IJEET Analysis and Simulation of Multilevel Inverter

International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME
200
ANALYSIS AND SIMULATION OF MULTILEVEL INVERTER USING
MULTI CARRIER BASED PWM CONTROL TECHNIQUE
Dr. Hina Chandwani1
, Himanshu N Chaudhari2
and Dhaval Patel3
1
(1Associate Professor, Dept. of Electrical Engineering, The M.S.University of Baroda,
Vadodara, India)
2
(2 Assistant professor, Dept. of Electrical Engineering, SNPIT&RC, Umrakh, Bardoli,
Gujarat, India)
3
(3Student, Dept. of Electrical Engineering, The M.S.University of Baroda, Vadodara, India)
ABSTRACT
Multilevel voltage source inverter (VSI) has been recognized to be very attractive in
high voltage dc to ac conversion.. It is based on the cascade connection of the several H-
bridge inverter cells. This Paper proposes a multi carrier based control techniques for
multilevel topology. Under multicarrier based PWM, different level shifted techniques has
been used for obtain desire output and comparatively analysis has been done for required
minimum harmonic distortion. Several tests to quantify the performance of the inverter under
the proposed modulation scheme are carried out using Matlab Simulink models.
Keywords: Matlab Simulink, Symmetrical type Cascaded Multilevel Inverter (SCMLI),Total
harmonic distortion(THD).
INTRODUCTION
The importance of multilevel inverters[MLI] has been increased since last few
decades. These new types of inverters are suitable for high voltage and high power
application due to their ability to synthesize waveforms with better harmonic spectrum and
with less THD. Numerous topologies have been introduced and widely studied for utility of
non-conventional sources and also for various drive applications. Amongst these topologies,
the multilevel cascaded inverter was introduced in Static VAR compensation and in drive
systems.
INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING
& TECHNOLOGY (IJEET)
ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 4, Issue 3, May - June (2013), pp. 200-208
© IAEME: www.iaeme.com/ijeet.asp
Journal Impact Factor (2013): 5.5028 (Calculated by GISI)
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201
It has the advantages like high power quality waveforms, lower voltage ratings of
devices, lower harmonic distortion, lower switching frequency and switching losses, higher
efficiency, reduction of dv/dt stresses etc. It gives the possibility of working with low speed
semiconductors in comparison with the two-levels inverters. Numerous of MLI topologies
and modulation techniques have been introduced. But most popular MLI topology is Diode
Clamp, Flying Capacitor and Cascaded Multilevel Inverter (CMLI). In this paper we are
using a CMLI that consist of several H-Bridge inverters and with equal voltage DC sources
named as Symmetrical type Cascaded Multilevel Inverter (SCMLI).
The total output voltage is the sum of the outputs of all the full-bridge modules in the
CMLI inverter and every full bridge can create the three voltages +V, 0 and -V. The sources
in each full-bridge need to be isolated if the inverter is going to be implemented in active
power transfer application, for voltage balance reasons since there isno common DC-bus
torecharge the sources energy content. However, since the CMLI uses separate energy
sources it is well suitable for renewable energy or energy/fuel cell applications there every
separate voltage source could be isolated. A drawback for the energy/fuel cell applications is
however that the sources must be charged individually or through the inverter.
Multilevel PWM methods uses high switching frequency carrier waves in comparison
tothe reference waves to generate a sinusoidal output wave, much like in the two-level
PWMcase. To reduce harmonic distortions in the output signal shiftingtriangular carrier
waves areused. There are several methods that change disposition of or shiftmultiple
triangularcarrier waves. The number of carrier waves used is dependent to the number of
switches tobe controlled in the inverter.
In addition to the sinusoidalcarrier wave modulation methods presented furtherdown
there are also two more well-known alternative methods that will not be discussed inthis
paper: Alternative Position Opposition Disposition (APOD) and Phase OppositionDisposition
(POD).
I. CASCADED MULTI LEVEL INVERTER(CMLI)
This method eliminates the excessively large number of bulky transformers required
by conventional multi-level inverters, the clamping diodes required by diode clamped
multilevel inverters and the bulky capacitors required by flying capacitor multilevel inverters.
This method consists a series connection of multiple H bridge inverters. Each H-bridge
inverter has the same configuration as a typical single-phase full-bridge inverter. This method
introduces the idea of using separate DC sources to produce an AC voltage waveform which
is nearly sinusoidal. Each H bridge inverter is connected to its own DC source. By cascading
the output voltage of each H-bridge inverter, a stepped voltage waveform is produced. If the
number of H-bridges is N, the voltage output is obtained by summing the output voltage of
bridges as shown in equation. Fig.1shows configuration of ACMLI of single-phase.

202
Fig.1. Single-phase cascaded multilevel inverter
If ACMLI has N no. of H-Bridges, The output voltage could be expressed as;
Vo (t) = Vo1 (t) + Vo2 (t) + ..... + Vo N (t) …………(1)
Where, Vo1 (t) ,Vo2 (t) , ..... Vo N (t) is the output of individual H-bridge.
II. CARRIER BASED PWM TECHNIQUES
The carrier-based modulation schemes for multilevel inverters can be generally
classified into two categories: phase-shifted and level-shifted modulations. Both modulation
schemes can be applied to the cascaded H-bridge(CHB) inverters. An m-level MLI using
multicarrier modulation scheme requires (m-1) triangular carriers, all having the same
frequency and amplitude. The (m-1) triangular carriers are horizontally disposed for phase
shifted modulation and vertically disposed vertically disposed for level shifted modulation
such that the bands they occupy are contiguous.
Phase shift PWM [2pp, 3pp, 4pp] involves the same principle of standard 2-level
PWM to gate the switches using the comparison between two signals, reference and carrier,
but exploit more than one carrier to generate the driving signals. Allcarriersare having same
amplitude and frequency but asthe name suggests, the carriers have to be displaced by
shifting their phases. The phase shift can be done choosing any delay but the minimum
harmonic distortion of the output is achieved using the delay ∆ given by equation (1), where
Ts is the switching period.
∆=Ts/((n-1)) -------(1)

203
Fig.2
The output switching frequencies results will be higher than carrier one and (2) shows
the relationship between output and carrier switching frequencies, fout and fcar respectively
for m-level converter.
fout= (m −1) x fcar. -----(2)
Most of the level shifted carrier based PWM techniques have been derived three
carrier dispositionstrategies. The phases of carrier signals are rearranged to produce three
main disposition techniques known as IPD, POD and APOD. The reference or modulating
wave is positioned at the Centre of the carrier set and continuously compared with the
carriers.Whenever the magnitude of reference wave is greater than a carrier wave positive
going switching pulse is obtained. When the reference goes above all the carriers maximum
output is obtained. As the reference falls below each carrier the corresponding levels in the
inverter output gets reduced. Carrier arrangements and corresponding switching patterns
generated by seven-level Disposition PWM are illustrated in Figs. 3–5.
(i) In-phase disposition (IPD), where all carrier waveforms are in phase
(ii) Phase opposition disposition (POD), where all carrier waveforms above zero
reference are in phase and are 1800
out of phase with those below zero

204
(iii) Alternate phase disposition (APOD), where every carrier waveform is in out of phase
with its neighbor carrier by 1800
III. SIMULATION, RESULT AND DISCUSSION
The computer software package Matlab Simulink was used to implement all of the
Modulation Techniques.
5-Level PSPWM
Fig 6: Simulink model using two bridges.
The Matlab Simulink Model for single phase 5-level MLI using Phase Shifted PWM
Technique(Common in all modulation techniques for CMLI using two H-bridges bridges) is
shown in Fig.6. In five level High Frequency modulation only two bridges will require. The
sub-circuit block for Modulation techniques holds the control circuit for phase shifted
modulation technique.

205
In PSPWM switching Frequency is four times higher than the carrier frequency
accordingly five level output using PSPWM is shown in Fig.7.
In seven level High Frequency modulation three bridges will require. The sub-circuit
block for Modulation techniques holds the control circuit for phase shifted modulation
Technique.
Fig.8 7-level output with three bridges using PSPWM
5-Level LSPWM
The Matlab Simulink Model for single phase 5-level MLI using Level Shifted PWM
Technique is shown in Fig.9. In five level High Frequency modulation only two bridges will
require. The sub-circuit block for Modulation techniques holds the control circuit for Level
Shifted (POD) modulation Technique and is shown in Fig.10.

206
Fig.9 5-level using LSPWM Control Pulse Generation
Fig.10 5-level output using LSPWM
7-Level Level Shifted PWM (IPD, POD, APOD)
The Matlab Simulink Model for single phase7-level MLI using Level Shifted PWM
Technique is shown in Fig.11. It can be easily implemented as shown in Fig.12, however few
changes of no. of carriers and phase change of triangular carrier waves are required according
to modulation techniques. Output and FFT of 7-level using IPD, POD and APOD modulation
techniques is shown in fig.13, 14 and 15 respectively.

207
Fig.13 7-Level using IPD LSPWM [FFT]
Fig.14 7-Level using POD LSPWM [FFT]
Fig.15 7-Level using APOD LSPWM [FFT]
0 0.1 0.2 0.3 0.4 0.5 0.6
-50
0
50
Selected signal: 30 cycles. FFT window (in red): 23 cycles
Time (s)
0 2 4 6 8 10 12 14 16 18 20
0
0.02
0.04
0.06
0.08
0.1
Harmonic order
Fundamental (50Hz) = 60.07 , THD= 0.67%
Mag(%ofFundamental)

208
THD RESULTS
The Matlab Simulink was used to implement all of the Modulation Techniques their
output and FFT analysis. The THD Comparison of different techniques is show in Table.1
Table. 1
No. of output levels Control Technique No of Bridge Required THD
5 MCPWM(POD) 2 1.00
7 MCIPD 3 0.80
7 MCPOD 3 0.67
7 MCAPOD 3 0.73
IV. CONCLUSION
Single phase cascaded type high frequency multi-level inverter employing different
multi carrier single reference modulation schemes has been investigated and their FFT
analysis has been performed. It is conclude from Table 1 that PODPWM technique provides
output with relatively low harmonic distortion. Itis observed that LSPWM have higher output
switching frequency than the carrier frequency and so useful for implementing with
microcontroller based devices where maximum triangular carrier frequency with better
sampling rate is limited due to limitation of operating frequency of devices.
REFERENCES
Journal Papers
[1] 2pp. B. P. McGrath, D. G. Holmes, “Multicarrier PWM Strategies for Multilevel
Inverters”,IEEE Trans. on Ind. Elect., Aug. 2002, Vol. 49, Num. 4, pp.858-867.
[2] 2pp. M. Calais, L. J. Borle, V. G. Agelidis, “Analysis of Multicarrier PWM Methods for
Single-Phase Five Level Inverter”, Power Electronics Specialists Conference PESC
2001, 17-21June 2001, Vol. 3, pp. 1351-1356.
[3] 3pp. B. Mwinyiwiwa, Z. Wolanski, B. T. Ooi, “Microprocessor-Implemented SPWM for
Multiconverters with Phase-Shifted Triangle Carriers”, IEEE Trans. on Ind. Appl.,
May/Jun.1998, Vol. 34, Num. 3, pp 487-494.
[4] Pradeep B Jyoti, J.Amarnath and D.Subbarayudu, “The Scheme of Three-Level Inverters
Based on SVPWM Overmodulation Technique for Vector Controlled Induction Motor
Drives”, International Journal of Electrical Engineering & Technology (IJEET),
Volume 4, Issue 2, 2013, pp. 245 - 260, ISSN Print : 0976-6545, ISSN Online:
0976-6553.
[5] B.Kiran Kumar, Y.V.Sivareddy and M.Vijayakumar, “Comparative Analysis of Sine
Triangle and Space Vector PWM for Cascaded Multilevel Inverters”, International
Journal of Electrical Engineering & Technology (IJEET), Volume 4, Issue 2, 2013,
pp. 155 - 164, ISSN Print : 0976-6545, ISSN Online: 0976-6553.
Book
[6] Bin Wu.”High-Power ConvertersAnd Ac Drives”.

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