111341644 phương phap Điều khiển mppt

7/21/2019 111341644 Phng Phap iu Khin MPPT

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MPPT (Maximum Power Point Tracker) l phng php d tm im lm vic c cngsut ti u ca h thng ngun in pin mt tri qua vic iu khin chu k ng m kho int dng trong b DC/DC. Phng php MPPT c s dng rt ph bin trongh thng pin mttri lm vic c lp v ang dn c p dng trong h quang in lm vic vi li. MPPTbn cht l thit b in t cng sut ghp ni ngun in PV vi ti khuych i ngun cng

sut ra khi ngun pin mt tri khi iu kin lm vic thay i, v t c th nng cao chiu sut lm vic ca h. MPPT c ghp ni vi b bin i DC/DC v mt b iu khin.

Hnh 1.12. B iu khin MPPT trong h thng pin mt tri

B iu khin MPPT c th l b iu khin tng t truyn thng. Tuy nhin, vic sdng b iu khin s ang ngy cng thnh hnh v n c nhiu u im hn b iu khintng t. Th nht l, b iu khin s c th lp trnh c v vy kh nng thc hin cc thutton cao cp s d dng hn. N d dng m ho biu thc, v d x = yxz, hn l thit k mtmch in tng t thc hin cng mt biu thc . Nh l do ny m vic hiu chnh biu khin s c thc hin d dng hn nhiu so vi b iu khin tng t. Mt khc b iukhin s khng b nh hng bi s thay i v nhit v thi gian v b ny hot ng ri rc,bn ngoi cc thnh phn tuyn tnh. V vy, b iu khin s c trng thi n nh lu hn.Khng ch c vy, b iu khin MPPT s khng ph thuc vo dung sai ca cc b phn khcv n thc hin thut ton phn mm, ni m cc thng s c th c gi n nh hoc thayi c.

B iu khin loi ny cho php gim s lng thnh phn v n ch dng mt chp n lm nhiu nhim v khc nhau. Nhiu b iu khin s c trang b thm b bin i A/Dnhiu ln v ngun to xung PWM, v vy n c th iu khin c nhiu thit b ch vi mtb iu khin n l.V nhng u im ca b iu khin s m n s chn phng php iukhin s cho MPPT. Vic thit k v m phng MPPT s c thc hin chng 3 vi b vi xl hoc DSP v cc thut ton thc hin.

Gii thiu chung


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Khi mt tm PV c mc trc tip vo mt ti, im lm vic ca tm PV s l giaoim gia ng c tnh lm vic I V v ng c tnh I V ca ti. Gi s nu ti l thun

tr th ng c tnh ti l mt ng thng tp vi dc l 1/Rti.

Hnh 3.1.V d tm pin mt tri c mc trc tip vi mt ti thun tr c th thay i gi tr

in tr c.

Hnh 3.2.ng c tnh lm vic ca pin v ca ti thun tr c gi tr in tr thay i c

Ni cch khc, tr khng ca ti bm theo iu kin lm vic ca pin. Ni chung, imlm vic him khi ng ti v tr c cng sut ln nht, v vy n s khng sinh ra cng sutln nht. Mng ngun pin mt tri thng b qu ti khi phi b cho mt lng cng sut thpvo thi gian nh sng yu ko di nh trong ma ng. S khng thch ng gia ti v cc tmpin mt tri thng lm cho ngun pin mt tri b qu ti v gy ra tn hao trong ton h thng. gii quyt vn ny, phng php MPPT c s dng duy tr im lm vic ca ngun

in pin ti ng im c cng sut ln nht MPPT. Phng php MPPT c th xc nh chnhxc n 97% im MPPT.

Phn ny cp n c tnh lm vic I V ca moun pin mt tri v ti, s tng thchca c ti v pin, phng php iu khin MPPT; vic p dng thut ton MPPT iu khinb bin i DC/DC trong h thng v gii hn ca phng php MPPT.

2. Nguyn l dung hp ti


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Nh ni trn, khi PV c mc trc tip vi mt ti, im lm vic ca PV s do c tnhti xc nh. in tr ti c xc nh nh sau:

Rti=V0/I0

Trong : V0 l in p ra, I0 l dng in ra.

Ti ln nht ca PV c xc nh nh sau:

Ropt=VMPP/IMPP

Trong : VMPPv IMPPl in p v dng in cc i.

Khi gi tr ca ti ln nht khp vi gi tr Roptth cng sut truyn t PV n ti s lcng sut ln nht. Tuy nhin, iu ny thng c lp v him khi khp vi thc t. Mc chca MPPT l phi hp tr khng ca ti vi tr khng ln nht ca PV. Di y l v d cavic dung hp ti s dng mch Boost. T cng thc (2 8):

Vin

=(1-D)V0

(3 3)

Ta gi s rng y l b bin i l tng, cng sut trung bnh do ngun cung cp phi bng vicng sut trung bnh ti hp th c.

Pin= Pout

Khi :

Iin/Iout=V0/Vin (3 5)

T 2 cng thc (3 3) v (3 5)

ta c:

Iin=I0/(1-D) (3 6)

Suy ra:

(3 7)

Rin=Vin/Iin=(1-D)2.V0/I0==(1-D)

2Rti

Hnh 3.3.Tng tr vo Rin c iu chnh bng D


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T hnh v 3.3 tr khng do PV to ra l tr khng vo Rincho b bin i. Bng cchiu chnh t l lm vic D, gi tr ca Rinc iu chnh gi tr ph hp vi Ropt. V vy, trkhng ca ti khng cn phi quan tm nhiu min l t l lm vic ca kho in t trong bbin i c iu chnh ng quy tc hp l.

3. Thut ton xc nh im lm vic c cng sut ln nht MPPT

Nh ni trn, im lm vic c cng sut ln nht MPP nh trn ng c tnh I V lun thay i di iu kin nhit v cng bc x thay i. Chng hn, hnh v 3.4 thhin ng c tnh lm vic I V nhng mc cng bc x khc nhau tng dn cngmt gi tr nhit (25oC) v hnh 3.5. th hin cc ng c tnh lm vic cng mt mc

cng bc x nhng vi nhit tng dn.

Hnh 3.4.ng c tnh lm vic ca pin khi cng bc x thay i cng mt mc nhit


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Hnh 3.5.c tnh lm vic I V ca pin khi nhit thay i cng mt mc cng bc x

T hai hnh v ny, ta nhn thy c s dch chuyn in p quan st c v tr ca im MPP.V vy im MPP cn phi dng thut ton xc nh. Thut ton ny l trung tm ca b iukhin MPPT.

Thut ton MPPT c coi l mt phn khng th thiu trong h PV, c p dng vimong mun nng cao hiu qu s dng ca dy pin mt tri. N c t trong b iu khin bbin i DC/DC. Cc thut ton MPPT iu khin ca b bin i DC/DC s dng nhiu thams, thng l cc tham s nh dng PV, in p PV, dng ra, in p ra ca b DC/DC.

Cc thut ton ny c so snh da theo cc tiu ch nh hiu qu nh im lm vicc cng sut ln nht, s lng cm bin s dng, phc tp ca h thng, tc bin i

Nhn chung c rt nhiu thut ton MPPT c nghin cu v ng dng trn nhiu hthng. Mt phng php o in p h mch Vocca cc pin mt tri c 30 giy mt ln bngcch tch pin mt tri ra khi mch trong mt khong thi gian ngn. Sau khini mch tr li,

in p pin c iu chnh ln 76% ca Voc. T l % ny ph thuc vo loi pin mt tri sdng. Vic thc hin phng php iu khin mch h ny n gin v t chi ph mc d hiuqu MPPT l thp (t 73% n 91%). Phng php tnh ton cngc th d on v tr ca imMPPT, tuy nhin trong thc t, phng php ny lm vic khng hiu qu v n khng theo cnhng thay i vt l, tui th ca tm pin v cc nh hng bn ngoi khc nh bng ca ccvt cn Hn na, mt hc nht x k o cng bc x c gi thnh rt t.

Cc thut ton s dng phng php iu khin kn mch c th cho hiu qu cao hn,nn cc thut ton ny c s dng ph bin hn cho MPPT. Trong khun kh ca n nych phn tch 2 phng php MPPT c ng dng rng ri v tr nn ph bin, quen thucv cho c mt s hiu qu lm vic sau y: Phng php nhiu lon v quan st P&O

Phng php in dn gia tng INC.

3.1. Phng php nhiu lon v quan st P&O


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y l mt phng php n gin v c s dng thng dng nht nh s n gintrong thut ton v vic thc hin d dng. Thut ton ny xem xt s tng, gim in p theochu k tm c im lm vic c cng sut ln nht. Nu s bin thin ca in p lmcng sut tng ln th s bin thin tip theo s gi nguyn chiu hng tng hoc gim.Ngc li, nu s bin thin lm cng sut gim xung th s bin thin tip theo s c

chiu hng thay i ngc li.Khi im lm vic c cng sut ln nht c xc nh trnng cong c tnh th s bin thin in p s dao ng xung quanh (im MPP) im lm

vic c cng sut ln nht .

Hnh 3.6.Phng php tm im lm vic cng sut ln nht P&O. Lu thut ton:


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Hnh 3.7.Lu thut ton Phng php P&O

S dao ng in p lm tn hao cng sut trong h quang in, c bit nhng khi iu kinthi tit thay i chm hay n nh. Vn ny c th gii quyt bng cch iu chnh logictrong thut ton P&O l s so snh cc tham s trong hai chu k trc. Mt cch khc gii

quyt vic hao ht cng sut quanh im MPP l gim bc tnh bin thin xung, nhng khiiu kin thi tit thay i, thut ton ny s tr nn chm chp hn trong vic bm theo imMPP v cng sut s b hao ht nhiu hn. Nh vy, nhc im chnh ca phng php ny lkhng tm c chnh xc im lm vic c cng sut ln nht khi iu kin thi tit thay i.c im ca phng php ny l phng php c cu trc n gin nht nht v d thc hinnht, trong trng thi n nh im lm vic s dao ng xung quanh im MPP, gy hao ht mtphn nng lng. Phng php ny khng ph hp vi iu kin thi tit thay i thng xuynv t ngt.

3.2. Phng php in dn gia tng INCy l phng php khc phc nhng nhc im ca phng php P&O trong trng hp iu

kin thi tit thay i t ngt. Phng php ny s dng tng in dn gia tng ca dy pin mt

tri d tm im cng sut ti u. Minh ho trn hnh v 3.8:

Hnh 3.8.Phng php in dn gia tng

Phng php ny c bn da trn c im l: dc ca ng c tnh pin bng 0 tiim MPPT, dc ny l dng khi bn tri im MPP, l m khi bn phi im MPP.

Bng cch so snh gi tr in dn tc thi (I/V) vi gi tr in dn gia tng (V/I),Thut ton ny s tm c im lm vic c cng sut ln nht. Ti im MPP,in p chunVref= VMPP. Mi khi im MPP c tm ra, hot ng ca pin li c duy tr im lm vic

ny tr khi c s thay i v dng in I, s thay i ca dng in I th hin s thay i caiu kin thi tit v ca im MPP.

ln ca in dn gia tng s quyt nh nhanh chm trong vic tm ra im MPP.Tuy nhin khi in dn gia tng ln qu s lm cho h thng hot ng khng chnh xc ti imMPP v s b dao ng.


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u im chnh ca phng php ny l cho kt qu tt nht khi thi tit thay i nhanh.Phng php ny cng cho dao ng nh nht quanh im MPP hn phng php P&O. Nhcim ca phng php ny l mch iu khin phc tp. N s dng 2 cm bin o gi trdng in v in p, nn chi ph lp t cao. Tuy nhin ngy nay vi s xut hin ca nhiuphn mm hay cc b x l lm gi thnh ca h ny gim i rt nhiu.

3.1.1.Bng tng kt so snh cc phng php MPPT Bng 3.1. Bng so snh thut ton MPPT

Hnh 3.9. Lu thut ton ca phng php in dn gia tng INC

3. Phng php iu khin MPPT.


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Nh trnh by trn, thut ton MPPT s ra lnh cho b iu khin MPPT phi lm g iu chnh in p lm vic. Sau nhim v ca b iu khin MPPT l iu chnh tnggim in p lm vic v duy tr n nh mc in p lm vic ca h ngun pin mt tri. C 3phng php ph bin iu khin MPPT.

3.1. Phng php iu khin PIMPPT s o gi tr in p PV v dng PV, sau da vo thut ton MPPT (P&O, INC

hay cc thut ton MPPT khc) tnh ton gi tr in p quy chiu Vref nng iu chnhin p lm vic PV ln theo Vref. Nhim v ca thut ton MPPT ch l nh gi tr in p Vrefv vic tnh ton ny s c lp li theo chu k (thng khong t 1n 10 ln ly mu trn 1

giy).

Hnh 3.10.S khi phng php iu khin MPPT s dng b b PI

B iu khin t l tch phn PI quy nh in p a vo b bin i DC/DC. B PI c

nhim v b sai lch gia Vrefv in p o c bng cch iu chnh h s ng ct D. PI ctc lm vic nhanh, cho p ng nhanh v n nh. Bn thn b iu khin PI c cu to tnhng thnh phn tng t Analog, nhng n c lm vic vinguyn tc iu khin x l tnhiu s DSP (Processing Signal Digital) v b x l tn hiu s c th thc hin c nhiunhim v khc nh xc nh im lm vic c cng sut ti u v vy s gim c mt s lngthnh phn trong h.

3.1.2.Phng php iu khin trc tip.

Phng php iu khin ny n gin hn v ch s dng mt mch vng iu khin, vn thc hin nhim v iu chnh h s lm vic trong thut ton MPPT. Vic iu chnh h slm vic hon ton da trn nguyn l dung hp ti trnh by mc 3.2


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Hnh 3.11.S khi ca phng php iu khin trc tip MPPT.

Tng tr ca PV c coi l tng tr vo b bin i. Nhc li cng thc (3 6)

Rin=Vin/Iin=(1-D)2.V0/I0==(1-D)

2Rti (3 8)

Trong : D l h s lm vic ca b bin i Boost.

Hnh v 3.12. cho thy vic tng D s lm gim tng tr vo Rin, t in p lm vic PV sdch sang bn tri (gim i). Tng t khi gim D s lm tng Rinkhi in p lm vic s dchsang phi (tng ln). Thut ton MPPT (P&O, INC, v cc thut ton khc ) s quyt nh vic

dch chuyn in p nh th no.

Hnh 3.12.Mi quan h gia tng tr vo ca mch Boost v h s lm vic D

Thi gian p ng ca cc tng cng sut v ngun PV tng i chm (10 50 miligiy tu thuc tng loi ti). Thut ton MPPT thay i h s lm vic D, sau ln ly muin p v dng PV tip theo nn c thc hin sau khi h t n trng thi n nh trnho phi gi tr ang trng thi chuyn tip. T l ly mu ca phng php ny thng t 1 n100 ln trn 1 giy trong khi t l ly mu ca b iu khin PI thng nhanh hn, v vyphng php iu khin trc tip ny cho bn vng i vis thay i t ngt ca ti. Tuynhin nhn chung p ng ca h thng li chm hn.Phng php iu khin trc tip c thlm vic n nh i vi cc thit b nh h thngc trang b c quy v h thng bm nc. V tl ly mu chm nn c th s dng b vi iu khin gi thnh thp.

3.2. Phng php iu khin o trc tip tn hiu ra.

Phng php ny l phng php c ci tin t phng php iu khin trc tip trn v c u im l ch cn hai cm bin o in p v dng in ra khi b bin i. Phngphp iu khin bng PI v phng php iu khin trc tip o tn hiu vo b bin i, c uim l cho php iu khin chnh xc im lm vic ca pin mt tri. Nhng nhng cm binvo thng cn phi c nhng cm bin khc o tn hiu ra trnh trng hp qu in p hay


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qu dng in ca ti. Nh vy hai phng php trn s fi cn n 4 cm bin hot ngc tt nht nn chi ph lp t s cao.

Phng php iu khin o trc tip ny o s thay i cng sut ca PV u ra ca bbin i v coi h s lm vic D nh mt bin iu khin. Phng php ny dngthut ton P&O

xc nh im MPP.

Hnh 3.13.Lu thut ton P&O dng trong phng php iu khin o trc tip tn hiu ra

c th coi D l mt bin iu khin th thut ton P&O phi c ci tin mt chtnhng v c bn vn l khng i. Thut ton P&O mi ny iu chnh D v o cng sut ra cab bin i. Nu cng sut ra ca b bin i DC/DC tng ln, h s lm vicD cng s tng lntheo, v ngc li nu cng sut ra gim i th D cng s gim theo. Khi cng sut ra ca b bini t n gi tr cc i th lc ny PV ang lm vic im MPP. Phng php ny ch ddng thc hin m phng vi mt b bin i l tng cn trong thc t vi b bin i khngphi l tng th khng th m bo rng liu gi tr cc i ca cng sut ra khi b bin i ctng ng vi im MPP hay khng. Mt nhc im khc l phng php ny ch c th thchin vi cc tham s ca thut ton P&O v hon ton khng p dng cho thut ton INC.

4. Gii hn ca MPPT.

Gii hn chnh ca MPPT l khng tc ng g n tn hiu ra trong khi xc nh imlm vic c cng sut ln nht. N khng th cng mt lc tc ng ln tn hiu vov tn hiu


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ra. V vy, nu h thng cn in p ra n nh th phi s dng n c quy duy tr in p nnh.

Mt nhc im khc ca MPPT na l: vic xc nh im lm vic c cng sut ti us dng li nu nh ti khng th tiu th ht lng cng sut sinh ra. i vi hPV lm vic

c lp c ti b gii hn bi dng v p ln nht th phng php MPPT s dch chuyn imlm vic ra khi im MPP v gy tn hao cng sut. Vi h ny, vic xc nh chnh xc dunglng ca ti l rt quan trng c th tn dng c ht dunglng ca cc pin mt tri.Ngc li, h PV lm vic vi li lun xc nh im lmvic c cng sut ln nht v nu thacng sut h thng c th bm vo li in tng li nhun.

Tuy nhin, hiu sut ca b bin i DC/DC thc t dng trong MPPT khng bao gi tc 100%. Hiu sut tng ln t phng php MPPT l rt ln nhng h thng pin mt tricng cn phi tnh n tn hao cng sut do b bin i DC/DC gy ra. Cng phi cn nhc giahiu sut v gi thnh. Vic phn tch tnh kinh t gia h thng pin mt tri vi cc h thngcung cp in khc cng nh vic tm ra cc cch thc khc nng cao hiu sut cho h thng

pin mt tri (chng hn nh dng my theo di mt tri)cng l vic lm cn thit.

111341644 phương phap Điều khiển mppt

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