Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and                     Applications (IJERA) I...
Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and                                  Applicati...
Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and                     Applications (IJERA) I...
Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and                      Applications (IJERA) ...
Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and                                           ...
Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and                                           ...
Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and                     Applications (IJERA) I...
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  1. 1. Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.637-643Harmonic Compensation and Load Balancing Using Cascaded H- bridge Multilevel Inverter in High Voltage Systems Ali Mehri*, DaryooshNazarpour** *(Department of Electrical Engineering, University of Urmia, Urmia-IRAN) ** (Department of Electrical Engineering, University of Urmia, Urmia-IRAN)ABSTRACT This paper presents detailed modeling Passive filters are used for harmonicand simulation of a compensator for Load mitigation due to their advantages of simplicity, lowbalancing and harmonics Compensation based on cost and easy maintenance. But passive LC filters fora five-level cascaded H-bridge multilevel voltage reducing the current harmonic pollution aresource inverter. This type of compensator, which ineffective, because those are large in size, resonateis installed in parallel with the load, is usually with the supply impedance, have ageing and tuningreferred to as the shunt active power filters (APF). problems and the filtering characteristics areNowadays use of high voltage non-linear loads are dependent on the source impedance which is notwidely used in industrial and commercial exactly known [3].applications and elimination of harmonics in HV To provide high power quality at the point ofsystem has become an important aspect. common coupling (PCC) of a distribution system,Implementation of multilevel inverter (MLI) as active power filters are widely studied recently, forcompensatorin HV system eliminates use of bulky the compensation not only of current harmonicsand high cost transformer.The compensation produced by fluctuating loads, but also of reactiveprocess is based on concept of p-q theory, which is power and unbalance of non-linear and distortingcomprised of positive sequence voltage and loads[4],[5].instantaneous real-power theory. The controller At low voltage levels, conventional two levelmethod successfully eliminates harmonics even the inverters are used. At medium voltage levels, thesupply voltage is distorted. The Phase Shifted conventional two level inverters either requireCarrier PWM (PSCPWM) technique is used to interface transformers between the inverter terminalsgenerate firing angles to cascaded H-bridge and the supply terminals or need active devices to bemultilevel inverter (CHBMLI) switches which connected in series to achieve the required voltagereduces the individual device switching levels [6]. In this case, use of transformer for mediumfrequency.The distribution network which or high voltage applications requires high VA ratingsupplies mixed linear and non-linear loads and of transformer which results in high magnitude ofemploying MLI is simulated by current on low voltage side and causes more losses.MATLAB/SIMULINK software. The simulation The system becomes bulky and costly [7]. Theresult validates the proposed control method in multilevel inverters are able to achieve the requiredhigh voltage system. voltage levels using devices of low voltage rating.Keywords-Load Balancing, Harmonic The use of MLI also eliminates the need ofCompensation, Multilevel Inverter, Active Power transformer to feed the power to HV system [8],[9].Filter, Phase Shifted Carrier PWM, Instantaneous P- Three major kinds of multilevel inverters topologiesQ Theory, High Voltage Systems. are realized, namely, diode-clamped, flying-capacitor clamped and cascaded h-bridge multilevel voltage I. INTRODUCTION source inverter for generating smooth sinusoidal Nowadays non-linear and fluctuating loads, voltage. The major advantages of the CHBMLI oversuch as a diode/thyristor rectifiers, semi converters, the other two types are summarized as follows [10]:arc furnaces, adjustable-speed drives, ac voltageregulators, etc., are widely used in industrial and 1) Construction and maintenance cost of H-commercial applications. These non-linear loads bridge is less.create harmonic and distortion current in electrical 2) Requires a low number of components pernetworks and have disadvantages such as: reducing level.electric power quality, increasing the losses of the 3) Simple voltage balancing modulation.distribution system and changing in power quality 4) Maximum output can be utilized from the DC[1]. On the other hand this electric power delivered sources.under conditions of unbalanced and non-sinusoidal 5) Possibility to implement soft-switching.source voltage system [2]. 637 | P a g e
  2. 2. Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.637-643 For higher-level applications, voltage balance bridges are used per phase as shown in Fig.1. If thecontrol of diode-clamped converter shows no dc voltage of each cell is set to the same valueadvantage with more than three DC capacitors, (Vdca1 = Vdca2 = E), then the resulting inverter canbecause the problem of capacitors‟ voltage balance is operate with five output voltage levels. Table I.complicated when the output level beyond four. shows the zero and positive voltage levels obtainableMoreover the higher the level is, the more serious the from this inverter as well as the voltage levels fromunbalance is. Many researchers have done much the individual H-bridge cells [13].work [11],[12] on this but no effective methodespecially for topologies higher than five levels until Table I. output voltage of inverter for phase anow. This is one of the main reasons that block its Vag = Vag1 + Vag2 Vag1 Vag2industry application. E -E In this paper, the configuration of compensator 0 0 0based on five-levelcascaded H-bridge inverter -E Ewithout using the transformer is presented. Then, theproposed control technique for load balancing and E 0 Eharmonics compensation is discussed in detail. 0 E This paper is organized as follows: Section II 2E E Edescribes the MLI topology and modulationstrategies in part A, B separately. Section III includesproposed controller method based on P-Q theory. B. ModulationSection IV gives the simulation results and analysis The modulation technique used is based onof five-level cascaded inverter simulation in two PSCPWMstrategy, In the phase shifted multicarrierconditions. Finally, section V presents our modulation, all triangular carriers have same peak toconclusions. peak amplitude and the same frequency but there is a phase shift between any two adjacent carrier waves of magnitude given byII. BASIC OF CASCADED MULTILEVELINVERTER 360° 𝛷 𝑐𝑟 = (1)A. Topology of the Inverter 𝑚−1 Cascaded multilevel inverter is one of the Wherem is the voltage levels of MLI. Gatemost important topology in the family of multilevel signals are generated by comparing the modulatinginverters. Multilevel inverters do not need a coupling wave with the carrier waves. In this PWM methodtransformer to interface it with high power system. A the equivalent switching frequency of the wholefive level cascaded H-bridge inverter at the high converter is (m-1)times as the each power devicevoltage level has been considered and is operated at a switching frequency. This means PSCPWM cancarrier frequency of 3 KHz. The system configuration achieve a high equivalent switching frequency effectis shown in Figure 1. at very low real device switching frequency which is most useful in high power applications [13]. The Linear & non-linear carrier 1 and carrier 2 are used to generate gating for Load the upper switches in left legs of power cells H1 and3-phase H2 in Fig. 1 respectively. The carrier 1 and carrier 2ac mains are two triangular carrier waves shifted by 90° from each other. The inverted signals are used for upper Vdc a1 Vdc c1 Vdc b1 + + + Vag1 - - Vbg1 - Vcg1 switches in the right legs. The gate signals for all lower switches operate in a complementary manner with respect to their corresponding upper switches. Vdc b2 Vdc c2 + + + Vdc a2 Vag2 Vbg2 - Vcg2 - - Phase A Phase B g Phase C Fig. 1. Cascaded Multilevel Inverter The cascaded multilevel inverter used herecomposed of six H-bridges and six dc capacitors. It isconnected to the power system in parallel. Thenumber of output phase voltage levels in acascadedinverter is given asm = 2s + 1, where s isthe number ofseparate dc sources and m is the Fig 2. Gating Signal Generation by PSCPWMinverter level. To obtain 5-level output, two H- 638 | P a g e
  3. 3. Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.637-643 Fig. 2 gives the block diagram to generate the  1 1  1    v a  2gating signals,wheremodulating signal is MLI v   2 2  reference current and is compared with carrier 1 and     vb (2)2. The advantage of PSCPWM that the v   3 3  3  0 v c   semiconductor device can be used at comparatively  2 2 low switching frequency so that switching loss is An integrated circuit with a VCO chip (PLLreduced greatly [13],[14]. circuit) should determine accurately the fundamental frequency(𝑓𝑣 +) of the system voltage, subsequently, PLL-circuit produced auxiliary signals i   and i   . These currents used to calculate the auxiliary powers p  and q  follows as p   v  i   v  i   (3) Similarly, the instantaneous reactive power is defined as q   v  i   v  i   (4) Using a first order Low Pass Filter (LPF), the Fig 3. Control block diagram for reference current generation average 𝑝′ and 𝑞′ powers are composed onlyfrom the fundamental positive sequence voltage, since the auxiliary currents are also composed only from aIII. PROPOSED CONTROLLER BASED ON P-Q fundamental positive sequence component. TheTHEORY The control block diagram Based Onp-q instantaneous voltagesv   andv   it can be derivedtheory for the three phases MLI is shown in Fig. as3.The sinusoidal and immediately extraction controlstrategy is applied to extract the reference current or v   1 i  i     p        (5)fundamental components from the distorted line v   (i   ) 2  (i   ) 2 i  current. This proposed controller is comprised of    i     q      positive sequence voltage detector and real-power Finally, the instantaneous three-phase voltagestheory concept. Fundamentals of this theory were    values (v a ,v b ,v c ) of the fundamental positivereported in [15] and many other publications. Thispostulate led to the formulation of the famous p-q sequence voltage, are determined by applying thetheory of reactive power. inverse Clarke transformation, it derived as   1 0  v a       2  1 3  v    v b   3  2   2  v   (6) v c          1  3  2  2  The positive sequence voltage detector prepares good dynamic response and satisfactory Fig 4.α-β coordinates transformation even under unbalanced or distorted voltage source conditions. The p-q theory is based on the α-βtransformation, also known as the Clarketransformation. With considering Fig. 4, for simplecalculation, the three-phase voltages and currents areconsidered only, excluding zero-sequencecomponents. The positive-sequence voltage detectorconsists of PLL circuit and instantaneous real-powercalculation is shown in fig. 5. The balanced ordistorted voltage sources are transformed into the α-βcoordinates using Clarke transformation Fig. 5. Block diagram of the fundamental positive- sequence voltage detector. 639 | P a g e
  4. 4. Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.637-643 After producing positive sequence of voltage, proposed controller calculates only the real-powerreference current generation is obtained. According losses [8]. The α – β coordinatecurrents i cα , i cβ areto Fig. 4, the instantaneous space vector voltage andcurrentv a , i a are set on the a-axis,v b , i b are on the calculated from the v α , v β voltages withb-axis, and v c , i c are on the c-axis. These space instantaneous real power ( p ) only and the instantaneous reactive power is set to zero. Thisvectors are easily transformed into α-β stationary. It approach reduces the calculations and implementsconsists in a real matrix to transform measured three- better than the conventional methods; thephase source voltages (v a , v b ,v c ) andsource compensating currents α – β coordinate are derived by using equationcurrents ( i a , i b , i c ) into the α-β stationary referenceframe as shown in (7) and (8). i c   1 v  v   p   2 v v    0  (12) i c   v   v  2       1 1 1  v a v   2 2 2   Finally, The compensation current referencesv     vb (7)  3 3  3  in the α −β coordinates are then transformed back 0 v c    2  into the a-b-c coordinates through the inverse  2  simplified Clarke transformation as given by: 1 1 1    i a i   2 2 2   1 0 i     ib (8)  i sa *     3 3  3   * 2  1 3  i c  i c  0  2 2    i sb   3 2   2  i c   (13)  i sc *   Conventional instantaneous real-powerfor three-  phase circuit can be defined as  1  3  2  2 𝑝 𝑎𝑐 = 𝑣 𝛼 𝑖 𝛼 + 𝑣 𝛽 𝑖 𝛽 (9) These reference currents are subjected to a PSCPWM in order to generate the switching pattern The instantaneous real-power (𝑝 𝑎𝑐 ) is passing for IGBT switches of MLI. The reference currentthrough Butterworth design based LPF. The LPF cut- waveforms and the six triangular carrier waveformsoff frequency 50 Hz that allows only the fundamental are compared to generate the PSCPWM signals for asignal to the active power section that calculates the five-level CHBMLI.AC components of the real-power losses. The DC-power loss is calculated from the IV. SIMULATION RESULTScomparison of the dc-side voltage of the cascaded The operation of cascade multilevel invertermultilevel inverter and desired reference voltage. The for APF is evaluated by simulating the proposedproportional integral-controller [𝐾 𝑝 = 1, 𝐾 𝑖 = 163,] scheme in MATLAB Simulink. Three phaseis determining the dynamic response and settling time uncontrolled converter with R-L elements towardsof the dc-side voltage. The DC component power their dc-side is used as non-linear load. Table IIlosses can be written as shows the simulation parameters.  k pDC(loss)  v DC ref  v DC   k p  i  (10) Table II.System parameters  s  AC Source Line Voltage 25 k Frequency 50 Hz The instantaneous real-power (p) is calculated Source Inductor 0.5 mHfrom the AC component real-power losses and the Source Resistance 0.6 ΩDC component power losses)PDC(Loss)(. It can be AC side Filter Inductance 10 mHdefined as follows DC Capacitor 5000 μFp  pac  pDC (loss ) (11) Carrier Frequency 3 KHz The AC and DC component of the The source-current detection control method byinstantaneous real power p is related to the harmonic detecting the current through section III is adopted incompensation currents. The instantaneous current on MLI. The performance of the APF is analyzed under various operating conditions via sinusoidal andtheα – β stationaryof i cα , i c are divided into two β distorted voltage source with load perturbation.kinds of instantaneous current components: real- Simulation waveforms of the combined system inpower losses and reactive-power losses, but this two cases are given as below. 640 | P a g e
  5. 5. Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.637-643A. Sinusoidal Voltage Source Condition 1000 source currents [ A ] In this case three-phase balanced sinusoidal 500voltages supplying to three phase uncontrolledconverter withR-L elements towards their dc-side as 0non-linear load. Three-phase source voltages, -500unbalanced non-linear load currents, 1-phasecompensation current of MLI and source currents -1000 0.4 0.41 0.42 0.43 0.44 0.45after compensation are shown in Fig. 6. A three- time [ sec ]phase non-linear load with a resistor and an Fig. 7. Waveforms of source current beforeinductance runs at first. Thus the load current compensation in distorted supply voltage condition.includes harmonic current and inductance reactivecurrent. The five-level inverter generates the distorted The harmonic spectrum and THD of sourceinjecting current to compensate the distorted current currents before and after compensation are shown inwhich 1-phase of that as shown in Fig. 6 (c). Similar Fig. 8. As observed the source current THD iscurrent but with 120° phase shift is injected by legs successfully minimized to 2.14 % as compared to the„b‟ and „c‟ of the MLI into phases „b‟ and „c‟ of the result before compensation which is 21.81 %.distribution system. The three phase source currents THD= 21.81% 40after compensation is shown in Fig. 6(d) which is Mag (% of Fundamental)perfectly balanced and in-phase with the respective 30voltages. (a) 20 4 x 10 4 10 source voltages [ V ] 2 0 0 5 10 15 20 25 30 35 40 45 50 Harmonic order 0(a) -2 THD= 2.14% 5 Mag (% of Fundamental) -4 0.4 0.41 0.42 0.43 0.44 0.45 4 time [ sec ] 3 (b) 2 1 load currents [ A ] 500 0 0 5 10 15 20 25 30 35 40 45 50 Harmonic order 0(b) Fig. 8 Order of harmonics of source currents -500 without (a) and with (b) five level cascaded h-bridge 0.4 0.41 0.42 0.43 0.44 0.45 inverter in sinusoidal voltage source condition. time [ sec ] 200 B. distorted Voltage Source Condition 1-phase compensation In order to get a non-sinusoidal voltage for current of MLI [ A ] 100 simulation study a 3rd and 5th harmonic voltage 0 source is added in series with phase „a‟, „b‟ and phase(c) -100 „c‟. The performance of MLI with p-q theory and -200 distorted mains voltage is represented in Fig. 9. The 0.4 0.41 0.42 time [ sec ] 0.43 0.44 0.45 distorted mains voltage affects the calculation accuracy of the reference current and there will be 1000 effective for harmonic compensation, which is shown after compensation [ A ] in Fig.9. source currents 500 The load current is unbalanced and polluted 0(d) with a harmonic distortion, since the load current -500 wave shape in each phase is different with each other. -1000 0.4 0.41 0.42 0.43 0.44 0.45 Compensated source currents are found to be time [ sec ] sinusoidal and balanced after compensation. The three-phase non-linear load currents before Fig. 6. Waveforms of ideal mains voltage (a), load compensation are shown in Fig 9 (b) that indicate that current (b), 1-phase compensation current of MLI(c) the source current is distorted or having harmonic and source current after compensation (d) in currents. 1-phase of distorted injecting current that sinusoidal voltage source condition. generated by MLI to compensate the distorted current asshown in Fig. 6(c). For phase b and c this current is Fig. 7 shows the three-phase source currents injected but with 120° phase shift. The three-phasebefore compensation. Fig. 6 (d) shows the three- source current after compensation is shown in Fig 9phase source current waveforms after the (d) that indicates that the current is sinusoidal.compensator run. 641 | P a g e
  6. 6. Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.637-643 4 distorted source voltages [ V ] 4 x 10 produces harmonics in the source current with the THD of 25.63% without MLI as given in the non- 2 sinusoidal waveform of the source current is shown(a) 0 in Fig.11. By injecting the compensating current -2 through the five-level cascaded H-bridge inverter the -4 source current has become almost sinusoidal as 0.4 0.41 0.42 time [ sec ] 0.43 0.44 0.45 depicted in Fig. 9 (d) and the source current THD is significantly reduced to 2.91 %. 500 load currents [ A ] 0 THD= 25.63%(b) Mag (% of Fundamental) 40 30 -500 (a) 20 0.4 0.41 0.42 0.43 0.44 0.45 time [ sec ] 10 300 1-phase compensation 0 200 0 5 10 15 20 25 30 35 40 45 50 current of MLI [ A ] Harmonic order 100 0(c) -100 THD= 2.91% Mag (% of Fundamental) -200 8 -300 0.4 0.41 0.42 0.43 0.44 0.45 6 time [ sec ] (b) 1000 4 after compensation [ A ] 2 source currents 500 0 0 5 10 15 20 25 30 35 40 45 50 0 Harmonic order(d) -500 Fig. 12 Order of harmonics of source currents -1000 without and with five level cascaded H-bridgeinverter 0.4 0.41 0.42 0.43 0.44 0.45 time [ sec ] in sinusoidal voltage source condition. Fig. 9. Waveforms of distorted supply voltage (a), load current (b), 1-phase compensation current of FFT analysis indicates that MLI with proposed MLI (c) and source current after compensation (d) in controller method brings down the THD of the source distorted voltage source condition current to be less than 5% in compliance with IEEE 519 and IEC 61000-3harmonic standards [16],[17]. In Fig.10 1-phase of line side AC voltage waveform Thus the simulation results prove that the proposed of MLI is shown. controller method successfully compensates the 4000 harmonics even the mains voltage is non-sinusoidal phase voltage of MLI [ V ] and distorted. 2000 0 V. CONCLUSION -2000 In this paper cascaded H-bridge multilevel -4000 0.4 0.41 0.42 0.43 0.44 0.45 0.46 0.47 0.48 0.49 0.5 inverter based APF is implemented in distribution time [ sec ] system. This eliminates need of high cost transformer Fig.10 Phase voltage of MLI with MLIin high voltage systems. Cascade type inverter has certain advantages as compared with Fig. 11 shows the three-phase source currents other types. Positive sequence voltage detector and before compensation in distorted voltage source instantaneous real-power theoryis used to generate condition. The three-phase source current waveforms reference currents of APF. The Phase Shifted Carrier after the MLI is connected are shown in Fig. 9 (d). PWM method reduces individual device switching 1000 frequency despite high frequency output of the source currents [ A ] 500 converter. Simulated results validate that the 0 cascaded multi-level inverter based APF can -500 compensate harmonics without use of transformer in high voltage system. It can be concluded that the -1000 0.4 0.41 0.42 0.43 0.44 0.45 proposed technique is best suited for load time [ sec ] compensation under unbalanced load, distorted and Fig.11. Waveforms of source current before unbalanced supply voltage conditions. Total compensation in distorted supply voltage condition. Harmonic Distortion of the source currenthas been The FFT analyses of source currents before reduced from a high value to an allowable limit and after compensation are shown in Fig. 12. This tomeet IEEE 519 and IEC 61000-3harmonic 642 | P a g e
  7. 7. Ali Mehri, DaryooshNazarpour/ International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.637-643standard. Adjustable DC Voltages for Induction”,Industry Applications Conference, 2000REFERENCES [13] Young-Min Park; Ji-Yoon Yoo; Sang-Bin Lee “Practical Implementation of PWM[1] Bhim Singh, Kamal Al-Haddad &Ambrish Synchronization and Phase-Shift Method for Chandra, “A New Control Approach to 3-phase Cascaded H-Bridge Multilevel Inverters Based Active Filter for Harmonics and Reactive on a Standard Serial Communication Power Compensation”-IEEE Trans. on Power Protocol”Industry Applications, IEEE Systems, Vol. 46, NO. 5, pp.133 – 138, Oct- Transactions on, March-April 2008 1999 [14] Waware, M.; Agarwal, P. “Performance[2] W. K. Chang, W. M. Grady, Austin, M. J. investigation of multilevel inverter based active Samotyj “Meeting IEEE- 519 Harmonic power filter in distorted high voltage supply Voltage and Voltage Distortion Constraints system” Sustainable Energy Technologies with an Active Power Line Conditioner”- IEEE (ICSET), 2010 IEEE International Conference Trans on Power Delivery, Vol.9, No.3, on, 10.1109/ICSET.2010.5684961,dec-2010 pp.1531-1537, 1994 [15] H. Akagi, Y. Kanazawa, and A. Nabae,[3] Hirofumi Akagi, “Trends in Active Power Line "Instantaneous reactive power compensators Conditioners”- IEEE Trans on Power comprising switching devices without energy Electronics, Vol.9, No.3, May-1994 storage components," IEEE Trans. Ind. Appl.,[4] ZhilingQiu; Wenqiang Zhao; Guozhu Chen vol. IA-20, pp. 625-630, May/June 1984. “Study on shunt active power filter with high [16] Duffey, C.K.; Stratford, R.P., “Update of quality grid current waveform”, Applied Power harmonic standard IEEE-519: IEEE Electronics Conference and Exposition, 2008. recommended practices and requirements for APEC 2008. Twenty-Third Annual IEEE harmonic control in electric power systems”[5] Hirofumi Akagi. Active harmonic filters. Industry Applications, IEEE Transactions on, Proceedings of the IEEE, 2005, 93 (12): Nov/Dec 1989 2128~2141. [17] McGranaghan, M.; Beaulieu, G. “Update on IEC 61000-3-6: Harmonic Emission Limits for[6] Basu, M.; Das, S.P.; Dubey, G.K., “Parallel Customers Connected to MV, HV, and EHV” converter scheme for high-power active power Transmission and Distribution Conference and filters”, Electric Power Applications, IEE Exhibition, 2005/2006 IEEE PES, 21-24 May Proceedings 2006[7] B.Geethalakshmi, M.Kavitha and K. DelhiBabu, “Harmonic Compensation using Multilevel inverter based shunt active power filter”, Proceedings of IEEE PEDES 2010 and 2010 Power India Conference, December 20- 23, 2010.[8] W.Liqiao, L Ping Z. Zhongchao“Study on shunt active power filter based On cascade multilevel converters”, in 35th Annual IEEE power electronics Specialists Conference 2004. Pp.3512- 3516[9] Karuppanan, P.; Mahapatra, K., “Cascaded multilevel inverter based active filter for power line conditioners using instantaneous real- power theory”, Power Electronics (IICPE), 2010 India International Conference on, 28-30 Jan. 2011[10] Jih-Sheng Lai; FangZhengPeng, “Multilevel inverters: a survey of topologies, controls, and applications”, Industrial Electronics, IEEE Transactions on, 49 , Issue: 4 , Aug-2002[11] GautamSinha, and Thomas A. Lipo, “A Four- Level Inverter Based Drive with a Passive Front End”, IEEE Trans on Power Electron., Vol. 15, No. 2, March 2000, pp285-294[12] Takashi Ishida, KoukiMatsuse, Tetsuya Miyamoto, etc., “Fundamental Characteristics of Five-Level Double Converters With 643 | P a g e

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