DESIGN AND IMPLEMENTATION OF A DIGITALLY-CONTROLLED PHASE-SHIFT FULL-BRIDGE CONVERTER WITH OUTPUT SYNCHRONOUS RECTIFIER AND CURRENT DOUBLER

Transcription

1 83 Jounal of Technology, Vol. 3, o. 4, pp (17) DESIG AD IMPLEMETATIO OF A DIGITALLY-COTROLLED PHASE-SHIFT FULL-BRIDGE COVERTER WITH OUTPUT SYCHROOUS RECTIFIER AD CURRET DOUBLER Shun-Chung Wang 1, * Li-Chung Shih Bo-Ruei Pen Yi-Hwa Liu 1 Depamen of Elecical Engineeing Lunghwa Univesiy of Science and Technology Taoyuan, Taiwan 333, R.O.C. Depamen of Elecical Engineeing aional Taiwan Univesiy of Science and Technology Taipei, Taiwan 16, R.O.C. Key Wods: cuen double, digial conol, phase-shifed full-bidge convee (PSFBC), zeo volage swiching (ZVS). ABSTRACT This pape pesens a digially-conolled phase-shifed full-bidge convee (PSFBC) wih oupu synchonous ecifie (SR)-ype cuen double. The poposed PSFBC can achieve a high efficiency and high powe densiy design ha is applicable o medium o high powe convees due o he capabiliy of powe swich wih zeo volage swiching (ZVS). The SR-ype cuen double (CD) can educe conducion losses, impove hemal disibuion, allow fo lowe cuen pofile, and possess he effec of ipple cancellaion on he oupu file capacio. The condiions needed fo achieving ZVS opeaion is fis deived and discussed in deail. Deducion of he gaing signals fo SRs a diffeen opeaing modes is done o peven he dawing back cuen caused by he conol mismach beween he pimay swiches and seconday SRs fom desoying he cicui. Compomise selecion of an adapive dead-ime is also povided o impove efficiency fo all load oupus. The opeaing pinciple, design consideaion, and gaing signal geneaion ae descibed exhausively. A laboaoy pooype is implemened and esed o validae he coecness and pefomance of he sudied convee. I. ITRODUCTIO owadays, many counies have expessly fomulaed he elevan sandads fo enegy consumpion. The dominan sandads ae he Enegy Sa [1] and Euopean Commission (EC) []. The enegy-saving emphasis specified in he sandads pimaily focus on boosing he enegy convesion efficiency and educing he sandby powe losses. Fo he powe convee wih had-swiching opeaion, when he swiching fequency of he powe device is inceased, he swiching losses ae also inceased and his esuls in he poblems of hemal managemen and efficiency deeioaion. To effecively educe swiching losses, he convees wih sof-swiching opologies and novel modulaion echniques ae pefeable and have been discussed exensively [3, 4]. The sof-swiching echniques achieve he swiching-loss educion hough he opeaions of zeo volage swiching (ZVS) and/o zeo cuen swiching (ZCS) on powe swiches o impove he efficiency and elecomagneic inefeence (EMI) poblems. The applicaions fo convees wih low oupu volage and high oupu cuen ae mainly in he fields of elecolyic *Coesponding auho: Shun-Chung Wang, wangsc@mail.lhu.edu.w

2 84 Jounal of Technology, Vol. 3, o. 4 plaing powe, seve powe, elecom powe supply, baey soage sysem, and inducion heaing ec. The pimay challenges fo he convenional PSFB accomplish high powe densiy and efficacy include ha (1) he ZVS is no easy o each a ligh load, () he addiional powe losses ae induced by he pimay-side ciculaing cuen, and (3) he conducion losses of he oupu ecified diodes esic he applicaion in high cuen. Theefoe, a few novel PSFBCs have been poposed o achieve he desied pefomances via he sudy and amendmen on cicui opology, conol echnique, and moe accuae componen design [4-9]. In ode o impove he dawback ha he ZVS opeaion canno be eached a ligh loads, he vaiable dead ime mehod is poposed in [1-1]. A ligh load opeaion, he dead ime of he lagging-leg swiches can be inceased o make ZVS opeaion eachable moe easily and lowe he dain-souce volage of he powe MOSFET duing he swiching ansiion o educe he swiching loss. On he ohe hand, he dead ime should be deceased a heavy loads o shoen he conducion ime of he swich s body diode and hus he conducion loss. A new online hybid conol of he dc-link bus volage is pesened in [13] o mainain he maximum duy opeaion fo PSFBC a ligh load. The efficiency is amelioaed due o he educion of he ciculaing cuen and swiching losses. In [14], a hybid-swiched PSFBC is invesigaed fo elecic vehicle baey chages. The poposed opology povides a wide ange of ZVS opeaion fo leading-leg swiches and ZCS opeaion fo lagging-leg swiches. The pesened hybidswiched mehod can significanly educe he feewheeling ciculaing losses. A dual full-bidge hybid sucue wih a small seies capacio in he pimay and a full-bidge ecifie wih wo addiional low-volage-aed diodes in he seconday side ae poposed in [15] o ovecome he dawbacks of a convenional PSFBC. The advanages of he poposed convee conain low ciculaing cuen, ZVS opeaion fo all pimay swiches, small size oupu induco, and low conducion loss of he ecifie sage. In [16], a pecise analyic mehod is addessed fo powe loss evaluaion on leading- and lagging-leg swiches hough he consideaion of exac cuen and volage wavefoms. The powe-loss disibuions of he convee unde vaious loads and opeaing modes have been analyzed in deail. A fullbidge invee wih phase-shif PWM echnique is pesened in [17] o achieve ZVS opeaion. A cuen double ecifie, fequency doubling in oupu capacio, and low cuen aing in seconday winding ae used o incease he convee efficiency. Ref. [18] poposes a new phase-shif con- ol echnique o educe he hemal imbalance of powe swiches. The new conol echniques, including alenaing conol, empeaue feedback, o pseudo andom me- hod, ae pesened o swap he leading- and lagging-leg swiches each ohe o achieve he hemal balance. The oupu diode ecifies ae eplaced wih SRs in [19] o e- duce he conducion losses and enhance he efficiency fu- he. The opeaing pinciple and dive mehod of he SR ae deived in deail in []. In [1], how o selec he po- pe SR is analyzed o opimize he convee efficiency based on he elecical specificaions and chaaceisics of he powe swiches. The digially-conolled saegies ae poposed in [-4] o povide conol flexibiliy and impoved pefomance. This pape aims a developing a high-efficiency digialconolled PSFBC. The educion of he swiching losses, suge and inging ae aainable hough ZVS opeaion, and hus he volage sesses and hemal dissipaion can also be impoved. The cuen double wih low on-saeesisance SRs ae employed o diminish he conducion losses and oupu cuen ipple. Besides, a simple dive mechanism fo SRs a diffeen opeaing modes is deived o peven he dawing back cuen caused by he conol mismach fom desoying he cicui. Tade-off selecion of an adapive dead-ime is also made o impove he lighand-heavy load efficiencies. The es of his pape is oganized as follows. Secion II inoduces he hadwae configuaion and opeaing analysis of he sudied PSFBC. The condiions equied fo compleing ZVS opeaion is deived in deail in Secion III. Secion IV focused on he digial conolle design and he fimwae pogamming. The design consideaion and analysis of he cicui paamees ae depiced in Secion V. Expeimenal esuls ae given and compaed in Secion VI o veify he sudied convee, and Secion VII concludes his pape. II. CIRCUIT ARCHITECTURE AD OPERATIO AALYSIS 1. Powe Sage Scheme Fig. 1 shows he configuaion of he sudied PSFBC wih cuen-doubling SR. Fom Fig. 1, i can be seen ha he full bidge sucue in he pimay side is composed of fou powe MOSFETs,, S,, and. In which he ss,1, ss,, ss,3, and ss,4 ae he oupu capaciances of he fou MOSFETs, and he D s,1, D s,, D s,3, and D s,4 ae hei body diodes, especively. The main ansfome T 1 seves as he volage and enegy convesion beween he pi-

3 Wang S. C. e al.: A Digially-Conolled Phase-Shif Convee 85 D s1 ss,1 D s3 ss,3 D s1 ss,1 D s3 ss,3 A i p C b L T 1 p:s L 1 i o R L V o A i p + enegize L T 1 p:s + enegize L 1 i o RL V o V p V s Vp V s B SR i L B SR i L S D s ss, D s4 ss,4 L S D s ss, D s4 ss,4 deenegize + L Fig. 1 Sudied PSFBC wih SR and cuen double Fig. 3 Enegy flow pah of Mode 1 VAB D s1 ss,1 D s3 ss,3 A i p deenegize + L T 1 p:s + enegize L 1 i o RL V o ip V p V s I I 1 I I3 I 4 B SR i L Dead ime S D s ss, D s4 ss,4 deenegize + L i L I Fig. 4 Enegy flow pah of Mode S1 S S3 S4 SR1 SR Fig. Timing diagam of he opeaing mode may and seconday sides. The L is he equivalen esonan induco and is value equals o he sum of he addiional esonan inducance and he leakage inducance of he T 1. The seconday side adops cuen double scheme wih SRs. L 1 and L ae he oupu file inducos and he is he oupu file capacio. Fo he aing demand of he low volage and high cuen applicaion, cuen double wih SRs is employed o educe he powe loss and oupu ipple, and hus can boos he enegy convesion efficiency fuhe.. Analysis of Opeaing Mode Fig. shows he iming diagam of he opeaing modes fo he sudied convee. In a swiching peiod, fo he nomal phase-shif conol, hee exis en opeaing modes i.e., Mode 1 o Mode 1 ( - 1 ). Heein only mode_1 o mode_5 wee analyzed because of he symmey of he posiive and negaive half cycle. Fom Fig., on he same leg, he pesence of dead ime peiods ( 1 - and 3-4 ) be- ween he manipulaions of he high-side and low-side swiches is needed o peven sho cicui acoss he DC souce. Duing he dead ime, he esonance aises fom he seies ss and L o achieve ZVS mechanism. The analysis and opeaing fundamenals of each mode ae illusaed as follows. i. Mode 1 ( < < 1 ): Enegy Delivey Ineval As shown in Fig., in Mode 1 he swich and ae on and S and ae uned off. The is off and SR is uned on. Fig. 3 shows he enegy flow pah. Fom Fig. 3, he enegy is deliveed fom pimay side o seconday side hough he main ansfome T 1 o povide he powe equied fo he load. The L and L 1 ae enegized and he L is demagneized. The Mode 1 opeaion is ove when he is uned off. Fom he equivalen cicui of he Mode 1, he pimay side cuen i p and volage can be deived by Eqs. (1)-() Vin ( V / ) ip() ip L L o ( 1 / ) (1) V () V () AB in whee uns aio is defined as s / p. The ime ineval duing his mode can be given by (3) I I L L 1 ( ~ 1) ( ( 1/ )) Vin ( V / ) (3)

4 86 Jounal of Technology, Vol. 3, o. 4 ii. Mode ( 1 < < ): The Fis Resonan Ineval Mode sas as he is uned off and sill on. Fig. 4 shows he enegy flow pah of Mode. In Mode he seconday side emains he same sae as Mode 1. The cuen i p sops ising bu he diecion is unchanged accoding o he Lenz s law. A he same ime he esonan cuen chages he ss,4 and dischages he ss,3 unil he volages acoss ss,4 and ss,3 each o and zeo, especively. The body diode D s,3 of he will be fowad biased when he volage acoss ss,3 is dischaged o zeo. A his ime, give he gaing signal of he can un i on and achieve ZVS opeaion. The cicui enes he nex mode when he is uned on. Fom he equivalen cicui of he Mode, he i p and can be deived by Eqs. (4)-(5) S A A D s1 D s ss,1 i p ss, Vin B D s3 deenegize + ss,3 D s4 ss,4 L Vin Vp T 1 p:s V s SR deenegize + i L deenegize + Fig. 5 Enegy flow pah of Mode 3 D s1 D s ss,1 ss, i p B D s3 ss,3 deenegize + D s4 ss,4 L Vp T 1 p:s V s SR deenegize + i L deenegize + L 1 L L 1 L i o R L i o R L V o V o S 1 V i () V sin i ( )cos o p in 1 p 1 1 L1 1 (4) Fig. 6 Enegy flow pah of Mode 4 V ( 1) o ip Vo VAB() VC () cos 1 sin 1 Vin 1C (5) whee L 1 = L L 1 / is he equivalen esonan induco, 1 1/ L1C is he esonan fequency in Mode, and he esonan capacio C can be expessed by Eq. (6) ' 8 ' Voss C Csay Coss (6) 3 V DS ' In Eq. (6), he Coss is he combinaion of he oupu ca- ' paciances in and a he condiion VDS Voss. Thei values can be found in he daashee povided by he vendo. The C say is he say capaciance which includes ansfome capaciance and scaeed capaciance. In Mode, he opeaing ime ineval can be given by Eq. (7) C Vin ( 1~ ) (7) i ( ) p 1 iii. Mode 3 ( < < 3 ): Linea Dischage Ineval The cicui enes Mode 3 opeaion when he is uned on unde zeo volage. Fig. 5 shows he enegy flow pah of Mode 3. The and boh ae on in Mode 3. Boh side volages of he ansfome ae zeo appoximaely. The SR keeps conducion coninuously o elease he oupu inducos enegy o he load. Fom he equivalen cicui of Mode 3, he i p and can be expessed as Eqs. (8)-(9) Vo / ip() ip( ) (8) L V () AB (9) The ime ineval duing Mode 3 can be calculaed by Eq. (1) i ( ) p I L (1) 3 ( ~ 3) Vo iv. Mode 4 ( 3 < < 4 ): The Second Resonan Ineval Afe uning off, Mode_4 is begins. Then he SR is uned off. The diecion of he cuen flowing hough L is unchanged, and i chages he ss,1 and dischages he ss, unil he volages acoss ss,1 and ss, each o and zeo, especively. The body diode D s, of he S will be fowad biased as he chage soed in ss, is fully eleased. A his ime, give he gaing signal of he S could un i on and achieve ZVS opeaion. In Mode 4, he ampliude of i p is no enough o supply he equied enegy fo he load. Thus, he ansfome says in a feewheeling sae. Boh he and SR ae off bu hei body diodes ae fowad biased simulaneously o povide he pahs fo he seconday cuen. Fig. 6 shows he enegy flow pah of Mode 4. This mode is ended as he S is closed. Fom he equivalen cicui of he Mode 4, he i p and can be obained by Eqs. (11)-(1)

5 Wang S. C. e al.: A Digially-Conolled Phase-Shif Convee 87 Table 1 Tuh able fo deducion of SRs gaing signals Mode Gaing signals fo powe swiches Gaing signals fo SRs S SR Powe delivey ineval ( - 1 ) on off off on off on Linea dischage ineval ( 1 - ) on off on off off on Powe delivey ineval ( - 3 ) off on on off on off Linea dischage ineval ( 3-4 ) off on off on on off D s1 ss,1 D s3 ss,3 S1 A i p deenegize + L T 1 p:s deenegize + L 1 i o RL V o S S3 S D s ss, B D s4 ss,4 Vp V s SR i L deenegize + L S4 I Fig. 7 Enegy flow pah of Mode 5 ILo1 I Lo SR1 p p 3 i () i ( )cos (11) i ( ) V V p 3 AB () C () sin C (1) whee L = L is he equivalen esonan induco, 1/ L C is he esonan fequency in Mode 4, and he opeaing ime ineval duing Mode 4 can be calculaed by Eq. (13) ( 3~ 4) 1 1 Vin sin C I3 L/ C (13) v. Mode 5 ( 4 < < 5 ): Cuen Commuaion Ineval Mode 5 is saing as he S is uned on unde zeo volage. The gaing signal of is he same as he S. Theefoe, he body diode of is foced o cuoff as he is uned on. Fig. 7 shows he enegy flow pah of Mode 5. In Mode 5, he diecion of he pimay cuen is commuaed o ene he opeaion of negaive half cycle. Fom he equivalen cicui of he Mode 5, he i p and, as well as he unning ime in his ineval can be especively obained by Eqs. (14)-(16) Vin ip() ip( 4) (14) L V () V (15) AB in SR Fig. 8 Wavefoms in wo elaed opeaing modes L I ( 4~ 5) ip( 4) Io V in 4 L (16) 3. Deivaion of Gaing Signals fo SRs The dawing back cuen, aising fom he conol signal mismach beween he pimay swiches and seconday SRs, would esul in he faul opeaion. A simple dive mehod is poposed in his pape fo appopiae conol of SRs and pevens he componens fom desucion. As he afoemenioned mode opeaion, if he effecs of esonan and cuen commuaion inevals on convee opeaion ae insignifican and hus can be omied, hee exiss only fou modes accoding o he powe swiches opeaion. Tha is, he powe delivey and linea dischage modes as shown in Fig. 8. Fom Fig. 8, he conducion ovelap of he and S occus in he powe delivey mode. The convee opeaes in he feewheeling mode as he wo high side ( and ) o low side (S and ) swiches ae uned on simulaneously. In powe delivey and linea dischage modes, he cuen pahs of he cuen double ecifie ae idenical. As a esul, fom he uh able as shown in Table 1, he desied gaing signals of he and SR can be deduced. Table 1 summaizes ha he gaing signal of he SR is compleely he same as ha of he lagging-leg swich. Simi-

6 88 Jounal of Technology, Vol. 3, o. 4 I3 i p,c i p ip ip I4 > i p,c I 4 = i p,c D D D I 3 I3 I 4 = The cuen equied fo he leading-leg swiches and o each ZVS opeaion can be compued as follows. Fom Fig., a = = 1 (/ 1 ), he eaches o zeo. In Eq. (5), leing =, he iniial value (I 1 ) of he fis esonan cuen can be obained by Eq. (19) -Vin Fig. 9 VAB 4 -Vin -Vin (a) (b) (c) Wavefoms of VAB and i p o illusae (a) ZVS opeaion, (b) ciical ZVS opeaion, and (c) nonzvs laly, he s dive signal is oally idenical o he swich S. III. CODITIOS OF ZVS OPERATIO The condiions equied fo ZVS opeaion in he PSFBC, including he ciical cuen, effecive duy cycle and he allowable maximum swiching fequency, ae exploed and discussed in his secion. 1. Ciical Cuen fo ZVS Opeaion Subsiuing fo - in Eq. (1), he angle as eaches o - can be obained by Eq. (17) 1 Vin C sin ip( 3) (17) Subsiuing Eq. (17) ino Eq. (11), he esonan cuen I 4 afe he second esonan ineval can be calculaed as Eq. (18) I i ( ) i ( )cossin V C 1 in 4 p 4 p 3 ip( 3) (18) Pas of and i p wavefoms ae shown in Fig. 9 o illusae whehe he convee can achieve he ZVS opeaion o no. In which he D indicaes he added dead ime. As he I 3 is moe han i p,c and I 4 is geae han zeo, as shown in Fig. 9(a), he convee absoluely can fulfill he cieion of ZVS opeaion, because he i p is capable of fully dischaging he ss and leading o he zeo volage acoss he powe swich. Fom Fig. 9(b), he ZVS ciical condiion is saisfied as he I 3 equals o i p,c and I 4 is zeo. On he conay, as shown in Fig. 9(c), he convee canno mee he ZVS opeaion as he I 3 is less han i p,c and I 4 is zeo due o he pesen i p is unable o compleely elease he chage of ss, esuling in he nonzeo volage acoss he powe swich. C Vo L V o Vin cos L 1 L 1 I1= ip( 1) (19) sin ( / ) L / L I 1 is he ciical cuen value, i.e., i is he minimum cuen equied fo he leading-leg swiches and o achieve ZVS opeaion. On he ohe hand, he iniial cuen I 3 in he second esonan ineval is used o idenify whehe he lagging-leg swiches and S could achieve ZVS opeaion o no. Fom Fig., a = 4 = 3 (/ ), he eaches o -. In Eq. (1), leing = -, he cuen I 3 can be obained by Eq. () I i ( ) i V C / L () 3 p 3 pc, in I 3 is he minimum cuen equied fo he lagging-leg swiches and S o achieve ZVS opeaion. 1. Deivaion of he Effecive Duy Cycle When he ansfome woks in he feewheeling sae, he enegy canno be ansfeed fom he pimay side o he seconday side. This causes he seconday effecive duy cycle D eff o be less han he oiginal duy cycle designed by he pimay paamees. The duy cycle loss D loss aising fom he ansfome leakage inducance and addiional esonan induco can be calculaed as Eq. (1) D loss il p 4iLf p s V ( T /) V s s s (1) oing ha, fom Eq. (1), he lage he value of L o f s is, he moe he duy cycle losses i becomes. Consequenly, he D eff can be deived as Eq. () D V 1 V () V V = p o o eff s S S Then he oiginal duy cycle can be obained by Eq. (3) 4L fs D Deff Dloss Deff 1 R (3)

7 Wang S. C. e al.: A Digially-Conolled Phase-Shif Convee 89 i p,f I D eff I 4 I 1 I I3 DZVS T D loss Fuhemoe, he linea dischage ineval of he second esonance is vey sho. As a esul, he cuen value i p ( F ) is appoximae o i p ( 3F ), and he diffeence beween F and 3F can be negleced. In pacice, he peiods of dead ime fo he wo legs ae equal and hey ae designed o be less han he quae of he second esonan peiod, i.e., D = /. Theefoe, he minimal swiching peiod T s,min can be evaluaed as Eq. (4) T ( ) s,min T,max D R 1 Deff (4) F 1F F 3F 4F 5F Fig. 1 Wavefoms of he i p and a full load 3. Allowable Maximal Swiching Fequency Fig. 1 shows he wavefoms of he i p and obained a full load opeaion. Fom Fig. 1, hee exis hee subduy-cycle inevals in each half swiching peiod. The effecive unning duaion D eff ( F - 1F ) is he same as ha of he enegy delivey mode. The peiod of he D zvs ( 1F - 4F ) includes wo esonan inevals fo he convee o achieve ZVS opeaion. The esonan induco is chaged and dischaged o commuae he pimay cuen and he duaion of he D loss ( 4F - 5F ) equals o he cuen commuaion ineval. As he afoemenioned analysis, he equivalen esonan induco (L 1 ) of he fis esonance is geae han ha (L ) of he second esonance. Theefoe, he esonan fequency ( 1 ) of he fis esonance is less han ha ( ) of he second esonance. Meanwhile, he esonan enegy of he fis esonance is also geae han he second esonance. As he angle of he second esonan cuen eaches o /4 and he esonan enegy is lage enough o make he ZVS opeaion fo lagging-leg swiches ( and S ) achievable, he fis esonan enegy mus be able o make he ZVS opeaion of leading-leg swiches ( and ) aainable. Typically, he dead ime ( 1 o 43 ) of he wo-leg swiches is designed o be idenical. In addiion, due o he exisence of cicui powe losses, he pimay cuen is less han he iniial value of iself. This will make he ansiion ime equied fo achieving ZVS opeaion in lagging-leg swiches longe han ha in leading-leg swiches. Accodingly, he longe ansiion ime 43 is consideed fo dead-ime design o saisfy he equiemen of he pefomance opimizaion fo all opeaing anges. whee he maximum commuaion ime T,max, dead ime D, and he second esonan ime R can be especively expessed by Eqs. (5)-(7) L i I ( i /4) (5) T,max 5F 4 F p, F o,max L Vin D R CV in (6) i pc, CV i in 1 pc, sin ipc, Io,max ( IL /4) (7) In which, I o,max is he oupu aed cuen a he maximal load. Due o he linea dischage ineval is vey sho, hus he esidual cuen i p,f1 in pimay side a = 3F can be denoed as Eq. (8) I ipf, 1= ip( 3F) ip( F) ip( 1 F) Io,max 4 L (8) Subsiuing Eq. (8) ino Eq. (18), he i p,f can be deived by Eq. (9) i I i 4 I L pf, o,max pc, (9) In pacical design, an appopiae ciical cuen value, I O,C, is pese in advance o evaluae a suiable cuen which can make he ZVS opeaion achievable. Thus he desied ciical cuen i p,c can be obained by Eq. (3) i I pc, O, C I L (3) By subsiuing Eq. (9) ino Eq. (5), he maximum commuaion ime T,max can be compued as Eq. (31)

8 9 Jounal of Technology, Vol. 3, o. 4 I L Io,max i p, C CV 4 I L Io,max 4 in T,max i pc, (31) Finally, subsiuing Eqs. (6), (7), and (31) ino Eq. (4), he allowable maximum swiching fequency f max can be expessed by Eq. (3) f s,max 1 T s,min 1 Deff 1 i CV in pc, CV in I L IL sin I o,max i p, C Io,max i pc, I L i pc, 4 4 I o,max 4 (3) A D s1 ss,1 C b i p D s3 ss,3 L T 1 p:s L 1 i o R L V o of implemenaion and uning. In he ime domain, based on he eo, he desied oupu u() of he PID conolle can be expessed as Eq. (33) S D s ss, B Gae Dive Opocouple S S PWM Oupu D s4 ss,4 PID Conol V p V s dspic33fj16gs5 SR Gae Dive FIR File Fig. 11 The sudied convee wih feedback conol loop SR SR i L L ADC IV. DIGITAL COTROLLER DESIG Fig. 11 illusaes he scheme of he sudied digiallyconolled convee wih he feedback conol loop. The DSC (dspic33fj16gs5) fom Micochip Cop. is uilized as he kenel o implemen he digial conol algoihm. Fom Fig. 11, he oupu volage is sensed and hen quanized ino digial daa by he analog-o-digial convee (ADC) in he DSC. The sampled daa ae sceened by he finie impulse esponse (FIR) digial file befoe hey ae ansmied o he popoional, inegal and diffeenial (PID) compensao. Accoding o he eo quaniy and compuing oucome, he digial PID compensao oupus he desied phase-shif modificaion quaniy. The phase-shif quaniy is sen o he pulse widh modulaion (PWM) module o geneae he conol signals of powe swiches and SRs fo convee oupu egulaion. The conolle fimwae consiss of a main pogam and an analog-o-digial ineupion subouine. The PID conol mehod is adoped in his pape o ealize he digial compensao due o is simpliciy, good sabiliy, and ease R 1 R d u () KP e () KI ed () K () D e (33) d whee he eo e() is he diffeence beween he command and oupu. K p, K I and K D ae he popoional, inegal and diffeenial consans, especively. Howeve, he coninuous ype conol algoihm in Eq. (33) canno be woked in he digial conol diecly. Accodingly, he disceizaion of he Eq. (33) would be able o achieve digial compuaion. The discee ype PID conol is expessed by Eq. (34) n en ( ) en ( 1) un ( ) K en ( ) K e( jt ) K (34) T P I D j in which, he Eq. (34) conains an inegal em. As he digial PID conol is ealized using he DSC, he sauaion poblem of he inegal accumulao mus be consideed o avoid he adjusable phase-shif value ove he uppe o lowe limis. Accodingly, an incemenal ype PID conolle is adoped in his pape and he oupu incemen of he conolle, u(n), can be denoed by Eq. (35) un () KPen () en ( 1) Ken I () KDe() n ( e n1) e( n) (35) Fig. 1 shows he flowcha of he fimwae conol. The pesen eo e(n) (also efeed o as ERROR ) can be obained by subacing he quanizaion value of he FIR oupu fom he command. Similaly, he eos e(n-1) and e(n-) a he (n-1)h and (n-)h saes ae efeed o as ERROR 1 and ERROR and can be calculaed, especively. As he pogam is saing, he A = ERROR ERROR 1,

9 Wang S. C. e al.: A Digially-Conolled Phase-Shif Convee 91 Table Specificaions of he sudied convee Inpu volage ( ) Oupu volage (V ou ) Oupu cuen (I ou ) Oupu powe (P ou ) Swiching fequency (f s ) Oupu volage ipple Effecive duy full load (D eff ) Expec efficiency () V dc 4 V dc 1A - 5A 6 W 75 khz < 1%.7 > 9% ove, accoding o he design guideline of he aea poduc (AP) mehod fo appopiae esimaion of coe size, he desied AP value of he pacical coe, should be a leas wo imes highe han ha of he calculaed value because of he insulaion hickness specified in he winding aea. Consequenly, fom he coe daashee, he PQ35/35 coe is seleced because is AP value can povide he available coe magneic coss-secion aea and winding window aea fo he ansfome. START ii. Deeminaion of Winding umbe of Tuns B = COMMAD FIR OUT A = (ERROR ERROR 1) C = (ERROR ERROR 1 + ERROR ) PID ou < PHASE min PID ou > PHASE min PHASE = PID ou Y Y PID ou = PHASE min PID ou = PHASE max Fom Faaday s inducion law, he numbe of uns fo he pimay winding, p, can be calculaed by Eq. (36) VD 1 in eff 8 p 4Bmax Ae f (36) s Δu = K P A + K I B + K D C PID ou = PHASE + Δu PID ED Fig. 1 Flowcha of he PID pogamming B = ERROR, and C = ERROR ERROR 1 ERROR ae compued a fis. Then he oupu incemen of he conolle, u, is equal o he A, B and C muliplied by K p, K I and K D afe he sum. The compensao oupu (PID ou ) deives fom he addiion of he u and he oiginal phase shif, PHASE. If he PID ou is less han he minimum phase shif (PHASE min) o geae han he maximum phase shif (PHASE max ), he PID ou mus be esiced wihin he bounday values o allow pefec egulaion. V. DESIG COSIDERATIO The design analysis and consideaion of he cicui paamee and componen specificaion ae discussed in his secion. Shown in Table is he design specificaion of he sudied PSFBC. The following subsecions descibe he design pinciple and selecion basis of he main ansfome, esonan induco, pimay swiches, and seconday SRs. 1. Main Tansfome Design i. Selecion of Coe Maeial The funcionaliy of he main ansfome in PSFBC is o delive powe ahe han soe enegy. Hence, he ai gap is no essenial. Based on he choice of he swiching fequency, he feie maeial PC44 suied o high fequency opeaion was seleced. Fom he coe daashee, a 1C empeaue, is sauaion flux densiy is 39 Gauss. Moe- whee B max is he maximum flux densiy and A e is he aveage aea of he magneic pah. In his pape, he B max is 195 Gauss and A e is 1.96 cm. Subsiuing hese values of he elevan paamees ino Eq. (36), he equied numbe of uns of he pimay winding p is 1.1. The acual numbe of uns wound fo pimay winding is 15 uns. Based on he uns aio, he numbe of uns of he seconday winding s can be calculaed by Eq. (37) p ( Vo+ VSR( on) ) s ( D /) V eff in (37) whee V SR(on) is he on-sae volage dop of he SR swich. Subsiuing hese values of he elaed paamees ino Eq. (37), he obained s value is 5.9. In pacice, 6 uns wee wound fo s. iii. Calculaion of Wie Size The pimay cuen ms value can be compued by he inpu volage, efficiency and oupu powe and he esul was 3. A. If he cuen densiy D cma is se a 5 CMs (cicula mils)/a, hen he equied cicula mil of he pimay wie is 161 CM. Fom he Ameican Wie Gauge (AWG) Sysem, he.3 mm (AWG 8) Liz enameled wie wih 8 shaes was seleced o wind he pimay winding. Similaly, he equied cicula mil of he seconday wie was 15 CM fo he 5A cuen. Theefoe, he.3 mm Liz enameled wie wih 3 shaes was seleced o wind he seconday winding.. Resonan Induco Design The main funcion of he esonan induco in PSFBC

10 9 Jounal of Technology, Vol. 3, o. 4 is enegy soage o elease chages of he ss and hus can make he ZVS opeaion of powe swiches eachable. Accodingly, he good sabiliy and low powe loss ae he essenial consideaion fo he coe selecion. In phase shif convee, hee exiss wo esonan inevals in he posiiveand negaive-half cycles. In he fis esonan ineval, he enegy equied fo eaching ZVS opeaion is soed in he esonan induco L and eflecive oupu fileing induco L 1. Howeve, he enegy equied fo he ZVS opeaion in he second esonan ineval is soed in he esonan induco only. Theefoe, he ZVS opeaion of he laggingleg swiches in he second esonan ineval mus be aained is he key consideaion fo he L design. Typically, he inducance of he L mus be saisfied wih Eq. (38) L CV in > ipc, (38) in which, he C and L ae equivalen esonan capaciance and inducance especively. Based on he daashee of he used MOSFET IPP6R15CP, he ss is 1 pf. Moeove, assuming ha he equivalen say capaciance C say, including he say capaciances caused by cicui layou and ansfome windings, is pf. Then he C can be deemined by he calculaion in Eq. (6). By subsiuing hese values of elaed paamees ino Eq. (38), he obained L mus be geae han 6.63 H. Wihou affecing he nomal supply of he load cuen, a 35 H induco was chosen fo he sudied convee. 3. Deeminaion of Pimay Swich Raing omally, he aed volage and cuen of he pimay MOSFET mus be seleced highe han hose of he inpu volage and cuen, bu he selecion beween he paasiic capaciances (C iss and ss ) and on-sae esisance (R ds(on) ) of he MOSFET mus be compomised also. The smalle he on-sae esisance is, he less he conducion loss does. eveheless, he smalle he R ds(on), he lage capaciances fo he C iss and ss. These esul in he lage L needed o achieve ZVS opeaion unde he same load cuen. The lage L will also incease he commuaion ime of he pimay cuen, and hus incease he volume and coe loss of he esonan induco. If only he conducion loss was consideed, and he swiching loss was negligible. The IPP6R15CP MOSFET fom Infineon Cop. was adoped o ealize he powe swich. Is aed volage and cuen ae 65 V and 5 A especively. The R ds(on) is.15 and ss is 1 pf. 4. Design of Oupu Fileing Induco and Capacio Oupu induco and capacio compise a second-ode file. Tooidal magneic coes wih low pemeabiliy and high sauaion flux densiy ae bee choice fo he fileing induco owing o he enegy soage essenialiy and flux leakage educion. The cuen double can educe he coppe loss because he aed cuen of he winding is half han ha of he cene-ap one. Fom he elaionship beween he volage and cuen, he inducance value can be calculaed by Eq. (39) L L 1 ( VS V )( Deff /) i f o s (39) If he cuen ipple (i o ) is limied o % of he load cuen a full load. By subsiuing values of he elaed paamees ino Eq. (39), he calculaed inducance is 41.6 H. In pacice, he inducance value of 7 H is adoped fo he wo file inducos. The equied fileing capacio is elaed o he specified volage and cuen ipples as well as he equivalen seies esiso (ESR) of he capacio. Assuming ha he cuen ipple (i o ) is limied o % of load cuen a full load and he volage ipple pecenage is lowe han 1%. Fom = (i o T s )/ v o, he desied capaciance is abou 1354 F. Taking he specificaions of he allowable volage and cuen ipples as well as he ESR ino accoun, eigh 33 F/1 V capacios in paallel ae used acually o implemen he fileing capacio. 5. Selecion of SR Swich Raing In addiion o he aed volage and cuen, he selecion of he SR swich mainly depends on he on-sae esisance R ds(on). The smalle he R ds(on), he lowe he conducion loss does. The maximum allowable cuen of each SR in he sudied convee can be expessed as Eq. (4) i i L1, L SR,max io,max (4) The volage wihsood fo each SR in he off sae can be compued by Eq. (41) V s SR Vin (41) p By subsiuing values of he elaed paamees ino Eqs. (4) and (41), he obained i SR,max and V SR ae 6.5 A and 8 V especively. Theeby, he MOSFET AOT918L was adoped o ealize he SR swich. Table 3 summaizes he

11 Wang S. C. e al.: A Digially-Conolled Phase-Shif Convee 93 Table 3 Specificaions of he key componens Componen Tansfome Coe Specificaions PQ35/35 (PC44) Tuns Raio ( p : s ) 15:6 L - L 1, L, SR 35 H IPP6R15CP, 65V/5A, R ds(on) =.15, ss = 1 pf 7 H 33 F/1 V 8 in paallel AOT918L, 1 V/9 A, R ds(on) = 7 m (a) Dead ime 54 ns V gs1 V gs Dead ime 54 ns V gs3 Phase shif full bidge V gs4 Isolaion opical couple Synchonous ecifie dspic + Cuen double Gae dive Fig. 13 Pphoogaph of he implemened pooype specificaions of he key componens implemened in he sudied convee. VI. EXPERIMETAL RESULTS In his secion he expeimenal esuls ae measued o veify he feasibiliy and coecness of he hadwae configuaion and digial conol appoach. The veificaions conain whehe he ZVS opeaion is compleed o no on vaious loads, compaisons of efficiency wih and wihou using SR, pefomance of he digial phase-shif conol, and he analysis and discussion of he measued esuls. Fig. 13 shows he phoogaph of he implemened convee pooype. Fig. 14 illusaes he PWM conol signals geneaed fo pimay swiches -. The 54 ns dead ime is applied o he opeaion of lagging-leg and leading-leg swiches o peven he souce fom sho and povide enough ime fo achieving ZVS opeaion unde ligh load condiions. Wavefoms of he ansfome pimay volage and cuen i p, dain-o-souce volage V ds and gaing signal V gs of he lagging-leg swich and leading-leg swich, opeaing (b) Fig. 14 PWM conol signals and added dead ime fo (a) and S, and (b) and. (Ch1-Ch4: 1 V/div, 4 s/div) in ligh, middle and heavy loads, ae shown in Figs. 15 and 16 especively. I can be obseved ha he pimay cuen changes wih he load vaiaion. Afe he dain-o-souce volages (V ds1 and V ds4 ) acoss and dop o zeo he gaing signals (V gs1 and V gs4 ) ae povided o dive he swiches. All he swiches in lagging-and-leading legs can accomplish ZVS un-on o educe swiching losses. The lage he oupu powe, he moe obvious he ZVS opeaion became. In addiion, he ciical cuen fo ZVS opeaion in he sudied convee was.8 A, which was also he ciical ZVS condiion fo a ligh load. Theefoe, in he design case, he ZVS opeaion fo would no be eached as he oupu load was less han 1 W. The induco cuens ( and i L ) in he CD ecifie and oupu cuen (i o ) opeaed a ligh, middle and heavy loads ae shown in Figs. 17(a)-(c) especively. I is noed ha he oupu cuen is he sum of he wo induco cuens. Owing o he cancellaion effec beween he wo induco cuen ipples, he oupu cuen ipple was effecively educed. Fig. 18 shows he efficiency compaisons obained a ligh load (1 W) wih diffeen dead ime peiods (15 ns, 5 ns and 35 ns). Obviously, he longe he dead ime is, he moe efficien he impovemen. Moe han % boos

12 94 Jounal of Technology, Vol. 3, o. 4 i i p p ip V ds1 V ds1 V ds1 V gs1 V gs1 V gs1 ZVS ZVS ZVS (a) (b) (c) : V/div, i p: 5 A/div, V gs1: 1 V/div, V ds1: 1 V/div, Time: μs/div Fig. 15 Wavefoms of, i p, V ds1 and Vgs1 of he a (a) ligh load, (b) middle load, and (c) heavy load. VAB i i p ip p V ds4 Vds4 V ds4 Vgs4 ZVS V gs4 ZVS V gs4 ZVS (a) (b) (c) : V/div, V gs4: 1 V/div, V ds4: 1 V/div, Time: μs/div Fig. 16 Wavefoms of, i p, V ds4 and Vgs4 of he a (a) ligh load, (b) middle load, and (c) heavy load. i o i o i o i i i L L L1 i L : A/div, i L: A /div, i o: A /div, Time: 4 μs/div (a) : A/div, i L: A /div, i o: 5 A /div, Time: 4 μs/div (b) : 5 A/div, i L: 5 A /div, i o: 1 A /div, Time: 4 μs/div (c) Fig. 17 Induco cuens (, i L ) and oupu cuen (i o ) opeaed a (a) ligh load, (b) middle load, and (c) heavy load Efficiency (%) Dead Time: 15 ns Dead Time: 5 ns Dead Time: 35 ns Oupu Cuen (A) Fig. 18 Efficiency compaison of ligh load a diffeen dead ime peiods can be achieved in he es ange. The fundamenal of he dead ime selecion is ha i equies lage dead ime a ligh load bu small as opeaing a heavy load. In his pape, in consideaion of he compomise and educion of he hadwae cicui changes, he soluion of he dead ime modulaion was adoped o impove he ZVS opeaions which could no be eached. As shown in Fig. 18, he maximum dead ime was se o a quae of he esonan ime of C and L, i.e., 35 ns. The minimum dead ime was 15 ns, which is he ime needed o peven simulaneous conducion of powe componens. Obviously, a ligh load, he longe he

13 Wang S. C. e al.: A Digially-Conolled Phase-Shif Convee 95 Efficiency (%) Synchonous Recifies Diode Recifies Oupu Cuen (A) Fig. 19 Compaison of measued efficiency o impove efficiency fo all load oupus, and evaluaion of he ciical cuen fo ZVS opeaion. The opeaing pinciples, design consideaions and he gaing signal geneaion abou he sudied convee have been descibed in deail. A 6 W laboaoy pooype has been designed and ealized. The esed esuls pove he feasibiliy of he devised scheme and expeimenal conol mechanism. This indicaes ha a 9.17% full-load efficiency and 93.93% maximum efficiency can be achieved. ACKOWLEDGEMETS dead ime is, he moe efficien he impovemen. Howeve, he longe he dead ime, he geae he powe loss a medium and heavy loads does. Accodingly, aking he equied effecive duy cycle a full load, hadwae design, and effec of efficiency impovemen a ligh load ino accoun, he 54 ns dead ime was adoped fo he sudied convee. Fig. 19 illusaes he measued efficiency cuves obained wih he SR and diode as he seconday ecifie, especively. Boh he dead ime peiods seleced fo he pimay swiches wee 54 ns. I can be seen ha boh he ligh-load efficiencies ae vey close; howeve, above he middle loads, moe han a % efficiency impovemen was achieved as he SR was used o insead of he diode. Moeove, he heavie he oupu load was, he bee he impovemen effec becomes. Consequenly, he use of SRs can educe he conducion losses and aises efficiency, ha is significan beneficial o he applicaion of low volage and high cuen oupu. VII. COCLUSIOS A digially-conolled phase-shifed full-bidge convee wih synchonous ecifie has been pesened and implemened in his pape. The educions of he swiching losses, suge and inging wee done hough he swich s ZVS opeaion, and hus he volage sesses, hemal dissipaion and EMI can also be impoved. In he seconday side, cuen double wih low on-sae-esisance SRs wee uilized o educe he conducion losses and oupu cuen ipple. The conibuions of his pape mainly focus on he deivaion and evaluaion of he condiions equied fo achieving ZVS opeaion, deducion of he exac gaing signal fo SRs a diffeen opeaing modes o peven he dawing back cuen caused by he conol mismach beween he pimay swiches and seconday SRs fom desoying he cicui, compomise selecion of an adapive dead-ime povided This wok was suppoed by he Minisy of Science and Technology of Taiwan unde Gan MOST E-6-5-CC3. REFERECES 1. Enegy Sa. 13. Poduc Specificaions & Pane Commimens Seach. Enegy Sa. Accessed. hp:// Euopean. 13. Euopean Commission. Accessed. hp://ec.euopa.eu/commission/index_en. 3. Kim, Y. H., S. C. Shin, J. H. Lee, Y. C. Jung, and C. Y. Won. 14. Sof Swiching Cuen-fed Push-pull Convee fo 5-W AC Module Applicaions. IEEE Tansacions on Powe Eleconics 9 (): doi: 1.119/TPEL Gauam, D. S., and A. K. S. Bha. 13. A Compaison of Sof-Swiched DC-o-DC Convees fo Elecolyze Applicaion. IEEE Tansacions on Powe Eleconics 8 (1): doi: 1.119/TPEL Zhao, C., X. Wu, P. Meng, and Z. Qian. 9. Opimum Design Consideaion and Implemenaion of a ovel Synchonous Recified Sof-swiched Phase-shif Full-bidge Convee fo Low-oupu-volage Highoupu-cuen Applicaions. IEEE Tansacions on Powe Eleconics 4 (): doi: 1.119/ TPEL Badsuebne, U., J. Biela, and J. W. Kola. 1. An Opimized, 99% Efficien, 5 kw, Phase-Shif PWM DC-DC Convee fo Daa Cenes and Telecom Applicaions. In IEEE Poceedings of Inenaional Confeence on Powe Eleconics, Sappoo, Japan, 1-4 June 1: doi: 1.119/IPEC Kim, J. W., D. Y. Kim, C. E. Kim, and G. W. Moon. 14. A Simple Swiching Conol Technique fo Im-

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15 Wang S. C. e al.: A Digially-Conolled Phase-Shif Convee doi: 1.119/TPEL López-Floes, D. R., J. L. Duán-Gómez, R. Heea- Salcedo, and J. A. Pineda-Gómez. 1. Analysis and Design of a Simple Digial Conol Algoihm fo a Phase-shif-full-bidge DC-DC Powe Convee. In IEEE Poceedings of Confeence on Powe Eleconics Congess, San Luis Poosi, Mexico, -5 Augues 1: 5-1. doi: 1.119/CIEP Lin, C.Y. 16. Developmen of Swiching Mode Con- ol Technique fo Phase-shifed Full-bidge Convees. Mase Thesis, aional Taiwan Univesiy of Science and Technology. Manuscip Received: Oc. 5, 16 Fis Revision Received: Oc., 16 Second Revision Received: Jan. 13, 17 and Acceped: Jan. 5, 17