A NOVEL HIGH STEP-UP CONVERTER BASED ON THREE WINDING COUPLED INDUCTOR FOR FUEL CELL ENERGY SOURCE APPLICATIONS

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1 A NOVEL HIGH STEPUP CONVERTER BASED ON THREE WINDING COUPLED INDUCTOR FOR FUEL CELL ENERGY SOURCE APPLICATIONS Thura Chatanya 1, V.Satyanarayana 2 1 EEE Branch, Vaagdev College of Engneerng, Bollkunta, (Inda) 2 EEE Department, Vaagdev College of Engneerng, Bollkunta, (Inda) ABSTRACT Ths paper presents a hgh stepup converter for fuel cell energy source applcatons. The proposed hgh stepup dc dc converter s devsed for enhancng the voltage generated from fuel cell to be a 4V dcbus voltage. Through the threewndng coupled nductor and voltage doubler crcut, the proposed converter acheve hgh stepup voltage gan whle not large duty cycle. The passve lossless clamped technology not only recycles leakage energy to mprove effcency but also allevates large voltage spke to lmt the voltage stress. Fnally, the electrc cell as nput voltage supply 6 9 V ntegrated nto a 2kW eptome convertor was enforced for performance verfcaton. Index Terms Coupled nductor, fuel cell energy source applcatons, hgh stepup converter. I. INTRODUCTION Recently, the cost ncrease of fossl fuel and new regulatons of co 2 emssons have strongly ncreased the nterests n renewable energy sources. Hence, renewable energy sources lke fuel cells, solar energy, and wnd power are wdely valued and used. Fuel cells are consdered as an excellent canddate to replace the conventonal desel/gasolne n vehcles and emergency power sources. Fuel cells wll gve clean energy to users whle not co2 emssons. Because of stable operaton wth hgheffcency and sustanable/renewable fuel supply, fuel cell has been ncreasngly accepted as a competently alternatve source for the future [1], [2]. the excellent features lke small sze and hgh converson effcency make them valuable and potental. Hence, the fuel cell s sutable as power supples for energy source applcatons [3][1]. 627 P a g e

2 Fg. 1.Fuel cell power supply system wth hgh stepup converter. Generally speakng, a typcal fuel cell power supply system contanng a hgh stepup converter s shown n Fg. 1. The generated voltage of the fuel cell stack s rather low. Hence, a hgh stepup converter s strongly needed to lft the voltage for applcatons lke dc mcrogrd, nverter, or battery. Ideally, a conventonal boost converter s able to acheve hgh stepup voltage gan wth an extreme duty cycle. In practce, the stepup voltage gan s lmted by effects of the power swtch, rectfer dode, and also the resstances of the nductors and capactors. n addton, the extreme duty cycle can result n a serous reverserecovery problem and conducton losses. A flyback converter s able to acheve hgh stepup voltage gan by adjustng the turn s rato of the transformer wndng. However, a large voltage spke leakage energy causes can destroy the man swtch. so as to protect the swtch devces and constran the voltage spke, a hghvoltagerated swtch wth hgh onstate resstance (R D S O N ) and a snubber crcut are typcally adopted n the flyback converter, however the leakage energy stll be consumed. Fg. 2. Proposed hgh stepup converter. Fg. 3.Equvalent crcut of the proposed converter. 628 P a g e

3 These strateges can dmnsh the power converson effcency. so as to ncrease the converson effcency and voltage gan, several technologes lke zerovoltage swtchng (ZVS), zerocurrent swtchng (ZCS), coupled nductor, actve clamp, etc. are nvestgated. Some hgh stepup voltage gan wll be acheved by usng swtchedcapactor and voltagelft technques, although swtches can suffer hgh current and conducton losses. In recent years, couplednductor technology wth performance of leakage energy recycle s developed for adjustable voltage gan; therefore, several hgh stepup converters wth the characterstcs of hgh voltage gan, hgh effcency, and low voltage stress are gven.. In ths project, the presented hgh stepup converter desgned for fuel cell energy source applcatons s shown n Fg. 2. II. OPERATING PRINCIPLE OF THE PROPOSED CONVERTER The proposed converter employs a swtched capactor and a voltagedoubler crcut for hgh stepup converson rato. The swtched capactor supples an extra stepup performance; the voltagedoubler crcut lfts of the output voltage by ncreasng the turn s rato of couplednductor. Fg. 4. Steadystate waveforms n CCM operaton. The advantages of proposed converter are as follows: 1) through adjustng the turns rato of coupled nductor, the proposed converter acheves hgh stepup gan that renewable energy systems requre; 2) leakage energy s recycled to the output termnal, whch mproves the effcency and allevates large voltage spkes across the man swtch; 3) due to the passve lossless clamped performance, the voltage stress across man swtch s substantally lower than the output voltage; 629 P a g e

4 4) low cost and hgh effcency are acheved by adoptng lowvoltagerated power swtch wth low R D S O N ; 5) by usng threewndng coupled nductor, the proposed converter possesses more flexble adjustment of voltage converson rato and voltage stress on each dode. The equvalent crcut of the proposed converter shown n Fg. 3 s composed of a coupled nductor T r, a man power swtch S, dodes D 1, D 2, D 3, and D 4, the swtched capactor C b, and the output flter capactors C 1, C 2, and C 3. L m s the magnetzng nductor and L k1, L k2, and L k 3 represent the leakage nductors. The turns rato of coupled nductor n 2 s equal to N 2 /N 1, and n 3 s equal to N 3 /N 1, where N 1, N 2, and N 3 are the wndng turns of coupled nductor. The steadystate waveforms of the proposed converter operatng n CCM are depcted n Fg. 4. The each operatng modes s shown n Fg. 5. Mode I [t, t 1 ]: Durng ths nterval, the swtch S s turned ON at t. The dodes D 1, D 2, and D 4 are reverse based. The path of current flow s shown n Fg. 5(a). The prmary leakage nductor current Lk1 ncreases lnearly, and the energy stored n magnetzng nductance stll transfers to the load and output capactor C 2 va dode D 3. Fg. 5. CCM operatng modes of the proposed converter. (a) Mode I [t, t 1 ]. (b)mode II [t 1, t 2 ]. (c)mode III [t 2, t 3 ]. (d)mode IV [t 3, t 4 ]. (e)mode V [t 4, t 5 ]. (f) Mode VI [t 5, t 6 ]. 63 P a g e

5 Mode II [t 1, t 2 ]: Durng ths nterval, the swtch S s stll n the turnon state. The dodes D 1 and D 4 are forward based; dodes D 2 and D 3 are reverse based. The path of current flow s shown n Fg. 5(b). The dc source V n stll charges nto the magnetzng nductor L m and leakage nductor L k 1, and the currents through these nductors rse lnearly. Some of the energy from dc source V n transfer to the secondary sde of the coupled nductor to charge the capactor C 3. The swtched capactor C b s charged by the LC seres crcut. Mode III [t 2, t 3 ]: Durng ths nterval, the swtch S s turned OFF at t 2. Dodes D 1 and D 4 are stll forward based; dodes D 2 and D 3 are reverse based. The path of current flow s shown n Fg. 5(c). The magnetzng current and LC seres current charge the parastc capactor C o of the MOSFET. Mode IV [t 3, t 4 ]: Durng ths nterval, S s stll n the turnoff state. The dodes D 1, D 2, and D 4 are forward based. The dode D 3 s reverse based. The currentflow path s shown n Fg. 5(d). The current d4 charges the output capactor C 3 and decreases lnearly. The total voltage of V n V Lm V Cb s chargng to clamped capactor C 1, and some of the energy s suppled to the load. Mode V [t 4, t 5 ]: Durng ths nterval, swtch S s stll n the turnoff state. The dodes D 1 and D 4 are turned OFF; the dodes D 2 and D 3 are forward based. The currentflow path s shown n Fg. 5(e). The energy of the prmary sde stll charges to the clamped capactor C 1 and supples energy to the load. Some of the energy from dc source V n s transferred to the secondary sde of the coupled nductor to charge the capactor C 2, and the current d3 ncreases lnearly. Mode VI [t 5, t 6 ]: Durng ths nterval, swtch S s stll n the turnoff state. The dodes D 1, D 2, and D 4 are reverse based; the dode D 3 s forward based. The currentflow path s shown n Fg. 5(f). The current Lk1 s dropped tll zero. The magnetzng nductor L m contnuously transfers energy to the thrd leakage nductor L k 3 and the capactor C 2. The energes are dscharged from C 1 and C 3 to the load. The current d3 charges C 2 and supples the load current. III. STEADYSTATE ANALYSIS In order to smplfy the CCM steadystate analyss, the followng factors are taken nto account. All the leakage nductors of the coupled nductor are neglected, and all of components are deal wthout any parastc components. The voltages V b, V C1, V C2, and V C3 are consdered to be constant due to nfntely large capactances StepUp Gan Durng the turnon perod of swtch S, the followng equatons can be wrtten as: (1) Durng the turnoff perod of swtch S, the followng equatons can be expressed as: (2) (3) 631 P a g e

6 Thus, the output voltage V O can be expressed as (4) By substtutng (1), (3), and (4) nto (5), the voltage gan of the proposed converter s gven by (5) Equaton (6) shows that hgh stepup gan can be easly obtaned by ncreasng the turns rato of the coupled nductor wthout large duty cycle. (6) 3.2. Voltage Stress The voltage stress on the man swtch s gven as follows: When the swtchng S s turned OFF, the dodes D 1 and D 3 are reverse based. Therefore, the voltage stresses of D 1 and D 3 are as follows: (7) (8) (9) When the swtch S s n turnon perod and the dodes D 2 and D 3 are reverse based. Therefore, the voltage stresses of dodes D 2 and D 3 are as follows: (1) Equatons (7) (11) can be llustrated to determne the maxmum voltage stress on each power drves. (11) 3.3. Analyss of Conducton Losses Some conducton losses are caused by resstances of semconductor components and coupled nductor. Thus, all the components n the analyss of conducton losses are not contnuously assumed to be deal, except for all the capactors. Dode reverse recovery problems, core losses, swtchng losses, and the ESR of capactors are not dscussed n ths secton. The characterstcs of leakage nductor are dsregarded because of energy recyclng. The correspondng equvalent crcut ncludes copper resstances r L1, r L2, and r L3, all the dode forward resstances r D1, r D2, r D3, and r D4, and the onstate resstance R DSON of the power swtch. 632 P a g e

7 TABLE 1 Comparson between ThreeWndng Coupled Inductor Hgh StepUp Converters Table 2 Components Parameters of the Presented Converter 3.4. Comparson Between the Proposed Converter and the Other Hgh StepUp Converters The performance of the proposed converter s verfed by an analytcal comparson wth other threewndng coupled nductor hgh stepup converters for fuel cell, and t s assumed that all the converters are operated n CCM. Moreover, for the sake of far comparson, the analyss wll also assume that the nput voltage and the turns ratos of coupled nductor are the same: n 2 = 1.5; n 3 = 1.5. Table I summarzes the voltage converson rato and the swtch stress for the proposed converter and the other sngle swtch hgh stepup converter topologes ntroduced. In ths comparson between the proposed converter and other converter, n2 s defned as the turns rato N 2 /N 1 ; and n3 s defned as the turns rato N 3 /N 1. The comparson of voltage gan and the swtch stress between the threewndng coupled nductor hgh step up converters. The voltage gan of the proposed converter s hgher than that of the other hgh stepup converters at duty cycle of.1< D <.6. The voltage stress of swtch of the proposed converter s lower than that of other hgh stepup converter at duty cycle of.1 < D <.6. Ths s a very attractve feature because the lowvoltage 633 P a g e

8 S g D rated MOSFET wth lower RDSON can be adopted to mprove the effcency. Under D >.6, although the voltage gan of the proposed converter s not the hghest and the voltage stress of the proposed converter s not the lowest, the operaton under large duty cycle D >.6 resultng n low effcency wll not be desgned n reasonable consderaton. IV. SIMULATION RESULTS The presented converter for fuel cell nput source, prototype crcut s tested to verfy the performance. I_Lk1 I_d1 I_d2 I_c1 Dscrete, Ts = 2e7 s powergu Lk1 I_Lk2 v V_c1 Lm 2 v V_cb 1 Lk2 I_n 3 I_Cb I_Lm Results v I_d3 I_c2 Vo v Vn [Vg] V_c2 v Io ILk ILm In Vg I_d4 I_Lk3 I_c3 Fg.6.Smulaton Model The range of duty cycle D under nput voltage 6 9 V s desgned as.2.5 and the turn s rato n 1 :n 2 :n 3 s selected as 1:1:1.5. The leakage nductance L k1 s measured as 3.3 μh. All of the major components parameters of the prototype used for smulaton are presented n Table II. Smulaton results are shown n fgure 7, 8 and Tme Fg.7. Smulaton results for V g, I n,i Lm and I Lk 634 P a g e

9 I_c1 V_cb I_c3 I_c2 I_d4 I_d3 I_d2 I_d Tme Fg.8. Smulaton results for I d1, I d2, I d3 and I d Tme V. CONCLUSION Fg.9. Smulaton results for I c2, I c3, V cb and I c1 In ths project, a hgh stepup dc dc converter for fuel cell hydrod electrc vehcle applcatons s clearly analyzed and successfully verfed. By employng technologes of threewndng coupled nductor, swtched capactor, and voltage doubler crcut, the hgh stepup converson wll be effcently obtaned. The leakage energy s recycled and large voltage spke s allevated; thus, the voltage stress s lmted and also the effcency s mproved. The fullload effcency s up to 91.32% and also the maxmum effcency s up to 96.81%. The voltage stress on the man swtch s clamped as 12 V at D max. The lowvoltagerated swtch wth low R D S O N wll be chosen for the reducton of conducton losses. Thus, the proposed devce s sutable for hghpower applcatons as fuel cell systems n hydrod electrc vehcles. 635 P a g e

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