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Comparison of modulation techniques for cascaded h bridge type multilevel current

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  • 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), © IAEME181COMPARISON OF MODULATION TECHNIQUES FOR CASCADEDH-BRIDGE TYPE MULTILEVEL CURRENT SOURCE INVERTERVinesh Kapadia1and Dr. Hina Chandwani21Research Scholar at CHARUSAT, Changa, Gujarat & Associate Prof. Dept of E.C.,SNPIT & RC, Umrakh, Bardoli, Gujarat, India2Associate Professor, Dept of Electrical Engineering, The M.S.University of Baroda,Vadodara, IndiaABSTRACTThis paper presents a comparison of the different modulation techniques for a singlephase five level cascaded h-bridge (CHB) type multilevel current source inverter. Majorityof the multilevel inverters are voltage sourced based. The popular carrier based PWMswitching techniques for MVSI are the phase shifted and level shifted modulationtechniques, the same techniques are tried out for the MCSI along with Selective HarmonicElimination method using angle control and the results have been presented.Index Terms: APOD, CHB, IPD, Multilevel Current Source Inverter (MCSI), MultilevelVoltage Source Inverter (MVSI), POD, PWM, THD.I. INTRODUCTIONMULTILEVEL voltage source inverters are very common and now in wide use.Compared to two-level inverters, multilevel inverters have advantages for higher powerapplications, including reduced harmonics and reduced switching device voltage andcurrent stresses. The CSIs have some advantages over VSIs such as more stable operatingconditions, direct control of the output current, faster dynamic response (in some cases) andeasier fault management [1]. In this paper a single phase five level MCSI with symmetricDC current sources is simulated with popular Multilevel Modulation techniques and resultsare compared with respect to total harmonic distortion (THD).INTERNATIONAL JOURNAL OF ADVANCED RESEARCH INENGINEERING 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.aspJournal Impact Factor (2013): 5.8376 (Calculated by GISI)www.jifactor.comIJARET© I A E M E
  • 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), © IAEME182II. THE POWER CIRCUIT DIAGRAMShown below is the circuit for 5 level single phase MCSI along with the switching tableTABLE ISwitching Combination for the 5 level MCSIFig-1 Circuit Diagram of the 5 level CHB MCSIThe above table shows one of the possible combinations for obtaining the desired currentamplitudes.Current Amplitude “ON” Switches0 S11, S12, S21, S22I S11, S14, S21, S222I 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), © IAEME183III. MODULATION TECHNIQUESA. Angle Control Method (Selective Harmonic Elimination)By proper selection of the firing (displacement angles α ) angles it is possible to tryand eliminate or say minimize those particular harmonics.The fourier series for unipolar output voltages per half cycle can be expressed as (due tosymmetry):vo = ∑ ‫ܤ‬௡ sin ݊߱‫ݐ‬∞௡ୀଵ,ଷ,ହ,..Bn =ସ௏ೞ௡గሾ 1 ൅ ∑ ሺെ1ሻ௞௠௞ୀଵ cosሺ݊ߙ௞ሻሿ ݂‫ݎ݋‬ ݊ െ 1,3,5, …Where ߙଵ ൏ ߙଶ … ൏ ߙ௞ ൏గଶThe third and fifth harmonics would be eliminated if1 - cos 3ఈଵ ൅ cos 3ఈଶ ൌ 01 - cos 5ఈଵ ൅ cos 5ఈଶ ൌ 0[2]-[3] Assuming and initial value of α1 = 0 and calculating in an iterative manner till theresults become stable we get;Initial Values α1= 0 , henceα2 = 0.523591stIteration α1= 0.28728α2 = 0.642422ndIteration α1= 0.31366α2 = 0.664783rdIteration α1= 0.31084α2 = 0.662294thIteration α1= 0.31127α2 = 0.662685thIteration α1= 0.31121α2 = 0.662626thIteration α1= 0.31122α2 = 0.66263The values are radians , hence in degrees, α1= 17.831oand 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), © IAEME184Fig-2 Output Current Waveform of the 5 level MCSI with Angle Control MethodFig-3 Harmonic Spectrum of the 5 level MCSI with Angle Control MethodB. Carrier Based PWM SchemesThe carrier-based modulation schemes for multilevel inverters can be generallyclassified into two categories: phase-shifted and level-shifted modulations. Both thetechniques have been applied1. Phase Shifted Multicarrier ModulationIn general, a multilevel inverter with m voltage levels requires (m – 1) triangular carriers. Inthe phase-shifted multicarrier modulation, all the triangular carriers have the samefrequency and the same peak-to-peak amplitude, but there is a phase shift between any twoadjacent carrier waves, given byØcr = 360°/(m – 1) [4]-[7]Fig-4 Triangular Carriers compared with Reference Sine0 100 200 300 400 500 600 700 800 900 1000024681012Frequency (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), © IAEME185Fig-5 Output Current Waveform of the 5 level MCSI with Phase Shifted MultiCarrierModulationFig-6 Harmonic Spectrum of the 5 level MCSI with Phase Shifted MultiCarrier Modulation2. Level Shifted Carrier Modulation SchemesSimilar to the phase-shifted modulation, an m-level Cascaded H-Bridge inverter usinglevel-shifted multicarrier modulation scheme requires (m – 1) triangular carriers, all havingthe same frequency and amplitude. The (m – 1) triangular carriers are vertically disposedsuch that the bands they occupy are contiguous. The frequency modulation index is givenby mf = fcr/fm, which remains the same as that for the phase-shifted modulation schemewhereas the amplitude modulation index is defined asma =௏೘^௏೎ೝ^ ሺ௠ିଵሻfor 0 < ma < 1(in our case m = 5) where ܸ௠^is the peak amplitude of the modulating wave Vm and ܸ௖௥^isthe peak amplitude of each carrier wave.Here three schemes for the level-shifted multicarrier modulation are simulated (a) in-phasedisposition (IPD), where all carriers are in phase; (b) alternative phase opposite disposition(APOD), where all carriers are alternatively in opposite disposition; and (c) phase oppositedisposition (POD), where all carriers above the zero reference are in phase but in oppositionwith those below the zero reference [4]-[7].0 100 200 300 400 500 600 700 800 900 100000.050.10.15Frequency (Hz)Fundamental (50Hz) = 0.9998 , THD= 2.92%Mag(%ofFundamental)
  • 6. 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), © IAEME186(a) IPD :Fig-7 Triangular Carriers compared with Reference Sine for IPD ModulationFig-8 Output Current Waveform of the 5 level MCSI with IPD ModulationFig-9 Harmonic Spectrum of the 5 level MCSI with IPD Modulation0 100 200 300 400 500 600 700 800 900 1000024681012141618Frequency (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), © IAEME187(b) APOD :Fig-10 Triangular Carriers compared with Reference Sine for APOD ModulationFig-11Output Current Waveform of the 5 level MCSI with IPD ModulationFig-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), © IAEME188(c) POD :Fig-13 Triangular Carriers compared with Reference Sine for POD ModulationFig-14 Output Current Waveform of the 5 level MCSI with POD ModulationFig-15 Harmonic Spectrum of the 5 level MCSI with POD Modulation0 100 200 300 400 500 600 700 800 900 1000012345678910Frequency (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), © IAEME189Fig-16 Circuit Diagram of the 5 level CHB MVSIIV. RESULTRepeating the simulations with different frequencies for lowest THD has been doneand then the modulation index ( M.I.) has been varied to further reduce the THD , theoptimum frequency and modulation index in each case was found to be 900Hz and 1(forphase shifted multicarrier) and 0.25 (for level shifted ) respectively. The same cases werealso tried out for a similar 5 level CHB MVSI (figure 16 shown above [8]-[9]) , the THDfor each modulation technique is as follows :TABLE IITHD (%) Results for Different Modulation Techniques for both MVSI and MCSIModulation Technique MVSI MCSIAngle Control Method 18.30 18.22Phase Shifted Multicarrier 2.99 2.92IPD 2.82 2.8APOD 2.90 2.88POD 2.72 2.7
  • 10. 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), © IAEME190V. CONCLUSIONIt is concluded that for such a 5 level MCSI in CHB configuration for both theMVSI and MCSI the results are very similar moreover the prominent multilevel invertermodulation topologies (i.e., Phase shifted multicarrier, IPD, APOD and POD) are alsogiving similar results a minimum THD of 2.7 % has been obtained using the PODmodulation scheme in both the MVSI and MCSI cases.VI. REFERENCES[1] Jian-yu Bao, Wei-bing Bao and Zhong-chao Zhang, “High Generalized multilevelcurrent source inverter topology with self-balancing current” , Journal of ZhejiangUniversity-SCIENCE C (Computers & Electronics), ISSN 1869-1951 (Print); ISSN1869-196X (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”, FifteenthNational Power Systems Conference (NPSC), IIT Bombay, December 2008.[4] Bin Wu, “High-Power Converters and ac Drives” ,The Institute of Electrical andElectronics Engineers, Published by John Wiley & Sons Inc, 2006.[5] Ilhami Colak, Ersan Kabalci and Ramazan Bayindir “A Review of multilevel voltagesource 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 inMultilevel inverter topologies”, Journal of Information Engineering and Applications,Vol 2, No.3, 2012.[7] Annetla Ramakrushna, Reddy & Suresh Kumar K S, “Comparative Study of MultiCarrier Sine and Space Vector Modulation Techniques for Cascaded H-BridgeInverter”, International Conference on Electrical and Electronics Engineering, ISBN :978-93-81693-85-8, 9thJune, 2012.[8] Ganesh Prasad Reddy, K. Ramesh Reddy , “ Design and Simulation of Cascaded H-Bridge Multilevel Inverter Based DSTATCOM”, International Journal of EngineeringTrends and Technology- Volume3Issue1- 2012, ISSN: 2231-5381.[9] M.Murugesan, R.Sakthivel, E. Muthukumaran and R.Sivakumar , “Sinusoidal PWMBased Modified Cascaded Multilevel Inverter”, International Journal OfComputational 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 FedAc 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 FedAc 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.