A Hybrid Wind-Solar Energy System: A New Rectifier Stage Topology

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1 A Hybr n-solar Energy Sysem: A New Recfer Sage Topology Joanne Hu*, IEEE Suen Member, Alreza Bakhsha IEEE Senor Member, an Praveen K. Jan, IEEE Fellow Deparmen of Elecrcal an Compuer Engneerng Queen s Cener for Energy an Power Elecroncs Research (epoer), Queen s Unversy Kngson, Onaro, Canaa *emal: [email protected] Absrac Envronmenally frenly soluons are becomng more promnen han ever as a resul of concern regarng he sae of our eerorang plane. Ths paper presens a new sysem confguraon of he fron-en recfer sage for a hybr wn/phoovolac energy sysem. Ths confguraon allows he wo sources o supply he loa separaely or smulaneously epenng on he avalably of he energy sources. The nheren naure of hs Cuk-SEPIC fuse converer, aonal npu flers are no necessary o fler ou hgh frequency harmoncs. Harmonc conen s ermenal for he generaor lfespan, heang ssues, an effcency. The fuse mulnpu recfer sage also allows Maxmum Power Pon Trackng (MPPT) o be use o exrac maxmum power from he wn an sun when s avalable. An aapve MPPT algorhm wll be use for he wn sysem an a sanar perurb an observe meho wll be use for he P sysem. Operaonal analyss of he propose sysem wll be scusse n hs paper. Smulaon resuls are gven o hghlgh he mers of he propose crcu. I. INTRODUCTION h ncreasng concern of global warmng an he epleon of fossl fuel reserves, many are lookng a susanable energy soluons o preserve he earh for he fuure generaons. Oher han hyro power, wn an phoovolac energy hols he mos poenal o mee our energy emans. Alone, wn energy s capable of supplyng large amouns of power bu s presence s hghly unprecable as can be here one momen an gone n anoher. Smlarly, solar energy s presen hroughou he ay bu he solar rraaon levels vary ue o sun nensy an unprecable shaows cas by clous, brs, rees, ec. The common nheren rawback of wn an phoovolac sysems are her nermen naures ha make hem unrelable. However, by combnng hese wo nermen sources an by ncorporang maxmum power pon rackng (MPPT) algorhms, he sysem s power ransfer effcency an relably can be mprove sgnfcanly. hen a source s unavalable or nsuffcen n meeng he loa emans, he oher energy source can compensae for he fference. Several hybr wn/p power sysems wh MPPT conrol have been propose an scusse n works []- [5]. Mos of he sysems n leraure use a separae DC/DC boos converer connece n parallel n he recfer sage as shown n Fgure o perform he MPPT conrol for each of he renewable energy power sources []-[4]. A smpler mulnpu srucure has been suggese by [5] ha combne he sources from he DC-en whle sll achevng MPPT for each renewable source. The srucure propose by [5] s a fuson of he buck an buck-boos converer. The sysems n leraure requre passve npu flers o remove he hgh frequency curren harmoncs njece no wn urbne generaors [6]. The harmonc conen n he generaor curren ecreases s lfespan an ncreases he power loss ue o heang [6]. In hs paper, an alernave mul-npu recfer srucure s propose for hybr wn/solar energy sysems. The propose esgn s a fuson of he Cuk an SEPIC converers. The feaures of he propose opology are: ) he nheren naure of hese wo converers elmnaes he nee for separae npu flers for PFC [7]-[8]; ) can suppor sep up/own operaons for each renewable source (can suppor we ranges of P an wn npu); ) MPPT can be realze for each source; 4) nvual an smulaneous operaon s suppore. The crcu operang prncples wll be scusse n hs paper. Smulaon resuls are prove o verfy wh he feasbly of he propose sysem. Fgure : Hybr sysem wh mul-connece boos converer /0/$ IEEE 55

2 II. PROPOSED MUTI-INPUT RECTIFIER STAGE A sysem agram of he propose recfer sage of a hybr energy sysem s shown n Fgure, where one of he npus s connece o he oupu of he P array an he oher npu connece o he oupu of a generaor. The fuson of he wo converers s acheve by reconfgurng he wo exsng oes from each converer an he share ulzaon of he Cuk oupu nucor by he SEPIC converer. Ths confguraon allows each converer o operae normally nvually n he even ha one source s unavalable. Fgure llusraes he case when only he wn source s avalable. In hs case, D urns off an D urns on; he propose crcu becomes a SEPIC converer an he npu o oupu volage relaonshp s gven by (). On he oher han, f only he P source s avalable, hen D urns off an D wll always be on an he crcu becomes a Cuk converer as shown n Fgure 4. The npu o oupu volage relaonshp s gven by (). In boh cases, boh converers have sep-up/own capably, whch prove more esgn flexbly n he sysem f uy rao conrol s ulze o perform MPPT conrol. c = () P c = () Fgure 5 llusraes he varous swchng saes of he propose converer. If he urn on uraon of M s longer han M, hen he swchng saes wll be sae I, II, I. Smlarly, he swchng saes wll be sae I, III, I f he swch conucon peros are vce versa. To prove a beer explanaon, he nucor curren waveforms of each swchng sae are gven as follows assumng ha > ; hence only saes I, III, I are scusse n hs example. In he followng, I P s he average npu curren from he P source; I s he RMS npu curren afer he recfer (wn case); an I c s he average sysem oupu curren. The key waveforms ha llusrae he swchng saes n hs example are shown n Fgure 6. The mahemacal expresson ha relaes he oal oupu volage an he wo npu sources wll be llusrae n he nex secon. Sae I (M on, M on): P P 0 < < T s vc c T s < < T s T s < < T s Sae I (M off, M off): P P v c T s < < T s c c T s < < T s vc c T s < < T s Fgure : Propose recfer sage for a Hybr wn/p sysem Fgure : Only wn source s operaonal (SEPIC) c vc v c 0 < < T s 0 < < T s Sae III (M off, M on): P P v c T s < < T s Fgure 4: Only P source s operaon (Cuk) 56

3 (I) Fgure 6: Propose crcu nucor waveforms (II) (III) (I) Fgure 5 (I-I): swchng saes whn a swchng cycle III. ANAYSIS OF PROPOSED CIRCUIT To fn an expresson for he oupu DC bus volage, c, he vol-balance of he oupu nucor,, s examne accorng o Fgure 6 wh >. Snce he ne n he volage of s zero, applyng vol-balance o resuls n (). The expresson ha relaes he average oupu DC volage ( c ) o he capacor volages (v c an v c ) s hen obane as shown n (4), where v c an v c can hen be obane by applyng vol-balance o an [9]. The fnal expresson ha relaes he average oupu volage an he wo npu sources ( an P ) s hen gven by (5). I s observe ha c s smply he sum of he wo oupu volages of he Cuk an SEPIC converer. Ths furher mples ha c can be conrolle by an nvually or smulaneously. ( v ) T ( v )( ) T ( )( ) T 0 v () c c s c s c s = c = vc vc (4) c = P w (5) The swches volage an curren characerscs are also prove n hs secon. The volage sress s gven by (6) an (7) respecvely. As for he curren sress, s observe from Fgure 6 ha he peak curren always occurs a he en of he on-me of he MOSFET. Boh he Cuk an SEPIC MOSFET curren consss of boh he npu curren an he capacors (C or C ) curren. The peak curren sress of M an M are gven by (8) an (0) respecvely. eq an eq, gven by (9) an (), represen he equvalen nucance of Cuk an SEPIC converer respecvely. 57

4 The P oupu curren, whch s also equal o he average npu curren of he Cuk converer s gven n (). I can be observe ha he average nucor curren s a funcon of s respecve uy cycle ( ). Therefore by ajusng he respecve uy cycles for each energy source, maxmum power pon rackng can be acheve. v = s pv (6) v = s (7) I T (8) s, pk P eq s, pk c, avg P s eq = (9) T I (0) eq P I P c, avg s eq = () o = () c I. MPPT CONTRO OF PROPOSED CIRCUIT A common nheren rawback of wn an P sysems s he nermen naure of her energy sources. n energy s capable of supplyng large amouns of power bu s presence s hghly unprecable as can be here one momen an gone n anoher. Solar energy s presen hroughou he ay, bu he solar rraaon levels vary ue o sun nensy an unprecable shaows cas by clous, brs, rees, ec. These rawbacks en o make hese renewable sysems neffcen. However, by ncorporang maxmum power pon rackng (MPPT) algorhms, he sysems power ransfer effcency can be mprove sgnfcanly. To escrbe a wn urbne s power characersc, equaon () escrbes he mechancal power ha s generae by he wn [6]. varables, he p spee rao (TSR) an he pch angle. The TSR, λ, refers o a rao of he urbne angular spee over he wn spee. The mahemacal represenaon of he TSR s gven by (4) [0]. The pch angle, β, refers o he angle n whch he urbne blaes are algne wh respec o s longunal axs. R ω b λ = (4) vw here R = urbne raus, ω b = angular roaonal spee Fgure 7 an 8 are llusraons of a power coeffcen curve an power curve for a ypcal fxe pch (β =0) horzonal axs wn urbne. I can be seen from fgure 7 an 8 ha he power curves for each wn spee has a shape smlar o ha of he power coeffcen curve. Because he TSR s a rao beween he urbne roaonal spee an he wn spee, follows ha each wn spee woul have a fferen corresponng opmal roaonal spee ha gves he opmal TSR. For each urbne here s an opmal TSR value ha correspons o a maxmum value of he power coeffcen (C p,max ) an herefore he maxmum power. Therefore by conrollng roaonal spee, (by means of ajusng he elecrcal loang of he urbne generaor) maxmum power can be obane for fferen wn spees. Fgure 7: Power Coeffcen Curve for a ypcal wn urbne p m = () 0.5ρAC p ( λ, β ) vw here ρ = ar ensy, A = roor swep area, C p (λ, β) = power coeffcen funcon λ =p spee rao, β = pch angle, v w = wn spee The power coeffcen (C p ) s a nonlnear funcon ha represens he effcency of he wn urbne o conver wn energy no mechancal energy. I s epenen on wo Fgure 8: Power Curves for a ypcal wn urbne A solar cell s comprse of a P-N juncon semconucor ha prouces currens va he phoovolac effec. P arrays 58

5 are consruce by placng numerous solar cells connece n seres an n parallel [5]. A P cell s a oe of a large-area forwar bas wh a phoovolage an he equvalen crcu s shown by Fgure 9 []. The curren-volage characersc of a solar cell s erve n [] an [] as follows: I (5) I ph I D q( R I) s ph I 0 exp Ak BT Rs I Rsh here I ph = phoocurren, I D = oe curren, I 0 = sauraon curren, A = ealy facor, q = elecronc charge.6x0-9, k B = Bolzmann s gas consan (.8x0 - ), T = cell emperaure, R s = seres ressance, R sh = shun ressance, I = cell curren, = cell volage Fgure 9: P cell equvalen crcu (6) Typcally, he shun ressance (R sh ) s very large an he seres ressance (R s ) s very small [5]. Therefore, s common o neglec hese ressances n orer o smplfy he solar cell moel. The resulan eal volage-curren characersc of a phoovolac cell s gven by (7) an llusrae by Fgure 0. [5] q I ph I 0exp kt (7) can be observe n Fgure ha here s a parcular opmal volage for each rraaon level ha correspons o maxmum oupu power. Therefore by ajusng he oupu curren (or volage) of he P array, maxmum power from he array can be rawn. Fgure : P cell power characerscs Due o he smlares of he shape of he wn an P array power curves, a smlar maxmum power pon rackng scheme known as he hll clmb search (HCS) sraegy s ofen apple o hese energy sources o exrac maxmum power. The HCS sraegy perurbs he operang pon of he sysem an observes he oupu. If he recon of he perurbaon (e.g an ncrease or ecrease n he oupu volage of a P array) resuls n a posve n he oupu power, hen he conrol algorhm wll connue n he recon of he prevous perurbaon. Conversely, f a negave n he oupu power s observe, hen he conrol algorhm wll reverse he recon of he pervous perurbaon sep. In he case ha he n power s close o zero (whn a specfe range) hen he algorhm wll nvoke no s o he sysem operang pon snce correspons o he maxmum power pon (he peak of he power curves). The MPPT scheme employe n hs paper s a verson of he HCS sraegy. Fgure s he flow char ha llusraes he mplemene MPPT scheme. Fgure 0: P cell volage-curren characersc The ypcal oupu power characerscs of a P array uner varous egrees of rraaon s llusrae by Fgure. I 59

6 Measure Conrol arable Conrol varable Reference reache? Power Measuremen P curren Increase reference proporonal o power Sore P curren as Pprevous -apply no reference prevously ncrease? P curren - P prevous > hreshol? Sore P curren as Pprevous Change n power posve? Decrease reference proporonal o power reference prevously ncrease? (I) Decrease reference proporonal o power Increase reference proporonal o power Fgure : General MPPT Flow Char for wn an P. SIMUATION RESUTS In hs secon, smulaon resuls from PSIM s gven o verfy ha he propose mul-npu recfer sage can suppor nvual as well as smulaneous operaon. The specfcaons for he esgn example are gven n TABE I. Fgure llusraes he sysem uner he conon where he wn source has fale an only he P source (Cuk converer moe) s supplyng power o he loa. Fgure 4 llusraes he sysem where only he wn urbne generaes power o he loa (SEPIC converer moe). Fnally, Fgure 5 llusraes he smulaneous operaon (Cuk-SEPIC fuson moe) of he wo sources where M has a longer conucon cycle (converer saes I, I an III see Fgure 5). TABE I. Desgn Specfcaons Oupu power () k Oupu volage 500 Swchng frequency 0kHz (II) Fgure 4 : Invual operaon wh only wn source (SEPIC operaon) (I) The njece hree phase generaor curren; (II) Top: Oupu power, Boom: Swch currens (M an M ) (I) Fgure : Invual operaon wh only P source (Cuk operaon) Top: Oupu power, Boom: Swch currens (M an M ) (II) Fgure 5 : Smulaneous operaon wh boh wn an P source (Fuson moe wh Cuk an SEPIC) (I) The njece hree phase generaor curren; (II) Top: Oupu power, Boom: Swch currens (M an M ) Fgure 6 an 7 llusraes he MPPT operaon of he P componen of he sysem (Cuk operaon) an he n componen of he sysem (SEPIC operaon) respecvely. 60

7 Fgure 6 : Solar MPPT P oupu curren an reference curren sgnal (Cuk operaon) [5] Y.M. Chen, Y.C. u, S.C. Hung, an C.S. Cheng, Mul-Inpu Inverer for Gr-Connece Hybr P/n Power Sysem, IEEE Transacons on Power Elecroncs, vol., May 007. [6] os Res, F.S., Tan, K. an Islam, S., Usng PFC for harmonc mgaon n wn urbne energy converson sysems n Proc. of he IECON 004 Conference, pp , v. 004 [7] R.. Erckson, Some Topologes of Hgh Qualy Recfers n he Proc. of he Frs Inernaonal Conference on Energy, Power, an Moon Conrol, May 997. [8] D. S.. Smone J. Sebas an, an J. Ucea, The Dsconnuous Conucon Moe Sepc an Cuk Power Facor Preregulaors: Analyss an Desgn IEEE Trans. On Inusral Elecroncs, vol. 44, no. 5, 997 [9] N. Mohan, T. Unelan, an Robbns, Power Elecroncs: Converers, Applcaons, an Desgn, John ley & Sons, Inc., 00. [0] J. Marques, H. Pnhero, H. Grunlng, J. Pnhero, an H. Hey, A Survey on arable-spee n Turbne Sysem, Proceengs of Brazlan Conference of Elecroncs of Power, vol., pp. 7-78, 00. [] F. asser an T. G. Ang, Phoovolac Engneerng Hanbook 990 [] Global n Energy Councl (GEC), Global wn 008 repor, June 009. []. Pang, H. ang, Y. J. ang, an Z. ang, Analyss of Phoovolac Chargng Sysem Base on MPPT, Proceengs of Pacfc-Asa orkshop on Compuaonal Inellgence an Inusral Applcaon 008 (PACIIA 08), Dec 008, pp Fgure 7 : n MPPT Generaor spee an reference spee sgnal (SEPIC operaon) I. CONCUSION In hs paper a new mul-npu Cuk-SEPIC recfer sage for hybr wn/solar energy sysems has been presene. The feaures of hs crcu are: ) aonal npu flers are no necessary o fler ou hgh frequency harmoncs; ) boh renewable sources can be seppe up/own (suppors we ranges of P an wn npu); ) MPPT can be realze for each source; 4) nvual an smulaneous operaon s suppore. Smulaon resuls have been presene o verfy he feaures of he propose opology. REFERENCES [] S.K. Km, J.H Jeon, C.H. Cho, J.B. Ahn, an S.H. Kwon, Dynamc Moelng an Conrol of a Gr-Connece Hybr Generaon Sysem wh ersale Power Transfer, IEEE Transacons on Inusral Elecroncs, vol. 55, pp , Aprl 008. [] D. Das, R. Esmal. Xu, D. Nchols, An Opmal Desgn of a Gr Connece Hybr n/phoovolac/fuel Cell Sysem for Dsrbue Energy Proucon, n Proc. IEEE Inusral Elecroncs Conference, pp , v [] N. A. Ahme, M. Myaake, an A. K. Al-Ohman, Power flucuaons suppresson of san-alone hybr generaon combnng solar phoovolac/wn urbne an fuel cell sysems, n Proc. Of Energy Converson an Managemen, ol. 49, pp. 7-79, Ocober 008. [4] S. Jan, an. Agarwal, An Inegrae Hybr Power Supply for Dsrbue Generaon Applcaons Fe by nconvenonal Energy Sources, IEEE Transacons on Energy Converson, vol., June