1. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
– 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME
181
COMPARISON OF MODULATION TECHNIQUES FOR CASCADED
H-BRIDGE TYPE MULTILEVEL CURRENT SOURCE INVERTER
Vinesh Kapadia1
and Dr. Hina Chandwani2
1
Research Scholar at CHARUSAT, Changa, Gujarat & Associate Prof. Dept of E.C.,
SNPIT & RC, Umrakh, Bardoli, Gujarat, India
2
Associate Professor, Dept of Electrical Engineering, The M.S.University of Baroda,
Vadodara, India
ABSTRACT
This paper presents a comparison of the different modulation techniques for a single
phase five level cascaded h-bridge (CHB) type multilevel current source inverter. Majority
of the multilevel inverters are voltage sourced based. The popular carrier based PWM
switching techniques for MVSI are the phase shifted and level shifted modulation
techniques, the same techniques are tried out for the MCSI along with Selective Harmonic
Elimination method using angle control and the results have been presented.
Index Terms: APOD, CHB, IPD, Multilevel Current Source Inverter (MCSI), Multilevel
Voltage Source Inverter (MVSI), POD, PWM, THD.
I. INTRODUCTION
MULTILEVEL voltage source inverters are very common and now in wide use.
Compared to two-level inverters, multilevel inverters have advantages for higher power
applications, including reduced harmonics and reduced switching device voltage and
current stresses. The CSIs have some advantages over VSIs such as more stable operating
conditions, direct control of the output current, faster dynamic response (in some cases) and
easier fault management [1]. In this paper a single phase five level MCSI with symmetric
DC current sources is simulated with popular Multilevel Modulation techniques and results
are compared with respect to total harmonic distortion (THD).
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN
ENGINEERING AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 4, Issue 2 March – April 2013, pp. 181-190
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2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
– 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME
182
II. THE POWER CIRCUIT DIAGRAM
Shown below is the circuit for 5 level single phase MCSI along with the switching table
TABLE I
Switching Combination for the 5 level MCSI
Fig-1 Circuit Diagram of the 5 level CHB MCSI
The above table shows one of the possible combinations for obtaining the desired current
amplitudes.
Current Amplitude “ON” Switches
0 S11, S12, S21, S22
I S11, S14, S21, S22
2I S11, S14, S21, S24
-I S12, S13, S23, S24
-2I S12, S13, S23, S22

3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
– 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME
183
III. MODULATION TECHNIQUES
A. Angle Control Method (Selective Harmonic Elimination)
By proper selection of the firing (displacement angles α ) angles it is possible to try
and eliminate or say minimize those particular harmonics.
The fourier series for unipolar output voltages per half cycle can be expressed as (due to
symmetry):
vo = ∑ ‫ܤ‬௡ sin ݊߱‫ݐ‬∞
௡ୀଵ,ଷ,ହ,..
Bn =
ସ௏ೞ
௡గ
ሾ 1 ൅ ∑ ሺെ1ሻ௞௠
௞ୀଵ cosሺ݊ߙ௞ሻሿ ݂‫ݎ݋‬ ݊ െ 1,3,5, …
Where ߙଵ ൏ ߙଶ … ൏ ߙ௞ ൏
గ
ଶ
The third and fifth harmonics would be eliminated if
1 - cos 3ఈଵ ൅ cos 3ఈଶ ൌ 0
1 - cos 5ఈଵ ൅ cos 5ఈଶ ൌ 0
[2]-[3] Assuming and initial value of α1 = 0 and calculating in an iterative manner till the
results become stable we get;
Initial Values α1= 0 , hence
α2 = 0.52359
1st
Iteration α1= 0.28728
α2 = 0.64242
2nd
Iteration α1= 0.31366
α2 = 0.66478
3rd
Iteration α1= 0.31084
α2 = 0.66229
4th
Iteration α1= 0.31127
α2 = 0.66268
5th
Iteration α1= 0.31121
α2 = 0.66262
6th
Iteration α1= 0.31122
α2 = 0.66263
The values are radians , hence in degrees, α1= 17.831o
and α2= 37.966 o
.

4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
– 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME
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Fig-2 Output Current Waveform of the 5 level MCSI with Angle Control Method
Fig-3 Harmonic Spectrum of the 5 level MCSI with Angle Control Method
B. Carrier Based PWM Schemes
The carrier-based modulation schemes for multilevel inverters can be generally
classified into two categories: phase-shifted and level-shifted modulations. Both the
techniques have been applied
1. Phase Shifted Multicarrier Modulation
In general, a multilevel inverter with m voltage levels requires (m – 1) triangular carriers. In
the phase-shifted multicarrier modulation, all the triangular carriers have the same
frequency and the same peak-to-peak amplitude, but there is a phase shift between any two
adjacent carrier waves, given by
Øcr = 360°/(m – 1) [4]-[7]
Fig-4 Triangular Carriers compared with Reference Sine
0 100 200 300 400 500 600 700 800 900 1000
0
2
4
6
8
10
12
Frequency (Hz)
Fundamental (50Hz) = 1.108 , THD= 18.22%
Mag(%ofFundamental)

5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
– 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME
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Fig-5 Output Current Waveform of the 5 level MCSI with Phase Shifted MultiCarrier
Modulation
Fig-6 Harmonic Spectrum of the 5 level MCSI with Phase Shifted MultiCarrier Modulation
2. Level Shifted Carrier Modulation Schemes
Similar to the phase-shifted modulation, an m-level Cascaded H-Bridge inverter using
level-shifted multicarrier modulation scheme requires (m – 1) triangular carriers, all having
the same frequency and amplitude. The (m – 1) triangular carriers are vertically disposed
such that the bands they occupy are contiguous. The frequency modulation index is given
by mf = fcr/fm, which remains the same as that for the phase-shifted modulation scheme
whereas the amplitude modulation index is defined as
ma =
௏೘
^
௏೎ೝ
^ ሺ௠ିଵሻ
for 0 < ma < 1
(in our case m = 5) where ܸ௠
^
is the peak amplitude of the modulating wave Vm and ܸ௖௥
^
is
the peak amplitude of each carrier wave.
Here three schemes for the level-shifted multicarrier modulation are simulated (a) in-phase
disposition (IPD), where all carriers are in phase; (b) alternative phase opposite disposition
(APOD), where all carriers are alternatively in opposite disposition; and (c) phase opposite
disposition (POD), where all carriers above the zero reference are in phase but in opposition
with those below the zero reference [4]-[7].
0 100 200 300 400 500 600 700 800 900 1000
0
0.05
0.1
0.15
Frequency (Hz)
Fundamental (50Hz) = 0.9998 , THD= 2.92%
Mag(%ofFundamental)

6. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
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(a) IPD :
Fig-7 Triangular Carriers compared with Reference Sine for IPD Modulation
Fig-8 Output Current Waveform of the 5 level MCSI with IPD Modulation
Fig-9 Harmonic Spectrum of the 5 level MCSI with IPD Modulation
0 100 200 300 400 500 600 700 800 900 1000
0
2
4
6
8
10
12
14
16
18
Frequency (Hz)
Fundamental (50Hz) = 1 , THD= 2.80%
Mag(%ofFundamental)

7. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
– 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME
187
(b) APOD :
Fig-10 Triangular Carriers compared with Reference Sine for APOD Modulation
Fig-11Output Current Waveform of the 5 level MCSI with IPD Modulation
Fig-12 Harmonic Spectrum of the 5 level MCSI with IPD Modulation

8. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
– 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME
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(c) POD :
Fig-13 Triangular Carriers compared with Reference Sine for POD Modulation
Fig-14 Output Current Waveform of the 5 level MCSI with POD Modulation
Fig-15 Harmonic Spectrum of the 5 level MCSI with POD Modulation
0 100 200 300 400 500 600 700 800 900 1000
0
1
2
3
4
5
6
7
8
9
10
Frequency (Hz)
Fundamental (50Hz) = 1 , THD= 2.70%
Mag(%ofFundamental)

9. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
– 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 2, March – April (2013), © IAEME
189
Fig-16 Circuit Diagram of the 5 level CHB MVSI
IV. RESULT
Repeating the simulations with different frequencies for lowest THD has been done
and then the modulation index ( M.I.) has been varied to further reduce the THD , the
optimum frequency and modulation index in each case was found to be 900Hz and 1(for
phase shifted multicarrier) and 0.25 (for level shifted ) respectively. The same cases were
also tried out for a similar 5 level CHB MVSI (figure 16 shown above [8]-[9]) , the THD
for each modulation technique is as follows :
TABLE II
THD (%) Results for Different Modulation Techniques for both MVSI and MCSI
Modulation Technique MVSI MCSI
Angle Control Method 18.30 18.22
Phase Shifted Multicarrier 2.99 2.92
IPD 2.82 2.8
APOD 2.90 2.88
POD 2.72 2.7

10. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
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V. CONCLUSION
It is concluded that for such a 5 level MCSI in CHB configuration for both the
MVSI and MCSI the results are very similar moreover the prominent multilevel inverter
modulation topologies (i.e., Phase shifted multicarrier, IPD, APOD and POD) are also
giving similar results a minimum THD of 2.7 % has been obtained using the POD
modulation scheme in both the MVSI and MCSI cases.
VI. REFERENCES
[1] Jian-yu Bao, Wei-bing Bao and Zhong-chao Zhang, “High Generalized multilevel
current source inverter topology with self-balancing current” , Journal of Zhejiang
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1869-196X (Online), 2010,pp. 555-561.
[2] Muhammad H. Rashid, “Power Electronics Circuits, Devices and Applications”,
Pearson Seventh Impression, 2009, pp. 280-282.
[3] Jagdish Kumar, Biswarup Das, Senior Member, IEEE, and Pramod Agarwal,
“Selective Harmonic Elimination Technique for a Multilevel Inverter”, Fifteenth
National Power Systems Conference (NPSC), IIT Bombay, December 2008.
[4] Bin Wu, “High-Power Converters and ac Drives” ,The Institute of Electrical and
Electronics Engineers, Published by John Wiley & Sons Inc, 2006.
[5] Ilhami Colak, Ersan Kabalci and Ramazan Bayindir “A Review of multilevel voltage
source inverter topologies and control schemes” Energy Conversion and Management,
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[6] T.Prathiba, P.Renuga , “A comparative study of Total Harmonic Distortion in
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[7] Annetla Ramakrushna, Reddy & Suresh Kumar K S, “Comparative Study of Multi
Carrier Sine and Space Vector Modulation Techniques for Cascaded H-Bridge
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978-93-81693-85-8, 9th
June, 2012.
[8] Ganesh Prasad Reddy, K. Ramesh Reddy , “ Design and Simulation of Cascaded H-
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[9] M.Murugesan, R.Sakthivel, E. Muthukumaran and R.Sivakumar , “Sinusoidal PWM
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[10] Vinesh Kapadia and Dr.Hina Chandwani, “A Review on Current Source Inverter Fed
Ac Drives and Multilevel Current Source Inverters: Part -1: CSI Fed Ac Drives”
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[11] Vinesh Kapadia and Dr.Hina Chandwani, “A Review on Current Source Inverter Fed
Ac Drives and Multilevel Current Source Inverters: Part -2: Multilevel CSIS”
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