Integrated Three-Voltage-Booster DC-DC Converter to Achieve High Voltage Gain with Leakage-Energy Recycling for PV or Fuel-Cell Power Systems

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1 Energies 2015, 8, ; doi: /en Aricle OPEN ACCESS energies ISSN Inegraed Three-olage-Booser C-C Converer o Achieve High olage Ga wih Leakage-Energy Recyclg for P or Fuel-Cell Power Sysems Chih-Lung Shen *, Hong-Yu Chen and Po-Chieh Chiu eparmen of Elecronic Engeerg, Naional Kaohsiung Firs Universiy of Science and Technology, Kaohsiung 82445, Taiwan; s: u @nkfus.edu.w (H.-Y.C.); u @nkfus.edu.w (P.-C.C.) * Auhor o whom correspondence should be addressed; clshen@nkfus.edu.w; Tel.: ; Fax: Academic Edior: Gabriele Grandi Received: 16 July 2015 / Acceped: 1 Sepember 2015 / Published: 9 Sepember 2015 Absrac: In his paper, an egraed hree-volage-booser C-C (direc curren o direc curren) converer is proposed o achieve high volage ga for renewable-energy generaion sysems. The proposed converer egraes hree volage-boosers o one power sage, which is composed of an acive swich, a coupled-ducor, five diodes, and five capaciors. As compared wih convenional high sep-up converers, i has a lower componen coun. In addiion, he feaures of leakage-energy recyclg and swichg loss reducion can be accomplished for conversion efficiency improvemen. While he acive swich is urned off, he converer can herenly clamp he volage across power swich and suppress volage spikes. Moreover, he reverse-recovery currens of all diodes can be alleviaed by leakage ducance. A 200 W prooype operag a 100 khz swichg frequency wih 36 pu and 400 oupu is implemened o verify he heoreical analysis and o demonsrae he feasibiliy of he proposed high sep-up C-C converer. Keywords: P (phoovolaic) module; fuel cell; high sep-up converer; leakage-energy recyclg

2 Energies 2015, Inroducion In recen years, owg o he shorage of fossil fuels and he serious problems of environmenal polluion, discoverg and developg alernaive energy resources has become more and more imporan. To alleviae he problems of risg global emperaures and he serious emission of greenhouse gases, green energy sources such as phoovolaic (P) power, wd energy, or fuel cells have been he cener of aenion [1,2]. Generally, a grid-ied renewable-energy sysem needs a C bus volage fallg he range from 380 o 420, as shown Figure 1. Unforunaely, he ermal volages of P module, fuel cells, or baery se are less han 45. Tha is, hese green-energy generaion unis require a high sep-up converer o serve as a volage boosg erface beween he generaion uni and he uiliy. Figure 1. A block diagram o illusrae he grid-ied green-energy power sysem. Convenional boos converers can achieve high volage gas by means of exreme duy raio operaion [3 6]. However, his will resul large curren ripple, significan conducion loss, and heavy curren sress on power devices. Tha is, converer efficiency drops dramaically. In order o resolve his problem, converers wih ransformers, such as flyback, forward, and push-pull unis, are considered [7 10]. Even hough hose converers can sep up pu volage by adopg high urns-raio ransformers, efficiency is degraded heavily due o he copper loss of wdgs. Besides, high volage spikes caused from leakage ducance will be imposed on semiconducor devices. To improve his shorcomg, snubber circuis or acive clamp circuis are used bu hen he cos is creased. In [11 14], ransformerless high sep-up converers are proposed o miigae he aforemenioned drawbacks. Those converers have he feaures of simple srucure, high volage ga, and low cos, neverheless, he problem of volage ga flexibiliy sill exiss. In he mos curren rend, swiched capacior and coupled ducor echniques are adoped o design high sep-up converers [15 19]. Those high sep-up converers have heir own advanages and disadvanages, and resul a compromise beween power componen coun, volage ga, curren sress, volage sress, and power rag. This paper proposes a novel high sep-up converer, which corporaes hree volage boosers and hen egraes hem o one sage. Tha is, only one acive swich is used. As a resul, low componen coun, concise srucure, high volage ga, easy conrol circui design, and high efficiency are is heren feaures. Figure 2 depics he configuraion of he power sage.

3 Energies 2015, Figure 2. Power circui of he proposed high sep-up converer. This paper is organized as follows: he operaion prciple of he proposed converer is described Secion 2. Secion 3 deals wih seady-sae analysis and performance comparison, while pracical measuremens are given Secion 4. Fally, he conclusions are described Secion Operaion Prciple of he Proposed Converer For he descripion of he operaion prciple, Figure 3 shows he defiion of circui variables, volage polariy, and curren direcion. In Figure 3, he noaions and I denoe he C pu volage and curren, respecively; Lm is he magneizg ducance of he coupled ducor, while Lk sands for he associaed leakage ducance; S represens he acive power swich; C1 and C4 are swiched capaciors; C2 and C3 are boosg capaciors; 1, 2, 3, and 4 are recifier diodes; o denoes oupu diode; o and Io are described as oupu volage and curren, respecively, while R is he oupu load. In addiion, he urns raio Ns/Np is defed as n. Figure 3. efiion of volage polariy and curren direcion. Assume ha he converer is operaed conuous conducion mode (CCM). The operaion prciple can be divided o six sages over one swichg period. Figure 4 shows he correspondg equivalen circuis of he six sages and Figure 5 depics he associaed concepual waveforms. The operaion prciple is described he followg paragraphs sage by sage: Sage 1 [0~1]: A ime = 0, swich S is urned on. iodes 1, 2 and 4 are reversely biased, bu 3 and o are forward biased. In his ime erval, he curren of leakage-ducor ilk creases learly and seeply. The energy sored magneizg-ducor Lm is released o he oupu via o and booss capacior C2 via 3. Meanwhile, he curren followg hrough o, io, is decreasg. Unil he curren io drops o zero, his operaion sage ends. There is no reverse-recovery loss on diode o. Figure 4a shows he equivalen circui of his sage.

4 Energies 2015, Sage 2 [1~2]: This sage begs a ime = 1, of which equivalen circui is shown Figure 4b. Swich S remas closed. iodes 1, 3 and o are reversely biased, bu 2 and 4 are forward biased. In his ime erval, he magneizg-ducor Lm and leakage-ducor Lk absorb energy from he C source. The swiched capacior C1 is charged by he secondary of he coupled ducor and capacior C3, while he oher swiched capacior C4 is by he secondary of he coupled ducor and capacior C2. urg his sage, only he oupu capacior Co provides energy o he load R. When swich S is urned off, operaion of his converer eners o he nex sage. Sage 3 [2~3]: Swich S is urned off a = 2. urg his sage, diodes 1, 2 and 4 are on-sae, bu diodes 3 and o are reversely biased. In his ime erval, he energy of leakage-ducor Lk releases o he parasiic capacior of swich S and hus, swich volage creases. When he volage across he parasiic capacior is higher han ha of boosg capacior C3, diode 1 becomes forward and his operaion sage is compleed. Figure 4c illusraes he correspondg equivalen of Sage 3. Sage 4 [3~4]: Swich S is sill kep off-sae over he period of Sage 4. iodes 2, 3 and o are reversely biased, bu diodes 1, and 4 are forward bias, as shown Figure 4d. The boosg capacior C3 is charged by magneizg-ducor Lm and leakage-ducor Lk. Tha is, leakage energy of Lk is recycled o C3 and he volage across acive swich is clamped by C3, which suppresses volage spike effecively. A he momen he volage polariy of magneizg-ducor Lm changes, his sage is fished. Sage 5 [4~5]: The equivalen circui is illusraed Figure 4e. Swich S remas off. The saus of diodes 1, 3 and o are on bu 2 and 4 off. In his ime erval, he energy of magneizg-ducor Lm is dumped o ideal ransformer, oupu ermal, and capacior C3 simulaneously. The secondary side of coupled ducor charges he boosg capacior C2 via diode 3. A he same ime, he oupu volage is sacked by pu volage, coupled ducor, and capaciors C1 and C4. Sage 6 [5~6]: This sage begs as C3 sops chargg. The diode 1 becomes reversely biased. The correspondg equivalen circui is shown Figure 4f. The energy sored Lm keeps dumpg energy o C2 via ideal ransformer. When power swich is urned on aga, his sage ends and converer operaion over one swichg cycle is compleed. (a) Figure 4. Con.

5 Energies 2015, C 2 L k N p C 1 N s 3 4 L m 1 2 C 4 o S C 3 C o R o (b) C 2 L k N p C 1 N s 3 4 L m 1 2 C 4 o S C 3 C o R o (c) C 2 L k N p C 1 N s 3 4 L m 1 2 C 4 o S C 3 C o R o (d) C 2 L k N p C 1 N s 3 4 L m 1 2 C 4 o S C 3 C o R o (e) C 2 L k N p C 1 N s 3 4 L m 1 2 C 4 o S C 3 C o R o (f) Figure 4. Equivalen circuis of he proposed converer. (a) Sage 1; (b) Sage 2; (c) Sage 3; (d) Sage 4; (e) Sage 5; and (f) Sage 6.

6 Energies 2015, T s v gs T s (1-)T s i Lm i Lk i L2 i 1 i 2 i 3 i 4 i o Mode I Mode II Mode III Mode I Mode Mode I Figure 5. Concepual key waveforms of he proposed converer. 3. Seady-Sae Analysis of he Proposed Converer To simplify he circui analysis, he ransien sae of he circui is ignored. In addiion, some assumpions are made as follows: (1) The values of all capaciors are large enough so ha volages across all capaciors are considered as consan; (2) All semiconducor componens he power circui are ideal; (3) The magneizg ducance is much greaer han leakage ducance. The fluence of he leakage ducance can be negleced. Tha is, he couplg coefficien of coupled ducor k is equal o uniy; (4) Equivalen series resisance of coupled ducor is ignored;

7 Energies 2015, (5) The acive swich is closed for Ts and open for (1-)Ts; (6) The converer is operaed CCM. Accordg o he precedg assumpions, Figure 4b is referred while swich S closed and Figure 4e is referred while swich S open erivaion of olage Ga To derive he volage ga of o o, he volages of C1, C2, C3, and C4 have o be calculaed advance. When acive swich S is urned on, referrg o Figure 4b and neglecg Lk, he volage across he secondary wdg of he coupled ducor, vl2(on), is: v L2( on) n (1) Therefore, he magniudes of he volages C1 and C4 can be expressed as: C1 n C3 (2) and: C 4n C2 (3) respecively. Wih respec o C2 and C3, he sae of swich off is conaced and he equivalen circui shown Figure 4e is referred. Similarly, accordg o he assumpions, he leakage ducance Lk Figure 4e is also negleced. The circui behaviors ha pu volage forwards energy o he capaciors C2 and C3 are similar o hose of flyback and boos converers, respecively. Therefore, he volages C2 and C3 can be expressed as: C2 n 1 (4) and: C3 1 1 (5) Subsiug Equaions (4) and (5) o Equaions (2) and (3), urn, yields: C1 1 n n 1 (6) and: C4 n 1 From Figure 4e, i can be found ha he oupu volage is he sum of, C1, C4, and he volages across Np and Ns. Thus, he followg relaionship holds: 1 n o 2 n 1 1 Rearrangg Equaion (8), one can fd he volage ga of he proposed high sep-up converer: (7) (8)

8 Energies 2015, M CCM o 2(1 n) 1 (9) To furher undersand he volage ga performance of he proposed converer, Figure 6 shows he volage ga versus duy cycle under various urns raios n. I dicaes ha when he duy cycle equals 0.5, he converer achieves an oupu volage sixeen imes of he pu volage under he urns raio of 3. As compared wih oher high sep-up converers he lieraure [19 21], he proposed converer has a higher volage ga han ha of he convenional converers if n = 1.5, which is shown Figure 7. olage Ga n = 1 n = 2 n = 3 uy Cycle Figure 6. Illusraion of volage ga versus duy cycle under differen urns raios. olage Ga Proposed Converer Converer Inroduced [19] Converer Inroduced [20] Converer Inroduced [21] uy Cycle Figure 7. olage ga comparison among he proposed converer and convenional converers [19 21] olage Sress of Power evice olage sress of power devices is an imporan parameer for choosg power semiconducor devices. A power semiconducor device wih lower volage sress will herenly have a lower on-sae resisance or forward volage, which domaes converer efficiency. The volage sresses across 1, 3 and o are deermed as acive swich is closed. On he conrary, he volage sresses of S, 2 and 4 are deermed as acive swich is open. When he swich is an on-sae, referrg o Figure 4b he volages across 1 and 3 are equal o C3 and C4, respecively. Therefore, he volage sresses 1,sress and 3,sress can be esimaed as:

9 Energies 2015, and: 1, sress 1 1 n 1 3, sress (10) (11) Meanwhile, he oupu diode endures a volage equal o o C3 + C4, ha is: o, sress 1 n 1 (12) Afer swich S is urned off, he volage of diode 2 will be clamped o C1 vl2, as shown Figure 4e. From Equaion (6), he susaed volage 2,sress is: 1 n 1 2, sress In addiion, durg off-ime erval, he blockg volages of S and 4 are C3 and C4, respecively, so ha: n 1 4, sress (13) (14) and: 3.3. Curren on Power evices ds, sress 1 1 (15) Sce leakage ducance is negleced, he equivalen circuis of Sage 2 and Sage 5, as shown Figure 4b,e are considered for swich on and off, respecively. Based on he amp-second balance heorem, he followg relaionship is suiable for any capacior he converer: IC, onsaeton sae IC, off saetoff sae 0 (16) In Equaion (16). IC,on-sae and Ton-sae sand for capacior curren and ime period durg on-sae, while IC,off-sae and Toff-sae are for off-sae. The raio of oupu curren o pu curren is reciprocal o ha of oupu volage o pu volage. From Equaion (9), one can fd: Io 1 (17) I 2(1 n) The currens of diodes 1, 3 and o can be esimaed as he swich is open. Referrg o Figure 4e and derivg wih Equaions (16) and (17), one can oba he average curren followg hrough 1, 3 and o: 1 1 I 1 I 3 I I I o 1 o 2(1 n) (18) Wih a similar derivaion procedure, while he swich is closed and Figure 4b is referred, he average currens of 2 and 4 can be found as:

10 Energies 2015, I 1 I I I 2(1 n) o 2 4 (19) Owg o capaciors C2 and C3 dischargg oward C1 and C4 durg on-sae erval, he average curren of swich S, Ids, is expressed as: Ids ILm (1 n) I2nI 4 (20) Equaion (20) reveals ha he ILm has o be known advance for he deermaion of Ids. From Kirchhoff s curren law (KCL), he pu curren is he sum of magneizg curren and he curren followg hrough ideal ransformer. Tha is: 2(1 n) I Lm [ I n( I2 I4)] +[( I n( I3+ Io )](1 ) I Io (21) 1 Subsiug Equaions (18), (19) and (21) o Equaion (20), he average curren of power swich S can be readily obaed as: I n I n I ds (1 ) o 2(1 n ) (22) 3.4. esign of Energy Sorage Componen To ensure ha he proposed converer can operae CCM, he mimum magneizg ducance has o be calculaed. Over whole swich-on period, he ne change magneizg curren, ΔiLm, can be expressed as: i Lm Ts L (23) m The boundary conducion mode (BCM) occurs when: 1 ILm i Lm 0 (24) 2 Subsiug Equaions (9), (17), (21) and (23) o Equaion (24) one can hen oba he mimum value of magneizg ducance for CCM operaion, Lm,m, as follows: L 2 (1 ) Ro m,m Ts 2 2ILm 8 f(1 n) Figure 8 illusraes he relaionship beween Lm and duy cycle under he condiions ha urns raio n = 1.5, swichg frequency fs = 100 khz, and he load resisance Ro = 3.2 kω. (25)

11 Energies 2015, Lm Inducance (mh) CCM CM L m,m Figure 8. Illusrag he relaionship beween magneizg ducance Lm and duy raio. Even hough a larger capaciance can resul a lower volage ripple, i creases cos. Adopg an appropriae capaciance for he converer is necessary. The capaciance is found by: q C v C uy Cycle where Δq is he change charge and ΔvC is he accompanied volage variaion. urg he ime erval when S is off, capaciors C2 and C3 are charged by he currens of I3 and I1, respecively. Accordgly, from Equaions (18) and (26), he followg relaionships hold: I3 IoTs Io C2 (1 ) Ts (27) v v v f C2 C2 C2 (26) and: C I IT I T v v v f 1 o s o 3 (1 ) s C3 C3 C3 (28) Opposie o he charge behavior of C2 and C3, boh capaciors C1 and C4 discharge wih he curren IO. Also, one can fd C1 and C4 from Equaions (18) and (26) wih he same procedure as for C2 and C3, and hen have: Io IoTs Io C1 (1 ) Ts (29) v v v f C1 C1 C1 and: C 4 I I T I (1 ) T v v v f o o s o s C4 C4 C4 (30) Wih regard o Co, he swich off erval is also considered. The magniude of capacior curren ICo is he difference beween load curren Io and oupu diode curren Io. Therefore, Co can be compued by: ( Io Io) I (1 ) ots Io Co Ts v v v f (31) Co Co Co

12 Energies 2015, Performance Comparison Performance comparison of he proposed converer wih oher high sep-up converers is summarized Table 1. The proposed converer has a lower power componen coun. Tha is, i is cos-effecive. In addiion, higher volage ga can be achieved. If he duy raio is 0.5 and urns raio is 1, he proposed converer has a volage ga of 8 and he oher wo high sep-up converers [19 21] are 6, 7 and 5 urn. Even hough he converer can accomplish higher volage ga, is volage sress across power swich is he lowes. This reveals ha a power swich wih low on-sae resisance can be adoped he converer for power loss reducion. From Table 1, i also can be seen ha he swichg loss of he converer is small, because he swich volage off-ime erval is clamped o C3. Table 1. Performance comparison of he proposed converer wih oher high sep-up converers. High sep-up converers Converer roduced [19] Converer roduced [20] Converer roduced [21] Proposed converer olage ga 2 n( n1) 1 2n n 1 ( n2n3) 2(1 n) n iodes Capaciors wdgs o olage sress on swich 2 n( n1) 1 2n n 1n2 n3 2(1 n) Conducion loss small middle small small Swichg loss small middle middle small 4. Experimenal Resuls To verify he proposed converer, a prooype is buil, wih he specificaions and parameers lised Table 2. In he prooype, semiconducor devices will domae circui losses. Their deails are discussed. The power MOSFET, IRFSL4615PbF, is seleced o serve as acive swich for conrollg he curren flow, of which maximum on-sae resisance RS(on) is only 42 mω. BYW29E-200 is employed as diode 1, of which he forward volage is and he reverse recovery ime is 25 ns. Wih regard o diodes 2, 3, 4, and o, he ulrafas recifier 8ETH03PbF is considered, which has 1.25 forward volage and 35 ns reverse recovery ime. Figure 9a shows he measured volage waveforms of he power swich and associaed conrol gae signal. The swich blocks a volage of 75, which mees he heoreical analysis Secion 3. Figure 9b is he diode currens of i2 and i4, while i0 and i3 are shown Figure 9c. From Figure 9b,c i is proven ha 2 and 4 are forward biased when he swich is closed bu 3 and o are forward biased while he swich is open. Figure 9e depics he waveforms of i1 and he conrol gae signal, which illusrae ha here is no reverse recovery curren problem diode 1. olages across C3 and Co are shown Figure 9e which oupu volage and C3 are kep a 400 and 72, respecively. This is consisen wih Equaions (5) and (9). To exame he converer ransien response, load changes from half load o full load and from full load o half load are carried ou. Figure 9f is he correspondg measuremen, from which i can be observed ha he proposed converer performs fas response and can provide a consan high volage even if under sep load change. o o o

13 Energies 2015, Figure 10 is he measured efficiency of he prooype. The maximum efficiency is up o 97.1% and an efficiency of 94.9% is achieved a full load. v gs v ds (a) v gs o i 2 i 4 (b) v gs i 3 i o (c) Figure 9. Con.

14 Energies 2015, v gs i 1 (d) o C3 (e) (f) Figure 9. Experimenal resuls a 200 W: (a) Power swich volage waveforms (vgs: 10 /div; vds: 50 /div; ime: 2 μs/div); (b) iode currens i2 and i4, (vgs: 10 /div; i2: 2 A/div; i4: 2 A/div; ime: 2 μs/div); (c) iode currens i3 and io, (vgs: 10 /div; i3: 2 A/div; io: 2 A/div; ime: 2 μs/div); (d) iode curren i1, (vgs: 10 /div; i1: 2 A/div; ime: 2 μs/div); (e) Waveforms of o and C3, (o: 100 /div; C3: 50 /div; ime: 2 μs/div); and (f) Sep change beween half load and full load, (o: 200 /div; Po: 200 W/div; Io: 500 ma/div; ime: 1 s/div).

15 Energies 2015, Table 2. Specificaions of he prooype. Symbols alues & Types (Inpu volage) 36 o (Oupu volage) 400 P o (Raed power) 200 W f s (Swichg frequency) 100 khz L m (Magneizg ducance) 55 μh L k (Leakage ducance) 1.03 μh n (Transformer urns raio) 1:1.6 C 1 and C 4 (Capaciance) 33 μf C 2 and C 3 (Capaciance) 22 μf C o (Capaciance) 82 μf S (Acive swich) IRFSL4615PbF (150 /33 A) 1 (iode) BYW29E-200 (200 /8 A) 2, 3, 4, and o (iodes) 8ETH03PBF (300 /8 A) Efficiency (%) P o (W) Figure 10. Measured efficiency of he proposed converer. 5. Conclusions This paper proposes a C-C high sep-up converer for renewable-energy generaion sysems. The proposed converer can achieve higher volage ga hough i needs fewer power componens. The energy sored he leakage ducor can be recycled and he volage power swich can be clamped o a low volage so as o improve converer efficiency and suppress volage spikes. Accordgly, low on-sae power swiches and Schoky diodes can be employed. Fally, a prooype is buil o validae he converer. Pracical measuremens have demonsraed he feasibiliy and correcness of he proposed high sep-up converer. Acknowledgmens The auhors graefully acknowledge fancial suppor from he Misry of Science and Technology, Taiwan under conrac No. MOST E

16 Energies 2015, Auhor Conribuions Chih-Lung Shen and Hong-Yu Chen conceived and designed he circui. Hong-Yu Chen performed he research and analyzed daa wih guidance from Chih-Lung Shen. Hong-Yu Chen and Po-Chieh Chiu wroe he manuscrip, and hen Chih-Lung Shen revised for he publicaion. Conflics of Ineres The auhors declare no conflic of eres. References 1. Wang, Z.; Li, H. Inegraed MPPT and bidirecional baery charge for P applicaion usg one muliphase erleaved hree-por C-C converer. In Proceedgs of he Applied Power Elecronics Conference and Exposiion, For Worh, TX, USA, 6 11 March 2011; pp Eid, A. Uiliy egraion of P-wd-fuel cell hybrid disribued generaion sysems under variable load demands. In. J. Elecr. Power Energy Sys. 2014, 62, Lu,.C.; Cheng, K.W.; Lee, Y.S. A sgle-swich conuous-conducion-mode boos converer wih reduced reverse-recovery and swich losses. IEEE Trans. Ind. Elecron. 2003, 50, Bryan, B.; Kazimiercuuk, M.K. olage-loop power sage ransfer funcions wih MOSFET delay for boos PWM converer operag CCM. IEEE Trans. Ind. Elecron. 2007, 54, a Silva, E.S.; Barbosa, L..R.; ieira, J.B.; de Freias, L.C.; Farias,.J. An improved boos PWM sof-sgle-swiched converer wih low volage and curren sresses. IEEE Trans. Ind. Elecron. 2001, 48, Jovanovic, M.M.; Jang, Y. A new sof-swiched boos converer wih isolaed acive snubber. IEEE Trans. Ind. Appl. 1999, 35, Roh, C.W.; Han, S.H.; Youn, M.J. ual coupled ducor fed isolaed boos converer for low pu volage applicaions. Elecron. Le. 1999, 35, Papanikolaou, N.P.; Taakis, E.C. Acive volage clamp flyback converers operag CCM mode under wide load variaion. IEEE Trans. Ind. Elecron. 2004, 51, Wang, C.M. A novel ZCS-PWM flyback converer wih a simple ZCS-PWM commuaion cell. IEEE Trans. Ind. Elecron. 2008, 55, L, B.R.; Hsieh, F.Y. Sof-swichg zea-flyback converer wih a buck-boos ype of acive clamp. IEEE Trans. Ind. Elecron. 2007, 54, Yang, L.S.; Liang, T.J.; Chen, J.F. Transformerless C-C converer wih high sep-up volage ga. IEEE Trans. Ind. Elecron. 2009, 56, Axelorod, B.; Berkovic, Y.; Ioovici, A. Transformerless C-C converers wih a very high C le-o-load volage raio. In Proceedg of he 2003 Inernaional Symposium on Circuis and Sysems, Bangkok, Thailand, May 2003; olume 3, pp. III-435 III Shu, L.J.; Liang, T.J.; Yang, L.S.; L, R.L. Transformerless high sep-up C-C converer usg cascode echnique. In Proceedgs of he 2010 Inernaional Power Elecronics Conference, Sapporo, Japan, June 2010; pp

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