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Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
Comparative analysis of a cascaded seven level and five level mli based distribution
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Comparative analysis of a cascaded seven level and five level mli based distribution

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  • 1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME358COMPARATIVE ANALYSIS OF A CASCADED SEVEN LEVEL ANDFIVE LEVEL MLI BASED DISTRIBUTION STATCOM FORCOMPENSATION OF HARMONICS AND REACTIVE POWER USINGREFERENCE FRAME THEORYD.MOHAN REDDY1, Dr.T.GOWRIMANOHAR21(Department of EEE, Sri Vasavi Institute of Engg & Tech., Machilipatnam, Krishna Dist,India)2(Department of EEE, SVU, Tirupati, Chittoor Dist, India)ABSTRACTThe general structure of the multilevel converter is to synthesize a sinusoidal voltagefrom several levels of voltages, Multilevel voltage source converters are emerging as a newbreed of power converter options for high power applications, These converter topologies cangenerate high-quality voltage waveforms with power semiconductor switches operating at afrequency near the fundamental. The “multilevel converter” has drawn tremendous interest inthe power industry. Among the available multilevel converter topologies, the cascadedmultilevel converter constitutes a promising alternative, providing a modular design that canbe extended to allow a transformer less connection. This paper presents a three-phase, five-level and seven level cascaded multilevel voltage source inverter based active filter for powerline conditioning to improve power quality in the distribution network. The active filtercompensates both reactive power and harmonic currents drawn by non-linear loads;additionally it facilitates power factor corrections. The compensation process is based onconcept of p-q theory. This proposed cascaded five level and seven level active power filtersystem is validated through MATLAB/SIMULINK.Keywords: Cascaded H- Bridge Multilevel Inverter, Distribution STATCOM(DSTATCOM), Reference Frame theory, Power quality, PWM, Triangular-sampling currentmodulator.INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING& TECHNOLOGY (IJEET)ISSN 0976 – 6545(Print)ISSN 0976 – 6553(Online)Volume 4, Issue 2, March – April (2013), pp. 358-371© IAEME: www.iaeme.com/ijeet.aspJournal Impact Factor (2013): 5.5028 (Calculated by GISI)www.jifactor.comIJEET© I A E M E
  • 2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME359I. INTRODUCTIONElectrical Power Quality had obtained more attention in power engineering in recentyears. In present day’s power distribution systems is suffering from severe power qualityproblems. These power quality problems include high reactive power burden, harmonicscurrents, load unbalance, excessive neutral current etc. The measure of power qualitydepends upon the needs of the equipment that is being supplied. What is good power qualityfor an electric motor may not be good enough for a personal computer. Usually the termpower quality refers to maintaining a sinusoidal waveform of bus voltages at rated voltageand frequency [1]. The waveform of electric power at generation stage is purely sinusoidaland free from any distortion. Many of the Power conversion and consumption equipment arealso designed to function under pure sinusoidal voltage waveforms. However, there are manydevices that distort the waveform. These distortions may propagate all over the electricalnetwork. In recent years, there has been an increased use of non-linear loads which hasresulted in an increased fraction of non-sinusoidal currents and voltages in Electric Network.The wave shape phenomena associated with power quality may be characterized intosynchronous and non synchronous phenomena. Synchronous phenomena refer to those insynchronism with A.C waveform at power frequency [2],[3].A group of controllers togethercalled Custom Power Devices (CPD), which include the DSTATCOM (distribution staticcompensator), The DSTATCOM, is a shunt-connected device, which takes care of thepower quality problems in the currents It consists of a dc capacitor, three-phase inverter(IGBT, thyristor) module, ac filter, coupling transformer and a control strategy. The basicelectronic block of the D-STATCOM is the voltage-sourced inverter that converts an input dcvoltage into a three-phase output voltage at fundamental frequency. The D-STACOMemploys an inverter to convert the DC link voltage Vdc on the capacitor to a voltage sourceof adjustable magnitude and phase. Therefore the D-STATCOM can be treated as a voltage-controlled source. The D-STATCOM can also be seen as a current-controlled source. Thegeneralized instantaneous reactive power theory which is valid for sinusoidal or non-sinusoidal and balanced or unbalanced three-phase power systems with or without zero-sequence currents were later proposed [4-8]. The construction controller of the D-STATCOMis used to operate the inverter in such a way that the phase angle between the inverter voltageand the line voltage is dynamically adjusted so that the D-STATCOM generates or absorbsthe desired VAR at the point of connection. The phase of the output voltage of the thyristor-based inverter, Vi, is controlled in the same way as the distribution system voltage, Vs.The DSTATCOM is based on the instantaneous real-power theory; it provides goodcompensation characteristics in steady state as well as transient states [9-11]. Theinstantaneous real-power theory generates the reference currents required to compensate thedistorted line current harmonics and reactive power. It also tries to maintain the dc-busvoltage across the capacitor constant. Another important characteristic of this real-powertheory is the simplicity of the calculations, which involves only algebraic calculation [12-16].A multilevel inverter, can reduce the device voltage and the output harmonics by increasingthe number of output voltage levels.There are several types of multilevel inverters: cascaded H-bridge (CHB), neutralpoint clamped, flying capacitor. In particular, among these topologies, CHB inverters arebeing widely used because of their modularity and simplicity. Various modulation methodscan be applied to CHB inverters. CHB inverters can also increase the number of outputvoltage levels easily by increasing the number of H-bridges. This paper presents a
  • 3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME360DSTATCOM with a proportional integral controller based CHB multilevel (five level andseven level) inverter for the harmonics and reactive power mitigation of the nonlinear loads.This type of arrangements have been widely used for PQ applications due to increase in thenumber of voltage levels, low switching losses, higher order harmonic elimination and lowelectromagnetic compatibility for hybrid filters.II. PROPOSED SYSTEMFig 1: Schematic Diagram of DSTATCOMInstantaneous real-power theory based cascaded multilevel inverter basedDSTATCOM is connected in the distribution network at the PCC through filter inductancesand operates in a closed loop. The DSTATCOM system contains a cascaded inverter, RL-filters, a compensation controller (instantaneous real-power theory) and switching signalgenerator (proposed triangular-sampling current modulator) as shown in the Fig 1. The three-phase supply source connected with non-linear load and these nonlinear loads currentscontains fundamental and harmonic components. If the active power filter provides the totalreactive and harmonic power, is (t) will be in phase with the utility voltage and would besinusoidal. At this time, the active filter must provide the compensation current therefore,active power filter estimates the fundamental components and compensating the harmoniccurrent and reactive power.
  • 4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME361A. Five level CHB InverterFig.2 Five level CHB inverterFig 2 Shows the five level multilevel inverter and Table I shows the switching statesof the 5 level inverter. Here even though we have eight switches at any switching state onlytwo switches are on/off at a voltage level of Vdc/2, so switching losses are reduced. In threelevel inverter dv/dt is Vdc, but in five level inverter dv/dt is Vdc/2. As dv/dt reduces thestress on switches reduces and EMI reduces.Table I Switching table for Full H-Bridge of five level inverterSwitches Turn ON Voltage LevelS1,S2,S6,S8 Vdc/2S1,S2,S5,S6 VdcS2, S4,S6,S8 0S3,S4,S6,S8 -Vdc/2S3,S4,S7,S8 -Vdc
  • 5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME362B. Seven level CHB InverterFig. 3 Seven level CHB inverterFig 3 Shows the seven level multilevel inverter and Table shows the switching states of theseven level inverter.Table I Switching table for Full H-Bridge of seven level inverterSwitches Turn ON Voltage LevelS1,S2,S6,S8,S10,S12 Vdc/3S1,S2,S5,S6,S10,S12 2Vdc/3S1,S2,S5,S6,S9,S10 VdcS2,S4,S6,S8,S10,S12 0S3,S4,S6,S8 S10,S12 -Vdc/3S3,S4,S7,S8,S10,S12 -2Vdc/3S3,S4,S7,S8,S11,S12 -VdcIII. REFERENCE CURRENT CONTROL STRATEGYThe control scheme of the shunt active power filter must calculate the currentreference signals from each phase of the inverter using instantaneous real-powercompensator. The block diagram as shown in Fig.3, that control scheme generates thereference current required to compensate the load current harmonics and reactive power. ThePI controller is tried to maintain the dc-bus voltage across the capacitor constant of the
  • 6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME363cascaded inverter. This instantaneous real- power compensator with PI-controller is used toextracts reference value of current to be compensated.Fig 4: Reference current generator using instantaneous real-power theoryThese reference currents isa*, isb *and isc * are calculated instantaneously without anytime delay by using the instantaneous α,β coordinate currents. The required referencescurrent derivate from the inverse Clarke transformation and it can be written as(1)The p-q theory performs a Clarke transformation of a stationary system of coordinatesa bc to an orthogonal reference system of coordinatesα ,β . In a bc coordinates axes are fixedon the same plane, apart from each other by 1200that as shown in Fig 2. The instantaneousspace vectors voltage and current Va , ia are set on the a-axis, Vb , ib are on the b axis, andVc , ic are on the c axis. These space vectors are easily transformed into α ,βcoordinates. Theinstantaneous source voltages vsa, vsb, vsc are transformed into the α ,βcoordinate’s voltageVα, Vβby Clarke transformation as follows:(2)Similarly, the instantaneous source current isa, isb, isc also transformed into theα ,βcoordinate’s current iα iβ by Clarke transformation that is given as:(3 a)
  • 7. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME364Where α and βaxes are the orthogonal coordinates. They Vα, iαare on the α-axis, and Vβ ,iβare on the β-axis. The reference currents isa*, isb * and isc * are compared with actual sourcecurrent isa , isb and isc that facilitates generating cascaded multilevel inverter switching signalsusing the proposed triangular-sampling current modulator. The small amount of real-power isadjusted by changing the amplitude of fundamental component of reference currents and theobjective of this algorithm is to compensate all undesirable components. When the powersystem voltages are balanced and sinusoidal, it leads to constant power at the dc bus capacitorand balanced sinusoidal currents at AC mains simultaneously. The orthogonal coordinates ofvoltage and current vα,iαare on theα -axis and vβ , iβare on the β -axis. Let the instantaneousreal-power calculated from the α -axis and β - axis of the current and voltage respectively.These are given by the conventional definition of real-power as :(3 b)IV. MATLAB/SIMULINK MODELING AND SIMULATION RESULTSHere the simulation is carried out by three cases1. Non-linear load Without Filter2. Non-linear load with five level cascaded multilevel Active power filter3. Non-linear load with seven level Cascaded multilevel Active power filter.Case 1: Nonlinear load without Active power FilterFig 5: Matlab/Simulink model of nonlinear load without active filter
  • 8. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME365Fig-6 shows the three phase source voltages, three phase source currents and loadcurrents respectively without active power filter. It is clear that without Active power filterload current and source currents are same.Fig 6: Source voltage, Source current, Load currentCase 2:. Non-linear load with five level cascaded multilevel Active power filterThe performance of the proposed instantaneous real-power compensator cascadedfive level multilevel inverter based active power filter is evaluated through Matlab/Simulinktools. The non-linear diode rectifier R-L load is connected with ac mains and cascaded activefilter is connected in parallel at the PCC for injecting the anti-harmonics and eliminating theharmonics and improving the Reactive power.Fig 7: Matlab/Simulink Model of Nonlinear load with Five level Cascaded multilevel Activepower filter
  • 9. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME366Fig 8: Source voltage, Source current, Load currentFig-8 shows the three phase source voltages, three phase source currents and loadcurrents respectively with Cascaded Multilevel five level Active power filter. It is clear thatwith Active power filter load current are same and source currents are compensated.Fig 9: Five level output VoltageFig 9 Shows the Five level output voltage, when system is connected to cascaded fivelevel multilevel active power filter.Fig-10 Harmonic spectrum of Phase-A Source current with Five level Active power filter
  • 10. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME367Fig-10 shows the harmonic spectrum of Phase –A Source current with cascaded MultilevelFive level active power filter. The THD of source current with seven level active filter is7.34%.Case 3: Non-linear load with Seven level Cascaded multilevel Active power filterFig 11: Source voltage, Source current, Load currentFig-11 shows the three phase source voltages, three phase source currents and loadcurrents respectively with Cascaded Multilevel Seven level Active power filter. It is clearthat with Active power filter load current are same and source currents are compensated.Fig12 Shows the Seven level output voltage , when system is connected to cascaded five levelmultilevel active power filter.Fig 12. Seven level output Voltage
  • 11. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME368Fig 13 shows the power factor waveforms of the designed system without DSTATCOM. Thewaveform clearly shows that there is no unity power factor.Fig 13: Power Factor without DSTATCOMFig 14: Unity power Factor with DSTATCOM connectedFig 14 shows the power factor waveforms of the designed system with DSTATCOM.The waveform clearly shows that there is unity power factor where both the voltage andcurrent are in phase.Fig 15: Harmonic spectrum of Phase-A Source current with Seven level Active power filterFig15 shows the harmonic spectrum of Phase –A Source current with cascaded MultilevelSeven level active power filter. The THD of source current with seven level active filter is4.37%.
  • 12. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME369V. CONCLUSIONA five-level and seven level cascaded multilevel voltage source inverter based activefilter using instantaneous real-power controller is found to be an effective solution for powerline conditioning. Shunt active filter with the proposed controller reduces harmonics andprovides reactive power compensation due to non-linear load currents; as a result sourcecurrents become sinusoidal and unity power factor is also achieved under both transient andsteady state conditions. The proposed instantaneous real-power controller uses reducedcomputation for reference current calculations compared to conventional approach. Thecascaded inverter switching signals are generated using triangular-sampling currentcontroller; it provides a dynamic performance under transient and steady state conditions. Asevident from the simulation studies, dc bus capacitor voltage settles early and has minimalripple because of the presence of PI-controller. The THD of the source current when fivelevel active power filter is 7.34% after compensation is used Seven level active power filter4.34% which is less than 5%, the harmonic limit imposed by the IEEE-519 standard.Table III: System SpecificationsS.No System Parameters Rating1 voltage 11kv,50Hz2 Inductance 0.9e-3h3 Resistance 0.1ohm4 Load R=60,L=30e-35 Inverter Parameters DC Link voltage=14kvREFERENCES[1] Bhim Singh, Kamal Al-Haddad & Ambrish Chandra, “A New Control Approach to 3-phase Active Filter for Harmonics and Reactive Power Compensation”-IEEE Trans. onPower Systems, Vol. 46, NO. 5, pp.133 – 138, Oct-1999[2] W. K. Chang, W. M. Grady, Austin, M. J. Samotyj “Meeting IEEE- 519 HarmonicVoltage and Voltage Distortion Constraints with an Active Power Line Conditioner”- IEEETrans on Power Delivery, Vol.9, No.3, pp.1531-1537, 1994[3] Hirofumi Akagi, “Trends in Active Power Line Conditioners”- IEEE Trans on PowerElectronics, Vol.9, No.3, May-1994[4] W.M.Grady, M.J.Samotyj, A.H.Noyola “Survey of Active Power Line ConditioningMethodologies” IEEE Trans on Power Delivery, Vol.5, No.3, pp.1536-1542, July-1990.
  • 13. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME370[5] L. Gyugyi, E. C. Strycula, “Active AC Power Filters”- in Proc. IEEE/IAS Annu. Meeting,Vol.19-c, pp 529-535, 1976[6] Hirofumi Akagi, Yoshihira Kanazawa, Akira Nabae “Instantaneous Reactive PowerCompensators Comprising Switching Devices without Energy Storage Components”- IEEETrans on Industry Appl, Vol.I1-20, No.3,pp.625-630, 1984[7] E. H. Watanabe, R. M. Stephan, M. Aredes, “New Concepts of Instantaneous Active andReactive Powers in Electrical Systems with Generic Loads”- IEEE Trans. Power Delivery,Vol.8, No.2, pp.697-703, 1993[8] Fang Zheng Peng & Jih-Sheng Lai, “Generalized Instantaneous Reactive Power Theoryfor Three-Phase Power Systems”, IEEE Trans. on Inst. and Meast, Vol.45, No.1, pp.293-297,1996[9] Joao Afonso, Carlos Couto, Julio Martins “Active Filters with Control Based on the p-qTheory”- IEEE Industrial Elects Society Nletter-2000[10] E. H. Watanabe, H. Akagi, M. Aredes “Instantaneous p-q Power Theory forCompensating Non sinusoidal Systems”- International School on Non sinlusoidal Currentsand Compensation Lagow, Poland-2008[11] Leszek S. Czarnecki “Instantaneous Reactive Power p-q Theory and Power Properties ofThree-Phase Systems”- IEEE Trans on Power, VOL. 21, NO. 1, pp 362-367, 2006[12] Karuppanan P and Kamala Kanta Mahapatra “Shunt Active Power Line Conditioners forCompensating Harmonics and Reactive Power”-Proceedings of the International Conferenceon Environment and Electrical Engineering (EEEIC), pp.277 – 280, May 2010[13] Hirofumi Akagi, Akira Nabae and Satoshi Atoh “Control Strategy of Active PowerFilters Using Multiple Voltage-Source PWM Converters” IEEE Trans on IndustryApplications, Vol.IA-22, No.3, pp.460-465, May/June 1986[14] Fang Zheng Peng, John W. McKeever, and Donald J. Adams “A Power LineConditioner Using Cascade Multilevel Inverters for Distribution Systems” IEEE Trans onIndustry Applications Vol.34, No.6, pp. 1293-98, Nov/Dec-1998[15] S.-J.Huang and J.-C.Wu “Design and operation of cascaded active power filters for thereduction of harmonic distortions in a power System” IEE Proc.-Gener. Transm. Distrib..Vol. 146, No. 2,pp. 193-199, March 1999[16] Rajesh Gupta, Arindam Ghosh and Avinash Joshi “Switching Characterization ofCascaded Multilevel-Inverter-Controlled Systems” IEEE Trans on Industrial Electronics,Vol.55, No.3, pp 1047-1058, March-2008[17] D.Mohan Reddy and T.Gowrimanohar, “A Seven Level Cascaded MultilevelDSTATCOM for Compensation of Reactive Power and Harmonics Using Pscpwm andLscpwm Techniques”, International Journal of Advanced Research in Engineering &Technology (IJARET), Volume 4, Issue 2, 2013, pp. 106 - 118, ISSN Print: 0976-6480, ISSNOnline: 0976-6499[18] Satyendra Kumar, Dr.Upendra Prasad and Dr.Arbind Kumar Singh, “Reactive PowerManagement and Voltage Control using Facts Devices”, International Journal of ElectricalEngineering & Technology (IJEET), Volume 4, Issue 1, 2013, pp. 184 - 189, ISSN Print:0976-6545, ISSN Online: 0976-6553[19] Dr. Leena G, Bharti Thakur, Vinod Kumar And Aasha Chauhan, “Fuzzy ControllerBased Current Harmonics Suppression using Shunt Active Filter with PWM Technique”,International Journal of Electrical Engineering & Technology (IJEET), Volume 4, Issue 1,2013, pp. 162 - 170, ISSN Print: 0976-6545, ISSN Online: 0976-6553
  • 14. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME371AUTHORSMr. D. Mohan Reddy received the B.Tech. Degree in Electrical andElectronics Engineering from the JNT University, Hyderabad, India and hereceived the M.E Power Systems Engineering from Anna UniversityChennai and presently pursuing PhD from S.V.University,Tirupati,India.Presently he is working as an Associate Professor in the department ofElectrical and Electronics Engineering in Sri Vasavi Institute ofEngineering and Technology, Machilipatnam. His research areas ofinterests are Power Electronic Converters, Electrical Drives and Power Quality.Dr T. Gowri Manohar received the B.Tech, M.Tech and PhD Degreesin Electrical and Electronics Engineering from the S.V.University, Tirupati,India. Presently he is working as an Associate Professor in the department ofElectrical and Electronics Engineering S.V.University, Tirupati, India. He ishaving 15 years of teaching experience and he was published more than 65numbers of various international and national conferences & journals. He is asenior Member of IEEE and also he is a member in Indian Society forTechnical Education. His research areas of interests are Modern Restructured Power Systems,Electrical Power Semi-Conductor Drives and Power Quality and harmonics –issues &challenges.

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