Novel High-Conversion-Ratio High-Efficiency. isolated bidirectional DC DC converter for. Tsorng-Juu Liang, Member, IEEE, and Jian-Hsieng Lee

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1 .9/TE , EEE Tranacion on ndurial Elecronic oel High-Conerion-Raio High-Efficiency olaed Bidirecional DC DC Conerer Torng-Juu Liang, Member, EEE, and Jian-Hieng Lee Abrac Thi paper propoe a noel high-conerion-raio high-efficiency iolaed bidirecional DC DC conerer. The propoed conerer i operaed in he ep-down age. The DCblocking capacior in he high-olage ide i ued o reduce he olage on he ranformer, and he curren-doubler circui are ued in he low-olage ide o reduce he oupu curren ripple. The energy ored in he leakage inducance i recycled o he DC-blocking capacior. When he propoed conerer i operaed wih a ep-up funcion, dual curren-fed circui on he lowolage ide are ued o reduce he curren ripple and conducion loe of he wiche in he low-olage ide. The olage-doubler circui in he high-olage ide increae he conerion raio. The propoed conerer can achiee high conerion wih high efficiency. Experimenal reul baed on a prooype implemened in he laboraory wih a high olage of, low olage of 4, and oupu power of W erify he performance of he propoed conerer. The peak efficiency of he propoed conerer in he high-ep-down and high-ep-up age i 96.3% and 95.6%, repeciely. ndex Term High conerion raio, curren-fed conerer, olage-doubler circui, curren-doubler recifier, ynchronou recifier.. TRODUCTO The exenie ue of foil fuel and nuclear energy ha caued major polluion and afey problem, uch a he nuclear acciden in a power plan in Fukuhima, Japan. Therefore, o reduce enironmenal damage, many counrie hae commied o deeloping green energy, uch a olar and wind energy [] [8]. n addiion o improemen in he conerion efficiency of green energy, he orage and reue of exce energy hae become imporan reearch opic. Thu, highep-up/ep-down conerer hae become imporan reearch ubjec. Conerer wih high conerion raio can be ued in energy orage yem, high-ineniy dicharge lamp, high power applicaion, communicaion power, olar power, and uninerrupible power upplie. Thee conerer are deigned by combining wiched-capacior cell, coupled-inducor echnique, and Z ource echnique [9] []. Manucrip receied January, 4; reied May 9, 4, Augu 5, 4 and oember 8, 4; acceped oember 6, 4. Copyrigh 4 EEE. Peronal ue of hi maerial i permied. Howeer, permiion o ue hi maerial for any oher purpoe mu be obained from he EEE by ending a reque o pub-permiion@ieee.org. T.-J. Liang and J.-H. Lee are wih he Deparmen of Elecrical Engineering / Adanced Opoelecronic Technology Cener (AOTC) / Green Energy Elecronic Reearch Cener (GREERC) aional Cheng-Kung Unieriy, Tainan, Taiwan, R.O.C. (Correponding auhor jliang@mail.ncku.edu.w) Compared wih high-ep-up and high-ep-down conerer, bidirecional high-conerion-raio conerer can ignificanly reduce he oerall yem olume, co, and number of componen. on-iolaed bidirecional opologie wih high conerion raio hae been preened in lecure [8] [7]. Thee non-iolaed bidirecional conerer can be conruced by uing coupled inducor [8] [], wiched-capacior echnique [] [5], and cacade echnique [6], [7] o obain a high conerion raio wih an appropriae duy raio. Howeer, non-iolaed conerer fail o mee he afey andard of galanic iolaion in many applicaion. umerou iolaed bidirecional conerer wih highconerion-raio applicaion hae been preened in many paper [8] [39]. Bidirecional iolaed DC DC conerer deried from puh pull opologie [8], full-bridge opologie [9]-[3], [4], and erie-reonan full-bridge [3] conerer can increae he conerion raio by adjuing he urn raio of he ranformer. Howeer, a high urn raio increae he ranformer ize. The conerion raio of bidirecional DC DC conerer can be improed wih curren-doubler echnique [33], [34], olage-doubler echnique [35], [36], Z ource [37], and cacade echnique [38], [39] o increae he conerion raio. Fig. Configuraion of a diribued generaion yem. The diribued generaion yem hown in Fig. indicae ha bidirecional dc-dc conerer play a ery imporan role beween energy orage deice (Baery) and olage bu. The funcion of he bidirecional conerer i o ranfer energy beween he baery and he DC bu. The energy generaed from he renewable ource() will be ranferred o he dc olage bu. Load() may be conneced wih dc olage bu and ac uiliy grid. Baery i ued o proide energy o dc olage bu when he grid olage ouage and renewable energy ource can' proide enough energy o he load conneced wih dc olage bu. Thi paper propoe a highconerion-raio iolaed bidirecional DC DC conerer for (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE

2 .9/TE , EEE Tranacion on ndurial Elecronic diribued generaion applicaion, he opology configuraion of which i hown in Fig.. The circui include high olage ; high-olage capacior C and DC-blocking capacior C ; four acie wiche S, S, S 3, and S 4 ; a ranformer T ; wo inducor L and L ; a low-olage capacior ; and low olage. The gae ignal of S and S in he high-epdown age are inerlaced by a phae hif of 8 degree, and S 3 and S 4 are ynchronou recifier. n he high-ep-up mode, he gae ignal of S 3 and S 4 are greaer han 5% and are conrolled by a phae hif of 8 degree. The gae ignal of S and S are maller han 5% and are conrolled by a phae hif of 8 degree wih ynchronou recifier [4],[4]. The funcion of he propoed bidirecional conerer i like he double olage ep-down inead of LLC mode. (When S i urned on, he olage on he primary winding i reduced by half becaue of he capacior C. Thu he olage gain can be reduced by half by adding C in erie wih he half bridge conerer.) Thi conerer i conrolled wih duy conrol on frequency conrol o ha he effec of leakage inducance can be negleced. The propoed canno achiee ZS on he high olage ide power wiche bu he low olage ide ynchronou recifier can achiee ZS. Thu, he urn raio can be reduced a compared wih he radiional half bridge conerer. The ize of he ranformer can be decreaed by uing a olage-doubler circui wih low urn raio, o ha a lower urn raio i needed on he econdary ide. The feaure of he propoed conerer are a follow: ) mee he afey andard of galanic iolaion; ) The ize of he ranformer can be reduced; 3) The energy in he leakage inducance of he ranformer can be recycled; 4) ha a high conerion raio; 5) The low-olage ide ha low ripple curren; 6) Synchronou recifier improe yem efficiency. 5) The paraiic inducor, capacior, and reior of circui race are ignored. (A) Sep-Down Sage The key waeform of he propoed conerer in he highep-down age in coninuou-conducion mode (CCM) operaion are illuraed in Fig. 3. The main wiche are S and S ; S 3 and S 4 are he ynchronou recifier. The operaing mode of he propoed conerer can be diided ino en operaing mode oer one wiching period: ) Mode [, ]: During hi ineral, S and S 3 are on, while S and S 4 are off. The equialen circui i hown in Fig. 4(a). The curren i Lk increae linearly. and C proide energy o L,, and ia T. C i charged by and C. The energy ored in L i ranferred o and. Swich curren i S i equal o i Lk, and wich curren i S3 i equal o i L +i L. The olage acro S i equal o, and ha acro S 4 i equal o ( C )/n. Thi operaing mode end when S i urned off a =. g g g3 g4 i Lk DT (-D)T T T (-D)T DT i S i S Fig.. Schemaic of propoed high-conerion-raio iolaed bidirecional DC DC conerer. S. OPERATG PRCPLES OF PROPOSED COERTER To implify he analyi of he propoed conerer, he following are aumed oer one wiching period: ) C, C, and are large enough; hu,, C, and are regarded a conan. ) All acie wiche are regarded a ideal. 3) L i equal o L. 4) The urn raio of ranformer T i n = /, and he leakage inducance i conidered in he analyi, where and are he winding urn in high-olage and low-olage ide, repeciely. S i L i L Mode Mode Mode Mode Mode Mode Mode Mode ModeX ModeX Fig. 3. Key waeform of propoed iolaed bidirecional conerer in highep-down age during CCM operaion (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE

3 .9/TE , EEE Tranacion on ndurial Elecronic ) Mode [, ]: During hi ineral, S 3 i on while S, S, and S 4 are off. The equialen circui i illuraed in Fig. 4(b). The leakage curren i Lk flow ino he ani-parallel diode of S o charge C and o clamp he maximum olage pike of S uch ha he energy ored in L lk can be recycled. The energy ored in L coninue o releae energy o and. The energy ored in L i releaed hrough he ani-parallel diode of S 4 o and. Thi operaing mode end when i Lk i equal o zero a =. 3) Mode [, 3 ]: During hi ineral, S 3 i on, while S, S, and S 4 are off. The equialen circui i illuraed in Fig. 4(c). The olage acro S and S are /. The olage acro winding i equal o zero. The ani-parallel diode of S 4 conduc o achiee zero-olage wiching (ZS) condiion. Through hi diode flow inducor curren i L o releae energy o and, which coninuouly receie he energy ored in L. Thi operaing mode end when S 4 i urned on a = 3. 4) Mode [ 3, 4 ]: During hi ineral, S and S are off, while S 3 and S 4 are on. The equialen circui i illuraed in Fig. 4(d). S 4 achiee ZS when i i urned on wih he ynchronou recifier and hu improe yem efficiency. The energy ored in L and L i imulaneouly deliered o and. Swich curren i S3 and i S4 are equal o i L and i L. Curren i L equal i L +i L ; hu, i ripple curren can be reduced. Thi operaing mode end when S 3 i urned off a = 4. 5) Mode [ 4, 5 ]: During hi ineral, S 4 i on, while S, S, and S 3 are off. The equialen circui i illuraed in Fig. 4(e). The energy ored in L and L i imulaneouly releaed o and. Thi operaing mode end when S i urned on a = 5. 6) Mode [ 5, 6 ]: During hi ineral, S and S 4 are on, while S and S 3 are off. The equialen circui i illuraed in Fig. 4(f). C proide energy o hrough T o releae energy o L,, and. Swich curren i S i equal o i Lk, and i S4 i equal o i L +i L. The olage acro S i equal o, and ha acro S 3 i equal o ( C )/n. The energy ored in L i ranferred o and. Thi operaing mode end when S i urned off a = 6. 7) Mode [ 6, 7 ]: During hi ineral, S, S, and S 3 are off while S 4 i on. The equialen circui i illuraed in Fig. 4(g). The leakage curren i Lk flow ino he ani-parallel diode of S o charge and C and o clamp he maximum olage pike of S uch ha he leakage energy can be recycled. The energy ored in L coninue o releae energy o and. The energy ored in L i releaed hrough he ani-parallel diode of S 3 o and. Thi operaing mode end when i Lk i equal o zero a = 7. 8) Mode [ 7, 8 ]: During hi ineral, S, S, and S 3 are off, while S 4 i on. The equialen circui i illuraed in Fig. 4(e). The ani-parallel diode of S 3 conduc o achiee ZS condiion. Through hi diode flow inducor curren i L o releae energy o and, which coninuouly receie he energy ored in L. Thi operaing mode end when S 3 i urned on a = 8. 9) Mode X [ 8, 9 ]: During hi ineral, S and S are off, while S 3 and S 4 are on. The equialen circui i illuraed in Fig. 4(d). S 3 achiee ZS when i i urned on wih he ynchronou recifier. The energy ored in L and L i imulaneouly deliered o and. Thi operaing mode end when S 4 i urned off a = 9. ) Mode X [ 9, ]: During hi ineral, S, S, and S 4 are off, while S 3 i on. The equialen circui i illuraed in Fig. 4(c). The energy ored in L and L i releaed ia S 3 and he ani-parallel diode of S 4, repeciely, o releae energy o and. Thi operaing mode end when S i urned on a =. S L C : (a) Mode S C T L C : (b) Mode S S S C L C : S (c) Mode and X C T T L L L (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE

4 .9/TE , EEE Tranacion on ndurial Elecronic S L C : S (d) Mode and X S C T L C : S L The operaing mode of he propoed conerer can be diided ino en operaing mode oer one wiching period: ) Mode [, ]: During hi ineral, S 3 and S 4 are on while S and S are off. The equialen circui i hown in Fig. 6(a). The energy ored in i releaed ia he aniparallel diode of S o and C. Therefore, he leakage energy can be recycled, and he olage of S i clamped a. and imulaneouly proide energy o L and L. Thi operaing mode end when i Lk i equal o zero a =. ) Mode [, ]: During hi ineral, S 3 and S 4 are on, while S and S are off. The equialen circui i hown in Fig. 6(b). and coninue o proide energy o L and L. i L and i L are equal o i L /. Thu, he conducion loe of L and L and S 3 and S 4 are reduced, and yem efficiency improe. The olage acro T i equal o zero, and ha acro S and S i equal o /. i L i equal o i S4, and i L i equal o i S3. C releae energy o. Thi operaing mode end when S 3 i urned off a =. C T L g4 DT (-D)T T (e) Mode and g3 (-D)T T DT S g L C : g S C T L i L (f) Mode i L S4 S3 i (g) Mode Fig. 4. Equialen circui of iolaed bidirecional DC DC conerer in highep-down age oer one wiching period during CCM operaion: (a) mode, (b) mode, (c) mode and X, (d) mode and X, (e) mode and, (f) mode, and (g) mode. (B) Sep-Up Sage The key waeform of he propoed conerer in he highep-up age in CCM operaion are hown in Fig. 5. The main wiche are S 3 and S 4 ; S and S are he ynchronou recifier. i S i S Mode Mode Mode Mode Mode Mode Mode Mode ModeX ModeX Fig. 5. Key waeform of propoed iolaed bidirecional conerer in highep-up age in CCM operaion (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE

5 .9/TE , EEE Tranacion on ndurial Elecronic 3) Mode [, 3 ]: During hi ineral, S 4 i on, while S, S, and S 3 are off. The equialen circui i hown in Fig. 6(c). L ore energy from and C. The ani-parallel diode of S conduc o achiee ZS conducion. The energy ored in L i releaed o C hrough T. i S4 i equal o i L +i L. The olage acro S 3 i equal o + L, ha acro he magneizing inducance i equal o n( + L ), ha acro C i equal o n( + L ), and ha acro S i equal o. C coninue o releae energy o. Thi operaing mode end when S i urned on a = 3. 4) Mode [ 3, 4 ]: During hi ineral, S and S 4 are on, while S and S 3 are off. The equialen circui i hown in Fig. 6(d). S achiee ZS when i i urned on wih he ynchronou recifier, and hu improe yem efficiency. L coninue o ore energy from and. The energy ored in L coninue o be releaed o C hrough T. C coninue o releae energy o. Thi operaing mode end when S i urned off a = 4. 5) Mode [ 4, 5 ]: During hi ineral, S 4 i on, while S, S, and S 3 are off. S achiee ZS when i i urned off. The equialen circui i hown in Fig. 6(c). L coninue o ore energy from and. The energy ored in L coninue o be releaed o C ia T and he ani-parallel diode of S. C coninue o releae energy o. Thi operaing mode end when S 3 i urned on a = 5. 6) Mode [ 5, 6 ]: During hi ineral, S 3 and S 4 are on while S and S are off. The equialen circui i hown in Fig. 6(e). The energy ored in i releaed ia he aniparallel diode of S o C. Therefore, he leakage energy can be recycled, and he olage of S i clamped a. and proide energy o L and L. Thi operaing mode end when i Lk i equal o zero a = 6. 7) Mode [ 6, 7 ]: During hi ineral, S 3 and S 4 are on, while S and S are off. The equialen circui i hown in Fig. 6(b). L and L imulaneouly ore energy from and. Thi operaing mode end when S 4 i urned off a = 7. 8) Mode [ 7, 8 ]: During hi ineral, S 3 i on, while S, S, and S 4 are off. The equialen circui i hown in Fig. 6(f). The ani-parallel diode of S conduc o achiee ZS condiion. The olage acro S i equal o, and ha acro S 4 i equal o L +. Energy from and i ored by L. The energy ored in L i releaed o. C and winding are linked in erie o releae energy o C and. Thi operaing mode end when S i urned on a = 8. 9) Mode X [ 8, 9 ]: During hi ineral, S and S 3 are on, while S and S 4 are off. The equialen circui i hown in Fig. 6(g). S achiee ZS when i i urned on wih he ynchronou recifier. The olage acro S 4 i + L, and ha acro S i. L coninue o ore energy from and. The energy ored in L coninue o be releaed o. C and are linked in erie o releae energy o C and. Thi operaing mode end when S i urned off a = 9. ) Mode X [ 9, ]: During hi ineral, S 3 i on, while S, S, and S 4 are off. The equialen circui i hown in Fig. 6(f). S achiee ZS when i i urned off. L coninue o ore energy from and. C and are linked in erie o releae energy o C and. Thi operaing mode end when S 4 i urned on a =. (a) Mode (b) Mode and (c) Mode and (d) Mode (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE

6 .9/TE , EEE Tranacion on ndurial Elecronic When S and S are he wiche ued in he urned-on period (DT ), inducor olage L and L and high-capacior olage C are gien by L L, n () C. () When S and S are he wiche no ued in he urnedoff period (( D)T ), L and L for hi ineral are (e) Mode L L. (3) The applicaion of he principle of ol-econd balance o L and L yield DT T (. (4) n DTS S S ) d d Baed on (4), he olage gain i M Sepdown D. (5) n (f) Mode and X S L C : From (5), he olage gain of he iolaed bidirecional fullbridge conerer [3], [3] are compared wih ha of he propoed bidirecional conerer in he high-ep-down age in CCM operaion wih a urn raio of n=.5 (Fig. 7). The olage gain of he propoed conerer i maller han ha of oher conerer [3], [3] when he duy cycle D i lower han.5. The olage ree of all four wiche are gien by S C T L S S, (6). (7) S 4 n Q3 (g) Mode X Fig. 6. Equialen circui of iolaed bidirecional conerer in high-ep-up age oer one wiching period during CCM operaion: (a) mode, (b) mode and, (c) mode and, (d) mode, (e) mode, (f) mode and X, and (g) mode X.. STEADY-STATE AALYSS OF PROPOSED COERTER To implify he eady-ae condiion analyi of he highep-down and high-ep-up age in CCM, he leakage inducance of he ranformer i negleced becaue he magneizing inducance of he ranformer i much larger han i leakage inducance. (A) Sep-Down Sage The urned-on period (DT ) and urned-off period (( D)T ) of S and S in one wiching period are defined a hown in Fig. 3. Fig. 7. Comparion of olage gain of he iolaed bidirecional full-bridge conerer [3], [3] and of propoed bidirecional conerer in high-epdown age in CCM operaion (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE

7 .9/TE , EEE Tranacion on ndurial Elecronic When he propoed conerer i operaed in boundaryconducion mode, he peak curren of i L and i L and he aerage curren of L, L, and can be expreed a When S 4 (S 3 ) i he wich no ued in he urned-off period (( D)T ) and S 3 (S 4 ) i he wich ued in he urned-on period (DT ), L, L,, and Lm for hi ineral are T, (8) i L il ( D) T ( D) L L L L ( D) T ( D) T, L L (9) ( D) T ( D) T. R L L () The boundary normalized magneizing-inducance ime conan in high-ep-down age i defined a L L Sep down. () RT RT The oluion of () yield he following expreion of τ Sepdown: D. () Sepdown Fig. 8 illurae he relaionhip of τ Sep-down and D a n=.5. f he normalized magneizing-inducance ime conan τ L i higher han τ Sep-down in he high-ep-down age, he conerer i operaed in CCM; oherwie, i i operaed in diconinuou-conducion mode (DCM). L L, (5) Lm Lm, (6) n. (7) C The applicaion of he principle of ol-econd balance o L and L yield DT T S S d ) d DTS (. (8) The oluion of (8) explain he olage gain a follow:. (9) D Equaion (8) can be rewrien a DT T n ( D. () n S S d ) d DTS From (), he high-ep-up olage gain can be explained a M CCM n. () D Fig. 8. Boundary-conducion mode of propoed iolaed bidirecional conerer in high-ep-down age wih n=.5. (B) Sep-Up Sage The urned-on period (DT ) and urned-off period (( D)T ) of S 3 and S 4 in one wiching period are defined a hown in Fig. 5. When S 3 and S 4 are he wiche ued in he urned-on period (DT ), L, L, and C are gien by L L, (3) n D C. (4) By (), he olage gain of he iolaed bidirecional fullbridge conerer [3], [3] and of he propoed iolaed bidirecional conerer in CCM operaion wih a urn raio of n=.5 are compared in Fig. 9. The olage gain of he propoed conerer i greaer han ha of he iolaed bidirecional full-bridge conerer [3], [3] in he high-epup age. M Sep-up Propoed Bidirecional Conerer Bidirecional Conerer [3], [3] D Fig. 9. Comparion of olage gain of bidirecional conerer [3], [3] and propoed bidirecional conerer in high-ep-up age in CCM operaion. The olage ree of all four wiche are gien by (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE

8 .9/TE , EEE Tranacion on ndurial Elecronic S S 3 S S 4 n, D (). D (3) When he propoed conerer i operaed in boundaryconducion mode, he peak curren of i L and i L and he aerage curren of L, L,, and can be expreed a L il DT DT, (4) L L i L L DT, (5) L L n, (6) D D D DT DT. (7) R nl nl Equaion (7) can be rewrien a ( D) DT ( D). (8) R 4n L 4n L The boundary normalized magneizing-inducance ime conan in he high-ep-up age i defined a L L Sep up. (9) RT RT The oluion of (9) yield he following expreion of τ Sep-up : D ( D ) Sep up. (3) 4n Fig. illurae he relaionhip beween τ Sep-up and D a n=.5. f he normalized magneizing-inducance ime conan τ H i higher han τ Sep-up in he high-ep-up age, he conerer i operaed in CCM; oherwie, i i operaed in DCM. Fig.. Boundary-conducion mode of propoed bidirecional conerer in high-ep-up age a n=.5. DT. DESG AD EXPERMET OF PROPOSED COERTER The laboraory prooype ample i implemened o demonrae he pracicabiliy of he propoed conerer. The yem pecificaion and componen are a follow: ) : 4 ) : 3) operaing frequency: 5 khz 4) maximum oupu power P o : W 5) C and C : μf/45, meallized polypropylene film capacior 6) S and S : XFH5T 7) ranformer: PQ3535, core PC-4, : =.5:, = mh, leakage inducance=.38 μh 8) S 3 and S 4 : FDP755A 9) L and L : 78 μh ) : μf/63, aluminum capacior The experimenal reul in high-ep-down age a full load P o = W and = are hown in Fig.. Fig. (a) and (b) how he waeform of g, S, C, i S, g, S, and i S. g and g indicae ha he gae ignal of S and S are inerlaced by a phae hif of 8 degree. The olage acro C i abou. The olage pike in S and S i abou 5. Thu, low olage ree and low on-reiance R on wiche can be eleced. i S i imilar o i S. Fig. (c) and (d) how he waeform of g3, S3, i S3, g4, S4, and i S4. g3 and g4 are gae ignal wih ynchronou recifier. g3, S3, g4, and S4 indicae ha S 3 and S 4 achiee ZS when hey are urned on. The olage pike on S 3 and S 4 i a lile bi high -- abou. S 3, S 4 uilize MOSFET wih olage raing of 5. The curren in S 3 and S 4 i increaed by he ani-parallel diode reere-recoery effec. Fig. (e) how he waeform of, i, and i L. The low-ide olage i 4. The curren frequency of i L i double he operaing frequency of he yem. i L indicae ha he curren i reduced. The meaured reul in high-ep-up age a full load P o = W and = 4 are hown in Fig.. Fig. (a) and (b) how he waeform of g4, S4, i S4, i L, g3, S3, and i S3. g4 and g3 are phae hif of 8 degree wih an oerlap, which enure ha he inducor energy can be deliered o. The olage increae in S 3 and S 4 i abou 75. The curren frequency of i L i khz. Fig. (c) how he waeform of i L and i L. The inerleaed inducor curren i L and i L reduce he ripple curren of i L. Furhermore, enable he elecion of a low capacior alue. Fig. (d) how he waeform of g, S, and i S. g i a gae ignal wih a ynchronou recifier. g and S indicae ha S achiee ZS when i i urned on and urned off. Fig. (e) how he waeform of, C, and i Lk. i, and he capacior olage C i abou. Figure 3 how he meaured conerion efficiency of he propoed conerer in he high-ep-down age. The maximum efficiency i 96.3% wih a ynchronou recifier. Compared wih he conerion efficiency, he efficiency wih he ynchronou recifier i higher han ha wih he aniparallel diode. Thu, he ynchronou recifier can ignificanly improe efficiency. Figure 4 how he meaured conerion efficiency of he propoed conerer in he high-ep-up age. Fig. 4 how ha he ynchronou recifier efficiency i (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE

9 .9/TE , EEE Tranacion on ndurial Elecronic higher han he ani-parallel diode efficiency, and ha he peak efficiency i 95.6% in he high-ep-up age. S ~S 4 will uffer from high curren pike, which occur due o he recoery problem of he wiche ani-parallel diode, o he wichcurren waeform preened in he experimen are lighly differen wih he operaing waeform in Figure 3 and 5. The propoed bidirecional conerer can be applied in phooolaic and alone yem, energy orage yem and emergency power yem. The oupu olage of a ingle P module i 4~4. A dc-dc conerer will be ued o conerer he P oupu olage o dc bu olage and alo achieing maximum power racking. The dc bu olage i uually deigned a for he ac power yem. Thi i why we eleced he dc bu olage ( ) i and baery olage ( ) i 4. n hi yem, he baery need o be charged or dicharged depending on he P power generaion and he load requiremen. The low olage (baery olage) wih 4 can proe he high efficiency of he propoed conerer. f he baery olage i eleced a 36 or higher olage leel, he yem efficiency will be higher becaue he conducion loe will be reduced. The propoed conerer i uiable for porable energy orage yem, emergency power yem and micro DC grid yem. The power-lo analyi of he propoed conerer in ep-down mode a W i hown in Table. The meaured efficiency i 96.3 % and he calculaed reul i 98. %, becaue he calculaed reul ignore he reere-recoery effec of he ani-parallel diode, iron, and reiance of circui race. g : /di g3 : /di S3 : /di i S3 : A/di : /di (c) (d) Time : 5 /di S : /di i : A/di C : /di i S : A/di i L : 5A/di (a) Time : 5 /di Time : 5 /di (e) Fig.. Experimenal waeform of high-ep-down age a P o = W. g4 : /di S4 : /di i S4 : A/di i L : 5A/di (b) (a) Time : 5 /di (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE

10 .9/TE , EEE Tranacion on ndurial Elecronic (b) Fig. 3. Experimenal conerion efficiency of propoed iolaed bidirecional conerer in high-ep-down age. (c) Fig. 4. Experimenal conerion efficiency of propoed iolaed bidirecional conerer in high-ep-up age. TABLE. POWER-LOSS AALYSS OF THE PROPOSED COERTER STEP- DOW MODE AT FULL LOAD ( W). Componen Parameer Lo (W) % : /di (d) Swiche S and S mω Conducion Swiching Reiance of Tranformer T 5 mω.3.7 Reiance of nducor L and L 35 mω.3.65 Swiche S 3 and S mω Conducion Swiching Toal Lo C : /di i Lk : A/di Time : 5 /di (e) Fig.. Experimenal waeform of high-ep-up age a P o = W.. COCLUSOS n hi paper, a high-efficiency and high-conerion-raio iolaed bidirecional DC DC conerer wih a low ranformer urn raio i preened. The ize of he capacior on he olage ide can be decreaed by uing curren-doubler circui wih low curren ripple. The ynchronou-recifier circui can achiee zero olage wiching and improe yem efficiency. The operaing principle, eady-ae analyi, and experimenal reul are dicued in deail. The efficiencie of (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE

11 .9/TE , EEE Tranacion on ndurial Elecronic he propoed conerer wih ynchronou recifier and aniparallel diode are compared in he experimenal reul. The full-load efficiency in he ep-down and ep-up age i near 96.3% and 95.6%, repeciely. REFERECES [] Z. Dong, onlinear adapie power-leel conrol for modular high emperaure ga cooled reacor, EEE Tran. ucl. Sci., ol. 6, no., pp , April 3. [] T. J. Liang, J. H. Lee, S. M. Chen, and L. S. Yang, oel iolaed high-ep-up DC DC conerer wih olage lif, EEE Tran. nd. Elecron., ol. 6, no. 4, pp , April 3. [3] A. Koran, T. Labella, and J. S. Lai, High efficiency phooolaic ource imulaor wih fa repone ime for olar power condiioning yem ealuaion, EEE Tran. Power Elecron., ol. 9, no. 3, pp , March 4. [4] M. Trifkoic, M. Sheikhzadeh, K. igim, and P. Daouidi, Modeling and conrol of a renewable hybrid energy yem wih hydrogen orage, EEE Tran. Conrol Sy. Technol., ol., no., pp , Jan. 4. [5] Y. K. Lo, H. J. Chiu, T. P. Lee,. Purnama, and J. M. Wang, Analyi and deign of a phooolaic yem DC conneced o he uiliy wih a power facor correcor, EEE Tran. Power Elecron., ol. 56, no., pp , o. 9. [6]. Laird and D. D. C. Lu, High ep-up DC/DC opology and MPPT algorihm for ue wih a hermoelecric generaor, EEE Tran. Power Elecron., ol. 8, no. 7, pp , July 3. [7] S. K. Chaopadhyay, C. Chakrabory, and B. C. Pal, Cacaded H- bridge & neural poin clamped hybrid aymmeric mulileel inerer opology for grid ineracie ranformerle phooolaic power plan, in Proc. Annu. Conf. EEE nd. Elecron. Soc., pp , Oc.. [8] W. L. Chen and J. S. Lin, One-dimenional opimizaion for proporional-reonan conroller deign again he change in ource impedance and olar irradiaion in P yem, EEE Tran. nd. Elecron., ol. 6, no. 4, pp , April 4. [9] B. Axelrod, Y. Berkoich, and A. oinoici, Swiched-capacior / wiched-inducor rucure for geing ranformerle hybrid DC-DC PWM conerer, EEE Tran. Circui Sy., Reg. Paper, ol. 55, no., pp , March 8. [] A. oinoici, C. K. Te, and H. C. H. Chung Common on" Deign and analyi of wiched-capacior-baed ep-up reonan conerer, EEE Tran. Circui Sy., Reg. Paper, ol. 53, no. 6, pp. 43, June 6. [] C. K. Cheung, S. C. Tan, C. K. Te, and A. oinoici, On energy of wiched-capacior conerer, EEE Tran. Power Elecron., ol. 8, no., pp , Feb. 3. [] D. Gu, D. Czarkowki, and A. oinoici, A large dc-gain highly efficien hybrid wiched-capacior-boo conerer for renewable energy yem, in Proc. EEE Energy Coner. Congr. Expo., pp , Sep.. [3] S. M. Chen, T. J. Liang, L. S. Yang, and J. F. Chen, A boo conerer wih capacior muliplier and coupled inducor for AC module applicaion, EEE Tran. nd. Elecron., ol. 6, no. 4, pp. 53-5, April 3. [4] T. J. Liang, S. M. Chen, L. S. Yang, J. F. Chen, and A. oinoici, Ulra large gain ep-up wiched-capacior DC-DC conerer wih coupled inducor for alernaie ource of energy, EEE Tran. Circui Sy., Reg. Paper, ol. 59, no. 4, pp , April. [5] S. M. Chen, T. J. Liang, L. S. Yang, and J. F. Chen, A afey enhanced, high ep-up DC-DC conerer for AC phooolaic module applicaion, EEE Tran. Power Elecron., ol. 7, no. 4, pp , April. [6] Y. P. Hieh, J. F. Chen, T. J. Liang, L. S. Yang, oel high ep-up DC-DC conerer wih coupled-inducor and wiched-capacior echnique, EEE Tran. nd. Elecron., ol.59,no., pp.998 7, Feb.. [7] S. M. Chen, T. J. Liang, K. R. Hu, Deign, Analyi, and implemenaion of olar power opimizer for DC diribuion yem, EEE Tran. Power Elecron., ol.8, no.4, pp , April 3. [8] Y. P. Hieh, J. F. Chen, L. S. Yang, C.Y. W, and W. S. Liu, Highconerion-raio bidirecional DC-DC conerer wih high coupled inducor, EEE Tran. nd. Elecron., ol. 6, no., pp. -, Jan. 4. [9] E. Sanchi, E. Mae, A. Ferrere, J. B. Ejea,. Eee, J. Jordan, J. Calene, A. Garrigo, and J. M. Blane, Bidirecional high-efficiency noniolaed ep-up baery regulaor, EEE Tran. Aeropace and Elecronic Syem., ol. 47, no. 3, pp. 3-39, July [] R. J. Wai, R. Y. Duan, and K. H. Jheng, High-efficiency bidirecional dc dc conerer wih high-olage gain, ET Power Elecron., ol. 5, no., pp , Feb.. [] L. S. Yang and T. J. Liang, Analyi and implemenaion of a noel bidirecional dc dc conerer, EEE Tran. nd. Elecron., ol. 59, no., pp , Jan.. [] Y. S. Lee and Y. Y. Chiu, Zero-curren-wiching wiched-capacior bidirecional dc dc conerer, in Proc. n. Elec. Eng. Elec. Power Appl., ol. 5, no. 6, pp , o. 5. [3] M. Kwon, S. Oh, and S. Choi, High gain of-wiched bidirecional DC-DC conerer for eco-friendly ehicle, EEE Tran. Power Elecron., ol. 9, no. 4, pp , April 4. [4] R. L. Anderen, T. B. Lazzarin, and. Barbi, A -kw ep-up/epdown wich capacior AC-AC conerer, EEE Tran. Power Elecron., ol. 8, no. 7, pp , July 3. [5] O. C. Onar, J. Kobayahi, D. C. Erb, and A. Khaligh, A bidirecional high-power-qualiy grid inerface wih a noel bidirecional noninered buck-boo conerer for PHE, EEE Tran. eh. Technol., ol. 6, no. 5, pp. 8 3, June. [6] H. W. Seong, H. S. Kim, K.B. Park, G. W. Moon, and M. J. Youn, High ep-up dc-dc conerer uing zero-olage wiching boo inegraion echnique and ligh-load frequency modulaion conrol, EEE Tran. Power Elecron., ol. 7, no. 3, pp , March. [7] C. M. Hong, L. S. Yang, T. J. Liang, and J. F. Chen, oel bidirecional DC-DC conerer wih high ep-up/down olage gain, in Proc. EEE Energy Coner. Congr. Expo., pp. 6 66, Sep 9. [8] K. Yamamoo, E. Hiraki, T. Tanaka, M. akaoka, and T. Mihima, Bidirecional DC-DC conerer wih full-bridge / puh-pull circui for auomobile elecric power yem, in Proc. 37h EEE Annu. Power Elecron. Spec. Conf., pp. -5, June 6. [9] B. Zhao, Q. Song, and W. Liu, Experimenal comparion of iolaed bidirecional DC DC conerer baed on all-i and all-ic power deice for nex-generaion power conerion applicaion, EEE Tran. nd. Elecron., ol. 6, no. 3, pp , March 4. [3] T. F. Wu, J. G. Yang, C. L. Kuo, and Y. C. Wu, Sof-wiching bidirecional iolaed full-bridge conerer wih acie and paie nubber, EEE Tran. nd. Elecron., ol. 6, no. 3, pp , March 4. [3] P. Xuewei and A. K. Rahore, oel bidirecional nubberle naurally commuaed of-wiching curren-fed full-bridge iolaed DC/DC conerer for fuel cell ehicle, EEE Tran. nd. Elecron., ol. 6, no. 5, pp , May 4. [3] F. banze, J. M. Echeerria, and L. Fonan, oel echnique for bidirecional erie-reonan DC/DC conerer in diconinuou mode, ET Power Elecron., ol. 6,no. 5, pp. 9 8, May 3. [33] A. K. Rahore and U. R. Praanna, Analyi, deign, and experimenal reul of noel nubberle bidirecional naurally clamped ZCS/ZS curren-fed half-bridge DC/DC conerer for fuel cell ehicle, EEE Tran. nd. Elecron., ol. 6, no., pp , Oc. 3. [34] U. R. Praanna, A. K. Rahore, and S. K. Mazumder oel zerocurren-wiching curren-fed half-bridge iolaed DC/DC conerer for fuel-cell-baed applicaion, EEE Tran. nd. Elecron., ol. 49, no. 4, pp , Aug. 3. [35] Z. Zhang, Z. Ouyang, O. C. Thomen, and M. Xu, Analyi and deign of a bidirecional iolaed DC DC conerer for fuel Cell and upercapacior hybrid yem, EEE Tran. Power Elecron., ol. 7, no., pp , Feb.. [36] L. Wang, Z. Wang, and H. Li, Aymmerical duy cycle conrol and decoupled power flow deign of a hree-por Bidirecional DC-DC conerer for fuel cell ehicle applicaion, EEE Tran. Power Elecron., ol. 7, no., pp , Feb.. [37] B. Zhao, Q. Yu, Z. Leng, and X. Chen, Swiched Z-ource iolaed bidirecional DC DC conerer and i phae-hifing hoo-hrough biariae coordinaed conrol raegy, EEE Tran. nd. Elecron., ol. 59, no., pp , Dec.. [38] D. Yu, A. Q. Hung, M. Wang, and S. M. Lukic, A noel high ep-up raio bi-direcional DC-DC conerer, in Proc. EEE Appl. Power Elecron. Conf.,, pp (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE

12 .9/TE , EEE Tranacion on ndurial Elecronic [39] S. M. Chen, T. J. Liang, and Y. H. Huang, A iolaed bidirecional inerleaed flyback conerer for baery backup yem applicaion, in Proc. EEE n. Symp. on Circui & Sy., 3, pp [4] D. Wang and Y. F. Liu, A zero-croing noie filer for driing ynchronou recifier of LLC reonan conerer, EEE Tran. Power Elecron., ol. 9, no. 4, pp , April 4. [4] J. Zhang, J. Wang, G. Zhang, and Z. Qian, A hybrid driing cheme for full-bridge ynchronou recifier in LLC reonan conerer, EEE Tran. Power Elecron., ol. 7, no., pp , o.. [4] H. Wen, W. Xiao, B. Su, onacie Power Lo Minimizaion in a Bidirecional olaed DC DC Conerer for Diribued Power Syem, EEE Tran. nd. Elecron., ol. 6, no., pp , Dec. 4. Torng-Juu (Peer) Liang (M 93 SM ) wa born in Kaohiung, Taiwan. He receied he B.S. degree in elecrophyic from aional Chiao Tung Unieriy, Hinchu, Taiwan, in 985 and he M.S. and Ph.D. degree in elecrical engineering from he Unieriy of Miouri, Columbia, MO, USA, in 99 and 993, repeciely. He i currenly he Direcor of he Green Energy Elecronic Reearch Cener, aional Cheng Kung Unieriy, Tainan, Taiwan, where he i alo a Profeor of elecrical engineering. Hi reearch inere include high-efficiency power conerer, high-efficiency lighing yem, renewable energy conerion, and power C deign. Dr. Liang i currenly an Aociae Edior of he EEE TRASACTOS O POWER ELECTROCS and he EEE TRASACTOS O CRCUTS AD SYSTEMS, and he Technical Commiee Chair of he EEE Circui and Syem Sociey Syem Power and Energy Circui and Syem Technical Commiee. Jian-Hieng Lee wa born in Miaoli, Taiwan, in 98. He receied he B.S. and M.S. degree in elecrical engineering from -Shou Unieriy, Taiwan, in 3 and 5, repeciely. He i currenly puruing he Ph.D. degree a aional Cheng-Kung Unieriy, Taiwan. Hi reearch inere include high efficiency power conerer, renewable energy conerion, elecronic balla, and high efficiency lighing yem (c) 3 EEE. Tranlaion and conen mining are permied for academic reearch only. Peronal ue i alo permied, bu republicaion/rediribuion require EEE