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International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of......

International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.

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  • 1. Miss Vani Mishra, Mrs.Paramjeet Kaur / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.863-872863 | P a g ePower Flow Control In Induction Motor By Using AssymmetricalMultilevel InverterMiss Vani Mishra, Mrs.Paramjeet KaurAssistant Professor,at NRI College,RGPV University,Bhopal))ABSTRACTThe Assymetrical multilevel invertertopology is used for the optimization of levelswith a mimimum no. of voltage sources. It isused where medium voltage and higher power isrequired.There are three or four H-bridge ofsingle phase inverter (consist of MOSFET orOptocoupler)connected to Induction motor.AllH-Bridges are working with different votagesources bases on the G.P ratio(2or3).Amultilevel inverter is more advantageous incomparison with a conventional two-levelconverter that uses high switching frequencypulse width modulation(PWM).The increase inthe number of level in multilevel inverterreduces the total harmonic distortion(THD),common mode voltages,the output filtersand the switching losses and hence power flowcan be controlled by providing smooth a.c sinewave to the induction motor to mainly preventthe reduction of the efficiency of the motor dueto harmonics which are present in normalpower supply.But in multilevel there are alsosome limitations if we will go for higher levelsi.e.beyond 27 level that we will also see here indetail description by the results of simulationdone on MATLAB7.10.Keywords- Assymetrical multilevel inverter,MOSFET, Optocoupler, Induction motor,H-Bridge(consist of MOSFET),G.P ratio,Conventional two-level converter, PWM,THD,common mode voltages,output filters, switchinglosses, harmonics, ac sine wave, efficiency,simulation1. INTRODUCTIONNumerous industrial applications havebegun to require higher power application in recentyears.Some mediun voltage motor drives and utilityapplications require medium voltage motor drivesand utility applications require medium voltage andmegawatt power level.For a medium voltage grid,itis troublesome to connect only one powersemiconductor switch directly.As a result amultilevel power converter structure has beenintroduced as an alternative in high power andmedium voltage situation.A multilevel converternot only achieves high power ratings,but alsoenables the use of renewable energysources.Renewable energy sources such asphotovoltaic,wind and fuel cells can be easilyinterfaced to a multilevel converter system for ahigh power application.The concept of multilevel converters hasbeen introduced since 1975.The elementaryconcept of multilevel converter to achieve higherpower is to use a series of power semiconductorswitches with several lower voltage d.c sources toperform the power conversion by synthesizing astair case voltage waveform. Capacitors, batteriesand renewable energy voltage sources can be usedas the multiple d.c voltage sources.Multilevel inverter topologies can work athigher voltage and higher power than conventionaltwo level converter.A multilevel converter hasseveral advantage over a conventional two levelconverter that uses high switching frequency pulsewidth modulation(PWM).The attractive features of a multilevel converter canbe briefly summarized as follows:1) Staircase waveform quality:Multilevel converters not only can generate theoutput voltage with very low distortion ,butalso can reduce the dv/dt stresses ;thereforeelectromagnetic compatability problem can bereduced.2) Common mode voltage(CM):Multilevel converters produce small CMvoltage; therefore, the stress in the bearingsconnected to a multilevel motor drive can bereduced. Furthermore, CM voltage can beeliminated by using advanced modulationstrategies such as that proposed in.3) Input current: Multilevel converters candraw input current with low distortion.4)Switching frequency: Multilevel converterscan operate at both fundamental switchingfrequency and high switching frequency PWM.It should be noted that lower switchingfrequency usually means lower switching lossand higher efficiency.Due to above feature we are using a multi level forpower control of induction motor.1) One particular disadvantage is the greaternumber of power semiconductor switchesneeded.
  • 2. Miss Vani Mishra, Mrs.Paramjeet Kaur / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.864 | P a g e2) Although lower voltage rated switches can beutilized in a multilevel converter, each switchrequires a related gate drive circuit.This maycause the overall system to be more expensiveand complex.INDEX1) Introduction2-32) Two types of multilevel inverter5-63) Methodology14-174) Note185) Harmonic effects of induction motor18-206) Conclusion217) Acknowledgement228) Literature survey23CONTENTSLIST OF FIGURES:1,2,3(a),3(b),3(c),3(d),4,5,6,72. - Two Types of Multilevel Inverter1) Symmetrical type Multilevel Inverter2) Asymmetrical type Multilevel InverterIn symmetrical multilevel inverter, all H-bridge cells are fed by equal voltages andhence all the arm cells produce similar outputvoltages.If all the cells are not fed by equal voltages, theinverter becomes an asymmetrical one. In thisinverter,the arm cells have different effect onthe output voltage.The cascade H-Bridge inverter consists ofpower conversion cells, each supplied by anisolated dc source on the dc side,which can beobtained from batteries, fuel cells, or ultracapacitors and series connected on the a.c side.Fig1 shows a one phase circuit for a machinedrive using 3cascade H-bridge inverter consistof MOSFETS.If we will provide voltage 1Vdc,1Vdc,1Vdcwith G.P ratio 1 to the three H-bridge then thesimulation output will be as shown in theFig2.It is called 7 level symmetrical output ofas we are providing symmetricalvoltages.V0,1(t)=1Vdc,V0,2(t)=1Vdc,V0,3(t)=1Vdc shows the output waveform of theindividual bridge and V0(t)=3Vdc shows thesummation of above 3 waveforms.If we will provide voltage 1Vdc,2Vdc,4Vdc,with G.P ratio 2 to the three H-bridge then thetotal simulation output V0(t)=15Vdc will beas shown in Fig3(d).It is called 15 levelsymmetrical output as we are providingasymmetrical voltages..V0,1(t)=1Vdc,V0,2(t)=2Vdc,V0,3(t)=4Vdcshows the output waveform of individualbridge as shown in Fig3(a),Fig3(b),Fig3(c)respectively.An output phase voltage waveform is obtainedby summing the bridges output voltages.V0(t)=V0,1(t) + V02(t) +……+V0,N(t) ;(1)Where N is the number of cascaded bridges.Again ,if all dc voltage sources in Fig1 areequal to Vdc, the inverter is then known as asymmetric multilevel And if all dc voltagesources are not equal it is called Asymmetricalmultilevel inverter.
  • 3. Miss Vani Mishra, Mrs.Paramjeet Kaur / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.863-872865 | P a g e
  • 4. Miss Vani Mishra, Mrs.Paramjeet Kaur / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.866 | P a g eFig2.
  • 5. Miss Vani Mishra, Mrs.Paramjeet Kaur / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.867 | P a g eAdvantages Of Asymmetrical Type Multi Level Inverter:
  • 6. Miss Vani Mishra, Mrs.Paramjeet Kaur / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.868 | P a g e The main advantage of asymmetrical multilevel inverters is the optimization of levels with a minimumnumber of power supplies. The increase in the number of voltage levels reduces the total harmonic distortion (THD), the common-mode voltages, the output filters, and the switching losses. The main bridges, which carry 80% of the total power, work at a very low frequency. In some particular operation it can be operated with a single dc source. It enables the use of the Renewable Power Sources.Disadvantages Of Asymmetrical Type Multi Level Inverter:• They need many independent power supplies that must be floating, isolated, and balanced.• In some particular levels of voltage, bidirectional power supplies are required, and the same happenswhen regenerative braking needs to be applied.• The direct relation between the number of levels and the voltage amplitude, which produce a loss ofquality when the output voltage is reduced. Costly and complex topologies have to be implemented to get the isolated supplies.Block Diagram:Fig4: Main Components Of 27 Level Asymmetrical Type Multi Level Inverter For 1 Phase
  • 7. Miss Vani Mishra, Mrs.Paramjeet Kaur / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.869 | P a g e3.METHODOLOGY:Refer to Fig4 the voltage supplied to the 3H-Bridge will be scaled in power 3 according toG.P ratio.The driver circuit will individually drivethe gates of the MOSFET’s connected in H-Bridgeor optocoupler can be used in place of drivercircuits.All individual bridge is supplied by the d.c voltagewhich is multiple of 3 as shown in Figure.The controller IC which generate the clock pulsewill be programmed according to the phase delaywe want in the clock pulse cycle and the durationwe want of each clock pulse. Here the phase delayare providing as 0.02*1/56 seconds. For one gatepulse i.e. in a graph paper if we will draw the gatewaveform for each bridge then for 1cm block weare providing as 0.02*1/56 seconds. The output wewill get is shown in Fig5. The 3 outputsVo1=1Vdc,V02=3Vdc,V03=9Vdc is showing theoutput of each bridge of the circuit and their totaloutput after summation is 13Vdc waveform whichis shown in Fig5. The maximum output voltage wewill get is 13Vdc. It is called as 27 level output or27 level symmetrical output.Now if we will increase the level from 27level to 81 level by increasing one more H-Bridgein Fig4. I.e. havingV01=1Vdc,V02=3Vdc,V03=9Vdc and V04=27Vdchaving same G.P ratio. As shown in Fig6. And thetotal output waveform is shown in Fig7.
  • 8. Miss Vani Mishra, Mrs.Paramjeet Kaur / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.870 | P a g eFig7
  • 9. Miss Vani Mishra, Mrs.Paramjeet Kaur / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.863-872871 | P a g eFrom 81 level total output waveform we have seenthat almost same output we are getting here as itwas in 27 level case at the cost of limitations in 81level circuitry. So it is not sensible to go uptohigher level. The limitations with 81 level circuitryare as follows:1) Switching frequency of the bridge whichshares the minimum power will increase.2) At the cost of the fourth bridge reduction inTHD is not appreciable.3) Master Bridge(higher rating voltage bridge)will have to share the max. Power4) Distribution of power will not be uniform.5) Rating of the master bridge will be too high incomparison with the rating of the bridge whichshares the minimum power.4-NOTE-We are considering here G.P ratio as 3instead of 2 because it Higher voltage output andhigher level output.5.HARMONIC EFFECTS ONINDUCTION MOTOR-Induction motors are commonly used inindustry and sensitive to voltages harmonics andtheir operation and efficiency can be affectedintensely their supplied power quality. Someoscillations in three phase induction motors torqueappear on launch time which these oscillationsdamped in very short time. Although the torqueamount can be negative in that time but averagevalue remain positive because of motors stableoperation. If we use from speed-torque curve fordepict of motor behavior in steady state. In everyapplications these oscillations will not beappreciable and can be negligible. In non sinusoidalsupply conditions the oscillations existing intransient state is not damped and survive to steadystate (with small value) which mainly leads toreduction of the efficiency of the motor. Variousindustrial loads including static converters (such aselectric furnace, induction heating devices andswitching power supply) inject current harmonicsin power systems Generally power electronicdevices such as switching sources and convertersare most important sources of harmonic generation.Converters usually generate harmonics from nthlevel in AC side.n = knp±1 (2)Where:k is a constant and np is the number ofconverter pulses.This phenomena lead to distortion in voltagelike as iron saturation in over loadeddistribution transformers. Induction motorunder perfect sinusoidal supply conditiongenerate little amount of current harmonics.Because of its coils structure and non linearbehavior of iron core. Most importantconsequent of this phenomena is efficiencydecrease of motor.Installation of capacitor placement indistribution systems for power factor correctionand series reactor in transmission lines fordecrease in short circuit current are not directcauses of harmonic generating but because ofprobability of resonance generation can intenseand magnify existed harmonics.Voltage harmonic because of heat andoscillations produce in rotor cause mostimportant damage to induction motor. Rotorsoscillations are because of torque ripples andthese ripples emerge from positive and negativeordinary harmonics. Rotors oscillations canincrease friction losses of bearings. Sincemotors temperature in present of any harmonicwould be higher than normal state and this willdamage to bearings and stator coil andconsequently motors life will be decreased. Forpreventing of excessive rise of motorstemperature, motors should be derated. Thisderating leads to increase of energyconsumption and cause more damages toconsumers.6.CONCLUSION:-The Assymetrical multilevel invertertopology is used for the optimization of levels witha mimimum no. of voltage sources. It is used wheremedium voltage and higher power is required.Amultilevel inverter is more advantageous incomparison with a conventional two-levelconverter that uses high switching frequency pulsewidth modulation(PWM).The increase in thenumber of level in multilevel inverter reduces thetotal harmonic distortion (THD),common modevoltages,the output filters and the switching lossesand hence power flow can be controlled byproviding smooth a.c sine wave to the inductionmotor to mainly prevent the reduction of theefficiency of the motor due to harmonics which arepresent in normal power supply.ACKNOWLEDGEMENTIt gives me immense pleasure to expressmy deepest sense of gratitude and sincere thanks tomy greatly respected guide Mrs.Paramjeet KaurAssistant Professor in the Department of Electricaland Electronics Engineering,NIIST ,Bhopal,fortheir valuable guidance encouragement and help forthis work.I express my deep sense of gratitude to Dr. AmitaMahor(Prof. & H.O.D), Electrical and ElectronicsEngineering,NIIST ,Bhopal,for his keeninterest,continued encouragement and support.
  • 10. Miss Vani Mishra, Mrs.Paramjeet Kaur / International Journal of Engineering Research andApplications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.872 | P a g eI am also thankful to all the staff members of theDepartment of Electrical and ElectronicsEngineering,Bhopal, for their cooperation in mywork.Literature survey:[1]. Juan Dixon, Javier Pereda “AsymmetricalMultilevel Inverter for Traction DrivesUsing Only One DC Supply” IEEETransactions On Vehicular Technology,Vol. 59, No. 8, October 2010[2]. Farid Khoucha, Mouna Soumia Lagoun,Abdelaziz Kheloui, and Mohamed ElHachemi Benbouzid “A Comparison ofSymmetrical and Asymmetrical Three-Phase H-Bridge Multilevel Inverter forDTC Induction Motor Drives” IEEETransactions On Energy Conversion, Vol.26, No. 1, March 2011[3]. Bambang Sujanarko, Mochamad Ashari“Advanced Carrier Based Pulse WidthModulation in Asymmetric CascadedMultilevel Inverter” International Journalof Electrical & Computer Sciences IJECS-IJENS Vol: 10 No: 06.[4]. Diorge Alex Báo Zambra, Cassiano Rech◊and José Renes Pinheiro “COMPARISONAMONG THREE TOPOLOGIES OFMULTILEVEL INVERTERS”