Research Article A Novel Power Electronic Inverter Circuit for Transformerless Photovoltaic Systems

Transcription

1 Ative d Pssive Eletroi Comoets, Artile ID 3943, 5 ges htt://dx.doi.org/1.1155/14/3943 Reserh Artile A Novel Power Eletroi Iverter Ciruit for Trsformerless Photovolti Systems Co Hi-Y Dertmet of Iformtio Egieerig, Shijizhug Uiversity of Eoomis, Shijizhug 531, Chi Corresodee should e ddressed to Co Hi-Y; etles888@16.om Reeived 8 Ferury 14; Revised 5 My 14; Aeted 5 My 14; Pulished 6 My 14 Ademi Editor: Gerrd Ghiudo Coyright 14 Co Hi-Y. This is oe ess rtile distriuted uder the Cretive Commos Attriutio iese, whih ermits urestrited use, distriutio, d rerodutio i y medium, rovided the origil work is roerly ited. Citive lekge urret is oe of the most imortt issues for trsformerless hotovolti systems. I order to del with the itive lekge urret, ew ower eletroi iverter iruit is roosed i this er. The iverter iruit osists of six swithes d oertes with ostt ommo mode voltge. Theoretil lysis is oduted to lrify the iruit oertio riile d the ommo mode hrteristi. The erforme evlutio test is rried out, d test results demostrte tht the itive lekge urret e sigifitly miimized with the roosed ower eletroi iverter iruit. 1. Itrodutio Photovolti (PV) ower systems re very ttrtive d widely used i reet yers. I order to itegrte the PV systems ito grid, ower eletroi omoet should e required to overt DC eergy soure geerted y PV rrys to AC omoet [1], whih is fed ito grid. eerl, trsformer is istlled etwee PV rrys d grid for glvi isoltio. The trsformer is hevy with lrge volume, log with the oer d iro losses durig trsformer oertio [, 3]. Therefore, the trsformerless PV system is oulr d reeived more d more ttetio [4 1], due to its low ost, smll size, d high effiiey. However, tehil hllege rises for trsformerless PV systems. More seifilly, the itive lekge urret is geerted etwee hotovolti modules d the groud [13]. I rtie, this itive lekge urret is very diffiult to hdle, euse the ite etwee hotovolti modules d groud is usully highly ureditle, d it vries sigifitly with temerture or humidity [14]. The resee of lekge urrets is very hrmful, sie they ould ut the life of hotovolti moduleistllertriskifhetouhesthehotovoltimodule [15]. Additiolly, they will rig high-frequey hrmois, whih my led to rolems with eletromgeti omtiility [16]. Therefore, it is imortt to del with the itive lekge urret rolem i the trsformerless PV system. The ojetive of this er is to reset ovel ower eletroi iverter iruit for trsformerless hotovolti system. The itive lekge urret e miimized with the roosed iverter iruit.. Ciruit Desritio The shemti digrm of the roosed ower eletroi iverter iruit is illustrted i Figure 1. Itshouldeoted tht the rsiti ite etwee groud d ositive termil of d us oit is oe of the ftors for the system stry ite. I this se, osiderig the etire stry ites of C v, the rsiti ite etwee groud d ositive termil of the iverter d us oit will e C v / d so is the ite of groud-egtive termil, s show i Figure 1. The ite vlue deeds o the PV el frme struture, wether oditios, humidity, d so o. Therefore, it is usully highly ureditle. I order to lrify the itive lekge urret miimiztio

2 Ative d Pssive Eletroi Comoets Tle 1: Oertio modes d voltges. U U U m Mode / Mode 1 / / / Mode / Mode4 1 / / / C v C v PV o Figure 1: Shemti digrm of roosed ower eletroi iverter iruit. C v U m U dm Figure : System s ommo mode model [17]. mehism, the system s ommo mode model is uilt, s show i Figure, whereu m istheommomodevoltge d U dm is defied s follows: U m = U U, (1) U dm = U ( ) ( ), () =. (3) I rtie, the filter idutors d re desiged with the equl vlue; tht is, =. So, the differetil mode voltge U does ot otriute to the itive lekge urret, s show i ()dfigure. O the other hd, if the ommo mode voltge U m is time vryig, the itive lekge urret will rise d flowitheloo,sshowifigure. I order to del with the itive lekge urret, it is of gret imorte tht the ommo mode voltge U m i Figure should e ket ostt. The followig will reset this ojetive hieved y the roosed ower eletroi iverter iruit. o The roosed iverter iruit oertes i four modes, s show i Figure 4 d Tle 1. I Mode 1, the swithes,,d re tured o, d other swithes re tured off. The differetil mode voltge U is,whiletheommomodevoltgeeexressed s U m = 1 (U U )= 1 ( )=. (4) I Mode, oly the swith is tured o, d other swithes re tured off. The urret flows through d diode of. I this se, the differetil mode voltge U is,whiletheommomodevoltgeremisuhgeds U m = 1 (U U ) = 1 ( ) =. (5) I Mode 3, the swithes,,d re tured o, d other swithes re tured off. The differetil mode voltge U is,whiletheommomodevoltgeeexressed s U m = 1 (U U )= 1 ( )=. (6) I Mode 4, oly the swith is tured o, d other swithes re tured off. The urret flows through d diode of. I this se, the differetil mode voltge U is, while the ommo mode voltge U m remis uhged s U m = 1 (U U )= 1 ( )=. (7) I summry, the ove lysis revels tht the ommo mode voltge e ket ostt s / ll the time. Therefore, the itive lekge urret e sigifitly miimized, ordig to theoretil lysis of Figure.The followig will reset the test results.

3 Ative d Pssive Eletroi Comoets 3 Figure 3: Swithig stte of the roosed iverter iruit. Vg () Mode 1 () Mode Vg () Mode 3 (d) Mode 4 Figure 4: Oertio modes of the roosed iverter. 3. Performe Evlutio I order to verify the effetiveess of the roosed ower eletroi iverter iruit, the iverter iruit is desiged i MATAB/Simulik. The iruit omoets d rmeters re listed s follows: system ower is 3 kw, d us voltge is 4 V, grid voltge is V, grid frequey is 5 Hz, iverter iruit swithig frequey is 1 khz, iruit filter idutor = = 3mH, d rsiti itor C PV = 1 F; see Figure 3. Figure 5() shows the test wveform of the swith sttes; it e oserved tht, t y give time, oly two swithes oerte i high-frequey mode d the other four swithes oerte i low-frequey mode, so the high effiiey e hieved. O the other hd, the iverter outut voltge wveform is show i Figure 5(), where three-level outut

4 4 Ative d Pssive Eletroi Comoets Swith stte 1 1 U (V) () Swith sttes (from ottom to to:,,,,,d ) () Iverter outut voltge U 3.3 Grid urret (A) ekge urret (A) Mg (fudmetl %) Fudmetl (5 Hz) =, THD = 1.9% Frequey (Hz) 1 4 ekge urret mg (A) Frequey (Hz) 1 4 () Gridurretdsetrum (d) Citive lekge urret d setrum Figure 5: Test results. voltge is hieved. It is eefiil to the grid urret rile redutio. Figure 5() shows the grid urret wveform d its setrum lysis. It e see tht the grid urret is siusoidl with the totl hrmoi distortio of 1.9%, whih is well elow 5% seified i IEEE Std. 99- [18]. Figure 5(d) shows the itive lekge urret wveform d its setrum lysis. It e see tht the lekge urret is well elow 3 ma seified i VDE , thks to the roosed ower eletroi iverter. 4. Colusio Thiserhsresetedewowereletroiiverter iruit. Its uique feture lies i tht the roosed iruit kee the system s ommo mode voltge ostt ll the time, d thus the itive lekge urret e sigifitly miimized, whih omlies with the itertiol stdrd IEEE Std. 99- d VDE Therefore, it is ttrtive to the trsformerless hotovolti system litios. It should e oted tht other differet iverter iruits re lsoiterestigdeusedforthetrsformerless hotovolti system litios; lese refer to [19, ] for further redig. Coflit of Iterests The uthor delres tht there is o oflit of iterests regrdig the ulitio of this er. Referees [1] S. B. Kjer, J. K. Pederse, d F. Bljerg, A review of siglehse grid-oeted iverters for hotovolti modules, IEEE

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6 Rottig Mhiery Egieerig The Sietifi World Jourl Distriuted Sesor Networks Sesors Cotrol Siee d Egieerig Adves i Civil Egieerig Sumit your musrits t Eletril d Comuter Egieerig Rootis VSI Desig Adves i OtoEletrois Nvigtio d Oservtio Chemil Egieerig Ative d Pssive Eletroi Comoets Ates d Progtio Aerose Egieerig Modellig & Simultio i Egieerig Shok d Virtio Adves i Aoustis d Virtio