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Performanceanalysis of Reduced switches Multi-Level inverter.

 B.S.V.Bharathi*, G. Durga Prasad**‡, W. Razia Sultana***     *Departmentof power electronics and drives, Faculty of W.Razia Sultana, Affiliation ofFirst Author, Postal address**Departmentof Second Author, Faculty of First Author, Affiliation of First Author, Postaladdress***Departmentof Third Author, Faculty of First Author, Affiliation of First Author, Postaladdress (FirstAuthor Mail Address, Second Author Mail Address, Third Author Mail Address)‡ Corresponding Author; Second Author, Postal address, Tel:+90 312 123 4567, Fax: +90 312 123 4567,[email protected]: xx.

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xx.xxxx Accepted:xx.xx.xxxx  Abstract- Multi-level inverter plays a crucial role inindustrial applications. In this paper we analyzed the performance of cascadedmulti-level inverter with reduced switch topology.

If we increase the switchesswitching losses also increase and THD also increase. This topology reduce theTHD of inverter. The simulation of seven level and fifteen level also done.

Theadvantage of this circuit is there are four switches are constant at all levelsand at fundamental frequency.Keywords- RCMLI; IPD; LSHPWM.   1.     IntroductionNow a day’s power electronics and drives plays acrucial role in every aspects.  In thispower electronics and drives multi-level inverters has wide range ofapplications.

This MLI has so many advantages compared to normal two levelinverters. This has lower harmonic distortion and less electromagneticinterference.  Number of switches is morein MLI. This is a one of the disadvantage in MLI.Multi-level inverters are classified into threedifferent types:Ø  Diodeclamped multi- level inverters.Ø  Flyingcapacitor multi-level inverters.

Ø  CascadedH-Bridge multi-level inverters. 1.1Diode clamped multi-1 level inverters:Diodeclamped MLI (DCMLI) is also known as Neutral point clamped MLI.

The main advantageof DCMLI is unequal switching device rating, high voltage rating for blockingdiodes and capacitor voltage unbalance.  These DCMLIs are used in high frequency applications. Harmonic contentwill be increase if the number of levels are increase.

In back to backconfiguration these MLIs are applicable in regenerative process. These are usedin line to redundancies.1.2 Flying capacitor multi-level inverter:          Flyingcapacitor MLI (FCMLI) is also known as capacitor clamped inverter and imprecatedcell inverter. This is same as the DCMLI. The difference is that instead ofdiodes, capacitor will be used.

But practically only six levels we can do withthis MLI. These are used in phase to phase redundancies. Control of real andreactive power is very easy with these FCMLIs.1.3 CascadedH-Bridge multi-level inverter:These cascaded H-bridges are numberof H-bridges connected in series.

The outputs of the H-bridges are efficient ifit is increased by the dc sources compared to the DCMLI and FCMLI. The numberof semi-conductor switches used in this MLI is less compare to other twoinverters. The below Table 1. Represents the number of components used forthese inverter configurations.Table 1.Components used in different MLIs  Inverter configuration Diode clamped Flying capacitor Cascaded H-bridge Main switching devices 2(m-1) 2(m-1) 2(m-1) Main diodes 2(m-1) 2(m-1) 2(m-1) Clamping diodes (m-1)(m-2) 0 0 DC bus capacitors (m-1) (m-1) (m-1)/2 Balancing capacitors 0 (m-1)(m-2)/2 0   1.4 Modulation techniquesTo control the gating signals ofthe switching devices many modulation techniques are came used.

The Figure 1 representsthe modulation techniques of MLI. In this topology carrier based PWM Techniqueis used. Here, sinusoidal wave is compared with the carrier triangular wave andthe resultant pulse will generate. This modulation is known as “SPWM” (sinusoidalpulse width modulation).

There are different types of SPWM such as phase shiftmodulation, level shift modulation. In this in-phase disposition, alternatephase opposition disposition and phase opposition disposition. When compared,in-phase disposition method gives the better efficient output.Figure1. Modulation Techniques of MLI2.      PV panel specifications The voltagesupplied by the renewable energy source i.

e. solar PV source. The voltage ofthe panel is taken as 150 volts and the power is 300 watts. The current of thepanel is taken as 6.8 amps.

These are the specifications for the PV panel. TheIV curve and PV curves of panel are shown in Figure 2.Figure 2.

IV andPV curves of PV panel 2. ReducedSwitch TopologyThe above circuit diagramrepresents the multi -level inverter of reverse voltage topology or reducedswitch topology (RCMLI). There are three isolated voltage sources, tenswitches, LC filter and R load. The first 6 switches (S1, S2,S3, S4, S5, S6) are used for the levelgeneration part and next four switches (Sa, Sb, Sc,Sd) are used for the polarity generation part.

Level generationswitches operates at the high switching frequency and polarity generationswitches operates at the low switching frequency or at fundamental or linefrequency. The advantage of this circuit is that four switches at linefrequency will generate polarity at any level of output voltage. So that numberof switches will decrease. Those four switches are fixed at fundamentalfrequency.

To increase the number of levels the switches are increased  at level generation side at high frequency.The modes of operation of RCMLI are explained in Table 2. In this circuit onemiddle switch is considered as duplicate switch. So, that switching losses willbe decreased. Figure 3. SevenLevel RCMLI The Table 2 shows switching states forvarious modes of operation of seven level RCMLI. Here, 0 represents the switchOFF state and 1 represents the switch ON state.

At 0v level switches S1, S2, S3are on and remaining switches are off at the level generation side. For 1v (S2,S3, S5), for 2V (S2, S5, S6), for 3V (S1, S5) is on at the level generationside and for the negative levels the same switches are off. And at the polaritygeneration side the switches Sa, Sb are ON for positivelevels and these switches are OFF for negative levels.Table2. Switching states of seven level MLI    Level generation Polarity generation   S1 S2 S3 S4 S5 S6 Sa Sb Sc Sd 0v 0 1 1 1 0 0 1 1 0 0 1V 0 1 1 0 1 0 1 1 0 0 2V 0 1 0 0 1 1 1 1 0 0 3V 1 0 0 0 1 0 1 1 0 0 -1V 1 0 0 1 0 1 0 0 1 1 -2V 1 0 1 1 0 0 0 0 1 1 -3V 0 1 1 1 0 1 0 0 1 1  3.      Fifteen Level RCMLI            InFifteen level RCMLI there are fourteen switches are used at the levelgeneration side and the four switches are used at the polarity generation side.

In this five switches are considered as duplicate switches. Comparing to normalcascaded H-Bridge in this topology the number of switches are decreased. Figure4. Fifteen Level RCMLIThe Table 3represents the switching states of fifteen level RCMLI. Here, 1 represents theswitch is ON and 0 represents the switch is OFF.

The first seven levels arepositive polarity because of the polarity generation switches or bridgenegative levels are also obtained.     Table3. Switching States of Fifteen Level RCMLI     Level Generation Unit Polarity Generation Unit SWITCHES/    LEVELS S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 0V 0 1 1 1 1 1 1 1 0 0 0 0 0 0 1 1 0 0 1V 0 1 1 1 1 1 1 0 1 0 0 0 0 0 1 1 0 0 2V 0 1 1 1 1 1 0 0 1 0 0 0 0 1 1 1 0 0 3V 0 1 1 1 1 0 0 0 1 0 0 0 1 0 1 1 0 0 4V 0 1 1 1 0 0 0 0 1 0 0 1 0 0 1 1 0 0 5V 0 1 1 0 0 0 0 0 1 0 1 0 0 0 1 1 0 0 6V 0 1 0 0 0 0 0 0 1 1 0 0 0 0 1 1 0 0 7V 1 0 0 0 0 0 0 0 1 0 0 0 0 0 1 1 0 0 0V 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 -1V 0 1 1 1 1 1 1 0 1 0 0 0 0 0 0 0 1 1 -2V 0 1 1 1 1 1 0 0 1 0 0 0 0 1 0 0 1 1 -3V 0 1 1 1 1 0 0 0 1 0 0 0 1 0 0 0 1 1 -4V 0 1 1 1 0 0 0 0 1 0 0 1 0 0 0 0 1 1 -5V 0 1 1 0 0 0 0 0 1 0 1 0 0 0 0 0 1 1 -6V 0 1 0 0 0 0 0 0 1 1 0 0 0 0 0 0 1 1 -7V 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 1  4.

      Results and discussionTable4. Specifications of Seven level and Fifteen Level RCMLI  Elements Seven level RCMLI Fifteen level RCMLI Switching Frequency 1 KHz 1 KHz Fundamental Frequency for polarity generation switches 50Hz 50Hz Inductor(L) 10mH 10mH Capacitor(C) 2?F 2?F Resistance(R) 50? 50? Number of PV panels used 7 14 Input voltage 30V 30V Output Voltage 90V 210V Current 1.8A 4.7A  Figure 5. Seven level RCMLI without filter       Figure 6. Seven level RCMLI with filter Figure.

5 shows that it is a seven level output without filter in which the outputhas different levels at a switching frequency of 1KHZ.  The levels 30,60,90 are said to be  first ,second and third level generation and -30,-60,-90 are said to be first ,second and third level  polarity generation.             Figure. 6  observed that it is a seven level output withfilters and same operation as said in the figure .5Figure 7.

THD analysis of sevenlevel RCMLI   Figure 8. THD analysis ofSeven level      withoutfilter                                                                     RCMLI with filter  Figure 7. and figure 8. shows that the THDanalysis of seven level for fundamental frequecny of 50KHZ.

The THD value forwithout filter  around 18.9% and  for with filter was 0.28%. So it is observedthat the difference between the  THDvalue for with filter and without filter is around 17.91%.Figure 9.

Fifteen level RCMLIwithout filter    Figure 10. Fifteenlevel RCMLI with                                                                                          Filter                              Figure 9. shows that it is a fifteen leveloutput without filters in which the output has different levels at a switchingfrequency of 1KHZ.  The levels  30,60,90,120,150,180, 210 are said to be  first , second, third, fourth, fifth, sisxthand seventh level generation and -30,-60,-90, -120,-150,-180 and -210 are said to be  polarity generation.

            Figure. 10  shows that it is a fifteen level output withfilters and same operation as said in the figure .9 Figure 9. THD analysis of fifteenlevel RCMLI   Figure10. THD analysis offifteen      withoutfilter                                                                      levelRCMLI with filter  Figure 9.

and Figure10.shows that the fifteen level output for fundamental frequecny of 50KHz. the THDvalue for without filter is around 7.94% and for with filter is around 0.15%. So it is observed that the differencebetween the  THD value for with filterand without filter is around 7.79%. Figure 11.

current waveform ofseven level        Figure 12. Currentwaveformof fifteen                  RCMLI                                                                level RCMLI  Figure 11. shows that itis a seven level RCMLI in which the current is about 1.8 Amps and  the Figure 12.

Shows that  it is a fiftheen level RCMLI  in which current is about 4.7 Amps.  5.     ConclusionThese reduced switch RCMLIs areused in high power drives and in this implemented the fifteen level RCMLI withR load. And the THD is taken for both with filter and without filter.

The levelshift modulation technique with phase opposition and disposition is the bettermodulation technique to get pulses. Comparing to the both seven level andfifteen level THD, Fifteen level THD is lesser than seven level. So finally thenumber of levels are increases THD value decrases so that switching losses willbe decreased. 6.      References1 K. Jang-Hwan, S.-K. Sul, and P.

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