A new hybrid multilevel inverter topology with harmonics profile improvement is presented in this paper. From the literature, it is agreed that hybrid multilevel inverter with its DC sources configured in trinary fashion presents the largest output levels and the lowest Total Harmonics Distortion (THD) percentage. However the output contains low order harmonics due to the impossibility of modulating all adjacent voltage levels at high frequency. With this proposed topology, all adjacent voltage levels are possible to be modulated at high frequency. As a result, the output voltage waveform presents better harmonics profile. The proposed topology and its modulation scheme are presented and verified with simulation results

Ayob, S. M.

Jusoh, A.

Muhamad, N. D.

Yee, C. H.

English

Universiti Teknologi Malaysia Institutional Repository

IEEE PEDS 2005A New Hybrid Multilevel Inverter Topology withHarmonics profile improvementS. M. Ayob C. H. Yee N. D. Muhamad A. JusohEnergy Conversion DepartnentFaculty of Electrical EngineeringUniversiti Teknologi Malaysia81310 UTM Skudai, Johor, MALAYSIAAbstract - A new hybrid multilevel inverter topology with multilevel inverter [4]. However, the output contains lowharmonics profile improvement is presented in this paper. From order harmonics, due to the impossibility of modulating allthe literature, it is agreed that hybrid multilevel inverter with its adjacent voltage levels at high frequencyDC sources configured in trinary fashion presents the largestoutput levels and the lowest Total Harmonics Distortion (THD) Thus, this paper proposed a new hybrid multilevel inverterpercentage. However the output contains low order harmonics topology, so that it is possible to modulate at high frequencydue to the impossibility of modulating all adjacent voltage levels among all adjacent levels of output waveform. As a result, theat high frequency. With this proposed topology, all adjacent output voltage presents a better harmonics profile.voltage levels are possible to be modulated at high frequency. Asa result, the output voltage waveform presents better harmonics II. THE PROPOSED HYBRID MULTILEVELprofile. The proposed topology and its modulation scheme are INVERTER TOPOLOGYpresented and verified with simulation results.Fig. 1 shows M modules of the proposed hybrid multilevelKeywords: voltage source inverter; cascaded multilevel inverter; topology. The topology is constructed of a series -connectedharmonics improvement, full bridge inverter module and is separated into two sets ofI. INTRODUCTION inverters, namely Low Frequency (LF) inverter and HighFrequency (HF) inverter. As shown in Fig. 1, HF inverterMultilevel voltage source inverter (VSI) has been consist a single full bridge inverter with laV dc source whilerecognized as an important alternative to the normal two levels Low Frequency (LF) inverter consists of (M-1) full bridgeVSI, especially in high power application. Using multilevel inverters with their dc sources are configured in geometrictechnique, the output voltage amplitude is increased, switching progression for example: trinary and binary fashion.devices stress is reduced and the overall harmonics profile is The number of voltage level N roduced is iven b 1improved. Several multilevel topologies are reported [1, 2, 3], g (N) p g y (1)and the most popular topology is Cascaded Multilevel Inverter(CMI). It offers several advantages compared to other N2a+3 (1)topologies such as simple circuit layout, less componentscounts, modular in structure and avoid unbalance capacitor Where :voltage problem. However as the number of output levelincreases, this topology becomes highly cumbersome because M -1the number of power devices is increases. a = 3(n) n = (1,2..) for trinary configurationThen, hybrid multilevel inverter is proposed. Thistopology generates larger number of output levels with the orsame number of power devices of the Cascaded MultilevelInverter with equal DC voltage sources. It consisted of a M-1series-connected full-bridge inverter module with its dc a = 2(ni) n = (1,2..) for binary configurationvoltage sources is configured in geometric progression e.g.trinary and binary. Moreover, different types of switchingdevices are used and modulated differently to reduce voltage III. TBE MODULATION SCHEMEstress on the devices and switching losses. The output waveform is a combination of stepped voltageFrom the literature, it is agreed that trinary hybrid waveform synthesized in LF inverter and a high frequencymultilevel inverter offers larger number of output voltage leveland smaller THD percentage compared to binar hybrid0-7803-9296-5/05/$20.00 C) 2005 IEEE 999HF Inverter Fig. 2 shows the block diagram of the control circuit forthe modulation scheme utilized to determine the switchingsignal for all inverter modules. From the figure, it shows thatthe reference signal (pure sinusoidal with frequency f, and1 aVdc ~~~~~~~~~amplitude A,) is the command signal for the I't comparatorlaVdc ~~~~VI block. The signal is compared with the HF Inverter's dcvoltage factor, which is unity. If the command signal isgreater than unity, the output must be equal to unity, otherwisethe output is set to zero.LF Inverter The command signal of the 2n comparator block is thedifference between the command signal of the 1' comparatorblock and the output of the Ist comparator block. Thiscommand signal is then compared again with HF Inverter's dc2"aVdc ~~~~~~~~~voltage factor. In the same way that presented for the 1SV2 ~~~~~block, the output is synthesized from the comparison of thesetwo signals. This process is repeated until reach the (a+l)lcomparator block. The command signal of the (a+1)'"comparator block is compared with a train of triangularwaveform with frequency f,, resulting the high frequencypulse width modulation waveform. Thus, the modulationindex can be determined by:IC (2)fsThe modulation ratio for the proposed scheme also can beFigure 1. M modules of the proposed hybrid multilevel invertergieasvariable pulse width modulation waveform synthesized in HF Asinverter. TABLE 1 and TABLE 2 show the switching ma =3combinations to synthesize specific voltage levels for the CT + (3proposed topology with LF inverter's dc source is configuredin binary and trinary, respectively. From TABLE 1, it can beseen that several specific levels for binary configuration couldbe generated using more than a single switching combination.TABLE 1. SWITCHING COMBINATIONS FOR THE PROPOSED TOPOLOGYWITH LF INVERTER'S DC SOURCE IS IN BINARY CONFIGURATION.1V 2V [2V 3V 3V 4V 4V 5V 6V 6V 7V 8VHF(1V)I 1 1 1 1 0 1 1 1 1 1 1[jF!..1aV)j 0 1IL-i 0 0 0 1 0 1 -1 0 1LF 2V 0 0 1 I -1 0 1 0 0 1 1 1LF(4V 0 1 I 0 1 1 1 1 1TABLE 2. SWITCHING COMBINATIONS FOR THE PROPOSED TOPOLOGYWITH LF INVERTER'S DC SOURCE IS IN TRINARY CONFIGURATION.lv 2V 13V 4V 5V 16V 7V IOViov1V 12V 13V 14VHF (laV 1 1 -1 -1 I 1 0 0 1 1 1LF1(3aV)I 00 1 1-1 -1 I ILF3 (9aV) 0 0 0 1 I -1 01 1Reference Signal,DC Voltage Factor _ __ +1)Carer SignalFigure 2. Block diagram ofgating signals generatorThen, all theoutputs of comparisonblocks arefedCforward Finally, it can be concluded that wih the proposedto the addition/subtraction block. Here, the signals are topology, better harmonics profile can be obtained. The Totalmanipulate to produce the desired switching signals for each Harmonic Distortion (THD) of the output voltage using theinverter module. Fig. 3 shows the reference signals for each proposed topology with its LF inverter's dc source isinverter modules for the proposed topology, configured in tinary yields 4.02%, while with binaryconfiguration yields 7.02%. It was also found that fordifferent m, values, different numbers ofoutput levels areobtained. Fig. 6 summarized the output levels obtainedaccording to m. for M=4.o Qm 000 0 00 1oaB Q 000 0014 0001 01 0m10 0.005 0.01 0.015 0.020 oaR 0ax1 an a0m 001 Q00 04 0Q=Qao Time (s)Fundamental (50Hz) = 80, THD= 7.02%2- 200 0 0 (0 008on 001O 000 0014 000 0018 00115Figure 3. Reference signalsfor 4 inverter modules with LF inverter's dc 10 Lsource are in trinary configuration. (a) Reference signalfor LFI U.(b) Reference signalfor LF2 (c) Reference signalfor LF3 (d) Reference tsignalfor HF inverter.5IV. SIMULATION RESULTFigure 4 and 5 present output voltage waveform for theproposed topology with LF inverter's dc source is configured H50 100 150 2odin binary (17-level output) and trinary (29-level output) with Harmonicordertheir harmonic spectrums, respectively. For both dcconfigurations, as can be seen from the figures, all adjacent Figure 4. Output waveformfor LF inverter's dc source is configured inlevels of their output waveforms are modulated in high binary and its harmonics spectrum.frequency. As a result, better harnonic profile is obtainedwithout the presence of low-order harmonics in theirwaveform harmonics spectrums.1001-200 bema,30 - - - 0triaryO0-~25 ~- -> ~~~~~~~20- - _15-----1-0 5 1 - - -50 - - _ - - - --0 0.005 0.01 0.015 0.02lime (s) 0.Fundamental (50Hz) 140, THD= 4.02%/ 1.0 0.8 0.6 0.4 0.220H modulation index(mi)i 15 Figure 6. Output level (N) obtained according to modulation indexfor10 ~~~~~~~~~~~~~~~M=4100-0 50 100 150 200Harmnonic orderFigure 5. Output waveform for LF inverter's dc source is configured intrinary and its harmonics spectrum.V. CONCLUSIONThis paper presents a new hybrid multilevel invertertopology for harmonics profile improvement. It is agreed thathybrid multilevel inverter with its DC sources configured intrinary fashion presents the largest output levels and thesmallest Total Harmonics Distortion (THD) percentage.However the output contains low order hannonics, due to theimpossibility of modulating all adjacent voltage levels ofoutput waveform at high frequency. With this proposedtopology, high frequency modulation among all adjacentvoltage levels can be made possible. As a result, the outputvoltage waveform presents better harmonics profile. It wasalso found that for different values of mi, different numbers ofoutput levels are obtained.VI. REFERENCES[1] B.P McGrath and D.G Holmes, "Multicarrier PWM strategies formultilevel inverter," IEEE Transaction on Industrial Electronics, vol.49,no.4, August 2002[2] Jose Rodriguez, Jih-Sheng Lai, Fang Zheng Peng, "Multilevel inverters:A survey of topologies, controls and applications," IEEE Transaction onIndustrial Electronics, vol.49, no.4, August 2002[3] G. Carrara, S. Gardella, M. Marchesoni, R. Salutari and G. Sciutto, " Anew multilevel PWM method: A theoretical analysis," IEEE Transactionon Power Electronics, vol.7, no.3, July 1992.[4] Rech C., Pinheiro H., Grundling H.A., Hey H.L., Pinheiro J.R.,"Analysis and comparison of hybrid multilevel voltage sourceinverters," Power Electronics Specialist Conference 2002 (PESC 2002),2002 IEEE 33rd Annual, vol. 2, pp 491-496, June 23-27h, 20021002

A new hybrid multilevel inverter topology with harmonics profile improvement

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