Power quality enhancement using cascaded multilevel inverter based shunt hybrid active power filter

Transcription

1 MultCraft Internatonal Journal of Engneerng, Scence and Technology Vol. 3, No. 9, 2011, pp INTERNATIONAL JOURNAL OF ENGINEERING, SCIENCE AND TECHNOLOGY MultCraft Lmted. All rghts reserved Power qualty enhancement usng cascaded multlevel nverter based shunt hybrd actve power flter S. Rajasekar 1*, A. Senthlkumar 2, Y. Shas Kumar 1, P. Ajay-D-VmalRaj 2 1 Department of Electrcal Engneerng, M.N.Natonal Insttute of Technology, Allahabad,, INDIA 2 Department of Electrcal Engneerng, Pondcherry Engneerng College, Pondcherry, INDIA * Correspondng Author: e-mal: rajasekarsmvec@gmal.com Abstract Ths paper nvestgates mtgaton of current harmoncs usng dfferent confguraton of cascaded multlevel nverter based shunt hybrd actve power flter (SHAPF) and to mprove power qualty of the system. The man objectve of ths paper s to develop and analyze the compensaton characterstcs of cascaded multlevel nverter based shunt hybrd actve power flter by employng ndrect current control algorthm. The ndrect current control algorthm s employed to generate reference current and phase dsposton pulse wdth modulaton technque s ncorporated to generate gatng sgnal for shunt hybrd actve power flter strategy. The nonlnear loads are connected to dstort the source current to 21% of harmoncs dstorton, as per IEEE 519 allowable current harmonc dstorton s 5%. To mtgate harmonc dstorton, cascaded multlevel nverter based shunt hybrd actve power flter s proposed and after compensaton the source current harmonc dstorton s reduced to 2.93%. The smulaton analyss s carred out usng SIMPOWERSYSTEMS block set of MATLAB/SIMULINK to determne whch of the nverter topology based shunt hybrd actve power flter strategy perform better on compensatng source current harmonc dstorton. Keywords: Cascaded Multlevel Inverter, Multcarrer PWM technque, power factor correcton, shunt hybrd actve power flter. DOI: 1. Introducton Recently, power qualty has been gven attenton due to wde applcaton of power converters for controllng and convertng ac power to feed electrcal loads. These converters are used at dfferent power levels, rangng from large adjustable speed drves (ASDs) to low power household applances, offce equpment and computer. The large amount of power polluton produced from these power converters or non-lnear load wll causes a low power factor effcency of the power system, mples to voltage dstorton, and ncreases losses n the transmsson and dstrbuton lne (Sngh et al., 1998). The conventonal compensaton, approaches s done usng passve LC flters to elmnate lne current harmoncs and mprove the system power factor. These passve flters have the dsadvantage of large sze, resonance and fxed compensaton (Sngh et al., 1999). In the last couple of decades, the concept of actve power flter has been ntroduced and many publcatons have appeared on ths subject. A comprehensve revew of actve power flter (APF) confguraton, control strateges, selecton of components and other related ssues s gven n El-Harouk et al. (2000). But the ntal and operatonal costs of ths flter are too hgh. Combnng the advantage of both passve and actve flters, hybrd flter topologes are developed (Senn and Wolfs, 2000; Karthk, and Quacoe, 2000; Yuwen et al., 2000; Jacobs et al., 2001; Lqao et al., 2004). Hybrd flters effectvely mtgate the problems of a passve and an actve flter and provde cost-effectve harmonc compensaton, partcularly for hgh-power nonlnear loads. A parallel hybrd power flter system conssts of a small-ratng actve flter n seres wth a tuned passve flter. Ths elmnates the possblty of seres and parallel resonances. Correspondngly, Pulse Wdth Modulaton (PWM) nverter (wth 10 khz of hgh swtchng frequency) has been used for harmonc and reactve power compensaton. However, the hgh ntal and runnng cost have been hnderng ther practcal use n power dstrbuton systems. In addton t s dffcult for PWM-nverter based actve flters to

2 38 comply wth electromagnetc nterference (EMI) requrements. A cascaded multlevel nverter has been proposed for both harmoncs and reactve power compensaton. Ths nverter generates almost snusodal starcase voltage wth only one tme swtchng per lne cycle. When cascaded nverter s appled to lne condtonng and actve power flterng of a dstrbuton system, t s expected that the ntal and runnng costs and the EMI wll be dramatcally reduced below that of the tradtonal PWM nverter (Lqao et al., 2004; Mranda et al., 2004). The varous topology for multlevel nverter based shunt actve power flter strategy for compensaton of power qualty problems are reported n lterature survey (Rodrguez et al., 2002; Holmes and McGrath, 2001). The applcaton of shunt actve power flter s appled to dstrbuton generator s dscussed n Crrncone et al. (2008). The artfcal ntellgence based actve flter strategy and other technques used to mtgate current harmonc n dstrbuton system s dscussed (Bhattacharya, and Dvan, 1995; Park et al., 2000a, b; Dxon et al., 1999; Rahman et al., 2003). In ths paper fve level, seven level and nne level cascaded multlevel nverter based shunt hybrd actve power flter by employng ndrect current control algorthm technque wth phase dsposton Pulse Wdth Modulaton were presented. The proposed work attempts to analyze compensaton the characterstcs of cascaded multlevel nverter based shunt hybrd actve power flter by employng ndrect current control algorthm wth a vew to mprove power qualty s analyzed n ths paper. The paper also dscusses a comparatve analyss of dfferent confguraton of cascaded multlevel nverter based shunt hybrd actve power flter wth respect to source current and ts harmonc spectrum and reactve power compensaton are to be analyzed and compared. The smulaton s carred out n MATLAB/SIMULINK envronment. 2. Basc Compensaton Prncple The basc compensaton prncple of actve power flter s llustrated n fgure 1. Fgure 1. Basc crcut topology for actve power flter. The nstantaneous nonlnear load current s as follows Fgure 1. Operaton of actve power flter. L () t = I sn( h t h) h 1 h ω + Φ = (1) = I 1 sn( ωt + Φ 1 ) + I h sn( hωt +Φ h) h= L The nstantaneous load power as been formulated as

3 39 P L () t = Vs () t L () t 2 = VmI 1 sn ( ωt) cos( Φ 1 ) + VmI 1 sn( ωt) cos( ωt) sn( Φ 1 )+ V sn( ωt) Ihsn( hωt +Φ h) m h= 2 (2) = P ( t) + P ( t) + P ( t) Lf Lq Lh Where, I 1 s the peak value of the fundamental load current, I h s the peak value of the harmonc load current Φ 1 and Φ hh are the phase angle of the fundamental and harmonc component of the load currents, respectvely. In (2) the nstantaneous power of nonlnear load s dvded nto three terms. The frst term P Lf (t) s the nstantaneous load fundamental power. The second term P Lq (t) s nstantaneous load fundamental quadrature (reactve) power and the thrd term P Lh (t) s the nstantaneous load harmonc power. A shunt APF s desgned to be connected n parallel wth the load, to detect ts harmonc and reactve current and to nject nto the system a compensatng current, dentcal wth the load harmonc and reactve current. Therefore, nstantaneous supply current I s havng only fundamental component whch s n-phase wth source voltage V s (t). 3. Proposed Cascaded Multlevel Inverter Based Shunt Actve Power Flter Cascade Multlevel Inverters (MLI) s ncreasngly used n hgh power applcatons. Cascade multlevel nverter uses multple H- brdge power cells connected n a seres to produce hgh ac output voltages [11-12]. An m-level cascade multlevel nverter conssts of (m-1)/2 sngle-phase full brdges n whch each brdge has ts own separate dc source. Ths nverter can generate almost snusodal waveform voltage wth only one tme swtchng per cycle as the number of levels ncrease. In Fg.2 nne level cascade multlevel nverter s shown. It conssts of four sngle phase full brdges connected n seres n each leg. In ths confguraton f S= no of full brdge cells, then the number of output levels s (2S+1). Wth S=4 there wll be nne levels n phase voltage and peak magntude s SVdc. In Fg.2. Is s the AC source current, IL s load current, Ic s the compensated current from APF then I s = I L + I c (3) Fgure 2. Nne level Cascaded Multlevel Inverter based SHAPF.

4 40 Shunt actve flter acts a current source njectng equal but opposte harmonc and quadrature components of load current at the pont of common couplng. In effect the system vews non lnear load together wth actve flter as an deal resstor. A PWM voltage source nverter operatng as a current controller devce can be used as Shunt actve Power flter. Latest researches nclude the use on multlevel nverter for hgh power energy converson. The advantage of multlevel nverter wll enable the crcut to operate wth less output voltage harmoncs and less electromagnetc nterference. Because of the stepped output voltage, multlevel nverters have fewer rpples n ts lne current. There s ndvdual capactor for each H-brdge module. The APF wll adopt small power from source to compensate the swtchng losses and capactor losses and for that purpose, the capactor voltages are sensed and compared wth reference and fed to PI controller to generate loss component of APF. As compared wth fve levels and seven levels output voltage waveform s mproved n nne levels multlevel nverter. 3. Reference Current Sgnal Generaton The ndrect current control technque usng a PI controller n shown n Fg. 3. The shunt hybrd actve power flter bus voltage V dc s sensed and compared wth ts reference V * dc, the error s fed to the controller, the output of the controller estmate the peak lne current I * sm, t take care of the actve power demand of the load and losses n the actve power flter crcut[14-15]. The nstantaneous reference supples current (I * sa, I * sb, I sc *) are evaluated by multplyng the peak lne current by three unty voltage vectors. The shunt actve power flter s used to compensate for reactve current absorbed by non-lnear load, the unbalanced current and mantan the dc lnk voltage at constant level. In ths control algorthm, the desred mans current s assumed to be the product of the magntude and a unt ampltude snusodal wave n phase wth the mans voltage. The mans s requred to supply only the actve porton of the load current as the shunt hybrd actve power flter s expected to provde compensaton for the harmonc and reactve porton of the three phase load current, and also for any mbalance n the three-phase load currents. Hence, only balanced current wll be drawn from the mans whch wll be purely snusodal and n phase wth the mans voltages. The reference compensaton currents for the shunt hybrd actve flter are thereby deduced as the dfference between the actual load current and the desred source current n each phase can be represented as follows a( comp) La sa( ref ) (4) bcomp ( ) Lb sbref ( ) ccomp ( ) Lc scref ( ) Where the desred (reference) source currents n the three phases are gven as, (5) (6) Fgure 3. Indrect current control algorthm for SHAPF sa( ref ) x Va.sn ωt (7) o sb( ref ) x V b.sn( ωt 120 ) (8)

5 41 o sc( ref ) x Vc.sn( ωt ) (9) V a, V b and V c are the unt ampltude templates of the phase to ground source voltages n the three phases respectvely. V a = 1. sn( ω t ) (10) o V b = 1. sn( ωt 120 ) o V c = 1. sn( ω t ) (11) (12) The magntude of the desred source current s ( ref ) can be expressed as the average of the magntude of the real components of the fundamental load currents n the three phases Re( La ) + Re( Lb ) + Re( Lb ) sref ( ) = 3 (13) La.cos φ a + Lb.cos φ b + Lc.cos φ c = 3 To generate frng pulse for shunt hybrd actve power flter, Phase dsposton (PD) Pulse Wdth Modulaton technque s used. Ths s basc sub harmonc PWM technque, n whch all the carrer trangles are n phase [18]. The number of carrers s one less than the number of levels. In ths technque, sgnfcant harmonc energy s concentrated at the carrer frequency f c, because t s co-phasal components, t does not appear n the lne voltage. It should be noted that the other harmonc components are centered around the carrer frequency as sdebands.fg.4. shows the arrangement of carrer for phase dsposton PWM technque. Fgure 4. Arrangement of carrers-pd. 5. Smulaton Results and Analyss In ths secton, smulaton results of three-phase shunt hybrd actve power flter based on fve level, seven level and nne level cascaded multlevel and ts comparatve analyss are presented. The goal of the smulaton s to examne harmonc and reactve power compensaton under balanced system. The system consst of a three-phase network feeds a three-phase dode brdge rectfer wth a resstor R and nductor L n seres at ts dc output. Smulaton nvestgaton was carred on usng MATLAB/SIMULINK smulaton software n power system block set toolbox. The system parameters used n these smulatons are shown n Table Harmonc and reactve power compensaton under balanced ac source and load by 5-Level cascaded MLI: Fg.6. demonstrates the steady state response of source voltage, source current, compensaton current, load current and output V dc voltage under balanced source and balanced load s clearly depcted. The harmonc spectrum of source current before and after compensaton s shown n Fg.5. and Fg.7. From the obtaned results, the total harmonc dstorton (THD) of source current s observed to be reduced from 21.03% before compensaton to 4.56% after compensaton.

6 42 Table.4.1 Smulaton Parameters System Parameter Values Sendng end voltage (Lne to Lne) V 415 V (RMS) Supply frequency F 50Hz Lne mpedance L s 1.2mH Lne mpedance R L,L L 20Ω,8mH Actve flter parameter R dc,l dc,c dc 0.5mH,0.1Ω,2400µF Carrer Frequency for PWM crcut 10KHz Passve flter parameter L µ,c p 7mH,40 µf Fgure 5. Harmonc Spectrum of Source current before compensaton. Fgure 6. Steady State Response of 5-level Cascaded MLI based SHAPF

7 43 Fgure 7. Harmonc Spectrum of Source current after compensaton. 5.2 Harmonc and reactve power compensaton under balanced ac source and load by 7-Level cascaded MLI: Fgure 8. Harmonc Spectrum of Source current after compensaton. Fgure 9. Steady State Response of 7-level Cascaded MLI based SHAPF

8 44 The harmonc spectrum of source current after compensaton s shown n Fg.8. The steady state response of source voltage, source current, compensaton current, load current and output V dc voltage under balanced source and balanced load s clearly depcted revealed n Fg.9. It shows the supply mans currents n the three phases after compensaton are expected to be snusodal and n phase wth the mans, ths shows shunt compensaton has been acheved farly. For before compensaton, nonlnear load dstorted the source current to 21.03% of harmonc dstorton whereas after compensaton usng 7-level Cascaded MLI based SHAPF harmonc dstorton s mnmzed to 3.44%. Ths demonstraton proves that 7-level Cascaded MLI based SHAPF s better on mtgatng current harmoncs compared to 3-level Cascaded MLI based SHAPF. 5.3 Harmonc and reactve power compensaton under balanced ac source and load by 9-Level cascaded MLI The steady state response of source voltage, source current, compensaton current, load current and output V dc voltage under balanced source and balanced load s hghlghted n Fg.10. It shows the supply mans currents n the three phases after compensaton are expected to be snusodal and n phase wth the mans, ths shows shunt compensaton has been acheved farly. The harmonc spectrum of source current before and after compensaton s shown n Fg.5 and Fg.11. Before compensaton, the total harmonc dstorton (THD) of source current s found to be 21.03% whle after compensaton usng 9-level Cascaded MLI based SHAPF source current harmonc dstorton s reduced to 2.93%. Fgure 10. Steady State Response of 9-level Cascaded MLI based SHAPF Fgure 11. Harmonc Spectrum of Source current after compensaton.

9 45 Table 5.2 shows the comparson of results obtaned from under harmonc and reactve power compensaton under balanced ac source and load. The harmonc spectrum of source current after compensaton s clearly ndcated n the table5.3. The overall nvestgatons, proved that the 9-level Cascaded MLI based SHAPF has found to be better compensaton capablty compared to 7 and 5-level Cascaded MLI based SHAPF and three phase voltage source nverter based shunt hybrd actve power flter. 6. Concluson Table 5.2 Comparson of 5-Level, 7-Level Cascaded Multlevel Inverter based Shunt hybrd Actve Power Flter Dfferent Confguraton Before After Compensaton Compensaton Fve Level Cascaded Multlevel Inverter based SHAPF 21.03% 4.56% Seven Level Cascaded Multlevel Inverter based SHAPF 21.03% 3.44% Nne Level Cascaded Multlevel Inverter based SHAPF 21.03% 2.93% Table 5.3 Indvdual harmonc content under non-lner load condton. Harmonc Order Compensaton wth fve level cascaded MLI (%) Compensaton wth seven level cascaded MLI (%) Compensaton wth nne level cascaded MLI (%) 180Hz(h3) Hz(h5) Hz(h7) Hz(h9) Hz(h11) Hz(h13) The paper has nvestgated the comparatve analyss of fve level, seven level and nne level cascaded multlevel nverter based shunt hybrd actve power flter for compensaton of current harmoncs and reactve power compensaton are presented. The test results brng out the advantage of cascaded multlevel nverter based shunt hybrd actve power flter for power qualty enhancement. The total harmonc dstorton of source current has been reduced from a hgh value to an allowable lmt and to meet the IEEE 519 standard. The smulaton results clearly shows that reducton n THD s better n nne level nverter as compared wth seven level and fve level nverter based shunt hybrd actve power flter. The ndrect current control algorthm wth phase dsposton pulse wdth modulaton method provdes better computaton effcency for generatng reference current. The proposed shunt actve flter topology realzed an acceptable power factor profle and compensates the wde range of power qualty problems. Acknowledgement The authors gratefully acknowledge the Management of Pondcherry Engneerng College, Pondcherry, INDIA for ther contnued support, encouragement and the facltes provded to carry out ths research work. References Bhattacharya S., and Dvan D., Synchronous frame based controller mplementaton for a hybrd seres actve flter system. Conf. Rec. IEEE-IAS Annu. Meetng, pp Crrncone M., Pucc M., and Vtale G., A sngle-phase DG generaton unt wth shunt actve power flter capablty by adaptve neural flterng, IEEE Trans. Ind. Electron., Vol. 55, No. 5, pp Dxon J.W., Contardo J.M., Morlan L.A, A fuzzy controlled, actve front end rectfer wth current harmonc flterng characterstcs and mnmum sensng varable, IEEE Trans. Power Electron., Vol. 14, No. 4, pp El-Harouk M., Darwsh M.L., and Mehta P., Actve power flters- A revew, Proc. IEE-Elect. Power Applcaton, Vol. 147, No. 5, pp Holmes D. G., McGrath B. P., Opportuntes for harmonc cancellaton wth carrer-based PWM for two-level and multlevel cascaded nverters, IEEE Trans. Ind. Applcat., Vol. 37, No. 2, pp

10 46 Jacobs J., Deten D., Doncker R., A new hybrd flter versus a shunt power flters, Proc. European Con. On Power Electroncs and Applcatons (EPE 2001), Graz, Australa. Karthk K., and Quacoe J.E., Voltage compensaton and harmonc suppresson usng seres actve and shunt passve flters, Proc. IEEE Canadan Conf. on Electrcal and Computer Engneerng, pp Lqao W., Png L., Zhongchao Z Study on shunt actve power flter based on cascade multlevel converters, 35th Annual IEEE power electroncs Specalsts Conference, pp Lqao W., Shreen W., Packebush P. and Ptel I., Analyss, desgn of a new actve power flters to cancel neutral current harmoncs n three-phase four-wre electrc dstrbuton systems, Conf. Record IEEE-IAS Annual Meetng, pp Mranda H., Cardens V., Perez J., A hybrd multlevel nverter for shunt actve flter usng space vector control, 35th Annual IEEE power electroncs Specalsts Conference, pp Park S., Han S.B., Jung, Cho S.H., and Jeong H.G., 2000a. A current control scheme based on multple synchronous reference frames for parallel hybrd actve flter. Proc. 3rd Int. Conf. on Power Electroncs and Moton Control (PIEMC), pp Park S., Han S.B., Jung, Cho S.H., and Jeong H.G., 2000b. A current control scheme based on multple synchronous reference frames for parallel hybrd actve flter. Proc. 3rd Int. Conf. on Power Electroncs and Moton Control (PIEMC), pp Rahman S., Al-Haddad K., Fnaech F Bpolar reference for PWM control of a sngle phase shunt hybrd power flter. IEEE ISIE2003, pp Rodrguez J., La S., Peng F.Z Multlevel nverters: a survey of topologes, controls, and applcatons, IEEE Trans. On Ind. Electroncs, Vol.49, No 4, pp Senn S. and Wolfs P.J., Hybrd actve flter for harmoncally unbalanced three phase three wre ralway tracton loads, IEEE Trans. on Power Electroncs, pp Sngh B., Al-Haddad K. and Chandra A., A new control approach to three phase harmoncs and reactve power compensaton, IEEE Trans. on Power Systems, Vol. 13, No 1, pp Sngh B., Al-Haddad K., and Chandra A., A revew of actve flter for power qualty mprovement, IEEE Trans. Ind Electron, Vol.46, pp Yuwen B., Jang X., and Zhu D., Study on the performance of the combned power flter wth unsymmetrcal condton. Proc. 3rd Int. Conf. Power Electroncs and Moton Control (PIEMC), pp Bographcal notes S. Rajasekar receved the Bachelor s degree and Master s degree from the Pondcherry Unversty, Pondcherry, Inda, n 2008 and 2010 respectvely. He was the recpent of the IEEE Industral Electroncs Socety Travel grant award for the year He s currently pursung the Ph.D degree from the M.N. Natonal Insttute of Technology, Allahabad, Inda. He s a student Member n IEEE, Member n Internatonal Assocaton of Engneers, Member n Natonal Msson on Power Electroncs Technology, Inda (NaMPET) and also IEEE/IES Student Member. Hs research ncludes Renewable energy ntegraton nto grd, Power electroncs applcaton n Power system and Power Qualty Issues. Emal: rajasekar6387@gmal.com A. Senthlkumar was born n Puducherry, Inda, n He receved the B.E. degree n Electrcal and Electroncs Engneerng from the Malam Engneerng College, Anna Unversty, Chenna, n 2008 and the Master of Technology degree n Electrcal Drves and Control from the Pondcherry Engneerng College, Pondcherry Unversty, Puducherry, Inda, n He s currently pursung the Ph.D. degree n the Department of Electrcal and Electroncs Engneerng, Pondcherry Unversty, Puducherry, Inda. Hs research nterests nclude power qualty enhancement, renewable energy systems, artfcal ntellgence technques, electrcal drves and control. Emal: senthl.pec14@gmal.com Yerraguntla Shas Kumar was born n Nellore, Inda, on June 10, He receved the B.Tech. degree n electrcal and electroncs engneerng from the CVR college of engneerng, Hyderabad, Inda, n He s currently pursung M.Tech. degree n power electroncs and ASIC desgn from the Motlal Nehru Natonal Insttute of Technology, Allahabad, Inda. He s a student member of IEEE. Hs research nterests nclude power electroncs, renewable energy, power qualty, and Industral electroncs. Emal: shaskumar154@gmal.com Dr.P. Ajay-D-Vmal Raj receved the B.E. degree from Madras Unversty n 1998, M.E. degree from Faculty of Engneerng, Annamala Unversty, Taml Nadu, Inda, n 1999, and the Ph.D. degree from Pondcherry Engneerng College, Pondcherry Unversty, Pondcherry, n Currently he s Assstant Professor n the Department of Electrcal and Electroncs Engneerng, Pondcherry Engneerng College, Pondcherry Unversty, Pondcherry, Inda. Earler he was Faculty workng n Madras Unversty, Pondcherry Unversty and Deemed Unversty afflated engneerng colleges. Dr. Raj s a lfe member of the Insttuton of Engneers (Inda), lfe member of Indan Socety of Techncal Educaton (Inda) and lfe member of Socety of Power Engneers (Inda). He has publshed more papers n natonal/nternatonal journals and conference proceedngs. Hs research nterests nclude power system control n renewable energy systems and conventonal power systems, power system optmzaton, analyss of power qualty ssues, and applcaton of artfcal ntellgence technques n power systems. Emal: ajayvmal@yahoo.com Receved December 2011 Accepted June 2012 Fnal acceptance n revsed form June 2012