Analysis and simulation of multilevel inverter using multi carrier based pwm

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 Chaudhari

2 and Dhaval Patel

3

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

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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)



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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 1800out of phase with those below zero



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(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.



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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.



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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 18 200

0.02

0.04

0.06

0.08

0.1

Harmonic order

Fundamental (50Hz) = 60.07 , THD= 0.67%

Mag (%

of Fundam

enta

l)



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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