A Low-Cost High-Performance Interleaved Inductor-Coupled Boost Converter for Fuel Cells

energes Artcle A Low-Cost Hgh-Performance Interleaved Inductor-Coupled Boost Converter for Fuel Cells Long-Y Chang 1,, Jung-Hao Chang, Kue-Hsang Chao, * and Y-Nung Chung 1 1 Department Electrcal Engneerng, Natonal Changhua Unversty Educaton, Changhua 574, Tawan; lychang@ncut.edu.tw (L.-Y.C.); ynchung@cc.ncue.edu.tw (Y.-N.C.) Department Electrcal Engneerng, Natonal Chn-Y Unversty Technology, Tachung 4117, Tawan; op5u@gmal.com * Correspondence: chaokh@ncut.edu.tw; Tel.: +886-4-39-455 (ext. 77); Fax: +886-4-39-6 Academc Edtor: Gabrele Grand Receved: 14 June 16; Accepted: 7 August 16; Publshed: October 16 Abstract: Ths paper presents an nterleaved nductor-coupled converter for a fuel cell. It s desgned to boost a low nput voltage from a fuel cell to a specfed voltage level for DC load or hgh voltage DC lnk, thus provdng a hgh-voltage converson rato. The presented converter manly nvolves coupled nductors and capactor voltage doublers for boostng purposes, but voltage ratngs nvolved power swtches and dodes, n partcular, reman unaffected as output voltage s boosted. Usng an nterleavng trgger mechansm, ths crcut confguraton can not only suppress nput current rpple, but also reduce current ratngs power swtches. In smple terms, t s a low-cost but hgh-voltage gan converter due to a smaller number requred components and lower current and voltage ratngs power swtches. The operaton prncples and desgn steps are detaled heren, and performance smulatons are expermentally valdated at end work. Keywords: nterleaved converter; fuel cell; hgh voltage converson rato; nductor-coupled converter; DC lnk; voltage doublers 1. Introducton Despte recent plunge n ol prces, development alternatve energy sources remans a key ssue for CO emssons reducton due to global warmng and clmate change. So far, fuel cells, solar energy, and wnd power stand as examples most successfully developed renewable energy sources. Yet fuel cells have dsadvantage provdng a low output voltage, and are unable to operate n parallel wth or types energy sources [1]. Furrmore, output voltage provded by a fuel cell s found to vary wth ts load, accordng to whch a power condtoner s requred to boost output voltage to a specfed level for a DC lnked load [ 7]. Currently, re exst a wde varety boost converters n lterature. As presented n [8 1], conventonal boost converters are characterzed as beng smple n structure and easy to control, whle a major concern s damage to overheated power swtches caused by an overlong duty cycle. An solated boost converter [11,1] has same advantage as conventonal boost converters, and s desgned to provde a hgh voltage gan and to reduce voltage ratng by means output capactors connected n seres. In such confguraton, a hgh turns rato between coupled nductors leads to a hgh voltage gan, but also gves rse to a large nput current rpple, meanng that hgh current rated power swtches are requred. Consequently, prce pad reflects a rse n faclty s costs and volume. As presented n [,13], although am a hgh voltage gan can be acheved usng coupled nductors connected n seres n nductor-coupled boosters, ths confguraton creates an excessve amount parastc capactance between coupled nductors and power swtches. As a result, crcut resonance s seen and power swtches are damaged due to excessve surge voltage across and Energes 16, 9, 79; do:1.339/en9179 www.mdp.com/journal/energes

Energes 16, 9, 79 nrush current through swtches. Hence, a snubber s ntroduced nto confguraton for swtch damage preventon. Over recent years, re have been a number nterleaved boost converters publshed n lterature [14 17]. The confguratons nterleaved boost converters not only have same advantages as conventonal counterparts, but also lower current stress n nductors and power swtches usng an nterleavng mechansm, and suppress nput current rpple. They cannot be appled to hgh output voltage operaton, due to fact that y provde same voltage gan as a boost converter. In contrast, nterleaved boost converters, as presented n [18 ], have a hgh voltage gan advantage over those n [14 17] usng capactor voltage doublers, and voltage stress across power swtches are lowered accordngly. Yet y are unable to boost output voltage fuel cells to a hgh voltage level due to an nadequate voltage gan. As presented n [1], a par hgh voltage rato nterleaved DC DC converters operate n parallel, such that nput current splts nto four branches and par converters delvers power to ts load n an nterleavng manner. Even though ths move s able to successfully suppress rpples nput current and output voltage, ths parallel confguraton, as opposed to a sngle counterpart, doubles converter cost, requres a complcated control mechansm, and occupes an overszed volume, whle voltage gan remans exactly same. As presented n [4], voltage multpler cells are employed to acheve a hgh voltage gan n an nterleaved boost converter, but voltage gan can be furr mproved at cost more voltage multpler cells. In addton, ths parallel confguraton requres hgher current rated power swtches, due to an nterleaved path. Although a two-phase nterleaved converter, as presented n [], provdes same voltage gan as those n [18 ], and am voltage double can be acheved usng capactors connected n seres, ths confguraton gves rse to hgh current stress n power swtches,.e., a rse n mplementaton cost, and provdes a voltage gan nadequate for hgh output voltage applcatons. A modular hgh step-up nterleaved boost converter, presented n [3], s developed as a combned form an nductor-coupled boost converter, as n [,13], and an nterleaved voltage double boost converter, as n [18 ]. Ths confguraton provdes a hgh voltage gan by use coupled nductors connected n seres wth capactor voltage doublers, whch nvolves a larger number components, hgher current rated power swtches and hgher voltage rated dodes. The coupled nductor connected n seres was adopted n [4] to acheve a hgh voltage converson rato, but t ncreased voltage ratng and current ratng swtches. In addton, when leakage nductance coupled nductor and stray capactance swtches produce resonance, t wll cause excess surge voltage and nrush current to swtches. As a result, swtches wth hgher voltage and current ratng were needed. As for [5], t operated two sets capactor voltage doublers, adoptng nterleaved control. By dong so, not only was voltage gan converter ncreased, but nput current rpple and voltage ratng were reduced. However, t caused a problem by ncreasng current stress swtches. Hence, t s mportant to develop a hgh-voltage gan converter wth low voltage/current power swtches for keepng faclty costs down. Ths paper presents an nterleaved nductor-coupled converter as a way to resolve above-stated problems. It s desgned to provde a hgh voltage converson rato, usng coupled nductors and capactor voltage doublers. In ths manner, voltage ratngs nvolved power swtches and dodes stay unaffected as output voltage s boosted. In addton, current stress on coupled nductors and power swtches can be lowered, and rpple level n nput current can be suppressed usng an nterleavng mechansm.. Fuel Cells Among fuel cells consstng varous types electrolytes, a proton exchange membrane (PEM) fuel cell s most common type seen n practcal applcatons due to advantages : (1) a low operatng temperature leadng to a hgh speed swtchng; () a low operatng temperature for safety concerns; (3) easy modularzaton and a superor response to load varaton; and (4) low emssons as well as a hgh converson rato. In lght ths, a par Horzon (H-5XP) PEM fuel cells, as specfed n Table 1 [6], s adopted as electrcty source n ths work.

Energes 16, 9, 79 3 Energes 16, 9, 79 3 Table 1. Specfcatons a Horzon (H-5XP) proton exchange membrane (PEM) fuel. Table 1. Specfcatons a Horzon (H 5XP) proton exchange membrane (PEM) fuel. Parameter Parameter Specfcatons Specfcatons Number Number Cells Cells 3 3 Rated Rated Power Power 5 W 5 W Rated Rated Performance 18 V@7.8 18 V@7.8 A A Operatng Operatng Voltage Voltage Range Range 3 V 3 V External External Temperature Temperature 35 C 35 C Reactants Reactants Hydrogen Hydrogen and Ar Max Stack Temperature 63 and Ar C Max Stack Temperature 63 C Hydrogen Pressure 7. 9.4 PSI Hydrogen Pressure 7. 9.4 PSI Hydrogen Flow Rate at Max Output 5.86 L/mn Hydrogen Stack Sze Flow Rate at Max Output 5.86 L/mn 13 3 5 mm Stack Weght Sze 13 3 3.9 kg5 mm Weght Hydrogen Purty Requrement 3.9 kg 99.99% dry Hydrogen Hydrogen Purty Requrement 99.99% dry Hydrogen 3. Inductor Coupled Interleaved Converter wth Hgh Voltage Converson Rato 3. Inductor Coupled Interleaved Converter wth Hgh Voltage Converson Rato As a low-voltage, hgh-current power source, a fuel cell requres a step-up converter for As a low voltage, hgh current power source, a fuel cell requres a step up converter for parallel parallel operaton wth or types power sources. Hence, ths paper presents an nterleaved operaton wth or types power sources. Hence, ths paper presents an nterleaved nductorcoupled converter, as llustrated n Fgure 1. It manly nvolves a par boost converters, a flyback nductor-coupled converter, as llustrated n Fgure 1. It manly nvolves a par boost converters, a flyback converter, and a clamp capactor. Desgned wth a hgh voltage converson rato, ths converter, and a clamp capactor. Desgned wth a hgh voltage converson rato, ths crcut crcut confguraton requres a low duty cycle, gvng rse to a consderable reducton n voltage confguraton requres a low duty cycle, gvng rse to a consderable reducton n voltage ratngs ratngs power swtches, n conducton and swtchng loss power swtches. Besdes, nput power swtches, n conducton and swtchng loss power swtches. Besdes, nput current current rpple can be suppressed and current ratng power swtches can be reduced usng rpple can be suppressed and current ratng power swtches can be reduced usng an an nterleavng mechansm. nterleavng mechansm. Fgure Fgure 1. 1. Confguraton Confguraton presented presented nterleaved nterleaved nductor-coupled nductor coupled boost boost converter. converter. good desgn a boost converter wth coupled nductor needs to acheve hgh voltage gan, A good desgn a boost converter wth coupled nductor needs to acheve hgh voltage gan, low voltage and current ratngs swtches, low voltage ratng dodes, and mnmum addtonal low voltage and current ratngs swtches, low voltage ratng dodes, and mnmum addtonal elements. Table lsts expected good desgn performance proposed boost converter wth elements. Table lsts expected good desgn performance proposed boost converter wth coupled nductors. coupled nductors.

Energes 16, 9, 79 4 Table. The expected good desgn performance proposed boost converter wth coupled nductor. Energes 16, 9, 79 4 Voltage Ratng Current Ratng Voltage Gan Voltage Number Number Table. The expected Swtches good desgn Number performance Swtches proposed boost converter wth coupled nductor. Ratng Inductors Capactors Dodes V o /V Voltage V ds1, VRatng ds Current I ds1 Ratng I ds Dodes Voltage Voltage Gan Number Number Number Swtches Swtches Vo V V I Ratng V Inductors I Dodes o Capactors 4 Dodes Vo/V Vds1, Vds Ids1 Ids 4 4 4 4. Operaton Prncple 4. Operaton Prncple Ths secton s devoted to mode analyss on presented nterleaved nductor-coupled Ths secton s devoted to mode analyss on presented nterleaved nductor coupled converter. There are four operaton modes nvolved n ths converter, and respectve voltage converter. There are four operaton modes nvolved n ths converter, and respectve voltage and and current waveforms across and through components are llustrated n Fgure. For llustraton current waveforms across and through components are llustrated n Fgure. For llustraton purposes, purposes, duty duty cycle cycle s set s set to to greater greater than than.5.5 n n contnuous contnuous conducton conducton mode mode (CCM), (CCM), and and followng followng assumptons assumptons are are made. made. V 1 D V 1 D V co1 N1 V N 11 V co N V N 1 Fgure. Respectve waveforms current through and voltage across components n Fgure. Respectve waveforms current through and voltage across components n converter n Fgure 1. converter n Fgure 1.

Energes 16, 9, 79 5 Energes 16, 9, 79 5 (1) All components nvolved are deal, meanng that parastc capactance and (1) All conducton components resstance nvolved each are swtch deal, and meanng voltage that drop parastc across capactance a forward based and dode conducton are not resstance taken nto account. each swtch and voltage drop across a forward-based dode are not taken () nto For smplfcaton account. purposes, t s assumed that Lm1 = Lm = L, and Lm1 = Lm. Hence, vlm1 = vlm = vl and Lm1 = Lm = Lm = 1/. () For smplfcaton purposes, t s assumed that L m1 = L m = L, and Lm1 = Lm. Hence, v Lm1 = v Lm = v L and Lm1 = Lm = Lm = 1/. 4.1. Mode 1 (t t1) 4.1. Mode The 1 equvalent (t t 1 ) crcut n ths mode s llustrated n Fgure 3. Both S1 and S are swtched on, and nput The equvalent voltage V crcut s appled n ths to mode Lm1 and s Lm. llustrated Wth both n Fgure nductors 3. Both as energy S 1 and Sstorage are swtched devces, on, Lm1 and and Lm nput rse lnearly voltagewth V stme, appled expressed to L m1 as: and L m. Wth both nductors as energy storage devces, Lm1 and Lm rse lnearly wth tme, expressed as: dlm 1 L V (1) m1 d dt L Lm1 m1 = V dt (1) dlm L V () m d L Lm dt m = V dt () The voltage drops across reverse based dodes D1 D4 are respectvely descrbed as: The voltage drops across reverse-based dodes D 1 D 4 are respectvely descrbed as: N1 vd1 VCo 1 v D1 = V Co1 + V (3) N11 1 V (3) N 11 vd VCo v D = V Co + V (4) N 1 V N (4) 1 v D3 vd= 3 V V Co3 3 V (5) c c1 1 (5) v V (6) v D4 D4= V c1 c1 (6) The energy s s released from output capactors CCo1 Co3 o3 toward load. Fgure 3. Equvalent crcut n Mode 1. Fgure 3. Equvalent crcut n Mode 1.

Energes 16, 9, 79 6 Energes 16, 9, 79 6 4.. Mode (t 1 t ) 4.. Mode (t1 t) The equvalent crcut n ths mode s llustrated n Fgure 4. S 1 s swtched f, whle S stays swtched The on. equvalent Meanwhle, crcut n Lm1 decreases ths mode lnearly s llustrated wth tme, n Fgure formulated 4. S1 s as: swtched f, whle S stays swtched on. Meanwhle, Lm1 decreases lnearly wth tme, formulated as: d L Lm1 m1 d = dt V c1 (7) Lm1 L V V (7) m1 c1 dt The stored nductve energy s released by way D 4 to clamp capactor C 1. In same The stored nductve energy s released by way D4 to clamp capactor C1. In same manner, energy s released va D 1 to output capactor C o1 due to reversed polarty N 1, manner, energy s released va D1 to output capactor Co1 due to reversed polarty N1, and output voltage across C o1 s expressed as: and output voltage across Co1 s expressed as: V Co1 = N1 1(V c1 V ) (8) VCo 1 11 ( Vc 1 V ) (8) N 11 Furrmore, L m serves as an energy storage devce as n Mode 1, and Lm s gven as: Furrmore, Lm serves as an energy storage devce as n Mode 1, and Lm s gven as: d L m dlm L = dt V (9) (9) m dt The The voltage voltage drops drops across across reverse-based reverse based dodes dodes D and D 3 are respectvely expressed as: D and D3 are respectvely expressed as: v D = + N v (1) D VCo V N 1 (1) 1 v D3 v = V Co3 V c1 (11) (11) D3 Co3 c1 4.3. 4.3. Mode Mode 3 (t (t t3) t 3 ) Fgure 4. 4. Equvalent crcut n n Mode.. The equvalent crcut n ths mode s llustrated n Fgure 5. As n Mode 1, S1 and S The equvalent crcut n ths mode s llustrated n Fgure 5. As n Mode 1, S both are 1 and S both swtched on, and nput voltage V s appled to nductors Lm1 are swtched on, and nput voltage V and Lm. Consequently, s appled to nductors L m1 and L m. Consequently, currents currents through through nductors, nductors, as as gven gven n n Equatons Equatons (1) (1) and and (), (), rses rses lnearly lnearly wth wth tme, tme, and and all all dodes are reverse based, as descrbed n Equatons (3) (6). Hence, electrcty s delvered from Co1 Co3 to load.

Energes 16, 9, 79 7 dodes are reverse-based, as descrbed n Equatons (3) (6). Hence, electrcty s delvered from C o1 C o3 to load. Energes 16, 9, 79 7 Fgure 5. 5. Equvalent crcut n n Mode 3. 3. 4.4. 4.4. Mode Mode 4 (t (t3 t4) 3 t 4 ) The equvalent crcut n ths mode s llustrated n Fgure 6. S1 remans swtched on, whle S The equvalent crcut n ths mode s llustrated n Fgure 6. S s 1 remans swtched on, whle S swtched f. In meantme, Lm1 and Lm s swtched f. In meantme, rses and decreases lnearly wth tme respectvely, Lm1 and Lm rses and decreases lnearly wth tme respectvely, descrbed descrbed as: as: d L d Lm1 m1 = V Lm1 L dt (1) (1) m1 dt d L Lm m d = V Lm L dt + V c1 V Co3 (13) m V Vc 1 VCo3 (13) Electrcty s released to C o3 va C 1 and Ddt 3, owng to a reversal voltage polarty across L m. Lkewse, Electrcty energy s released s released to to Co3 va CC1 o by and way D3, owng D due to a toreversal voltage polarty voltage reversal polarty across across NLm., and Lkewse, voltage energy drop across s released C o sto expressed Co by way as: D due to voltage polarty reversal across N, and voltage drop across Co s expressed as: V Co = N (V N Co3 V c1 V ) (14) 1 VCo ( VCo3 Vc 1 V ) (14) N1 The voltage drops across D 1 and D 4 are respectvely expressed as: The voltage drops across D1 and D4 are respectvely expressed as: v D1 = V Co1 + N 1 V N () 1 vd 1 VCo 1 11 V () N11 v D4 = V Co3 (16) v V (16) D4 Co3

Energes 16, 9, 79 8 Energes 16, 9, 79 8 Fgure Fgure 6. 6. Equvalent Equvalent crcut crcut n n Mode Mode 4. 4. Followng nductor volt second balance prncple, combned use Equatons (1), (), (7), Followng nductor volt second balance prncple, combned use Equatons (1), (), (7), and (13) gves: and (13) gves: V DT VDT + (V ( V V c1 V) ) (1 DT D)T ) = (17) c1 V DT VDT + (V + ( VV c1 V V Co3 ) (1 DD)T ) T = (18) c1 Co3 Back substtuton Equaton (17) nto Equaton (18) now gves: ( V V V V V ) (1 D) T (19) ( V + V c1 + c1v + V c1 c1 V Co3 3) (1 D)T = (19) Rearrangement Equaton (19) gves voltage drop across clamp capactor: Rearrangement Equaton (19) gves voltage drop across clamp capactor: Vco3 V () c1 V c1 = V co3 () Substtuton Equaton () nto er Equaton (18) or Equaton (19) gves voltage drop across Substtuton output capactor Equaton Co3: () nto er Equaton (18) or Equaton (19) gves voltage drop across output capactor C o3 : V Co3 VCo= 3 V (1) 1 D VVCo1 VCo3 Co3 are aresummed summedas as total totaloutput outputvoltage, formulated formulatedas: as: V V V V () V o = ov Co1 Co+ 1 V Co + V Co3 3 () Substtuton Equatons (8), (14), and (1) nto Equaton () gves: Substtuton Equatons (8), (14), and (1) nto Equaton () gves: N DV N DV V 1 V o (3) V o = N 1 DV N 1 D N 1 D N 11 1 11 1 D + N DV N 1 1 D + V (3) 1 D or, expressed n a concse form: or, expressed n a concse form: [( ) ] N1 N 1 11 + N N D 1 + V o = D V N N 11 1 (4) V 1 D (4) V o As a graphc representaton Equaton (4), 1 Da famly voltage gan-duty cycle curves s llustrated n Fgure 7, wth N = N As a graphc representaton 1 /N Equaton 11 = N /N (4), 1 as a parameter. a famly voltage gan duty cycle curves s llustrated n Fgure 7, wth N = N1/N11 = N/N1 as a parameter.

Energes 16, 9, 79 9 Energes 16, 9, 79 9 1 N1 N N 9 N11 N1 8 7 6 5 4 3 1.5.6.7.8.9 1 5. Performance Comparson Fgure 7. A famly voltagegan duty gan-duty cycle curves wth N as a parameter. To demonstrate performance superorty ths work, Table 3 gves a comparson on voltage gan, voltage/currentratngs ratngs power power swtches, voltage voltage ratng ratng dodes, dodes, and and numbers numbers requred requred nductors, nductors, capactors, capactors, and anddodes dodes n nths ths proposaland and or representatve peces work [4,17,19, 5]. As can be be seen n n Table Table 3, 3, presented presented converter converter s found s found to outperform to outperform ts counterparts ts counterparts n terms n terms number number components components requred requred and and voltage voltage ratngs ratngs swtches swtches and dodes. and dodes. It alsoit meets also meets expected expected performance performance lsted n lsted Table n. Table. Table 3. Performance and requrement comparson among representatve types boost converters and ths proposal. Current Voltage Voltage Voltage Ratng Gan Voltage Ratng Ratng Current Ratng Voltage Ratng Voltage Number Number Converters Gan Swtches Swtches Swtches Swtches Dodes Ratng Inductors Capactors Vds1, V Vds V o /V ds1, V ds I ds1 I ds Dodes Inductors Capactors Vo/V Ids1 Ids Number Dodes Dodes Convertern 3 [4] n [4] 3 VV o o I I V o 1 D I 3 I V o 3 4 3 4 1 D 3 3 Converter n [17] 1 11 D V I I I Convertern [17] V I o V o V o 1 o 1 1 D Converter n [19] V o I 1 D I V Convertern [19] o I V o I V 1 D o Converter n [] V o 1 D I I V o V Convertern [] o I 1 D I V n [3] o 1 D + ND V o I V +ND(1 D) I o +ND(1 D) 3 3 4 Convertern [3] 1 D ND V o I ND(1 D) I V n [4] 1+ND V o+nv o 1 D (1 + N)I 1+N V o + NV 3 1 1 1 3 4 ND(1 D) Converter n [5] 3 V 1 ND Vo NV o 1 D I 3 Convertern [4] (1 I V o NI ) 3 3 1 D Vo NV 3 1 1 1 Proposed 1 N ND+ V o I NV converter 31 D ND+ I o V Convertern [5] o I V ND+ 4 4 1 D I o 3 3 3 3 Proposed ND V o I I NV o 6. 4 4 converter Converter Desgn 1 D ND ND The presented nterleaved nductor-coupled converter s developed as a combned form a boost 6. converter Converter and Desgn a flyback one. Table 4 lsts electrcal specfcatons boost converter. The presented nterleaved nductor coupled converter s developed as a combned form a boost converter and a flyback one. Table 4 lsts electrcal specfcatons boost converter.

Energes 16, 9, 79 1 Table 4. Desgn parameters and settngs for presented boost converter. Parameter Range nput voltage range (V n ) Output voltage (V o ) Power ratng (P o ) Swtchng frequency (f ) Specfcatons 3 V 35 V 1 W 5 khz (1) Choce nductance Turns rato L m1 to L m s specfed as 1: heren, and n substtuted nto Equaton (4), smplfed as: V o = V [4D + ] (5) 1 D For smplfcaton purposes, nevtable power loss n each component s not taken nto account, meanng that nput power completely reaches output converter,.e., V I Lm(avg) = P o (6) Substtuton turns rato and Equaton (4) nto Equaton (6) gves average nductor current: I Lm(avg) = P o = V [4D + ] V (1 D) (7) R As llustrated n Fgure, maxmum and mnmum currents through L m1 and L m can be expressed n terms average value and current swng, respectvely, as: I Lm1,(max) = P o + 1 V DT (8) V L m I Lm1,(mn) = P o 1 V DT (9) V L m For operaton n CCM, t s requested that I Lm1,(mn) be greater than zero, that s, I Lm(mn) = P o 1 V DT (3) V L m Rearrangement Equaton (3) gves lower bound nductance: L m(mn) V D P o f (31) Desgned to operate n CCM under a lght load 3 W, presented converter must drve a 4 Ω load. Accordngly, Equatons (4) and (31) gve a duty cycle (D).78 and a mnmum nductance 3 µh, respectvely. In consderaton redundancy, a 35 µh nductor s employed heren. () Choce capactance In vast majorty DC/DC converters, output s followed by a shunt capactor as a way to reduce output rpple voltage caused by on/f swtchng. Wth C o1 = C o = C o3 = C o, as llustrated n Fgure 8, t s observed that Co1 Co3 share same waveform, and change charge s gven as: Q = ( V o R o )DT = C o V o (3)

Energes 16, 9, 79 11 Energes 16, 9, 79 11 Rearrangement Equaton (3) gves: D C o = (33) o ( V( V o /V/ V o ))R R o ff (33) o o o Under arbtrary load condtons, substtuton a rpple rato below.5% to Equaton (33) gves Co C o = 5 μf. µf. Hence, a commercally avalable 47 μf/45 µf/45v capactor s employed heren. S 1 t S t co1 -V o /R o ΔQ t co -V o /R o ΔQ t co3 -V o /R o ΔQ t t t 1 t t 3 t 4 Fgure 8. 8. Swtch Swtchcontrol controlsgnals sgnalsand and current current waveforms waveforms through through output output capactors capactors over over an operatng an operatng cycle cycle (t t4). t 4 ). The above analyss ndcates an equvalent mpedance 1.5 Ω and an output voltage The above analyss ndcates an equvalent mpedance 1.5 Ω and an output voltage approxmately at an output power 1 n fuel cell. Substtuton above results nto approxmately V at an output power 1 W n a fuel cell. Substtuton above results nto Equaton (4) gves =.78, and Equaton (8) results n ILm1,(max) 41 A. Furrmore, Fgure Equaton (4) gves D =.78, and Equaton (8) results n I llustrates waveforms current through and voltage Lm1,(max) 41 A. Furrmore, Fgure drop across power swtches and llustrates waveforms current through and voltage drop across power swtches and dodes, accordng to whch commercally avalable IGBT MMG1J3U (6 V/1 A) swtches dodes, accordng to whch commercally avalable IGBT MMG1J3U (6 V/1 A) swtches (IXYS, Mlptas, CA, USA) and IQBD3E6A1 (6 V/6 A) dodes (IXYS, Mlptas, CA, USA) are (IXYS, Mlptas, CA, USA) and IQBD3E6A1 (6 V/6 A) dodes (IXYS, Mlptas, CA, USA) are employed heren. employed heren. 7. Smulaton Results 7. Smulaton Results Power smulaton (PSIM) stware smulatons are conducted on an nterleaved nductorcoupled converter wth a hgh voltage converson rato as llustrated n Fgure 9. Wth a fuel cell Power smulaton (PSIM) stware smulatons are conducted on an nterleaved nductor-coupled converter wth a hgh voltage converson rato as llustrated n Fgure 9. Wth a fuel cell output voltage output voltage V, llustrated n Fgure 1 are smulated nput and output voltage/current V, llustrated n Fgure 1 are smulated nput and output voltage/current waveforms waveforms presented DC/DC converter at an output voltage 35 V and an output power presented DC/DC converter at an output voltage 35 V and an output power 1 W. Exhbted n 1 W. Exhbted n Fgures 11 and 1 are smulated waveforms trgger sgnals for S1 and Fgures 11 and 1 are smulated waveforms trgger sgnals for S 1 and S, currents through S, currents through dodes ds1 and ds and voltage drops across power transstors vds1 dodes ds1 and ds and voltage drops across power transstors v ds1 and v ds. Presented and vds. Presented n Fgure 13 are smulated waveforms currents through coupled n Fgure 13 are smulated waveforms currents through coupled nductors L m1 and nductors Lm1 and Lm, whle n Fgures 14 17 are smulated voltage/current waveforms L m, whle n Fgures 14 17 are smulated voltage/current waveforms across/through dodes across/through dodes D1 D4, and n Fgure 18 are smulated current waveforms through capactors Co1 Co3. A good agreement s found between all above stated smulaton results and Fgure.

Energes 16, 9, 79 1 D 1 D 4, and n Fgure 18 are smulated current waveforms through capactors Co1 Co3. A good Energes 16, 9, 79 1 agreement Energes 16, s 9, found 79 between all above-stated smulaton results and Fgure. 1 Fgure 9. 9. Crcut confguraton for power smulaton (PSIM) stware smulatons. V 16V 16.5.5 14.5 14.5 14 14 avg_fc 8avg_fc 8 6 6 4 4 Vo 4 Vo 43 3 1 1 4 3 1 Io 4 Io 3 1.4.5.6.7.8.9 1.4.5.6.7.8.9 1 Fgure 1. Smulated nput and output voltage/currents at an nput voltage V, an output voltage Fgure 35 1. V, and an output power 1 W. Fgure 1. Smulated nput and output voltage/currents at an nput voltage V, V, an an output output voltage voltage 35 35 V, V, and andan an output power 1 W.

Energes 16, 9, 79 13 Energes Energes 16, 16, 9, 9, 79 79 13 13 1 1.8.8.6.6.4.4.. 8 8 S1 S1 Vds_s1 Vds_s1 6 6 4 4 4 4 Is1 Is1 3 3 1 1.9999.99994.99996.99998 1.9999.99994 Tme.99996 (s).99998 1 Fgure Fgure 11. 11. Smulated Smulated waveforms waveforms related related to to power power swtch swtch SS1. S1. 1. 1 1.8.8.6.6.4.4.. 8 8 S S Vds_s Vds_s 6 6 4 4 8 8 I(MOS) I(MOS) 6 6 4 4.9999.99994.99996.99998 1.9999.99994 Tme.99996 (s).99998 1 Fgure 1. Smulated waveforms related to power swtch S. S. Fgure 1. Smulated waveforms related to power swtch S.

Energes 16, 9, 79 14 Energes Energes 16, 16, 9, 9, 79 79 14 14 ILm1 ILm1 4 4 3 3 1 1 ILm ILm 4 4 3 3 1 1.9999.99994.99996.99998.9999.99994.99996.99998 1 13. Lm1 Fgure 13. Smulated current waveforms through coupled nductors L LLm. Lm1 and Lm.. Vd1 Vd1 1 1 5 5-5 -5 Id1 Id1 1 1 5-5 -5.9999.99994.99996.99998.9999.99994.99996.99998 1 Fgure 14. Smulated voltage and current waveforms for for dode D1. Fgure 14. Smulated voltage and current waveforms for dode DD1. 1.

Energes 16, 9, 79 Energes Energes 16, 16, 9, 9, 79 79 Vd Vd 1 1 5 5-5 -5 Id Id 1 1 5-5 -5.9999.99994.99996.99998.9999.99994.99996.99998 1 Fgure. Smulated voltage and current waveforms for dode DD.. Vd3 Vd3 8 8 6 6 4 4 - - Id3 Id3 4 4 3 3 1 1-1 -1.9999.99994.99996.99998.9999.99994.99996.99998 1 D3. Fgure 16. Smulated voltage and current waveforms for dode D 3.

Energes 16, 9, 79 16 Energes Energes 16, 16, 9, 9, 79 79 16 16 Vd4 Vd4 1 1 5 5-5 -5 Id4 Id4 4 4 3 3 1 1-1 -1.9999.99994.99996.99998.9999.99994.99996.99998 1 Fgure 17. Smulated voltage and current waveforms for dode DD4. D4. 4. 1 1 5-5 -5 1 1 5-5 -5 4 4 3 3 1 1-1 -1 Ico_1 Ico_1 Ico_ Ico_ Ico_3 Ico_3.9999.99994.99996.99998.9999.99994.99996.99998 1 Fgure 18. Smulated waveforms for output capactor current Co1 Co3. Fgure 18. 18. Smulated waveforms for for output capactor current Co1 Co1 Co3. Co3. 8. Expermental Results Ths secton s devoted to expermental valdaton PSIM smulatons on a DC/DC converter wth electrcal specfcatons lsted n Table 5. A photo realzed converter s presented n Fgure 19, and Fgure llustrates measured output voltage and current waveforms

Energes 16, 9, 79 17 8. Expermental Results Ths secton s devoted to expermental valdaton PSIM smulatons on a DC/DC converter wth electrcal specfcatons lsted n Table 5. A photo realzed converter s presented n Fgure 19, and Fgure llustrates measured output voltage and current waveforms at an output Energes 16, 9, 79 17 power 1 W. Wth an extremely low level rpples n nput and output current and at o, an output converter power was 1 found W. to Wth be an able extremely to boostlow an level nput voltage rpples n 18 nput V to and output voltage current and 35o, V. For converter comparson was found purposes, to be able waveforms to boost an nput measured voltage at P o 18 = V 35 to Wan output are presented voltage n Fgure 35 V. For 1. As comparson expected, purposes, a good performance waveforms agreement measured s seen at once Po = 35 more W between are presented smulaton n Fgure and 1. expermental As expected, results. a good Fgures performance and 3agreement llustrate s measured seen once waveforms more between trgger smulaton sgnals forand man expermental swtchesresults. S 1 and SFgures, currents and ds1 3 and llustrate ds, and measured voltage drops waveforms v ds1 and v ds. trgger As before, sgnals refor s a good man agreement swtches between S1 and S, smulaton currents ds1 and and expermental ds, and results, voltage and drops converter vds1 and vds. confguraton As before, meets re s a desgn good requrement agreement between components smulaton current/voltage and expermental ratngs. Moreover, results, Fgure and 4 llustrates converter confguraton measured current meets waveforms desgn through requrement coupled components nductorscurrent/voltage L m1 and L m, where ratngs. rpple Moreover, level Fgure nput 4 llustrates current s suppressed measured current usng an waveforms nterleavng through mechansm. coupled Fgures nductors 5 8 llustrate Lm1 and Lm, measured where current rpple level and voltage nput waveforms current through s suppressed and across usng an dodes nterleavng D 1 D 4. Amechansm. good agreement Fgures s seen 5 8 agan llustrate between measured smulaton current and and expermental voltage waveforms results. through and across dodes D1 D4. A good agreement s seen agan between smulaton and expermental results. Table 5. Electrcal specfcatons and component model numbers nvolved n mplemented Table boost 5. Electrcal converter. specfcatons and component model numbers nvolved n mplemented boost converter. Parameter Parameter Specfcaton Specfcaton Range nput voltage range (V) V = 3 V Range nput voltage range (V ) V = 3 V Output Output voltage voltage (V o ) (Vo) Vo = 35 V V o = 35 V Swtchng Swtchng frequency frequency (f ) (f) f = 5 khz f = 5 khz Power Power ratng ratng (P o )(Po) Po = 1 W P o = 1 W Coupled Coupled nductance (L m1 (Lm1,, L m Lm) ) Lm1 = Lm = LLm m1 = 35 L m μh = L m = 35 µh Turns Turns rato rato coupled coupled nductor nductor (N) (N) N = N = Clamped Clamped capactance capactance (C 1 )(C1) C1 = 47 μf C 1 = 47 µf Power Power swtches swtches (S 1,(S1, S ) S) MMG1J3U MMG1J3U (6 V/1 (6 A) V/1 A) Dodes Dodes (D 1, (D1, D, D, D 3, D3, D 4 ) D4) IQBD3E6A1 IQBD3E6A1 (6 V/6 (6 A) V/6 A) Output capactance (C o1, C o, C o3 ) C o1 C o = C o3 = 47 µf Output capactance (Co1, Co, Co3) Co1 = Co = Co3 = 47 μf Fgure 19. A photo realzed nterleaved nductor coupled boost converter. Fgure 19. A photo realzed nterleaved nductor-coupled boost converter.

Energes 16, 9, 79 18 Energes 16, 9, 79 18 Energes 16, 9, 79 18 Energes 16, 9, 79 18 Fgure Fgure. and at an power Fgure.. Measured Measured voltage voltage and and current current waveforms waveforms n n nput nput and and output output at at an an output output power power 1 Fgure 1W W for. Measured mplemented voltage boost boost and converter. current waveforms n nput and output at an output power 1W for mplemented boost converter. 1W for mplemented boost converter. Fgure 1. Measured voltage and current waveforms n nput and output at an output power Fgure Fgure 1. and at an power Fgure 35W 1. for 1. Measured Measured mplemented voltage voltage boost and and current converter. current waveforms waveforms n n nput nput and and output output at at an an output output power power 3535W W for for mplemented boost converter. 35W for mplemented boost converter. Fgure. Measured waveforms related to power swtch S1. Fgure. Measured waveforms related to power swtch S1. Fgure.. Measured waveforms related to power swtchs1. S 1.

Energes 16, 9, 79 19 Energes 16, 9, 79 19 Fgure 3. 3. Measured waveforms related to power swtch swtch S. S. Fgure Lm1 Fgure 4. 4. Measured Measured current current waveforms through coupled nductors L m1 and L m. Lm1 and Lm. Fgure 5. 5. Measured voltage and current waveforms for dode D1. D 1.

Energes 16, 9, 79 Energes 16, 9, 79 Fgure 6. 6. Measured voltage and current waveforms for dode D. D. Trgger sgnal S 1 5V 5V Trgger sgnal S v D3 1V D3 1A 1µs Fgure 7. 7. Measured voltage and current waveforms for dode D3. D 3. Fgure 8. 8. Measured voltage and current waveforms for dode D4. D 4.

Energes 16, 9, 79 1 9. Conclusons Ths paper presents an nterleaved nductor-coupled converter to boost output voltage fuel cells to a hgh voltage level and to overcome problems voltage ratngs nvolved power swtches and dodes. By usng proposed crcut scheme converter, not only was voltage gan ncreased, but voltage ratngs power swtches were also reduced. In addton, current stress on coupled nductors can be lowered, and rpple level n nput current can be suppressed by usng an nterleavng mechansm. It s valdated by smulaton and expermental means to provde a hgh voltage converson rato, boostng an nput voltage V to an output voltage 35 V. In addton, as output voltage s boosted, voltage ratng power swtches stays at V/(1 D), meanng that t has no dependence on output voltage, and current ratng s merely one half nput current. In concluson, ths paper presents a DC/DC converter wth low cost but hgh performance due to a smaller number requred components, a hgh voltage converson rato, and low voltage and current stress on power swtches. Acknowledgments: Ths paper was sponsored by Mnstry Scence and Technology, Tawan, under Grant No. MOST 14-63-E-167--ET, and authors feel deeply ndebted to Green Energy and Envronment Research Laboratores, Industral Techncal Research Insttute Tawan, for all techncal support. Author Contrbutons: The mode analyss on proposed nterleaved nductor-coupled converter was made by Long-Y Chang. Jung-Hao Chang carred out smulatons and experments proposed converter. Kue-Hsang Chao was responsble for wrtng paper and serves as correspondng author. Kue-Hsang Chao also completed components desgn proposed converter. Y-Nung Chung measures dynamc and steady-state performance proposed converter. Conflcts Interest: The authors declare no conflct nterest. References 1. Chen, Y.S.; Ln, S.M.; Hong, B.S. Expermental study on a passve fuel cell/battery hybrd power system. Energes 13, 6, 6413 64. [CrossRef]. Hseh, Y.P.; Chen, J.F.; Lang, T.J.; Yang, L.S. A novel hgh step-up DC-DC converter for a mcrogrd system. IEEE Trans. Power Electron. 11, 6, 117 1136. [CrossRef] 3. Hseh, Y.P.; Chen, J.F.; Lang, T.J.; Yang, L.S. Novel hgh step-up DC-DC converter for fuel cell energy converson system. IEEE Trans. Ind. Electron. 1, 57, 7 17. 4. Prudente, M.; Pftscher, L.L.; Emmendoerfer, G.; Romanel, E.F.; Gules, R. Voltage multpler cells appled to non-solated DC-DC converters. IEEE Trans. Ind. Electron. 8, 3, 871 887. [CrossRef] 5. Pan, C.T.; La, C.M. A hgh-effcency hgh step-up converter wth low swtch voltage stress for fuel cell system applcatons. IEEE Trans. Ind. Electron. 1, 57, 1998 6. 6. Jung, D.Y.; J, Y.H.; Park, S.H.; Jung, Y.C.; Won, C.Y. Interleaved st-swtchng boost converter for photovoltac power-generaton system. IEEE Trans. Power Electron. 11, 6, 1137 1145. [CrossRef] 7. Grötsch, M.; Mangold, M.; Kenle, A. Analyss couplng behavor PEM fuel cells and DC-DC converters. Energes 9,, 71 96. [CrossRef] 8. Walker, G.R.; Serna, P.C. Cascaded DC-DC converter connecton photovoltac modules. IEEE Trans. Ind. Electron. 4, 19, 113 1139. [CrossRef] 9. Alam, M.K.; Khan, F.H. Relablty analyss and performance degradaton a boost converter. IEEE Trans. Ind. Appl. 14, 55, 3986 3994. [CrossRef] 1. Hwang, T.S.; Park, S.Y. Seamless boost converter control under crtcal boundary condton for a fuel cell power condtonng system. IEEE Trans. Power Electron. 1, 7, 3616 366. [CrossRef] 11. Tseng, K.C.; Lang, T.J. Novel hgh-effcency step-up converter. IEEE Trans. Power Electron. 4, 1, 18 19. [CrossRef] 1. Keum, M.H.; Cho, Y.; Han, S.K. Hgh effcency voltage-clamped coupled-nductor boost converter. In Proceedngs 39th Annual Conference IEEE Industral Electroncs Socety, Venna, Austra, 1 13 November 13; pp. 88 833. 13. Ln, B.R.; Dong, J.Y. New zero-voltage swtchng DC-DC converter for renewable energy converson systems. IET Power Electron. 1, 5, 393 4. [CrossRef]

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