The inverters are becoming one of the resources in many industries and enterprises for powerquality and Uninterrupted Power Supply (UPS). The three-phase inverter with six switches isthe main implementation circuit in any UPS system. But this inverter supplies harmonics to theload. Due to harmonics, the loss is high. So the multilevel inverters are used in the place of allthe three-phase inverter. The multilevel inverter reduces the harmonics. The number of stepsincrease reduces the number of harmonics in the output. Number of increase in switch createscomplications. In this work, reduced switch, increased level multi-level inverter is comparedwith cascaded H-Bridge multilevel inverter using fundamental switching technique. The variouslevels of multi-level inverter can be implemented with proposed strategy. The simulation is carriedout using Matlab software.
Keywords: Cascaded H-bridge, Multilevel dc link inverter, Pulse width modulation, Totalharmonic distortion
INTRODUCTIONThe voltage source inverters produce an outputvoltage or current with levels either 0 or±Vdc.They are known as the two-levelinverters. To produce a quality output voltagewave form with less amount of ripple content,they require high switching frequency. In high-power and high voltage applications these twolevel inverters, however, have some limitationsin operating at high frequency mainly due toswitching losses and limitations of deviceratings. These limitations can be avoided usingmultilevel inverters.[1]
1 Department of Electrical &, Electronics St. Joseph Engineering College, Mangalore.
Multilevel inverters are of 3types: flyingcapacitor multilevel inverter diode clampedmultilevel inverter, and cascaded multilevelinverter. More number of components such asswitches, capacitors, clamping diodes arerequired for these multilevel inverters. 2 (m-1)active switches are required for m number ofvoltage levels for the cascaded H-bridgemultilevel inverters. Multilevel inversion is apower conversion technique in which outputvoltage obtained is step waveform which iscloser to a sine wave and thus Total HarmonicDistortion (THD) [2,3,4] is reduced.
Research Paper
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Int. J. Elec&Electr.Eng&Telecoms. 2015 Dinesh Kumar S B and Satisha K, 2015
In this work a 1– seven level cascaded H-bridge multilevel inverter based on anmultilevel DC link (MLDCL) and a bridgeinverter. Compared with the existing cascadedmultilevel inverters, the proposed MLDCL [1]inverter topologies can have enhancedperformance. In this work comparing theperformance of the proposed scheme with thatof the existing cascaded H-bridge multilevelinverter is done using Fundamental switchingtechnique. The proposed MLDCL inverter [1]can significantly reduce the switch count as wellas the number of gate drivers as the numberof voltage levels increases. For a givennumber of voltage levels m, the cascadedMLDCL inverter requires m+3 active switches,roughly half the number of switches.
CASCADED H-BRIDGEINVERTERThe cascade H-bridge inverter is a cascadeof H-bridges, or H-bridges in a seriesconfiguration. A single H-bridge inverter isshown in Figure 1 and three phase cascadedH-bridge inverter for seven-level inverter isshown in Figure 2. Figures 1 and 2 shows thebasic power circuit of single H-bridge inverterand the cascade of H-bridge inverter for seven-level inverter respectively. An N level CascadedH bridge inverter consists of series connected(N-1)/2 number of cells in each phase. Eachcell consists of single phase H bridge inverterwith separate dc source. There are four activedevices in each cell and can produce threelevels 0, Vdc/2 and –Vdc/2. Higher voltagelevels can be obtained by connecting thesecell in cascade and the phase voltage van isthe sum of voltages of van = v1 + v2 + v3 + ::::+ vN.
Figure 1: Configuration of Single-PhaseH-Bridge Inverter
Active Switches Output Voltage (Vab)
S1, S2 +Vdc
S3, S4 –Vdc
S1, S4 or S2, S3 0
Table 1: Load Voltage with CorrespondingConducting Switches
Figure 2: Configuration of Single PhaseCascaded Seven Level H-Bridge Inverter
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Table 2: Switching Sequence for 1– 7 Level Cascaded Inverter
PROPOSED MULTILEVEL DCLINK INVERTER TOPOLOGYThe configuration of the proposed inverter isgiven in Figure 4. single-phase seven-level
Figure 4: Configuration of Single-PhaseMultilevel DC Link Inverter
MLDCL inverter involves various steps ofoperation and is Compared with the existingcascade H-bridge inverter, number of switchesand gate drivers count are significantly reduced
Output Voltage S1 S2 S3 S4 S5 S6 S7 S8 S9 S10
0Vdc 1 0 1 0 1 0 1 1 0 0
Vdc 0 1 1 0 1 0 1 1 0 0
2Vdc 0 1 0 1 1 0 1 1 0 0
3Vdc 0 1 0 1 0 1 1 1 0 0
–Vdc 0 1 1 0 1 0 0 0 1 1
–Vdc 0 1 0 1 1 0 0 0 1 1
–Vdc 0 1 0 1 0 1 0 0 1 1
Table 3: Switching Sequence for Single Phase 7 Level MLDCL Inverter
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by the new MLDCL inverters as the number ofvoltage levels increases. For a m numbervoltage levels given, the new MLDCL inverterrequires m+3 active switches, nearly half of theno. of switches, clamping diodes, and voltage-splitting capacitors in the diode clampedconfiguration or clamping capacitors in theflying capacitor configuration. Simulationresults are included to verify the operatingprinciple of the proposed MLDCL inverters.
Comparison of the cascaded inverter andproposed MLDCL inverter based on requirednumber of switches and number of levels isshown in the Figure 5. From this comparisonit is clear that as the no. of voltage levels, m,grows, the number of active switchesincreases according to m+3 for the MLDCLinverter, compared to 2(m-1) for the cascadedH-bridge multilevel inverters.
MODULATION TECHNIQUEA number of modulation techniques are usedin the application of multilevel powerconversion. Generally they can be classifiedinto 3 categories:
• Fundamental frequency switching technique
• Carrier based PWM techniques
• Space Vector PWM techniques
For cascaded multilevel inverter, carrierbased PWM methods and space vectormethods are most used techniques of all thePWM methods but the space vector methodwill be very complicated with the increase ofswitching states if the number of output levelis more than five. Therefore the carrier basedPWM method is preferred if the number ofoutput level is more than five in multilevelinverters. This paper focuses on Fundamentalfrequency switching technique.
SIMULATION RESULTSThe Simulation was conducted to verify theoperation of the Cascaded H-Bridge MLI andproposed MLDCL inverter using Fundamentalfrequency switching technique.
Seven Level Cascaded H-bridgeMLI for 1–
Fundamental Frequency SwitchingTechnique
Figure 5: Comparison of Required Numberof Switches
Figure 6: Line Voltage of 1– Seven LevelCascaded H-Bridge MLI Using SPWM
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Proposed Seven Level MLDCLI for 1–
Fundamental Frequency SwitchingTechnique
Comparison of Results:Input voltage = 36 v
Output voltage = 72 v (peak to peak)
Load = 12
A summary of THD and fundamental outputvoltage for various multilevel invertertopologies with their control strategies arepresented. i.e., 1– 7-Level cascaded inverterand 1– 7-level MLDCL inverters weresimulated using Fundamental frequencyswitching technique. And it is concluded that1– 7-level MLDCL inverter usingFundamental frequency switching techniquevoltage (28.3 V) with less THD (21.21%).
Figure 7: FFT Analysis of Line Voltageof 1– Seven Level Cascaded H-Bridge
MLI Using Fundamental FrequencySwitching Technique
Figure 8: Line Voltage of 1– Seven LevelMLDCL Inverter Using Fundamental
Frequency Switching Technique
Figure 9: FFT analysis of Line Voltageof 1– Seven Level MLDCL Inverter Using
Fundamental Frequency Switching
Table 4: Comparison of THD for SinglePhase 7 Level MLDCL Inverter and
H-Bridge MLI Fundamental FrequencySwitching Technique
CONCLUSIONThe presented seven level MLDCL inverterscan eliminate roughly half the number ofswitches, their gate drivers compared with theexisting cascaded MLI counterparts. Thecascaded MLDCL inverters are cost less dueto the savings from the Reduced gate.
The simulation results with harmonicspectrum are presented for cascaded andproposed MLDCL inverters usingFundamental frequency switching techniqueand in this paper it is concluded that 1– 7-level MLDCL inverter using Fundamentalfrequency switching technique has given good
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fundamental output voltage (28.3 V) with lessTHD (21.21%) when compared with 1– 7-Level cascaded inverter.
REFERENCES1. Gerardo Ceglia, Viìctor Guzmaìn, Carlos
Saìnchez, Fernando IbaìnÞez, Julio Walterand Mariìa I Gimeìnez (2006), “A NewSimplified Multilevel Inverter Topology forDC-AC Conversion”, IEEE Transactionson Power Electronics, Vol. 21, No. 5.
2. Gui-Jiasu (2005), “Multilevel DC-LinkInverter”, IEEE Trans. on Ind.Applications, Vol. 41, No. 4, pp. 724-738.
3. Mariethoz S and Rufer A (2004),“Resolution and Efficiency Improvementsfor Three-Phase Cascaded MultilevelInverters”, IEEE Transaction.
4. Nagaraja Rao, Ashok Kumar D V et al.(2013), “New Multilevel Inverter Topologywith Reduced Number of Switches UsingAdvanced Modulation Strategies”,International Conference on Power,Energy and Control.
5. Ohsato M H, Kimura G and Shioya M(1991), “Five-Stepped PWM InverterUsed in Photo-Voltaic Systems”, IEEE
Transactions on Industrial Electronics,Vol. 38, October, pp. 393-397.
6. Rodriguez J, Lai J-S and Peng F Z (2002),“Multi-Level Inverter: A Survey ofTopologies, Controls, and Applications”,IEEE Trans. Ind. Electron., Vol. 49,No. 4, pp. 724-738.
7. Salmon J C, Olsen S and Durdle N (1991),“A Three-Phase PWM Strategy Using aStepped 12 Reference Waveform”, IEEETransactions on Industry Applications,Vol. IA27, No. 5, pp. 914-920.
8. Thorborg K and Nystorm A (1988),“Staircase PWM: An Uncomplicated andEfficient Modulation Technique for acMotor Drives”, IEEE Transactions onPower Electronics, Vol. PE3, No. 4,pp. 391-398.
9. Wells J R, Geng X, Chapman P L, KreinP T and Nee B M (2007), “Modulation-Based Harmonic Elimination”, IEEETrans. Power Electron., Vol. 22, No. 1,pp. 336-340.
10. Zhong Du and Leon M Tolbert (2009),“Fundamental Frequency SwitchingStrategies of a Seven – Level HybrideCascaded H-Bridge Multilevel Inverter”,IEEE Transactions on, Vol. 24, No. 1.
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