comparison of modulation techniques for cascaded h bridge type multilevel current

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 © IAEME: www.iaeme.com/ijaret.asp Journal Impact Factor (2013): 5.8376 (Calculated by GISI) www.jifactor.com

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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



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 = ∑ �� sin ��∞

��, ,�,..

Bn = ��

�� 1 � ∑ ��1��

�� cos�� !"# � � 1,3,5, …

Where �� ' �( … ' �� ' �

(

The third and fifth harmonics would be eliminated if

1 - cos 3)� � cos 3)( * 0 1 - cos 5)� � cos 5)( * 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.



184

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 10000

2

4

6

8

10

12

Frequency (Hz)

Fundamental (50Hz) = 1.108 , THD= 18.22%

Ma

g (

% o

f F

un

dam

en

tal)



185

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 = �,

^

�./^ ��0��

for 0 < ma < 1

(in our case m = 5) where 1�^ is the peak amplitude of the modulating wave Vm and 123

^ 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 10000

0.05

0.1

0.15

Frequency (Hz)

Fundamental (50Hz) = 0.9998 , THD= 2.92%

Ma

g (

% o

f F

und

am

en

tal)



186

(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 10000

2

4

6

8

10

12

14

16

18

Frequency (Hz)

Fundamental (50Hz) = 1 , THD= 2.80%

Mag (

% o

f F

unda

men

tal)



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



188

(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 10000

1

2

3

4

5

6

7

8

9

10

Frequency (Hz)

Fundamental (50Hz) = 1 , THD= 2.70%

Mag (

% o

f F

und

am

enta

l)



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



190

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 University-SCIENCE C (Computers & Electronics), ISSN 1869-1951 (Print); ISSN 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, Elsevier September 2010 pp. 1-2.

[6] T.Prathiba, P.Renuga , “A comparative study of Total Harmonic Distortion in Multilevel inverter topologies”, Journal of Information Engineering and Applications, Vol 2, No.3, 2012.

[7] Annetla Ramakrushna, Reddy & Suresh Kumar K S, “Comparative Study of Multi Carrier Sine and Space Vector Modulation Techniques for Cascaded H-Bridge Inverter”, International Conference on Electrical and Electronics Engineering, ISBN : 978-93-81693-85-8, 9th June, 2012.

[8] Ganesh Prasad Reddy, K. Ramesh Reddy , “ Design and Simulation of Cascaded H-Bridge Multilevel Inverter Based DSTATCOM”, International Journal of Engineering Trends and Technology- Volume3Issue1- 2012, ISSN: 2231-5381.

[9] M.Murugesan, R.Sakthivel, E. Muthukumaran and R.Sivakumar , “Sinusoidal PWM Based Modified Cascaded Multilevel Inverter”, International Journal Of Computational Engineering Research, ISSN: 2250–3005, Mar-Apr 2012, Vol. 2, Issue No.2, pp.529-539.

[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” International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 3, 2012, pp. 80 - 88, ISSN Print : 0976-6545, ISSN Online: 0976-6553.

[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” International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 3, 2012, pp. 102 - 109, ISSN Print : 0976-6545, ISSN Online: 0976-6553.

comparison of modulation techniques for cascaded h bridge type multilevel current

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