ZCS sonant Convt Basd Paalll Balancing of Sially Connctd Battis Sting Ilya Zlts, Mmb, IEEE Pow Elctonics Dpatmnt afal Advancd Dfns Systms Ltd. P.O. Box 50, Haifa 3101, Isal. ilyaz@afal.co.il www.afal.co.il Abstact This pap intoducs a nw topology fo paalll balancing of sially connctd battis sting. Th main advantag of th balancing concpt is that ngy is tansfd only whn th s a unbalancd. As a sult, th pow losss a significantly ducd sinc no cunt ciculats though th systm whn balancd. This has bn nabld by a modification of an isolatd sis-sonant convt opating in DCM and fatus zo cunt switching (ZCS). Anoth attactiv fatu is that on tansfom fo two s is usd, as opposd to convntional isolatd topologis that qui a tansfom p. Th alization is simpl and quis simpl cunt polaity dtcto. Expimntal sults hav bn obtaind by a pototyp of two sis connctd battis, which dmonstats th balancing capabilitis of th systm. I. INTODUCTION Sially connctd battis stings hav bn usd fo many high voltag DC applications. Among thm, lctic vhicls (EV) [1], hybid lctic vhicls (HEV) [], plug-in hybid lctic vhicl (PHEV) [3] and oth batty powd applications [4], [5]. Du to manufactuing and nvionmntal vaiancs, dgadation with aging, intnal impdanc diffnc and thmal conditions, th chags tansfd to o consumd fom ach batty a not qual. As a sult, th liftim and fficincy of th battis sting a ducd. Moov, th ovchag of th battis in th sting can caus xplosion o fi in th cas of snsitiv battis s [6]. Thfo, a chag qualiz (i.., balancing cicuit) is ssntial to duc th imbalancs and consquntly to impov th ovall pfomanc of th systm [7], [8]. Sval balancing cicuits hav bn invstigatd ov th cnt yas [9]-[33]. Ths can b gnally classifid into two main catgois: passiv and activ. Passiv balancing fatus O Kishnboim, Studnt Mmb, IEEE, Nadav Dahan, Studnt Mmb, IEEE, and Mo Modchai Ptz, Mmb, IEEE Th Cnt fo Pow Elctonics and Mixd-Signal IC Dpatmnt of Elctical and Comput Engining Bn-Guion Univsity of th Ngv P.O. Box 653, B-Shva 84105, Isal. oki@post.bgu.ac.il, nadad@post.bgu.ac.il, mop@.bgu.ac.il www..bgu.ac.il/~pmic simpl dsign and implmntation and lativly low cost [9], but du to inhnt ngy loss, it is lss attactiv in tms of ngy saving. Th activ balancing achitctus includ vaity of topologis such as switchd-capacito convts [10]-[1], isolatd and non-isolatd unidictional and bidictional DC-DC convts [13]-[4], and multi-winding tansfom-basd convts [5]-[7]. Th main challngs of th activ solutions oftn lat to implmntation issus such as high componnt count and complx contol algoithms [8], [9]. In addition, incasing th balancing spd is tadd fo quiscnt pow loss, i.. losss that xist whn no balancing action is quid. cnt studis hav potd impovd balancing schms that a basd on paalll balancing tchniqus [30], xhibiting high qualization spd whn compad to sis balancing tchniqus. On paticula challng of th paalll balancing is th complxity in implmnting lag aays. This has bn addssd by a modulaization concpt psntd in [31]-[34]. Th, n battis sting is dividd into M moduls, ach of thm is balancing K s so that n=m*k. This concpt has stablishd a solid foundation fo a paalll balancing achitctu, allowing high fficincy that is pusud in this study. Th objctiv of th study is to intoduc a nw activ balancing convt topology fo sis connctd battis sting, as dtaild in Fig. 1. Th concpt is alizd by a modification of an isolatd sis-sonant convt such that on tansfom is usd to balanc two s, ducing th complxity of th systm. Th convt opats in DCM and thfo ZCS is assud. Balancing occus only whn ncssay, i.. ngy dos not ciculat though th systm whn th battis a balancd. As a sult, th quiscnt pow loss is minimal. Th convt is contolld by simpl contol mthod and can b asily scald up and modulaizd. 978-1-4673-9550-/16/$31.00 016 IEEE 80
Th pap is oganizd as follows: Sction II dscibs th topology, its pincipl of opation and th majo fatus of it, Sction III dlinats th systm s implmntation and povids dsign guidlins. Expimntal sults and conclusion a thn povidd in Sctions IV and V, spctivly. V,1 S 11 S 1 S 13 T 1 S 15 S 16 S 17 S 18 II. PINCIPLE OF OPEATION Th systm in Fig. 1 can b dividd into m = n/ doubl- moduls, wh ach modul is constuctd of a top (oddnumbd s) and a bottom (vn-numbd s). Each of th m doubl-s is balancd using a balancing modul, built of a half-bidg loadd by a sonant tank in sis with th pimay sid of th tansfom. Th sconday sid conncts to th bus capacito via a full-bidg tansisto assmbly. Th bus capacito is th common voltag fo all of th m doubl- moduls and acts as a link that is usd to tansf ngy btwn th s. As a sult of th tansfom s isolation, ach of th n batty s can b qualizd indpndntly of th action in oth s, that is, no synchonization btwn th moduls is quid, and thfo th complxity of th systm is significantly ducd. Additionally, du to th tansfom s isolation, th voltag stss on th switchs is no mo than th voltag and is indpndnt on th numb of s in th sting. Th switching fquncy f s is st to b low than th sonant fquncy f (i.. f s<f ) to allow opation in DCM with ZCS. Th balancing action fo ach batty is dividd into two stps: cunt polaity dtction and thn dictional ngy tansf basd on th polaity. Th opation of th switchs is dscibd in Fig. fo th upp, assistd by th cunt and voltag wavfoms which a dpictd in Fig. 3. In th fist stp, switchs,, and a tund on at t=t 0, and main on fo t 0<t<t 1 ((Fig. (a), Fig. (d)), wh t 1<t 0+1/f, allowing bi-dictional cunt flow. Duing this intval, th cunt polaity snso dtmins th cunt diction in th sonant tank. Th cunt diction dpnds on th diffnc btwn th batty voltag and th bus voltag flctd to th pimay ( fo th unity tansfom atio). Cll voltag that is high than twic th bus capacito voltag (> ) sults in a positiv cunt i, whas <, sults in a ngativ cunt diction. In cas that th voltag quals twic th bus capacito voltag (=), i.., no balancing is ndd, th cunt is zo and no ngy is tansfd in ith diction. Th cunt polaity is dtctd by a snso at th pimay sid, as shown in Fig. (a) and in Fig. (d), that dtmins th conscutiv switching squnc in th scond stp. It should b notd that th switching configuation at th bginning of th switching cycl (t 0<t<t 1) is simila gadlss of th diffnc btwn th and th bus voltags, that is fo both positiv and ngativ cunt. In th scond stp, aft th cunt polaity has bn dtctd, th opation smbls a convntional sonant V, S 14 Fig. 1. Batty managmnt systm fo n sially connctd battis. convt in DCM. Fo positiv dtctd cunt, and tun off at t 1, and thi body diods a conducting until th cunt bcoms zo at t=t 0+1/f (Fig. (b)). It should b notd that tuning and off at a low, nonzo cunt (bfo t 1) futh allows ZVS at tun off. Th cunt mains zo until half of th switching piod t =t 0+1/f s. At t, tuns off and, followd by a shot dad-tim, tuns on (Fig. (c)). This dischags th sonant capacito with a ngativ cunt duing t <t<t +1/f and thn th cunt is discontinud by th body diods of and until th nxt switching cycl at t 3=t 0+1/f s. Fo a ngativ dtctd cunt at t 0<t<t 1, th opation is miod with spct to th and th bus sid. is tund off at t 1, as shown in Fig. (). Th switchs, a tund off and, a tund on (aft a shot dad-tim) at t (Fig. (f)). It should b notd that th switching timing can b loosly st. ZCS is natually obtaind by th body diods as long as th switchs hav bn tund off pio to th zo cossing point [35]. Simulatd typical convgnc duing balancing opation of th systm is psntd in Fig. 4, wh fou batty s (mulatd by lag capacitancs) hav bn pst to diffnt voltags. As can b obsvd, th s voltags convg to th avag of th initial voltags, validating th balancing opation of th systm. Th bus voltag convgs to th avag of half th voltag lvls of th s in th pack, and is givn by N 1 Vbus V, k (1) N k 1 To div th xpssions fo th systm s ky wavfoms and paamts, in th following analysis, it is assumd that th voltag (V ) and th bus voltag a constant and that th avag voltag acoss th sonant capacito has achd a 803
stady-stat valu of half th voltag, i.. V C=0.5V. It is futh assumd that th chag capacity of th bus capacito is significantly low than th s capacity. As a sult, th bus voltag apidly convgs to th half of th avag s voltags as in (1) which tanslats to a lativly small voltag diffnc V=0.5V - duing stady-stat. Du to symmtical opation, th divations a applid fo th cas that V >. Th sonant cunt i can b xpssd as 0.5 1 i t f t t t t f f V V t bus Q sin( f t ), t 0 t t 0 1/ f Z f 0.5V V t bus Q sin( ), 1/ 1 Z 0, lswh wh, th sonant tank s chaactistic impdanc Z, sonant fquncy f and th quality facto Q a: () L 1 1 L Z ; f ; Q (3) C LC C and, and a th sonant ntwok componnts and is th total paasitic o stay sis sistanc in th sonant ntwok. i v C ΔV C t 0 t 1 t t 3 V C0 Tim [μs] Fig. 3. Typical wavfoms of th sonant inducto cunt and sonant capacito voltag duing balancing fo th cas whn >. 1/f s V C1 Sm7 i i Cunt Polaity Snso t 0 <t<t 1 (a) Cunt Polaity Snso t 0 <t<t 1 (d) i t 1 <t<t (b) i t 1 <t<t () i t <t<t 3 (c) i t <t<t 3 (f) Fig.. Mods of opation: (a), (b) and (c) whn >, (d), () and (f) whn <. (a) and (d): cunt polaity dtction at t 0<t<t 1, (b), (c), () and (f): ngy tansf. 804
Fom (), th pak amplitud of th sonant cunt and th avag cunt flowing though th can b xpssd as: I I pak I 0.5V Vbus Z 1 pak, (4) 0.5V Vbus Z 1, (5) wh δ=0.5f s/f. Th voltag swing of th sonant capacito V C duing on switching cycl T s=1/f s can b xpssd as: V I Z (6) C wh, V C0 and V C1 a th initial and final voltags (Fig. 3), spctivly, givn by: C1 pak VC 0.5( V 0 VC ). (7) V 0.5( V V ) Th pow pocssing fficincy fo a givn voltag diffnc of V can b xpssd as: C Ploss Ipak Z V 1 1 1 1. (8) P V Q V Q 1 As mntiond ali and xpsss by (1), th bus voltag convgs to half of th s avag voltag. This pocss can b assumd instantanous whn compad to th at that s voltags vay. As can b sn in (8), th pow pocssing fficincy linaly dpnds on V, which flcts on th voltag diffnc btwn th s. This implis whn balanc is achivd th convt xhibits idal pow pocssing fficincy, a consqunc of th fact that no cunt ciculats though th systm whn balancd. It should b futh notd that fo a asonabl stting of th sonant paamts of Q>4, (8) can b appoximatd to: V 1 1.73, (9) V which highlights that th fficincy dpnds pimaily on th s status and is vitually indpndnt on th systm paamts. A cla advantag in a balancing systm o any systm that compiss multipl convts o convts sting. III. IMPLEMENTATION, DESIGN CONSIDEATIONS AND TOPOLOGY EXPANSION Implmntation of ach of th m moduls in Fig. 1 is staightfowad and is dpictd in Fig. 5. Th batty sid is built aound a convntional sonant half-bidg 1. 1.1 1 11.9 11.8 V, V, 1 V, 4 V, 3 0 5 10 15 0 Tim (ms) Fig. 4. Simulatd convgnc of s with diffnt initial voltag pst. configuation whas th bus capacito sid is constuctd by a standad full-bidg ctifi configuation. As a sult, th dsign of th MOSFET s gats divs is standad low-sid and bootstappd pais. Th dsign of th sonant inductanc and tansfom follows a classical LLC magntic lmnt dsign, wh can b th lakag inductanc L lkg of th tansfom which has bn stimatd as dscibd in [36]. A. Dsign Considations Th analysis divd ali stablishd th main attibuts of th convt. Utilizing th abov divations, calculations of th ky componnts of th convt can b stablishd by th following pocdu. Givn: Tagt avag cunt p I fo maximum stting of V; th switching fquncy f s and quality facto Q>4. a. Calculat th xpssion L lkg i 1:k s V CC F Q 3 1 amp 1 V CC V CC 1 cmp 1 cmp Out- Out+ Fig. 5. Implmntation of ach of th m balancing cicuits including th cunt polaity dtction cicuity. (10) 805
b. Fom (5), (10), and considing δ < 1/, and can b slctd accoding to F Q V L (11) ( ) I f s Winding Aa Lakag flux I 1 1 L C F Q V fs L c. Vify that th sonant tank s sis sistanc satisfis Z Q If (13) dos not hold, itat (11) and (1). (1). (13) d. Th tansfom s aa of poduct A ' p (without th lakag inductanc considation) should b slctd accoding to A V I f bus pak p (14) BJK fs wh B is th magntic flux dnsity at satuation, J is th cunt dnsity and K is th winding fill facto.. To achiv th dsid lakag inductanc L lkg th tansfom s windings configuation should b dsignd as illustatd in Fig. 6 (fo an E-typ magntic co). As pscibd in [36], th lakag inductanc in E co can b stimatd by 0n ATL b1 b Llkg ( c) H, (15) a 3 wh µ 0 is th pmability constant, n is th numb of tuns in th pimay winding, ATL is th avag lngth of tun, a is th winding hight, b 1 and b a th thicknsss of th pimay and sconday winding, spctivly, and c is th distanc btwn th pimay and th sconday winding. All lngths a assignd in mm. In this study, th tansfom is with a tuns atio and thfo b 1=b =b. f. Adjust th aa poduct to includ th addition of th lakag inductanc by B. Pactical implmntation c Ap Ap 1 b. (16) Th cunt polaity dtcto cicuity (Fig. 5) is alizd using a cunt tansfom, summing amplifi and two compaatos, as dpictd in Fig. 5. Th opation mods a dtctd positiv, ngativ and zo cunt. Th cunt is V,1 V, V,3 V,4 E-Co Pimay Balancing Modul Balancing Modul b 1 c b,1, considd zo if its absolut maximum valu, masud within t 0<t<t 1, is lss than th thshold dtmind by th following xpssion: 0.5V CC k Ith, (17) 1 d wh d= / 1, k is th tuns atio of th cunt tansfom, s is th sns sisto at th sconday sid of th cunt tansfom, >> s, and > 1. Th outputs of th compaatos dtmin th polaity of i as dtaild in Tabl I. TABLE I CUENT POLAITY SENSO DETECTION Out+ Out- Cunt Polaity 1 0 i > 0 0 1 i < 0 0 0 i 0 Th voltag stss of th tansistos is th voltag fo th sid tansistos and th bus capacito voltag fo th bus sid. Th low voltag stss allows tansistos with low DS(on) p silicon aa. Cunt stsss dpnd on th dsid convgnc spd. s Balancing Modul Fig. 7. Modulaization of th balancing systm fo fou batty s. a Sconday Fig. 6. Convntional tansfom winding configuation fo an E-co. 806
Th isolation btwn th bus capacito and th batty s povidd by th tansfom nabls th topology to b xtndd, as dmonstatd in Fig. 7, fo fou batty s. This modulaization, as mntiond in [31], povids anoth stag of balancing and nabls th opation at low voltag stss which can xpdit th balancing spd sinc high cunt can b dlivd fo th sam pow dissipation. IV. EXPEIMENTAL VEIFICATION In od to dmonstat th balancing action and to vify th analysis and simulation sults, xpimnts hav bn caid out using two lag capacitos (mulating th battis opation, in od to shotn th convgnc tim) as two s in sis. Tabl II shows th componnt typs and valus usd in th xpimntal pototyp. Fig. 8 psnts th masud wavfoms of th sonant tank duing th balancing opation. Basd on th pincipl of opation dscibd ali, th balancing tim is shad qually btwn th s. Th duation of ach -balancing has bn st to 10 switching cycls. Th pocdu is dmonstatd in Fig. 9, wh th sonant cunt and th capacito voltag a masud ov 0 switching cycl. Duing th fist 10 switching cycls th having th high voltag is balancd (i.. conncts to th bus via th convt), whas in th nxt 10 switching cycls th balancing is don fo th with low voltag. Convgnc of th sonant capacito voltag to th stady-stat valu can b obsvd in Fig. 9, suppoting th analysis conjctu that th majoity of ngy tansf opation is caid und stady-stat conditions. Fig. 10 shows th s (alizd by lag capacitos to allow timly convgnc) voltags and th tank s sonant cunt ov a long piod of tim whn s a p-chagd to diffnt voltags. As can b obsvd, th voltags of th two s a qualizd on to anoth and th cunt dcay to zo. Simila xpimnt was caid out using two 1 V, 7Ah, Lad-Acid battis. Fig. 11 shows th battis voltags ov a long piod of tim whn p-chagd to diffnt voltags. As can b obsvd, th voltags of th two battis a bing balancd up to a small voltag diffnc. Fig. 8. Expimntal sults of sonant tank cunt (top) and sonant capacito voltag (bottom) duing balancing opation. Cunt 00mA/div, voltag 500mV/div, tim scal 0μs/div. Fig. 9. sonant tank cunt (top) and sonant capacito voltag (bottom) duing balancing of upp and low s with diffnt voltags, ach of thm is balancd fo 10 switching piods. Cunt 500mA/div, voltag 500mV/div, tim scal 100μs/div. 1.3V TABLE II EXPEIMENTAL POTOTYPE VALUES 11.7V Componnt Clls: Battis Whn alizd by capacitos Tansfom s lakag inductanc Llkg sonant tank capacito C Tansfom s magntizing inductanc Lm MOSFETs Sm1-Sm8 Bus capacito Cbus sonant fquncy f Switching fquncy fs Valu 1 V, 7Ah 100 mf 5 μh 5.7 μf 3 mh Si4178DY 15 mf 30 khz 0 khz i Fig. 10. Expimntal sults of voltag convgnc of two s with diffnt initial voltags, and th tank s sonant cunt. Tim scal s/div, Clls voltags 00mV/div, tank s sonant cunt 500mA/div. 807
V. CONCLUSION In this wok, a nw soft switchd isolatd balancing topology and opation mthod hav bn intoducd. Th cicuit is basd on a modifid sis sonant convt opating in DCM. Th nw balancing cicuit uss on tansfom fo balancing of two nighboing s and as a sult, lss magntic componnts a quid compad to oth isolatd topologis. Anoth significant advantag of th topology is th xtmly low quiscnt losss du to th nativ bhavio of th convt wh no cunt ciculats though th systm whn th s a balancd. Th balancing opation is facilitatd by a simpl cunt polaity dtction and dos not qui synchonization btwn moduls. Futhmo, th topology can b asily scald-up and modulaizd fo as many s as quid. ACKNOWLEDGEMENTS This sach was suppotd by Kn Pazi. EFEENCES [1] A. Emadi, L. Young Joo, and K. ajashkaa, Pow lctonics and moto divs in lctic, hybid lctic, and plug-in hybid lctic vhicls, IEEE Tans. Ind. Elcton., vol. 55, no. 6, pp. 37 45, Jun. 008. [] M. Ehsani, G. Yimin, J. M. 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