A New Three-Level Soft-Switched Converter

Transcription

1 New Three-Level of-wched onverer Yungaek Jang and Mlan M. Jovanovć ower Elecroncs Laboraory Dela roducs orporaon.o. ox 73, 50 Davs Dr. Research Trangle ark, N 7709, U... bsrac hree-level, consan-frequency, solaed converer whch employs a coupled nducor o acheve zero-volage swchng (ZV) of he prmary swches n he enre lne and load range s descrbed. ecause he coupled nducor does no appear as a seres nducance n he load curren pah, does no cause a loss of duy cycle or severe volage rngng across he oupu recfers. The operaon and performance of he proposed converer was verfed on a -kw prooype. I. INTRODUTION In recen years, mullevel power converers have receved a lo of aenon due o her suably for applcaons wh hgh npu volages []. pecfcally, mullevel nverers and dc-dc converers can be mplemened wh semconducor swches raed a a fracon of he npu volage, whch are ypcally less expensve and more effcen han her hghvolage-raed counerpars. ecause he mplemenaon complexy of mullevel converers s ncreased dramacally by he number of levels, whch dmnshes he benefs of mullevel converson, he majory of developmen effors n dc-dc mullevel converson have been focused on hree-level converers. Generally, hree-level dc-dc converers feaure power converson wh semconducor swches raed a one-half of he npu volage. Varous solaed mplemenaons of hreelevel dc-dc converers have been descrbed n [] [5]. To furher enhance her performance, all of hese four-prmaryswch mplemenaons feaure sof swchng of all prmary swches. pecfcally, he mplemenaons n [] [4] offer ZV, whereas he mplemenaon n [5] feaures ZV and zero-curren swchng (Z). The major dfference among he mplemenaons descrbed n [] - [5] s n he conrol of he swches [6]. The mplemenaons n [] and [3] ulze consan frequency WM conrol, whereas he mplemenaons n [4] and [5] employs consan-frequency phase-shf conrol. Generally, he major defcences of he ZV mplemenaons descrbed n [] - [4] are brough abou by an ncreased nducance n he prmary crcu ha s requred o acheve a complee ZV of all prmary swches down o lgh loads. Ths nducance, whch s obaned by nenonally ncreasng leakage nducance of he ransformer and/or by addng an exernal nducance n seres wh he prmary of he ransformer, has a dermenal effec on he performance. I nroduces a crculang curren on he prmary sde, causes a secondary-sde loss of duy cycle, and produces severe parasc rngng on he secondary sde of he ransformer as resonaes wh he recfer s juncon capacance. The crculang curren caused by excessve energy sored n he nducance employed o exend he ZV range down o lgh loads ncreases he curren sress of he prmary swches and he prmary-sde conducon losses a heavy load. The prmary-sde conducon losses are furher ncreased due o he secondary sde duy cycle loss whch mus be compensaed by reducng he urns rao of he ransformer. Furhermore, a smaller urns rao of he ransformer also ncreases he volage sress on he secondary-sde recfers so ha recfers wh a hgher volage rang ha ypcally exhb a hgher conducon loss may be requred. Fnally, o conrol he rngng volage across he oupu recfers, a lossy snubber crcu s requred on he secondary sde whch also reduces he converson effcency. In hs paper, a new hree-level ZV converer s nroduced. The proposed hree-level ZV converer employs a coupled nducor on he prmary sde o acheve ZV n he enre lne and load range. nce hs coupled nducor does no appear as a seres nducance n he load curren pah, does no cause a loss of duy cycle or severe volage rngng across he oupu dode. s a resul, he proposed crcu exhbs an ncreased converson effcency. The performance of he proposed hree-level converer crcu was expermenally verfed on a -kw prooype crcu ha was desgned o operae from a 750 V D npu and delver 48 V D oupu volage. II. THREE-LEVEL ZV ONVERTER WITH OULED INDUTOR Fgure shows a crcu dagram of he proposed hreelevel sof-swched dc-dc converer ha employs a coupled nducor on he prmary sde o exend he ZV range of he prmary swches wh a mnmum crculaon energy and conducon loss. The hree-level converer n Fg. consss of a seres connecon of four prmary swches hrough 4, ral-splng capacors IN and IN, flyng capacors and, solaon ransformer TR, and coupled nducor L. In hs crcu, he load s coupled o he converer hrough a full-wave recfer conneced o he cener-apped secondary of he ransformer. In addon, clampng dodes D and D are used o clamp he volage of ouer swches and 4, respecvely, o / afer he swches are urned off. Fnally, blockng capacor s employed o preven /03/$7.00 () 003 IEEE

2 IN IN Fg.. ransformer sauraon n case of a vol-second mbalance on he ransformer wndngs ha may be generaed by crcu parascs, a msmachng of he swch componens' characerscs, and mng sgnals. To faclae he explanaon of operaon of he crcu n Fg., Fg. shows s smplfed crcu dagram. In he smplfed crcu, s assumed ha nducance of oupu fler L F s large enough so ha durng a swchng cycle he oupu fler can be modeled as a consan curren source wh = V = D D 3 4 D D L D 3 D N roposed hree-level ZV converer wh coupled nducor. D D 3 4 L M L n = L N D R N DR n TR N N V TR DR L F F TR D R R L = /4 = /4 Fg.. mplfed crcu dagram of proposed hree-level ZV converer showng reference drecons of currens and volages. V O he magnude equal o oupu curren I O. lso, s assumed ha he capacances of capacors IN and IN, whch form a capacve dvder ha spls he npu volage n half, are large so ha capacors IN and IN can be modeled by volage sources = / and V = /, respecvely. mlarly, s assumed ha he capacances of capacors and are large enough so ha he capacors can be modeled as consan volage sources and, respecvely. ecause he average volages of he coupled nducor wndngs and he ransformer wndngs durng a swchng cycle are zero and for he phase-shf conrol he ouer par of swches and he nner par of swches operae wh 50% duy cycle, he magnude of volage sources and n Fg. s equal o /4,.e., = = /4. To furher smplfy he analyss of operaon of he crcu n Fg., s also assumed ha he ressance of he conducng semconducor swches s zero, whereas he ressance of he non-conducng swches s nfne. In addon, he leakage nducances of boh ransformer TR and coupled nducor L, as well as he magnezng nducance of ransformer TR are negleced snce her effec on he operaon of he crcu s no sgnfcan. However, he magnezng nducance of coupled nducor L and oupu capacances 4 of prmary swches are no negleced n hs analyss snce hey play a major role n he operaon of he crcu. onsequenly, n Fg., coupled nducor L s modeled as he deal ransformer wh urns rao n L = and wh parallel magnezng nducance L M across he seres connecon of wndngs and, whereas ransformer TR s modeled only by he deal ransformer wh urns rao n TR. I should be noed ha magnezng nducance L M of nducor L represens he nducance measured beween ermnals and wh ermnal open. Wh reference o Fg., he followng relaonshps beween currens can be esablshed: =, () + + M M =, () =. (3) nce he number of urns of wndng and wndng of coupled nducor L are he same, mus be ha =. (4) ubsung Eq. (4) no Eqs. ()-(3) gves = =, (5) = + M, (6) = M. (7) s can be seen from Eqs. (6) and (7), currens and are composed of wo componens: prmary-curren componen / and magnezng-curren componen. The prmarycurren componen drecly depends on he load curren, whereas he magnezng curren does no drecly depend on /03/$7.00 () 003 IEEE

3 V V V V 3 V V V V V (a) [T 0 - T ] (e) [T 4 - T 5 ] () [T 8 - T 9 ] V V V V V V V V V 4 (b) [T - T ] (f) [T 5 - T 6 ] (j) [T 9 - T 0] V V V V V 3 V V V V (c) [T - T 3 ] (g) [T 6 - T 7 ] (k) [T 0- T ] V V V V V V V V V 4 (d) [T 3 - T 4 ] (h) [T 7 - T 8 ] (l) [T - T ] Fg. 3. Topologcal sages of proposed hree-level ZV converer power sage. he load, bu raher on he vol-second produc across he magnezng nducance. Namely, a change of he magnezng curren wh a change n he load curren occurs only f he phase shf beween he urn on nsans of ouer swches and and respecve nner swches and s changed o manan he oupu regulaon. Usually, he change of phase shf wh a load change s greaer a lgh loads,.e., as he load decreases oward no load han a /03/$7.00 () 003 IEEE

4 heaver loads. nce n he crcu n Fg. he phase shf ncreases as he load approaches zero, he vol-second produc of L M also ncreases so ha he crcu n Fg. exhbs he maxmum magnezng curren a no load, whch makes possble o acheve ZV a no load. ecause magnezng curren does no conrbue o he load curren, as seen n Fg., represens a crculang curren. Generally, hs crculang curren and s assocaed energy should be mnmzed o reduce losses and maxmze he converson effcency. Due o an nverse dependence of he vol-second produc of L M on he load curren, crcu n Fg. crculaes less energy a full load han a lgh load, and, herefore, feaures ZV n a wde load range wh a mnmum crculang curren. lso from Fg. can be seen ha v = v + v. (8) nce boh wndngs of coupled nducor L have he same number of urns,.e., snce he urns rao of L s n L =, mus be ha or v v OFF ON v = v, (9) ON OFF v 3 v 4 v v v 4 OFF 4n TR ON OFF ntr T 0 T T T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 0 T T T 3 Fg. 4. Ts/ + = I M M = / + M = / - M DTs/ ON L M - = - I M M Key waveforms of proposed hree-level ZV converer. Ts/ v v = v =. (0) Generally for consan-frequency phase-shf conrol, volage v s a squarewave volage conssng of alernang posve and negave pulses of magnude / ha are separaed by me nervals wh v =0. ccordng o Eq. (0) and wh reference o Fg., durng he me nervals when eher of nner swches and s closed and when v =0, he prmary volage magnude s v = /4, whereas durng me nervals when v = /, he prmary volage magnude s v =0. To furher faclae he analyss of operaon, Fg. 3 shows he opologcal sages of he converer durng a swchng cycle, whereas Fg. 4 shows key waveforms. s shown n Fg. 4, snce durng me nerval T 0 -T swches and are closed whle swches and are open, volage v = = / so ha prmary volage v =0. In addon, durng hs opologcal sage, whose equvalen crcu s shown n Fg. 3(a), oupu curren I O flows hrough oupu recfer D R and he correspondng secondary of he ransformer so ha prmary curren = -I O /n TR, where n TR =N /N s he urns rao of he ransformer, N s he number of prmary wndng urns, and N s he number of secondary wndng urns. ecause he prmary curren s negave, boh currens and are also negave as shown n Fg. 4. he same me, magnezng curren s lnearly ncreasng wh slope /(L M ), snce volage v s posve and equal o half of he npu volage,.e., v = /. s a resul, curren ncreases whle curren decreases. Durng hs nerval, volage v whch s equal o he secondary wndng volage s zero because prmary wndng volage v s zero. Ths sage ends a =T when swch s urned off. fer swch s urned off a =T, he curren whch was flowng hrough he ranssor of swch s dvered o swch s oupu capacance, as shown n Fg. 3(b). In hs opologcal sage, curren charges capacor and dscharges capacor 4 a he same rae snce he sum of he volages across capacors and 4 s equal o consan volage /. s a resul, volage across swch ncreases whle volage across swch decreases, as llusraed n Fg. 4. In addon, durng hs sage he poenal of pon decreases causng a decrease of volage v from / oward zero and he smulaneous ncrease of prmary volage v from zero oward /4, as llusraed n Fg. 4. The posve prmary volage naes he commuaon of oupu curren I O from recfer D R o recfer D R. nce he leakage nducance of ransformer TR negleced, hs commuaon s nsananeous. However, n he presence of leakage nducance, he commuaon of curren from one recfer o he oher akes me. ecause durng hs commuaon me boh recfers are conducng,.e., he secondary wndngs of he ransformer are shored, volage v s zero, as shown n Fg /03/$7.00 () 003 IEEE

5 fer capacor 4 s fully dscharged a =T,.e., afer volage v 4 reaches zero, curren connues o flow hrough anparallel dode D 4 of swch and clamp dode D nsead of hrough capacors and 4, as shown n Fg. 3(c). Due o posve volage /4 appled across prmary wndng N, currens,, and begn o ncrease from negave o posve drecon. To acheve ZV of swch, swch needs o be urned on durng he me nerval when s anparallel dode D 4 s conducng, as llusraed n Fg. 4. The sage n Fg. 3(c) ends a =T 3 when he oupu curren I O s compleely commuaed from recfer D R o recfer D R,.e., when prmary curren equals o I O /n TR. Durng me nerval T 3 T 4 curren, whch flows hrough closed swch, s suppled from volage source, whereas curren, whch flows hrough closed swch, s suppled from volage source V, as shown n Fg. 3(d). The sage n Fg. 3(d) ends a =T 4 when swch s urned off. fer swch s urned off, he curren whch was flowng hrough he ranssor of swch s dvered o s oupu capacance, as shown n Fg. 3(e). In hs opologcal sage, curren charges capacor and dscharges capacor 3 a he same rae snce he sum of he volages across capacors and 3 s equal o consan volage + = /. s a resul, volage across swch ncreases whle volage across swch decreases, as llusraed n Fg. 4. he same me, he poenal of pon sars o decrease and causes a smulaneous decrease of volage v from zero oward - / and prmary volage v from /4 oward zero, as llusraed n Fg. 4. nce he decrease of he prmary volage s refleced no he secondary volage, volage v also decreases oward zero as shown n Fg. 4. Ths sage ends a =T 5 when capacance 3 s fully dscharged and when curren sars flowng hrough anparallel dode D 3 of swch, as shown n Fg. 3(f). ecause afer =T 5 negave volage / s appled across magnezng nducance L M, magnezng curren sars lnearly decreasng oward zero wh consan slope - /(L M ), as shown n Fg. 4. fer curren reaches zero a =T 6, connues o flow n he negave drecon as ndcaed n Fg. 3(g). Ths opologcal sage n Fg. 3(g) ends a =T 7 when swch s urned off and he converer eners he second half of he swchng cycle. The operaon durng he second half of he swchng cycle,.e., he operaon durng me nerval T 7 T 3, s dencal o he operaon durng he descrbed nerval T T 7 wh he roles of swches and and swches and exchanged. s can be seen from curren waveforms and n Fg. 4, for all four prmary swches hrough he magnude of he curren flowng hrough he swch a he momen of urnoff s he same,.e., ( = T ) = ( = T ) = ( = T ) = ( T ) 4 7 = 0 I O = + IM = + M, () n TR I where, I O s he load curren, n TR s he urns rao of he ransformer, and I M s he amplude of magnezng curren. ccordng o Eq. (), he commuaon of he swches, durng whch he capacance of he urned-off swch s chargng (volage across he swch s ncreasng) and he capacance of he swch ha s abou o be urned on s dschargng (volage across he swch s decreasng), s done by he energy sored by boh prmary curren and magnezng curren. Whle he commuaon energy conrbued by magnezng curren s always sored n magnezng nducance L M of coupled nducor L, he commuaon energy conrbued by curren s sored eher n he fler nducance of he secondary-sde oupu crcu, or he leakage nducances (no shown n Fg. ) of ransformer TR and coupled nducor L. pecfcally, for nner swches and, he commuaon energy conrbued by s sored n oupu-fler nducor L F, whereas for ouer swches and, s sored n he leakage nducance of he ransformer. nce s desrable o mnmze he leakage nducance of ransformer TR o mnmze he secondary-sde parasc rngng, he energy sored n s leakage nducances s relavely small,.e., much smaller han he energy sored n oupu-fler nducance. s a resul, n he crcu n Fg., s easy o acheve ZV of nner swches and n he enre load range, whereas ZV of he ouer swches and requres a proper szng of he magnezng nducance L M snce a lgh loads almos he enre energy requred o creae ZV condon of ouer swches and s sored n he magnezng nducance. III. DEIGN GUIDELINE s prevously explaned, n he proposed hree-level ZV crcu wh a coupled nducor, s more dffcul o acheve ZV of he ouer par of swches han he nner par of swches because he avalable energes for creang he ZV condons n he wo pars of swches are dfferen. Generally, o acheve ZV hs energy mus be a leas equal o he energy requred o dscharge he capacance of he swch whch s abou o be urned on and a he same me charge he capacance of he swch ha jus has been urned off. heaver load currens, ZV s prmarly acheved by he energy sored n he leakage nducances of ransformer TR. s he load curren decreases, he energy sored n he leakage nducances also decreases, whereas he energy sored n nducance L ncreases so ha a lgh loads nducance L provdes an ncreasng share of he energy requred for ZV. In fac, a no load, hs nducance L provdes he enre energy requred o creae he ZV condon. Therefore, f he value of nducance L s seleced so ha ZV s acheved a no load and maxmum npu volage (max), ZV s acheved n he enre load and npuvolage range /03/$7.00 () 003 IEEE

6 Neglecng he capacances of he ransformer s wndngs, magnezng nducance L M necessary o acheve ZV of he ouer swches n he mplemenaons n Fg. s L M, () 3f where s he oal capacance across he prmary swches (parasc and exernal capacance, f any) n he correspondng swch pars. IV. EXERIMENTL REULT The performance of he proposed hree-level ZV converer was verfed on a -kw (48 V/ ) prooype crcu operang a 00 khz from a 750 V dc npu. s shown n Fg. 5, he expermenal crcu ha employs a curren doubler recfer was mplemened wh he followng componens: swches - 4 = IRF460L (500 V, 0 ); prmary dodes D - D = RHR3060 (600 V, 30 ); oupu dodes D R - D R = YV74W (400 V, 40 ); prmary capacors,, and =. µf polypropylene capacor. The core of ransformer TR s a par of ER The prmary and secondary wndng of ransformer TR conss of egheen urns and welve urns of Lz wre (70 srands, WG #40), respecvely. The core of coupled nducor L s V [50 V/dv] [00 V/dv] V [400 V/dv] [0 /dv] V [50 V/dv] [00 V/dv] V [400 V/dv] (a) Duy ycle Loss < 3% 470uF/450V IRF460L [0 /dv] IN 750 V IN D RHR3060.uF/50V IRF460L D 3 RHR uF/450V IRF460L 4 IRF460L L core: urns:6urns N V L F 5uH N V N :8urns core:er4 TR.uF/50V N :urns YV74W D R YV74W D R YV6 D LM LM 0.0uF /00V YV6 D LM R LM.5k /4W F 4x000uF/68V.uF/50V L F 5uH Fg. 5. rcu dagram of -kw expermenal prooype bul o evaluae performance of proposed hree-level ZV converer. 48V (b) Fg. 6. Measured key waveforms of proposed hree-level ZV converer: (a) a O = 50 W; (b) a O = kw. From op o boom: prmary volage V [50V/dv]; secondary volage [00V/dv]; coupled nducor volage V [400V/dv]; prmary curren [0 /dv]. Tme base: µs/dv. M The wndngs of coupled nducor L conss of sxeen urns of Lz wre (70 srands, WG #40) each. Measured magnezng nducance L M of coupled nducor L s approxmaely 76 µh. To conrol he parasc rngng on he secondary sde caused by he resonance beween leakage nducance of he ransformer and juncon capacance of he recfer, he expermenal crcu employs a R--D clamp crcu ha consss of D LM, D LM, LM, and R LM. The loss of he clamp crcu s less han 3 W, whch s much lower han he loss of he convenonal hree-level converer ha generally requres a large leakage nducance or even an exernal nducance o exend he ZV range. The conrol crcu was mplemened wh a U3895 consan-frequency phase-shf conroller /03/$7.00 () 003 IEEE

7 EFFIIENY (%) Inpu Volage = 750 V Oupu Volage = 48 V wchng Frequency = 00 khz OUTUT OWER (W) Fg. 7. Measured effcency of he proposed hree-level ZV converer as funcon of oupu power Fgure 6 shows he measured waveforms of he proposed converer a full load and 5% load. The proposed converer has a very small duy cycle loss (< 3 %) even a full load, as well as a small parasc rngng because of he mnmzed leakage nducance of he ransformer ha s less han µh measured on he prmary sde of he ransformer. The effcency measuremens for he proposed opology s summarzed n Fg. 7. V. ONLUION new solaed, consan-frequency, hree-level ZV converer whch employs a coupled nducor on he prmary sde o acheve ZV n a wde range of load curren and npu volage wh reduced crculang energy and conducon losses has been descrbed. nce hs coupled nducor does no appear as a seres nducance n he load curren pah, does no cause a loss of duy cycle or severe volage rngng across he oupu recfers. The operaon and performance of he proposed crcu was verfed on a -kw (48-V/-) prooype. REFERENE [] J.. La and F.Z. eng, Mullevel converers new breed of power converers, IEEE Trans. Indusry pplcaons, vol. 3, no. 3, pp , 996. [] J.R. nhero and I. arb, The hree-level ZV-WM D-o-D converer, IEEE Trans. ower Elecroncs, vol. 8, no. 4, pp , 993. [3] I. arb, R. Gules, R. Redl, and N.O. okal, D/D converer for hgh npu volage: Four swches wh peak volage of V n/, capacve urn-off snubbng, and zero-volage urn-on, IEEE ower Elecroncs pecalss onf. (E) roc., pp. - 7, 998. [4] F. anales,.m. arbosa, J.M. urdo, and F.. Lee, zerovolage swchng hree-level D/D converer, IEEE Inernaonal Telecommuncaons Energy onf. (INTELE) roc., pp. 5-57, 000. [5].J. Jeon, F. anales,.m. arbosa, and F.. Lee, prmary-sdeasssed zero-volage and zero-curren swchng hree-level D-D converer wh phase-shf conrol, IEEE ppled ower Elecroncs onf. (E) roc., pp , 00. [6] X. Ruan, L. Zhou, and Y. Yan, of-swchng WM hree-level converers, IEEE Trans. ower Elecroncs, vol. 6, no. 5, pp. 6 6, /03/$7.00 () 003 IEEE