IGBTs and driver
circuits and 10 numbers of dc voltage sources. However,
the cascaded multilevel inverter that presented in [20]
requires 44 numbers of power diodes, IGBTs and drivercircuits and 11 numbers of dc voltage sources. Therefore,the developed proposed inverter has better performance and
needs minimum number of power electronic devices that
lead to reduction the installation space and total cost of theinverter. Finally, the accuracy performance of the
developed proposed single-phase cascaded multilevel
inverter in generation all voltage levels is verified by usingthe experimental results on a 15-level inverter.
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Ebrahim Babaei (M’2010) was born in Ahar,
Iran, in 1970. He received his B.S. and M.S.
degrees in Electrical Engineering from the
Department of Engineering, University of Tabriz,
Tabriz, Iran, in 1992 and 2001, respectively,
graduating with first class honors. He received his
Ph.D. degree in Electrical Engineering from the
Department of Electrical and Computer
Engineering, University of Tabriz, in 2007. In
2004, he joined the Faculty of Electrical and
Computer Engineering, University of Tabriz. He was an Assistant
Professor from 2007 to 2011 and has been an Associate Professor since
2011. He is the author of more than 280 j ournal and conference papers. He
also holds 17 patents in the area of power electronics and has more
applications pending. Dr. Babaei has been the Editor-in-Chief of the
Journal of Electrical Engineering of the University of Tabriz, since 2013.
In 2013, he was the recipient of the Best Researcher Award from of the
University of Tabirz. His current research interests include the analysisand control of power electronic converters and their applications, power
system transients, and power system dynamics.
Sara Laali (SM’2012) was born in Tehran, Iran,in 1984. She received her B.S. degree in
Electronics Engineering from the Islamic Azad
University, Tabriz Branch, Tabriz, Iran, in 2008,and her M.S. degree in Electrical Engineering
from the Islamic Azad University, South Tehran
Branch, Tehran, Iran, in 2010. In 2010, she
joined the Department of El ectrical Engineering,Adiban Higher Education Institute, Garmsar,
Iran. She is presently pursuing her Ph.D. degree
in Electrical Engineering with the faculty ofElectrical and Computer Engineering, University of Tabriz, Tabriz, Iran.
Her current research interests include the analysis and control of power
electronic converters, multilevel converters, and FACTS devices.
Zahra Bayat was born in Zanjan, Iran, in 1983.
She received her B.S. and M.S. in Electrical
Engineering from the Department of Engineering,University of Zanjan, Iran in 2006 and Islamic
Azad University, Ahar Branch, Ahar, Iran in 2011,
respectively. She has been a Lecturer at Islamic
Azad University, Zanjan Branch, Zanjan, Iran. Her
current research interests include the analysis and
control of power electronic converters.