WSEAS TRANSACTIONS on CIRCITS nd SYSTEMS S Pn, Ynd Li, Sn-Bo Pn, Chendong Lin Mximum Power Point Trking Algorithm with Turn Round Mesurement nd Curve Fitting Method for Solr Genertion System S Pn, Ynd Li, Dept of Eletril Engineering, Anyng Norml niversity PRChin pnsn@ynuedun, liyd@ynuedun Sn-Bo Pn, Chendong Lin Dept of Eletril Engineering, Shnghi Dinji niversity PRChin pns@sdjuedun Astrt: - A vel mximum power point trking (T lgorithm is proposed in this pper The vel lgorithm dopted round k mesurement whih mkes it esy to void misjudge when the irrdition vries rpidly, espeilly omprison to trditionl T strtegy Wht s more, round k mesurement mkes it possile to imitte PV rry s P- urve with mthemtil method whih mkes it possile to redue the osilltion ner PV s mximum power point ( Lgrnge Interpoltion Formul is used in this pper to fit PV s P- urve nd simultion with Mtl/Simulink tool to verify the proposed hs een done The result revels proposed T lgorithm is more ury in irrdition vrition sitution nd less osilltion ner the These fetures mke the lgorithm good ide in high-power solr genertion system Key-Words: T, solr genertion system, irrdition vrition, osilltion, urve fitting, mtl/simulink 1 Introdution Photovolti (PV power genertion system is widely studied reently for energy risis nd the hevily polluted environment As the hrteristi of PV rry is nliner nd pt to e influened y mient temperture nd irrdition ondition A mximum power point trking (T tehlogy is essentil in PV system to mximize PV s output power PV system s performne is mostly ffeted y T ontroller s stility, effiieny nd dynmi hrteristi Widely used T lgorithms n e onluded s perturtion nd oservtion (P&O nd inrement ondutne (InCond These two lgorithms filed to trk PV s mximum power point ( when the irrdition vries rpidly The min reson is tht trditionl T lgorithm doesn t tke the reltionship etween power nd voltge into ount in detil To solve this prolem, vel T lgorithm using turn round mesurement method hs een proposed in this pper Wht s more, turn round mesurement mkes it possile to lulte the erene voltge of PV rry t whih redues the osilltion ner the nd the effiieny is prominent improved The operting priniple nd simultion result with Mtl/Simulink tool hs een given nd disussed in this pper in detil Fig1 shows the hrteristis of PV Cell P P V _ or _ I Fig1 Power urve of PV ell V or I The prolem fixed y the T tehnique is to find the Vmpp or Impp of PV ell Mximiztion output power n e otined when the PV ell opertes t V mpp or I mpp udner speifi irrdition nd temperture ondition It is ted tht prtil shding sitution resulted multiple of PV ell However, there is still single true overll Different T tehniques n respond to oth irrdine nd temperture But some re pt to del with irrdine or temperture situtions speifilly Some T tehniques n e filed when irrdition vries fst 3 T Tehniques 31 T priniple Aording to optil eletroni theory, PV rry s mthemtil module is s Fig shown Prolem Overview E-ISSN: 4-66X 101 Volume 16, 017
Iph WSEAS TRANSACTIONS on CIRCITS nd SYSTEMS S Pn, Ynd Li, Sn-Bo Pn, Chendong Lin Is Rs I r ID Ish Rsh VJ Cj o DC/DC R L Fig Equivlent iruit model for photovolti ell The reltionship etween PV s output urrent nd voltge n e desried s eqution (1 q( V IRS V IRS I IL I0 exp[ ] 1 (1 AKT RSh PV s I- urve nd P- urve re shown s Fig3 nd Fig4 respetively Fig3 I- urve of PV ells Fig4 P- urve of PV ells PV ell s model n e simplified s Fig5 o represents the open iruit voltge nd resister r n e onsidered s the output impedne of PV ells When PV ell s lod resister R equls to output resister r, PV ell s output power n e mximized Fig6 shows the T topology with Boost onverter Equivlent impedne of oost onverter nd the lod R L n e desried s R eq : Req (1 D RL ( Among whih, D represents oost onverter s duty yle PV ell output mximum power when R equls to r o r Fig5 PV ell s simplified model RL eq Fig6 T with DCDC topology As irrdition vries, P&O nd InCond lgorithm filed to response fst Thus, the T lgorithm need to trk the gin whih mkes PV s effiieny redue signifintly under irrdition rpid hnge irumstne Most ommonly used T tehniques re desried in this hpter nd the filure priniple re nlyzed in detil 3 Hill-Climing/Perturtion nd Oservtion Hill-Climing/Perturtion nd Oservtion re most fvored T tehniques Hill-liming method perturs the duty rtio of the power onverter nd tht results the output urrent hnge of PV ell Perturtion nd oservtion method perturs the erene of PV ell When the output voltge of PV ell hnges, the output urrent vries onsequenetly Hill-Climing nd P&O method re different wy to envision the sme fundmentl method In Fig1, it n e seen tht inresing(deresing the voltge inreses(dereses the power when PV ell operting on the left of the nd deresing (inresing the voltge dereses (inreses the power when on the right of the Theore, next step s perturtion diretion is determined y the output power s vrition If the power inreses, the prior perturtion diretion is orret, otherwise reversed the perturtion diretion The reltions etween hnging in power nd next perturtion diretion re s Tle1 shown Tle1 Summry of hill-liming nd P&O method Perturtion Chnge in Power Next Perturtion Positive Positive Positive Positive Negtive Negtive Negtive Positive Negtive Negtive Negtive Positive The perturtion nd oservtion proess is repeted periodilly until the is rehed The system then osilltes round the The osilltion wstes PV s power if the step size is too lrge In order to minimize the osilltion ner the, the step size should e deresed However, tht will slow down T speed In some thesis, two stge step size is dopted to trk the A E-ISSN: 4-66X 10 Volume 16, 017
WSEAS TRANSACTIONS on CIRCITS nd SYSTEMS S Pn, Ynd Li, Sn-Bo Pn, Chendong Lin igger step size is used in first stge to offer fst trking speed nd finer step size is dopted in the seond stge to derese the osilltion Hill-liming nd P&O methods fil under rpidly hnging irrdition onditions s shown in Fig7 P P P1 A C B Inputs:V(t,I(t I I( t I( t t V V ( t V ( t t V 0 I / V I / V I 0 O V V V Fig7 Hill liming method invlid shemti digrm Assume the PV ells opertes t point A under irrdition P1 The output power will derese from A to B if the perturtion V is positive The next step should derese the voltge of PV ells The output power will hnge from A to C if the irrdition hnges from P1 to P The ontroller will keep on inresing the operting voltge for the output power inreses It is ovious tht the perturtion diretion is wrong for the reson of irrdition rpidly hnging 33 Inrementl Condutne The inrementl ondutne method is sed on the ft tht the slope of the PV rry power urve is zero t the, positive on the left of the, nd negtive on the right, s given y formul (3 dp / dv 0, t _ dp / dv 0, left _ of _ (3 dp / dv 0, right _ of _ Sine dp / dv d( IV / dv I VdI / dv I VI / V (4 (n e rewritten s I / V I / V, t _ I / V I / V, left _ of _ (5 I / V I / V, right _ of _ The n thus e trked y ompring the instneous ondutne(i/v to the inrementl ondutne ( I / V s shown in Fig8 V is the erene voltge t whih the PV rry is fored to operte At the, V equls to V One the is rehed, the opertion of the PV rry is mintined t this point unless hnge in I is ted, inditing hnge in tmospheri onditions nd the The lgorithm derements or inrements V to trk the new Inrement V I / V I / V Derement V I( t t I( t V ( t t V ( t return I 0 Derement V Fig8 InCond lgorithm flowht Inrement V The inrement size determines how fst the is trked Fst trking n e hieved with igger inrements ut the system might t operte extly t the nd osillte out it insted; so there is trdeoff Referenes [] nd [3] propose method tht rings the operting point of the PV rry lose to the in first stge nd then uses InCond to extly trk the in seond stge By proper ontrol of the power onverter, the initil operting point is set to mth lod resistne proportionl to the rtio of the open-iruit voltge Vo to the short-iruit urrent I s of the PV rry This two-stge lterntive lso ensures tht the rel is trked in se of multiple lol mxim A less ovious, ut effetive wy of performing the InCond tehnique is to use the instntneous ondutne nd the inrementl ondutne to generte n error signl e I / V di / dv (6 s suggested in [5,6] From (6, we kw tht e goes to zero t the A simple proportionl integrl (PI ontrol n then e used to drive e to zero Mesurements of the instntneous PV rry voltge nd urrent require two sensors InCond method lends itself well to DSP nd miroontroller ontrol, whih n esily keep trk of previous vlues of voltge nd urrent E-ISSN: 4-66X 103 Volume 16, 017
WSEAS TRANSACTIONS on CIRCITS nd SYSTEMS S Pn, Ynd Li, Sn-Bo Pn, Chendong Lin For ll other pplitions t mentioned here, we put together Tle, ontining the mjor hrteristis of ll the T tehniques Tle should help in hoosing n pproprite T method T Tehnique Tle T tehniques omprison Converg Sensed e Prmeters speed Irrdition Chnge? Hill-liming/ Vri es Voltge, P&O Current InCond Vries Voltge, Current Frtionl Vo Medium Voltge Frtionl Is Medium Current Fuzzy Logi Fst Vries Control Neurl Network Fst Vries Current Sweep Slow Voltge, Current DC Cpitor Medium Voltge Droop Control Liner Current Control Fst Irrdition 4 Proposed T lgorithm with turn round mesurement nd urve fitting lultion 41 Turn round mesurement operting priniple Control system detets the open-iruit voltge o of photovolti (PV ells The initil erene voltge is set s 08 o ording to ppers relted Reord PV s urrent voltge nd power s (, P A perturtion voltge 001 is given to hieve two different o opertion point nd The dt is reorded s (, P nd (, P respetively The next perturtion diretion is determined y the reltion etween P, P, P nd,, Given P P P nd it mens is the proximl point to the Grdient e1 n e P P e otined s 1 nd fter PI ontroller we get the fresh perturtion voltge PI ontroller is designed to mke the perturtion voltge self-dption vlue whih mkes the trking proess fster when it is fr wy from the trget vlue Wht s more, PI ontroller derese the perturtion step ner the nd tht redue the osilltion ner the After onfirmtion the new perturtion step, is set s the new voltge strting point The new trking proess is the sme s efore A turn round mesurement retes more operting steps for the ontrol system However, it is essentil to tke this step to void misjudge when the irrdition vries rpidly Trditionl perturtion nd oservtion lgorithm filed under this sitution It is explined s Fig9 P O 400W/m 00W/m P P P P Fig9 Photovolti rry s output power nd voltge The origin point of PV is (, P nd re otined with the perturtion voltge Suppose the irrdition inreses t point nd the P- urve of PV trnsfer from A to B The output power of PV t point is P If trdition P&O lgorithm is used here,, P P, nd tht mens the is on the right side of nd the ontroller should derese PV s output voltge It is ovious tht the trking diretion is wrong The turn round method proposed in this pper n otin three operting points t the sme moment A riterion is used in this pper to judge the irrdition sitution T lgorithm dopts the ltest PV output point if irrdition vries A new trking proess is initited fter the irrdition The riteri proposed in this pper re shown s Tle3 Tle 3 T trking diretion riteri PV voltge PV power Trking diretion << P<P<P Inrese voltge << P<P<P Curve fitting << P<P<P Irrdition vried << P<P<P Irrdition vried << P<P<P Curve fitting << P<P<P Derese voltge As the tle showed, P P P or P P P revels the is loted t the setion, When this ondition is stisfied, turn-round method is stopped nd Lgrnge Interpoltion Formul is used to find the Curve fitting hs een done to simulte PV s P- urve with Lgrnge Interpoltion Formul Aording to the derived P- A B o E-ISSN: 4-66X 104 Volume 16, 017
WSEAS TRANSACTIONS on CIRCITS nd SYSTEMS S Pn, Ynd Li, Sn-Bo Pn, Chendong Lin urve eqution, is lulted nd the erene voltge for PV is given 4 Curve fitting ner the When the PV s operting point is ner the, for the reson of turn round mesurement method, three points of PV ells re otined t the sme moment Tht mkes it possile to restore PV s P- urve when it is ner the nd the error will e deresed signifintly With Lgrnge Interpoltion Formul, PV s P- urve re fitted y three operting point ner the The urve fitting of PV s P- urve mkes it possile to trk the with the derived urve whih is muh esier nd fster thn trditionl T lgorithm The osilltion round the will e prominently deresed with the lultion method rther thn perturtion method Whih mkes it suit for high-power photovolti modules pplition The operting priniple of urve fitting is desried s follow: Assume the interpolted point re (, P, (, P nd (, P The interpoltion polymil of PV s P- urve is s follow: L ( ( ( ( P l P l P l (7 Among whih: ( ( l ( P (8 ( ( ( ( l ( P ( ( ( ( l ( P (10 ( ( Mrix Hishmn-Sigmr model of qudrti funtion n e derived s follow: L ( x x x (11 1 3 P P x1 ( ( ( ( P ( ( P ( P ( x ( ( ( ( P ( ( ( P P x3 ( ( ( ( (9 (1 (13 P (14 ( ( The fitted urve s mximum point x 4x1 x3 x is(, Only three points (, P, (, P x1 4x1 nd (, P re needed to fit PV s P- urve With the sustitution into the formul with three points, the oeffiient x 1, x nd x 3 re derived Aording to the derived P- prol urve of PV ells, the erened voltge t point n e desried x s Set the PV s output voltge to m x1 m y the ontroller PV s output power m P t operting point m need to e reorded Three mximum power points re seleted from (, P, (, P, (, P nd ( m, P m The seleted points re mrked s ( 1, P 1, (, P nd ( 3, P 3 If urve fitting is implemented sequentilly with the fresh three points, they must meet the onditions P1 P P3 nd 1 3 Itertion with the fresh operting points y Lgrnge Interpoltion Formul s efore until the is trked PV s urrent output power P w is ompred with the previous yle s power P efore When the reltionship etween P w nd P efore stisfies Pw Pefore, the is trked nd urve fitting proess need to e hlted The lgorithm flow ht is s Fig10: Detet PV s open iruit voltge o Set PV s erene voltge =08o Reord PV s voltge nd power s(,p PV s erene voltge s:=- ;=+ P P P P P e1 PI 001o Reord PV s urrent voltge nd power s:(,p,(,p,(,p Reord PV s voltge nd power s:(,p,(,p P P P P P e PI Reord PV s urrent voltge nd power s(,p,(,p,(,p P P P P P P Curve fitting for PV s P- urve with (,P,(,P,(,P nd lulte s erene voltge m m Reord PV s voltge nd power (m,pm Selet three mximum power points nd mrked s(1,p1,(,p,(3,p3 respetively whih stisfy P1<P<P3 mx P P, P P 3>1nd 3> Fig10 Flow ht of proposed lgorithm T stopped P P P P P P =,P=P 001o Reord PV s voltge nd power s:(,p,(,p,(,p E-ISSN: 4-66X 105 Volume 16, 017
WSEAS TRANSACTIONS on CIRCITS nd SYSTEMS S Pn, Ynd Li, Sn-Bo Pn, Chendong Lin 5 Simultion nd Experiment Results The simultion nd experiment results show the differene etween InCond T ontrol lgorithm nd proposed T ontrol lgorithm Fig14 P- urve with Proposed T lgorithm when irrdition hnges Fig11 Fig6 Proposed T model Irrdition vries t point A from P1 to P Aording to the simultion model, the irrdition vrition proess is ontinuous proess T lgorithm s trking proess re showed s A to B B point re PV ell s fresh under P irrdition Fig13 nd Fig14 revel tht proposed T lgorithm osilltes lesser ner the nd it n respond to the fresh point B fster Tht mens the proposed lgorithm is more effiient thn InCond lgorithm when irrdition vries rpidly Fig1 Proposed T lgorithm The simultion onditions re s follow: Temperture: 5 C Irrdition P1: 600W / m Irrdition P: 800W / m PV ell s key prmeters under different irrdition re s Tle4 shows Tle4 PV ell s key prmeter Irrdition Condition P1 P Open iruit voltge(v 4 46 Short iruit Current(A 41 567 voltge(v 345 375 urrent(a 75 378 Power(W 95 14 Fig13 P- urve with InCond when irrdition hnges Fig15 PV s output power with proposed lgorithm when irrdition hnges Fig15 shows the output power of PV ell Aording to the result, proposed T lgorithm onvergene speed is exellent when irrdition vries from time(ms 15 to time 0 Tht mens the proposed T lgorithm n trk to the fresh fstly in 5ms whih mkes it proper to irrdition vries fst irumstne Tle5 Theoretil V, I nd P of PV ell Cse No G (W/m^ T ( V (V I (A P (W 1 1000 5 3370 356 1000 1000 30 337 357 1038 3 000 5 3531 706 499 4 000 30 3577 711 543 5 3000 30 3584 1066 3805 6 3000 40 367 1074 39437 7 400 30 3618 1417 5167 8 4000 40 3636 147 51886 9 5000 35 3609 178 6431 E-ISSN: 4-66X 106 Volume 16, 017
WSEAS TRANSACTIONS on CIRCITS nd SYSTEMS S Pn, Ynd Li, Sn-Bo Pn, Chendong Lin 10 5000 45 3731 1793 66897 Tle6 V, I nd P lgorithm Cse G T No (W/m^ ( of PV ell with InCond V I P (W (V (A 1 1000 5 377 347 11371 1000 30 390 357 11745 3 000 5 387 688 615 4 000 30 3380 694 3457 5 3000 30 3404 1030 35061 6 3000 40 3475 1043 3644 7 400 30 3459 1318 45590 8 4000 40 3511 1371 48136 9 5000 35 3578 1719 61506 10 5000 45 3603 1777 6405 Tle7 V, I nd P lgorithm Cse G T No (W/m^ ( (V of PV ell with proposed V I P (W (A 1 1000 5 3367 356 11987 1000 30 3370 357 1031 3 000 5 3501 693 46 4 000 30 356 707 5183 5 3000 30 3603 1037 37363 6 3000 40 3676 1046 38451 7 400 30 3631 139 50544 8 4000 40 3687 1398 51544 9 5000 35 3643 1741 6345 10 5000 45 3711 1798 6674 Tle5-7 re dt reorded of PV ells respetively under different irrdition nd temperture irumstne These three tles show InCond method nd proposed T method s effiieny nd lso the dt re ompred to the theoretil vlue of PV ell The dt tells tht PV ells with proposed lgorithm outputs more power thn InCond lgorithm 6 Conlusion The proposed T lgorithm flututes less ner PV s when the irrdition vries rpidly Simultion result in Fig15 shows the proposed T lgorithm respond to irrdition hnge fst When irrdition vries, proposed T lgorithm tkes less time to trk the new For the ondition of rpidly hnging solr rdition, the proposed T lgorithm will e very useful Shnghi Muniipl Edution Commission (14YZ160 Referenes: [1] LZhng,B Yunfei nd A Al-Amoudi, GA-RBF neutrl network sed mximum power point trking in photovolti systems, Int Power Eletronis Mhines nd Drives Conf, pp18-3,00 [] K Irisw, T Sito, I Tk, nd Y Swd, "Mximum power point trking ontrol of photovolti genertion system under nuniform insoltion y mens of monitoring ells," in Conf Reord of the Twenty-Eighth IEEE Photovolti Speilists Conf, 000, pp 1707-1710 [3] K Koyshi, I Tk, nd Y Swd, "A study on two stge mximum power point trking ontrol of photovolti system under prtilly shded insoltion onditions," in IEEE Power Eng Soiety Generl Meeting, 003, pp 61-617 [4] H Koizumi nd K Kurokw, "A vel mximum power point trking method for PV module integrted onverter," in 36th Annul IEEE Power Eletron Speilists Conf, 005, pp 081-086 [5] E N Costogue nd S Linden, "Comprison of ndidte solr rry mximum power utiliztion pprohes," in Intersoiety Energy Conversion Eng Conf, 1976, pp 1449-1456 [6] J Hrd nd G Zho, "Controlled powerinterfe etwee n solr ells nd soures," in IEEE Teleommun Power Conf, 1989, pp 1/1-1/7 [7] Bidrm, A, Dvoudi, A, Blog, RS: Control nd iruit tehniques to mitigte prtil shding effets in photovolti rrys,ieee J photovolt, 01,,(4,pp53-546 [8] Kerekes, T, Koutroulis,E, Ser,D, Teodoresu, R, Ktsnevkis, M, An optimiztion method for designing lrge PV plnts, IEEE J Photovolt, 013,3,(,pp814-8 Akwledgments This work ws supported in prt y the Ntionl Nturl Siene Foundtion of Chin (104515, in prt y the Supported y Invtion Progrm of E-ISSN: 4-66X 107 Volume 16, 017