A New Isolaed DCDC Boos nverer using hreesae Swiching Cell René P. orricobascopé (1) Grover V. orricobascopé () Francisco A. A. de Souza (1) Carlos G. C. Branco (3) Cícero M.. Cruz (1) Luiz H. C. Barreo (1) (1) Federal Universiy of Ceará Elecrical Engineering Deparmen Energy Processing and nrol Group Foraleza CE Brazil rene@dee.ufc.br () Elek Valere Dep. of Research and Developmen Hammarbacken 4A, 4r. 191 4, Sollenuna, Sockholm, Sweden grover.orrico@elkenergy.com (3) echnological Educaion Federal Cenre of Ceará Indusry Area Foraleza CE Brazil gusavo@cefece.br AbsracIn his paper, a new isolaed DCDC boos converer based on hreesae swiching cell (3SSC) is proposed. he menioned cell allows he use of only wo windings in he isolaion ransformer, as well as, he series connecion of only one DC curren blocking capacior o avoid is sauraion. Oher relevan characerisics of he converer are, he blocking volage across he conrolled swiches is low, which allows he uilizaion of lower drainosource conducion resisances (RDSon) MOSFEs, and he curren hrough he auoransformer winding is almos coninuous minimizing he hyseresis losses on he magneic core. In his way, he efficiency of he proposed converer is high, and i is recommended for he developmen of power supplies using low volage sources commonly found on renewable energy conversion sysems and baeries. he converer was analyzed in overlapping of he conrol signals or duy cycle higher han.5 operaing in coninuous conducion mode (CCM). In order o verify he feasibiliy of his opology; principle of operaion, heoreical analysis, and experimenal waveforms are shown for a 1kW assembled prooype. I. INRODUCION When he desired applicaion needs o raise a low level inpu volage, commonly presened in baeries, phoovolaic solar panels, fuel cells and small wind generaors (1Vdc o 15Vdc), o high oupu DC bus volage (3Vdc 4Vdc) required in volage source inverers (VSI) for applicaions such as power supply sysems, moor drives, ec, he classical curren fed DCDC pushpull converer is commonly he firs choice. he convenional pushpull converer was sudied deailed in [1]. he advanages of he pushpull converer are: he opology is suiable for low inpu volage applicaion because is involved only one conrolled swich in series during energy sorage or energy ransfer, he swiches are referenced o he same poenial ha improves is gaing drive circui. As disadvanages are: he leakage inducance of he isolaed ransformer may causes overvolages sresses across he conrolled swiches during commuaion, and he asymmerical consrucion of he ransformer and asymmerical PWM pulses of he conrol circui causes sauraion problems o he ransformer. he opologies presened in [3] are modified pushpull converers based on he nonisolaed Weinberg converer. o improve is efficiency and o minimize volage sresses on he conrolled devices, nondissipaive auxiliary circuis were added. Also, ohers modified pushpull converers wih sof swiching were proposed in [47]. A woinducor isolaed boos converer wihou and wih auoransformer were presened in [89]. hey operae as an inerleaved boos converer. As relevan feaures of he converer is ha he inpu curren of he volage source is nonpulsaing wih low ripple, and he maximum volage sress across he swiches is fixed o he primary side volage of he isolaing ransformer. In [1] was implemened an isolaed boos converer ha exhibis as advanages non parasiic volage ringing across all of semiconducor devices on he primary and secondary sides of he ransformer. he proposed converer in his work is based on he hreesae swiching cell (3SSC) [11]. he opology is shown in Fig. 1. mpared o he convenional pushpull converer, he proposed converer presens he following advanages: he 3SSC allows he uilizaion of only one primary winding ha permis o add a DC curren blocking capacior in series connecion, in order o avoid he ransformer sauraion problem; less copper and magneic core are involved during he ransformer assembly; and he moderae leakage inducance of he ransformer allows he reducion of he commuaion losses of he swiches. he auoransformer of he 3SSC has small size, because i is designed for half oupu power of he converer and for a high magneic flux densiy since he curren hrough he windings is almos coninuous wih low ripple. D5 N i1 v1 i v i v i is vp vs i r v v Fig. 1. Proposed isolaed DCDC boos converer using 3SSC opology. ip Io
II. PROPOSED ISOLAED DCDC CONVERER USING 3SSC A. Descripion of he Circui he proposed converer shown in Fig. 1 is composed by he following devices: a sorage coupled inducor L b wih urns number N 1 and N, an auoransformer wih uniary urns raio, one DC curren blocking capacior C b, an isolaed ransformer r wih urns number N p and N s, wo conrolled swiches S 1 and S, four recifier diodes D 1 D 4, one filer capacior C o, one flyback diode D 5, and load resisor R o. B. Principle of Operaion he proposed converer is analyzed wih overlapping of conrol signals or wih duy cycle higher han.5, operaing in coninuous conducion mode (CCM). In his analysis, all he componens involved in he converer are considered ideals. During one commuaion period i presens four operaing inervals ha are described as follows. he key waveforms of he corresponding inervals are shown in Fig. 3. Inerval (, 1 ): he swiches S 1 and S are urned on. he inpu volage is applied o he sorage inducor L b, and as consequence he curren increases linearly hrough i. he auoransformer is shorcircuied because he resulan magneic flux of he core is null. he diodes D 1 D 4 are reverse biased. he load resisor is feed by he filer capacior C o. his sage is shown in Fig..a and i finishes when swich S 1 is urned off. Inerval ( 1, ): In his inerval he swich S remains urned on. he volage across swich S 1 is equal o he primary side volage of he isolaion ransformer r. he diodes D 1 and D are direcly biased. he energy sored in he inducor in he firs inerval, as well as, he energy from he volage source are ransferred o he filer capacior C o and resisor R o. he resulan circui from his operaing sage is shown in Fig..b. Inerval (, 3 ): his inerval is similar o he firs one, where swiches S 1 and S are urnedon, and he energy is again sored in he inducor L b. he diodes D 1 D 4 are reverse biased I is finished when swich S is urnedoff. his sage is shown in Fig..c. Inerval ( 3, 4 ): During his inerval, he swich S 1 remains urnedon. he volage across swich S is equal o he volage across primary side of he isolaed ransformer r. he recifier diodes D 3 and D 4 are direcly biased. he energy sored in he inducor L b during he hird sage, as well as, he energy from he volage source are ransferred o he filer capaciors C o and load resisor R o. his sage is shown in Fig..d v i v1 i1 v i v i s D*s (1D)*s 1 3 4 Fig. 3. Key waveforms of he proposed converer. r r (a) Inerval ( 1 ) (b) Inerval ( 1 ) r r (c) Inerval ( 3 ) Fig.. Operaion sages of he proposed converer. (d) Inerval ( 3 4 )
III. ANALYSIS OF HE PROPOSED CONVERER A. lage Saic Gain he ideal volage saic gain of he converer and he ransformer urns raio of he ransformer r is given respecively by a Gv = =, (1) (1 D) a =, () where is he oupu volage, is he inpu volage, D is he duy cycle of he converer, is he secondary urns number of he ransformer r, and is he primary urns number of he ransformer r. he volage saic gain curves as funcion of he duy cycle, aken as parameer of ransformer urns raio a, are shown in he Fig. 4. 3 Gv 5 15 1 5 a=6 a=5 a=4 a=3 a= a=1.5.55.6.65.7.75.8.85.9.95 1 D Fig. 4. Normalized volage saic gain aken as parameer ransformer urns raio. B. Inducor Design he curren ripple on he inducor is given by ( D 1)( 1 D) Δ I =, (3) afs where ΔI is he curren ripple on he inducor L b and f s is he swiching frequency of he converer. Rearranging (3), he normalized curren ripple in he inducor is given by af ( 1)( 1 sδ I D D ) Δ I = =. (4) he Fig. 5, which is obained using (4), shows he normalized curren ripple on he inducor as a funcion of he duy cycle. herefore, i is possible o conclude ha he maximum curren ripple on he inducor occurs when he duy cycle is equal o.75 and he normalized curren ripple is equal o.63. ΔI.8.7.6.5.4.3..1.5.55.6.65.7.75.8.85.9.95 1 Fig. 5. Normalized ripple curren on he inducor L b. hus, for a given value o he curren ripple, i is possible o deermine he inducor value as L b =. (5) 16afsΔI he urns number of he sorage inducor L b can be deermined as I _ pk N 1 =. (6) AeBmax where I _pk is he inducor peak curren, A e is he core cross secion, and B max is he maximum flux densiy. An auxiliary winding wih N urns number and opposed polariy is coupled o he sorage inducor L b wih N 1 urns number. his auxiliary winding is used o discharge he sorage inducor L b when occurs an open circui problem in he primary side of he ransformer. Oherwise, high damage overvolages may occur mainly in he conrolled swiches. From he flyback converer crierion operaing in he coninuous conducion mode is deermined he urns number N as ( 1 D ) N N. 1 (7) D C. Auoransformer Design he high frequency auoransformer mus be designed for half acive oupu power, and high magneic flux densiy, B, because he curren hrough he windings is coninuous and wih low ripple. he auoransformer urns raio mus be uniary. hus, P o P =, (8) where P is he acive power processed by he auoransformer, and Po is he oupu power of he converer. D. ransformer Design he isolaed high frequency ransformer r mus be designed for he oal acive oupu power. he ransformer urns raio is aken from (1) and from characerisic curves shown in Fig. 4. D
In order o reduce Eddy currens loss in he core, so as leakage inducance, he winding layers of he primary and he secondary of he ransformer are mouned as he sandwich assembly [1]. he power of he isolaion ransformer is deermined by Pr = Po. (9) E. DC Curren Blocking Capacior he DC curren blocking capacior avoids he sauraion problem of he isolaed ransformer. his capacior mus be made of polypropylene due o is low inernal resisance and AC polariy, because he oal load curren circulaes hrough i. nsidering a peak o peak volage variaion, and curren circulaion hrough i, he capaciance of he capacior C b can be deermined by I _ avg (1 D ) C b =, (1) fsδv where Δ V is he peak o peak volage variaion across capacior defined as ΔV = ξ, (11) a Iavg is he average curren circulaing in he sorage inducor L b, ξ is an absolue value lower han 1 relaive o he primary side volage of he ransformer r (in pracical applicaions can be chosen beween.5 o.15). F. Curren and lage Sresses in Swiches S 1 and S he RMS curren hrough he swich S 1 ha is equal o he swich S, considering a small curren ripple hrough he sorage inducor L b, can be deermined by 3 D I _ rms I _ avg. (1) 4 he maximum volage across of swiches S 1 and S, wihou considering he parasiic inducances ha causes overvolages, is almos equal o he primary side volage of he isolaed ransformer. he volage across he swiches is dependen of he leakage inducance of he ransformer r and oher parasiic inducances. herefore, a snubber circui is recommended o limi such value. he maximum volage sress across he conrolled swiches is given by V = V. (13) a S G. Curren and lage Sresses in Diodes D 1 D 4 he average curren hrough he recifier diodes D 1 D 4 is given by Io I _ avg. (14) he maximum reverse volage across of he recifier diodes D 1 D 4, wihou considering overvolages, is equal o he oupu volage ha is expressed by VD 1. (15) H. Oupu Filer Capacior Design he capaciance of he oupu filer capacior, for purely resisive load, can be deermined by Io( D 1 ). (16) Δf IV. EXPERIMENAL RESULS A. Specificaions his secion presens experimenal resuls from he proposed isolaed boos converer using hreesae swiching cell. he experimenal prooype was buil accordingly he specificaions shown in able I. ABLE I SPECIFICAIONS OF HE ISOLAED DCDC CONVERER USING SSC Inpu lage Range 4 54 [V DC ] Oupu Power Po 1 [kw] Oupu lage 4 [V] Swiching Frequency f s 5 [khz] he assumed design parameers are: he maximum boos inducor curren ripple is ΔI =.18I _avg, he ransformer urns raio is a=/=3, he maximum fixed duy cycle of he swiches for minimum inpu volage is D max =.7, he coefficien o find DC curren blocking capacior is ξ =.1, and he oupu volage ripple is Δ=.1. he componens used for experimenal implemenaion are lised in able II ABLE II PARAMEERS OF HE IMPLEMENED CONVERER Diodes D 1 D 5 Boos Inducor L b Oupu Filer Capaciors C o Blocking Capacior C b Swiches S 1 S High Frequency ransformer r High Frequency Auoransformer s HFA15PB6 L b = 7μH re NEE55/8/1 (hornon Ipec) = 17 urns N=8 urns 47μF / 45V (elecrolyic) 1uF/5V (polypropylene) IRFP47 re NEE65/6 (hornon Ipec) =17 urns =51 urns re NEE4/ (hornon Ipec) = N = 19 urns B. Experimenal Waveforms and Curves Fig. 6 shows he measured inpu volage and curren hrough he boos inducor L b. As can be seen, he curren drawn by he proposed converer presens a low curren ripple, suiable for baery powered applicaions, where is requiremen is relevan o improve is useful lifeime. I s also imporan o noe ha he curren ripple frequency is double of he swiching frequency.
Figs. 7 and 8 shows he volage and curren hrough he auoransformer windings. hese waveforms are similar ha concludes ha a good curren balance wih very low curren ripple is achieved. Fig. 9 shows drain o source volage and drain curren in he swich S 1. he commuaion deail of his waveform during he swich S 1 urnon and urn off are shown in Fig. 1 and 11, respecively. As can be seen, he swich presens a suiable commuaion reducing losses and higher frequency inerferences. Figs. 1 and 13 shows he volages and currens hrough he primary side and secondary side of he isolaed ransformer r, respecively. I can be seen ha he DC componen of he primary side curren is eliminaed using he blocking capacior C b. Finally, Fig. 14 presens he measured converer efficiency curve as a funcion of he oupu power. Accordingly o his graph evaluaion, his converer presened a good efficiency ha can be opimized if beer devices were used. A picure of he developed prooype is shown in he Fig. 15, where can be seen he power conversion sage. I V Fig. 8. lage and curren hrough he auoransformer winding. (5V/div.; 1A/div.; 1us/div.) V I I Fig. 6. Inpu volage and curren hrough he inducor. (V/div.; 1A/div.; 1us/div.) Fig. 9. lage and curren hrough swich S 1. (5V/div.; 1A/div.; 1us/div.) V V1 I urnon deail I1 Fig. 7. lage and curren hrough he auoransformer winding 1. (5V/div.; 1A/div.; 1us/div.) Fig. 1. urnon swiching deail of he swich S 1. (5V/div.; 1A/div.; 5ns/div.)
V I urnoff deail Fig. 11. urnoff swiching deail of he swich S 1. (5V/div.; 1A/div.; 5ns/div.) Fig. 14. Measured efficiency of he converer as funcion of he oupu power. Vp Ip Fig. 1. Primary ransformer volage and curren. (1V/div.; 1A/div.; 1us/div.) Fig. 15. Picure of he assembled prooype. Is Vs Fig. 13. Secondary ransformer volage and curren. (V/div.; 5A/div.; 1us/div.) V. CONCLUSION his paper presened a new isolaed DCDC boos converer based on he hreesae cell (3SSC). Accordingly o he obained experimenal resuls, he major feaures ha are imporan o emphasize are: lower blocking volages across he conrolled swiches which allows he uilizaion of MOSFEs swiches wih lower drainosource resisances, he DC curren across isolaed ransformer could be eliminaed using blocking capacior, and he reasonable leakage inducance value of he isolaed ransformer is suiable for commuaion of he conrolled swiches. hus, a high efficiency of he converer was obained (up o 95.%) for a full load condiion. mpared o he previous proposed opologies for he same purpose, his proposal is a compeiive alernaive for pracical applicaions. I s imporan o noe ha if he design is opimized i could also increase is efficiency.
ACKNOWLEDGMEN he auhors would like o hank Brazilian Research and Projec Financing FINEP and CNPq for he financial suppor. Also, would like o hank exas Insrumens, Inernaional Recifier, On Semiconducor, Cree, and Epcos for supplying he samples. REFERENCES [1] V. J. houvelil,. G. Wilson, H. A. Owen Jr., Analysis and Design of a PushPull CurrenFed nverer, in Proc. of PESC 81 IEEE Power Elecronics Specialiss nference Proceedings, pp. 193, 1981. [] G. Sojcic, D. Sable, B. H. Cho, F. Lee, A New zerolage Swiching Weinberg nverer for High lage Space Power Disribuion Sysem, in Proc. of European Space Power nference, pp. 4154, 1993. [3] J. J. Albrech, J. Young, W. A. Peerson, Boosbuck pushpull converer for very wide inpu range single sage power conversion, in Proc. of APEC 95 IEEE Applied Power Elecronics Specialiss Proceedings, pp. 33 38, 1995. [4] S. Xie, F. Li, A Novel Sof Swiching Isolaed Boos nverer, in Proc. of APEC 5 IEEE Applied Power Elecronics Specialiss Proceedings, vol. 3, pp. 13751379, 5. [5] I. Aude, D. B. e, L. Yves, F. J. Paul, B. Jean, mparison of wo sof swiching DCDC converers for fuel cell applicaions, in Proc. of IAS Annual Meeing 6 IEEE Indusry Applicaions Sociey nference Proceedings, vol. 5, pp. 1118, 6. [6] F. J. Nome, I. Barbi, A ZVS Clamping ModeCurrenFed Push Pull DCDC nverer, in Proc. of ISIE '98 IEEE Inernaional Symposium on Indusrial Elecronics Proceedings, vol., pp. 61761, 1998. [7] J. C. Hung,. F. Wu, J. Z. sai, C.. sai, Y. M. Chen, An aciveclamp pushpull converer for baery sourcing applicaions, in Proc. of APEC 5 IEEE Applied Power Elecronics Specialiss Proceedings, vol., pp. 1186119, 5. [8] W. C. P. Aragão Filho, I. Barbi, A mparison Beween wo Curren Fed PushPull DCDC nverers Analysis, Design and Experimenaion, in Proc. of INELEC '96 IEEE Inernaional elecommunicaions Energy nference Proceedings, pp. 3133, 1996. [9] J. Yungaek, M. M. Jovanovic, New woinducor Boos nverer Wih Auxiliary ransformer, IEEE rans. Power Elecron., vol. 19, no. 1, pp. 169175, 4. [1] J. Yungaek, M. M. Jovanovic, Isolaed Boos nverers, IEEE rans. Power Elecron., vol., no. 4, pp. 1514151, 7. [11] G. V. orrico Bascopé, I. Barbi, Generaion of a family of nonisolaed DCDC PWM converers using new hreesae swiching cells, in Proc. of PESC IEEE Power Elecronics Specialiss nference Proceedings, vol., pp. 858863,. [1] N. Mohan,. M. Undeland, W. P. bbins, Power Elecronics nverers, Applicaions, and Design. John Wiley & Sons, Inc. hird Ediion,.