DESIGN OF CASCADED NINE LEVEL
ASYMMETRICAL H-BRIDGE INVERTER
USING CARRIER BASED PWM
S.Kalaivani1 K.Kavinelavu2 S.Kanimozhi
1,2,3
PG Student, Department of EEE
Sri Manakula Vinayagar Engineering College, Pondicherry – 605107, India.
E-mail: kalaivani02dec@gmail.com
ABSTRACT
This paper presents the nine level asymmetrical cascaded
H-bridge multilevel inverter. Carrier based pulse width
modulation technique is used to improve the
performance of multilevel inverter. This proposed
inverter widely used in industrial applications such as
speed control of induction motor, brushless dc motor etc.
The proposed switching scheme reduces the switching
loss and total harmonic distortion (THD) and increase
the output level. The performance evaluation of the
proposed PWM technique for 9-level inverter is done
using MATLAB/SIMULINK software and THD is
determined by using FFT analysis.
Keywords: Multilevel inverters, Carrier based pulse
width modulation, THD, induction motor.
I.INTRODUCTION
Multilevel inverters are found in many applications
such as industrial motor drives, utility interfaces for
renewable energy systems ,flexible AC transmission
systems, high voltage direct current transmission and
traction drives systems[1-2]. Concept of a multilevel
inverter to achieve higher power is to use a series of
power semiconductor switches with several lower
voltage dc sources to perform the power conversion by
synthesizing a staircase voltage waveform. Capacitors,
batteries, and renewable energy voltage sources can be
used as the multiple dc voltage sources. Various
modulation methods are available for multilevel
inverter [3].In recent years, asymmetric multilevel
inverters have received increasing attention because it
is possible to synthesize voltage waveforms with
reduced harmonic content, even using a few seriesconnected cells. The number of voltage levels
increases, the harmonic content of the output voltage
decreases [4-7]. Increasing the number of voltage
levels in the inverter without requiring higher ratings
on individual devices can increases the power rating.
Now days, PWM techniques achieving more
importance in industrial applications and also used in
many applications uninterruptible power supplies,
induction heating, HVDC power transmission and
variable frequency drives[8].
II. PROPOSED MULTILEVEL INVERTER
A multilevel inverter works with the usage of several
levels of DC-voltages constructing a staircase formed
AC-voltage. Capacitors, batteries and renewable
energy sources can be used as the DC sources. The
advantage of this multilevel system is that it induces
good power quality, has good electromagnetic
compatibility, low switching losses and high
capability. Classifications of multilevel inverter are
given as follows: 1.Diode clamped 2.Flying capacitor
and 3.Cascaded H-bridge multilevel inverter.
Compared to inverter topologies, cascaded H-bridge
multilevel inverters have several advantages. The main
features of the asymmetrical cascaded inverter are as
follows:





Less number of components is required to
achieve the same number of voltage.
To reduce switching losses and device stress
Soft switching techniques can be used.
It requires the less number of components to
achieve the same number of voltage levels
when compared with the diode clamped and
flying capacitor inverters.
Connecting dc sources between two
converters in a back to back fashion is not
possible because short circuit can be
introduced when two back to back converters
are not switching synchronously.
Simple circuit layout and packaging are easy
because each level has the same structure
and there is no extra clamping diodes and
voltage balancing capacitors.
Fig 2.Circuit diagram for nine level inverter
Fig 1 .Structure of cascaded multilevel inverter
Circuit configuration of a Asymmetrical cascaded Hbridge multilevel inverter employing Trinary DC input
source shown in fig 2.By using Vdc and 3Vdc, it can
synthesize nine output levels; 0, Vdc, 2Vdc, 3Vdc,
4Vdc, -Vdc, -2Vdc, -3Vdc, -4Vdc. Here, the final
output voltage levels becomes the sum of each
terminal voltage of H-bridge, and it is given as
Vout = VHB1 + VHB2
(1)
In the proposed circuit topology, if n is number of
H-bridge module has independent DC sources in
sequence of the power of 3, an expected output voltage
level is given as
Vn = 3n , n = 1,2,3
(2)
Fig 3. Pulse pattern for nine level inverter
The pulses generated using the proposed modulation
technique is used to trigger the switches in a sequential
manner such that the desired output is obtained. The
gating pulse obtained in MATLAB/SIMULINK is
shown in Fig.3.
Vout
S1
S2
S3
S4
S5
S6
S7
S8
4Vdc
1
0
0
1
1
0
0
1
3Vdc
0
1
0
1
1
0
0
1
2Vdc
0
1
1
0
1
0
0
1
Vdc
1
0
0
1
0
1
0
1
0
0
1
0
1
0
1
0
1
-Vdc
0
1
1
0
0
1
0
1
-2Vdc
1
0
0
1
0
1
1
0
-3Vdc
0
1
0
1
0
1
1
0
-4Vdc
0
1
1
0
0
1
1
0
where,
Ar = Amplitude of reference signal
Ac = Amplitude of carrier signal
FREQUENCY MODULATION INDEX
In frequency modulation index, the modulation
index depends on the frequency of the reference signal
and the carrier signal used. The frequency modulation
index of the mf of the multilevel inverter can be
defined as
mf=fc/fr
(4)
where,
fc = frequency of carrier signal
fr = frequency of reference signal
Table1.conduction Sequence for Nine Level Inverter
The above table. 1 shows the conduction sequence for
the proposed 9 level inverter. Switching signal are
generated based on the conduction sequence.
III. CONTROL TECHNIQUES
IV.SIMULATION RESULTS
The Simulation of Symmetrical carrier based pulse
width modulation is carried out using MATLAB/
Simulink. It is shown in Fig .4
CARRIER BASED PULSE WIDTH
MODULATION
The most important and popular technique is carrier
based pulse-width-modulation (CBPWM). In carrier
based PWM gating signals are generated by
comparing a sinusoidal reference with triangular
carriers. The number of carriers used equal to (n-1)
where n is the number of levels. For an m-level
inverter, m-1 carriers with the same frequency fc and
the same amplitude Ac.
MODULATION INDEX
Modulation index can be classified into two types
 Amplitude modulation index
 Frequency modulation index
AMPLITUDE MODULATION INDEX
In amplitude modulation index, modulation index
depends on the amplitude of carrier signal and the
reference signal used. In general the value of
modulation index varies between 0 and 1. Amplitude
modulation index (ma) can be defined as
ma=Ar/Ac
(3)
Fig 4 .Simulation of symmetrical nine level inverter
The Simulink model of symmetrical nine level inverter
is shown in fig.4
The output voltage waveform and FFT analysis for
symmetrical nine level inverter is shown in Fig.5 and
Fig.6 respectively.
The output voltage waveform and FFT analysis for
Asymmetrical nine level inverter is shown in Fig.8
and Fig.9 respectively.
Fig 5. Output Voltage Waveform For Symmetrical
Nine Level Inverter
Fig 8.Output Voltage Waveform For Asymmetrical
Nine Level Inverter
Fig 6. FFT analysis for Symmetrical output voltage
Fig 9. FFT analysis for Asymmetrical output voltage
The Simulation of Asymmetrical carrier based pulse
width modulation is carried out using MATLAB/
Simulink. It is shown in Fig .7
TABLE 1.COMPARISON TABLE OF TOTAL
HARMONIC DISTORTION FOR OUTPUT
VOLTAGE
Modulation
Techniques
(CBPWM)
Number of
output
levels
Total
Harmonic
distortion for
voltage (%)
Symmetrical(1-phase)
9
15.63
Asymmetrical(1-phase)
9
13.17
Here, the THD values of single phase Symmetrical
and Asymmetrical techniques using carrier based pulse
width modulation for R load is shown in above
Table1. It can be seen that Asymmetrical nine level
inverter yields a better performance Symmetrical nine
level inverter.
Fig 7.Simulation of Asymmetrical nine level inverter
V. CONCLUSION
In Asymmetrical multilevel inverter topology the
output voltage yields nine level by using two Hbridges (8-switches).Therefore, in Symmetrical
multilevel inverter topology uses four H-bridges(16switches).Finally,the number of switches reduced in
asymmetrical multilevel inverter topology is compared
to symmetrical multilevel inverter with the same
number of output levels.The total harmonic
distortion(THD) is reduced in asymmetrical nine level
inverter when compared to symmetrical inverter.
The advantages of the proposed method are
summarized as:
1. Simple circuit configuration to produce
multilevel outputs by using Trinary input
sources.
2. It is suitable for high voltage application and
high power applications and easy to
implement in the hardware.
3. Reduced THD and EMI problem.
REFERENCES
[1] Fang
Zheng
Peng, Jih-Sheng Lai , And
Rodriguez-Multilevel inverter: A Survey of topologies
,controls and applications, Industrial Electronics, IEEE
Transactions,Volume:49, issue:4 :4.pp 724-738, Aug
2002 .
[2] R.Bharath, V.Arun, “9-Level Trinary DC Source
Inverter Using Embedded Controller” IOSR Journal of
Engineering (IOSRJEN) Volume 2, Issue: 10, October
2012,pp 90-95.
[3] K. Vinoth Kumar, Prawin Angel Michael, Joseph
P. John and Dr. S. Suresh Kumar,” Simulation and
Comparison Of Spwm and Svpwm for three phase
Inverter”, Arpn Journal of Engineering and Applied
Sciences, Volume:5, No.7,July 2010.
[4] Zhong Du , LeonM.Tolbert, JohnN.Chiasson and
Burak Ozpineci, “A Cascaded Multilevel Inverter
Using a Single DC Source” 2006 IEEE.
[5] Bharath. K, R.J.Satputaley,” Single Phase
Asymmetrical Cascaded Multilevel Inverter Design
For Induction Motor: International Journal Of
Electrical, Electronics and Data Communication,
ISSN: 2320-2084, Volume:1, Issue:3.
[6] G.Murali Krishna, V.V.N.Murthy, K.Lakshmi
Ganesh , “THD Analysis Of Symmetrical and
Asymmetrical Cascaded H-bridge Multilevel inverters
with PV Arrays “et al./IJAIR.
[7] Reza Salehi , Naeem Farokhnia, Mehrdad Abedi,
and Seyed Hamid Fathi, “ Elimination of Lower order
Harmonics in Multilevel Inverters using Genetic
Algorithm “ volume:11,No.2,March 2011.
[8] Preetha.S.L, J. Merry Geisa, “A New PWM
Generation Scheme For Multilevel Inverter “,
International Journal of Engineering Research and
Technology (IJERT), ISSN: 2278-0181, Volume:2
Issue:9.September-2013.
[9] Dhaval patel , Himanshu.N.Chaudhari,Hind
Chandwani, Anand Damle, “ Analysis And Simulation
Of Asymmetrical Type Multilevel Inverter Using
Optimization angle Control Technique” ISSN (print):
2278-8948, Volume-1,Issue:3.2012.
[10] J.Rodriguez, J.S.Lai,and, and, and F.Z.Zeng,Multilevel Inverters: A Survey Topologies ,Controls
andApplication,IEEETrans.Ind.Electron.,Volume:49,n
o.4, pp.724-738,August-2002.
[11] Muhammad H.Rashid, Power Electronics
Circuits, Devices and Applications, Prentice Hall, 2nd
Ed.
[12] B.K.Bose, Modern Power Electronic and AC
Drive. Upper Saddle River, Nj:Prentice-Hall,2002.