Investigations on Three Phase Five Level Cascaded type ... - IOSRJEN

IOSR Journal of EngineeringMay. 2012, Vol. 2(5) pp: 1056-1063hybrid topologies and multicarrier SPWM applied tomultilevel inverter, the paper makes a deep study onvarious modulation strategies applied to hybridtopologies.Fig. 1 shows a configuration of the three phase fivelevel H bridge type FCMLI. The concept of thisinverter is based on connecting H bridge inverters inseries to get a sinusoidal voltage output. The outputvoltage is the sum of the voltage that is generated byeach cell. The number of output voltage levels are2n+1 where n is the number of cells. The switchingangles can be chosen in such a way that the THD isminimized. The output voltage obtained from FCMLIcascade is E/2. An n level cascaded H-bridgemultilevel inverter needs 2(n-1) switching devicesSimilarly for FCMLI cascaded 2(n-1) switchingdevices are used. The gate signals for chosen fivelevel cascaded type FCMLI are simulated usingMATLAB-SIMULINK. The gate signal generatordeveloped is tested for various values of modulationindex m a and for various PWM strategies. Fig.2shows a sample SIMULINK developed for PDPWMtechnique. The simulation results presented in thispaper in the form of the outputs of the chosen FCMLIcascaded are compared and evaluated.Fig. 1 A three phase five level H-bridge type FCMLIFig. 2 Sample PWM generation logic usingSIMULINK developed for PDPWM techniqueIII. MODULATION STRATEGIESDevelopment of concerns PWM control strategies thedevelopment of techniques to reduce the THD of thecurrent. It is generally recognized that increasing theswitching frequency of the PWM pattern reduces thelower frequency harmonics by moving the switchingfrequency carrier harmonics and associated sidebandharmonics further away from the fundamentalfrequency component. The modulating/referencewave of multilevel carrier based PWM strategies canbe sinusoidal. In general for a five level inverter fourcarriers are needed for symmetrical multilevelinverter. As far as the particular reference wave isconcerned, there is also multiple Control FreedomDegree (CFD) including frequency, amplitude, phaseangle of the reference wave. This paper focuses onhybrid power circuit with sinusoidal reference andtriangular carrier which have been used in chosenthree phase cascaded type FCMLI. The followingstrategies are employed in this study which have usedthe intersection of a sine wave with a triangular waveto generate firing pulses.The amplitude modulation index forPD/POD/APOD/VFPWM = 2A m /(m-1)A c.The amplitude modulation index forPSPWM = A m / (A c /2).The amplitude modulation index forCOPWM = A m /(m/4) A C.m f = f c /f mwheref c – Frequency of the carrier signalf m – Frequency of the reference signalA m –Amplitude of the reference signalISSN: 2250-3021 www.iosrjen.org 1057 | P a g e

IOSR Journal of EngineeringMay. 2012, Vol. 2(5) pp: 1056-1063A c – Amplitude of the carrier signalm – number of levels.III. (a) APOD strategyAs can be seen in the Fig.3 for a five level inverter atotal of four carrier waves are used.i) They are arranged in such a manner that eachcarrier is out of phase with its neighbor by 180degrees.ii) The converter switches to + V dc / 2 when the sinewave is higher than all carrier.iii) The converter switches to +V dc / 4 when the sinewave is lower than the uppermost carrier waveformand greater than all other carrier.iv) The converter switches to 0 when the sine wave islower than the two uppermost carrier waveform andgreater than two lowermost carrier.v) The converter switches to - V dc / 4 when the sinewave is higher than the lowermost carrier waveformand lesser than all other carriers.vi) The converter switches to - V dc / 2 when the sinewave is lesser than all carrier.e) The converter switches to - V dc / 4 when the sinewave is higher than the lowermost carrier waveformand lesser than all other carriers.f) The converter is switched to - V dc / 2 when the sinewave is less than both carrier waveforms.In the PWM scheme there are four triangles, uppertwo triangle have magnitude from 2 to 0 and thelower two triangles exist from 0 to –2 and these twotriangle waveforms are out of phase.Fig. 4 Carrier arrangement for PODPWM strategy(m a = 0.8 and m f = 40)Fig. 3 Carrier arrangement for APODPWM strategy(m a = 0.8 and m f = 40)III. (b) POD strategya) Four carrier waveforms are arranged so that allcarrier waveforms above zero are in phase and are180 degrees out of phase with those below zero.b) The converter is switched to + V dc / 2 when thesine wave is higher than both carrier waveforms.c)The converter switches to +V dc / 4 when the sinewave is lower than the uppermost carrier waveformand greater than all other carrier.d) The converter is switched to zero when the sinewave is greater than the lower carrier waveform butless than the upper carrier waveform.III. (c) PD strategyThe rules for phase disposition method for amultilevel inverter area) 4 carrier waveforms in phase are arranged.b) The converter is switched to + V dc / 2 when thesine wave is greater than both carriers.c)The converter switches to +V dc / 4 when the sinewave is lower than the uppermost carrier waveformand greater than all other carriers.d) The converter is switched to zero when sine waveis lower than upper carrier but higher than the lowercarrier .e)The converter switches to - V dc / 4 when the sinewave is higher than the lowermost carrier waveformand lesser than all other carriers.f) The converter is switched to - V dc / 2 when the sinewave is less than both carrier waveforms.As can be seen from the Fig.5 in the PWM schemethere are four triangles, the upper two trianglesranges from 2 to 0 and the lower two triangle rangesfrom 0 to –2.ISSN: 2250-3021 www.iosrjen.org 1058 | P a g e

IOSR Journal of EngineeringMay. 2012, Vol. 2(5) pp: 1056-1063properly increased to balance the number ofswitchings for all the switches.Fig. 5 Carrier arrangement for PDPWM strategy(m a = 0.8 and m f = 40)III. (d) Carrier Overlapping (CO) strategyFor an m-level inverter using carrier overlappingtechnique, m-1 carriers with the same frequency f cand same peak-to-peak amplitude A c are disposedsuch that the bands they occupy overlap each other;the overlapping vertical distance between each carrieris A c /2. The reference waveform has amplitude of A mand frequency of f m and it is centered in the middle ofthe carrier signals. The reference wave iscontinuously compared with each of the carriersignals. If the reference wave is more than a carriersignal, then the active devices corresponding to thatcarrier are switched on. Otherwise, the devices switchoff.Fig. 7 Carrier arrangement for VFPWM strategy(m a = 0.8 and m f = 40)III. (f) PS strategyThe phase shift multicarrier PWM technique usesfour carrier signals of the same amplitude andfrequency which are shifted by 90 degrees to oneanother to generate the five level inverter outputvoltage.Fig.8 Carrier arrangement for PSPWM strategy(m a = 0.8 and m f = 40)Fig. 6 Carrier arrangement for COPWM strategy(m a = 0.8 and m f = 40)III. (e) VF strategyThe number of switchings for upper and lowerdevices of chosen MLI is much more than that ofintermediate switches in PDPWM using constantfrequency carriers. In order to equalize the number ofswitchings for all the switches, variable frequencyPWM strategy is used as illustrated in which thecarrier frequency of the intermediate switches isIV. SIMULATION RESULTSThe cascaded type FCMLI is modeled in SIMULINKusing power system block set. Switching signals forFCMLI are developed using bipolar PWM techniquesdiscussed previously. Simulation is performed fordifferent values of m a ranging from 0.6 – 1. Thecorresponding %THD values are measured usingFFT block and they are shown in Table 1. Table 2displays the V RMS of fundamental of inverter outputfor same modulation indices. Figs 9-20 show thesimulated output voltage of FCMLI and thecorresponding FFT plots with above strategies but foronly one sample value of m a = 0.8. Fig.9 shows thefive level output voltage generated by APOD strategyISSN: 2250-3021 www.iosrjen.org 1059 | P a g e

IOSR Journal of EngineeringMay. 2012, Vol. 2(5) pp: 1056-1063and its FFT plot is shown in Fig.10. From Fig.10 it isobserved that the APOD strategy produces significant35 th and 37 th harmonic energy. Fig.11 shows the fivelevel output voltage generated by POD strategy andits FFT plot is shown in Fig.12. From Fig.12 it isobserved that the POD produces significant 33 rd and35 th harmonic energy. Fig.13 shows the five leveloutput voltage generated by PD strategy and its FFTplot is shown in Fig.14. From Fig.14 it is observedthat the PD strategy produces significant 30 th , 32 nd ,36 th and 38 th harmonic energy. Fig.15 shows the fivelevel output voltage generated by CO strategy and itsFFT plot is shown in Fig.16. From Fig.16 it isobserved that the CO strategy produces significant 3 rdand 38 th harmonic energy.Fig.17 shows the five level output voltage generatedby VF strategy and its FFT plot is shown in Fig.18.From Fig.18 it is observed that the VF strategyproduces significant 34 th and 38 th harmonic energy.Fig.19 shows the five level output voltage generatedby PS strategy and its FFT plot is shown in Fig.20.From Fig.20 it is observed that the PS strategy doesnot produce significant harmonic energy. Thefollowing parameter values are used for simulation:V DC =440V, f c = 2KHz and R (load) = 100 ohms.Fig.11 Output voltage generated by PODPWMstrategyFig.12 FFT plot for output voltage of PODPWMstrategyFig.9 Output voltage generated by APODPWMstrategyFig.13 Output voltage generated by PDPWM strategyFig.10 FFT plot for output voltage of APODPWMstrategyFig.14 FFT plot for output voltage of PDPWMstrategyISSN: 2250-3021 www.iosrjen.org 1060 | P a g e

IOSR Journal of EngineeringMay. 2012, Vol. 2(5) pp: 1056-1063Fig.15 Output voltage generated by COPWMstrategyFig.18 FFT plot for output voltage of VFPWMstrategyFig.16 FFT plot for output voltage of COPWMstrategyFig.19 Output voltage generated by PSPWM strategyFig.17 Output voltage generated by VFPWM strategyFig.20 FFT plot for output voltage of PSPWMstrategyTable-1 % THD for different modulation indicesm a PD POD APOD CO VF PS1 27.41 27.33 27.92 32.31 27.44 27.550.9 34.24 34.14 34.65 38.84 34.1 33.420.8 39.18 38.94 39.41 44.16 39.13 39.060.7 42.9 42.71 42.97 55.44 43.31 42.220.6 45.02 45.07 44.95 66.62 45.06 44.91ISSN: 2250-3021 www.iosrjen.org 1061 | P a g e

IOSR Journal of EngineeringMay. 2012, Vol. 2(5) pp: 1056-1063Table-2 V RMS (fundamental) for different modulation indicesm a PD POD APOD CO VF PS1 154.4 154.4 154.2 157.8 154.4 154.50.9 138.6 138.6 138.4 144 138.6 138.80.8 122.7 122.9 122.6 128.9 122.8 122.40.7 106.7 106.5 106.7 110.5 106.4 107.10.6 90.86 90.66 90.91 91.01 91.06 90.11Table-3 Crest factor for different modulation indicesm a PD POD APOD CO VF PS1 1.41386 1.41386 1.414397 1.414449 1.415155 1.4129450.9 1.414141 1.414141 1.414017 1.414583 1.415584 1.4121040.8 1.414018 1.414158 1.414356 1.571761 1.409609 1.4183010.7 1.413308 1.415023 1.414246 1.413575 1.422932 1.4052290.6 1.414264 1.414075 1.414586 1.41413 1.399078 1.429364Table-4 Form factor for different modulation indicesm a PD POD APOD CO VF PS1 199.32 175.5 174.47 10.24 28343.42 140.610.9 150.76 128.09 127.44 7.44 11433.27 151.490.8 86.71 98.08 98.15 6.42 12578.35 111.940.7 105.74 77.11 76.54 4.07 11028.73 87.350.6 75.9 61.92 61.71 2.99 11576.31 64.12V. CONCLUSIONIt is observed from Table 1 PSPWM techniqueprovides output with relatively low distortion.COPWM strategy is found to perform better since itREFERENCES[1] B.P.McGrath and D.G. Holmes, SinusoidalPWM of Multilevel Inverters in theOvermodulation Region, IEEE Transactions onIndustrial Applications, Vol.3, No.7, 2002,pp.574-582.[2] J.S.Lai and F.Z.Peng, Multilevel Inverters ASurvey of Topologies, Controls, andApplications, IEEE Transactions on IndustrialElectronics, Vol.49, No.4, 2002, pp.724-738.[3] Keith A. Corzine, Mike W. Wielebski, FangZ. Peng and Jin Wang, Control of Cascadedprovides relatively higher fundamental RMS outputvoltage (Table 2) and also relatively lower stress onthe devices. Table 3 shows crest factor. Next table 4provides FF for all modulation indices.Multilevel Inverter, IEEE Transactions onPower Electronics, Vol.19, No.3, 2004,pp.732-738.[4] Haiwen Liu, Leon M.Tolbert, Surin Khomfoi,Burak Ozpineci and Zhong Du, HybridCascaded Multilevel Inverter with PWMControl Method, IEEE Conf. Rec: 978-1-4244-1668-4/08, 2008, pp.162-166.[5] Jing Zhao, Xiangning He and Rongxiang Zhao,A Novel PWM Control Method for Hybrid-Clamped Multilevel Inverters, IEEEISSN: 2250-3021 www.iosrjen.org 1062 | P a g e

IOSR Journal of EngineeringMay. 2012, Vol. 2(5) pp: 1056-1063Transactions on Industrial Electronics, Vol.57,No.7, 2010, pp.2365-2373.[6] Zhou Jinghua and Li Zhengxi, Research onHybrid Modulation Strategies Based onGeneral Hybrid Topology of MultilevelInverter, International Symposium on PowerElectronics Electrical Drives, Automation &Motion, Rec: 978-1-4244-1664-6, 2008,pp.784-788.[7] C.Govindaraju and K.Baskaran, OptimizedHybrid Phase Disposition PWM ControlMethod for Multilevel Inverter, InternationalJournal of Recent Trends in Engineering,Vol.1, No.3, 2009, pp.129-134.[8] Zhong Du, Leon M. Tolbert, Burnk Ozpineciand John N. Chiasson, Fundamental FrequencySwitching Strategies of a Seven Level HybridCascaded H-Bridge Multilevel Inverter, IEEETransactions on Power Electronics, Vol.24,No.1, 2009, pp.25-33.[9] Georgious S. Konstantinou, Sridhar R.Pulikantiand Vassilios G. Agelidis, HarmonicElimination Control of a Five-Level DC-ACCascaded H-bridge Hybrid Inverter, 2 nd IEEEInternational Symposium on Power Electronicsfor Distributed Generation Systems, 2010,pp.352-357.[10] Farid Khoucha, Soumia Mouna Lagoun,Khoudir Marouani, Abdelaziz Kheloui andMohamed Ei Hachemi Benbouzid, Hybridcascaded H-Bridge Multilevel InverterInduction Motor Drive Direct Torque ControlFor Automotive Applications, IEEETransactions on Industrial Electronics, Vol.57,No.3, 2010, pp.892-899.[11] Hossein Sepahvand, Mostafa Khazraei, MehdiFerdowsi and Keith Corzine, A HybridMultilevel Inverter with Both Staircase andPWM Switching Schemes, IEEE Conf. Rec:978-1-4244-5287-3/10, 2010, pp.4364-4367.[12] K.Satyanarayana, J.Amarnath and A.KailasaRao, Hybrid PWM Algorithm Based VectorControlled Induction Motor Drive to AchieveSuperior Waveform Quality, InternationalJournal of Engineering & AdvancedTechnology(IJEAT), ISSN:2249-8958, Vol.1,No.2, 2011, pp.56-63.ISSN: 2250-3021 www.iosrjen.org 1063 | P a g e