High Step up Switched Capacitor Inductor DCDC Converter for UPS System with Renewable. Energy Source

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1 nternatinal Jurnal f Electrnics and Electrical Engineering Vl. 3, N. 2, April, 25 High Step up Switched Capacitr nductr DCDC fr UPS System with Renewable Energy Surce Maheshkumar. K and S. Ravivarman K.S. Rangasamy Cllege f Technlgy, Tiruchengde, Namakkal marshalmahesh@gmail.cm, silicnravi@yah.in s have gd perfrmance and high step up as well. n recent years, many researchers are trying t take these types f cnverters afrementined int a new type f cmbinatin cnverters t btain high step-up vltage gains [7]-[2]. Specifically, tw step-up SC cells have been intrduced t zeta, cuk, and sepic cnverters, respectively, t btain high step-up vltage cnversin ratis in [7]. n the literature [8], sme step-up SC cells are presented and cmbined with bst and buck cnverters t achieve high step-up vltage gains. An ultra-step-up cnverter is presented in [9], which is prduced by cnnecting a Step-up switched-inductr cell and a step-up SC cell; and anther high step-up cnverter based n cupled inductr and SC cell is intrduced in []. n additin, tw step-up cnverters integrating different step-up SC cells within a bst cnverter are intrduced in [] and [2], respectively. Even thugh these cnverters have different structures and can prvide different vltage cnversin ratis, they have a characteristic in cmmn which is that all f them are multistage cmbinatin f switched-inductr cells and SC cells. Like ther cascaded high step-up cnverters [3][5], in which energy is transferred frm ne unit t next unit and gradually t utput stage, their efficiency is therefre generally nt prmising and is equal t the prduct f Efficiency. n this paper, a high efficiency Switched Capacitr nductr DC-DC cnverter is prpsed and different cnverters efficiency and switching stress is cmpared. All members f the cnverter are cmpsed f the same number f electrnic cmpnents: include tw energy transfer cmpnents, i.e., ne Switched Capacitr C and ne switched inductr L, a small resnant inductr Lr that is emplyed t limit the current peak caused by SC, three active r passive switches and ne utput filter capacitr. The greatest feature f these cnverters is that energy flwing frm input pwer surces is directly transferred t the tw energy transfer cmpnents (C and L) and then directly released t utput terminal, i.e., these cnverters are actually single-stage dc dc cnverters rather than like afrementined cnverters btained high vltage gain by using different cascading methds. When the tw energy transfer cmpnents perate in parallel manner during a charging prcess and then in series manner during a discharging perid, the Abstract A new cnverter using a switched-inductr cell integrated with a switched-capacitr cell within a bst-like structure is prpsed. The cnverter can achieve a very high dc cnversin rati. t can serve as the frnt-end dc-dc cnverter fr a fuel cell in a UPS system. The inductrs and capacitrs are switched in a parallel-series cnfiguratin. The charging circuit f the inductrs frm the surce is separated frm the lad. A dc analysis f the new circuit leading t the frmula f the dc gain and a breakdwn calculatin f the lsses are given. The prpsed Switched Capacitr nductr (SC) cnverter circuit can meet the high efficiency requirement and simple structure. A small resnant inductr is used in these cnverters t limit the current peak caused by switched capacitr. Therefre, the SC cnverters have gd perfrmance and high efficiency as well the vltage stress f the cnverter is reduced. n rder t verify the prpsed Switched Capacitr nductr (SC) dc-dc cnverter, mdeling and simulatin was carried ut by using MATLAB. ndex Terms switched capacitr, switched inductr, high vltage gain. NTRODUCTON The need fr a DC/DC cnverter f this caliber is a great ne. The future is lking twards alternative pwer surces all f which will need t be regulated in ne Frm r anther. T make this pssible, a highly efficient lw cst prduct will have t be designed. Amng all the different cnverter designs nly a few are capable f prviding high pwer with high efficiency. The basic switched-mde dc dc cnverters including buck, bst, buck-bst, cuk, zeta, and sepic have been used in varius electrnic applicatins due t their numerus advantages such as simple structure, gd perfrmance, high efficiency, easy design, and simple cntrl circuit []. The resnant cnverters such as single-ended and bridge type are als very ppular in the last decade [2], [3]. And the basic switched-capacitr (SC) cnverters als have wide applicatin as their advantages f nnmagnetic cmpnents emplyed and small size and high pwer density [4], [5]. A small resnant inductr has been added in SC cnverters t eliminate the current peak and achieve sft switching in [6] and, therefre, the SC Manuscript received January 2, 24; revised May 2, Engineering and Technlgy Publishing di:.272/ijeee

2 nternatinal Jurnal f Electrnics and Electrical Engineering Vl. 3, N. 2, April, 25 higher utput level can be prduced. Similarly, this principle is nt nly suitable fr deriving single-input cnverters, but can als be extended t dual-input dc-dc cnverters that are ppularly used in dual-level dc distributinal and renewable energy system. T distinguish the prpsed family f cnverters frm cnventinal SC/S cnverters intrduced in literatures, the prpsed cnverters are hence named high efficiency switched capacitr inductr (SC) cnverters. This paper is rganized as fllws: Sectin intrduces the blck diagram f prpsed UPS system. Sectin intrduces the prpsed SC dc-dc cnverter, which cnsists the detailed analysis f the perating principle and utput wavefrm f SC cnverter. The utput vltage and vltage stress f SC cnverter is analyzed with cnventinal methds in Sectin V. And the simulatin results are given in Sectin V. Finally, this paper is cncluded in Sectin V.. PROPOSED UPS SYSTEM The classical UPS cntains a dc-dc cnverter needed t step-up the 48V vltage f the back-up battery t the main bus dc vltage. n recent years, the battery is replaced by an alternative surce f the energy, a fuel cell, as shwn in Fig.. n additin f being envirnmentfriendly, the fuel cell has mre advantages: lnger backup time and up t 2 years f peratin withut maintenance. Hwever, the typical utput vltage f a fuel cell is V, within a range frm 7V t 2V, and an ac three-phase pwer system with 23V rms bus requires an utput vltage f the dc-dc cnverter f 23V, s a high step-up dc-dc cnverter is needed here. Previus research prvided switched-capacitr cnverters able t step-up many times the vltage. Hwever, this slutin features a very pulsating input current. nsertin f a switched-capacitr cell in a bst cnverter, r use f switched-inductr cells has als been tried. Very high dc gain has been btained by using a bst-flyback structure with paralleled utputs. Hwever, in the applicatin presented abve, cupled-inductr r transfrmers have t be avided fr nt affecting the efficiency. Figure. Prpsed UPS system. SC DC-DC CONVERTERS The prpsed SC dc-dc cnverter circuit is shwn in Fig. 2. The circuit uses nly ne active switch Q and a very small resnant inductr L r which is emplyed t limit the current peak caused by capacitr C when the switch Q is turned ON. The tw energy strage cmpnents C and L are alternately cnnected in parallel and series accrding t different switching states. Figure 2. Prpsed SC cnverter The vltage transfer relatinship can be derived and expressed as fllws, V 2 d d There are tw inductrs emplyed in the new SC cnverter, the energy transfer inductr L and the resnant inductr L r. The functin f L is t transfer energy while L r is just used t limit the current peak caused by the capacitr C when the switch Q is turned ON. Specifically, when switch Q is turned ON, the capacitr C begins t be charged r t discharge, the charging r discharging current will sar t a very high peak at the mment f Q being ON if there are nt any measures t limit it. Fr this reasn, a small inductr L r is added and cnnected in series with C t frm a resnant tank with the resnant frequency, f =/2π L r C during the switching ON perid. With the resnant inductr, the charging r discharging current f C gradually increases frm zer when switch Q is turned ON. n rder t ensure that the current changes back t zer befre switch Q is turned OFF, the switch cnductin time `d be lnger than half f a perid f the resnant frequency, i.e., d T S >π L r C (where T S and d are the switching cycle perid and duty rati, respectively). The SC Step-up cnverter scillatin amplitudes f capacitr vltage and current are related t the parameters f the resnant tank and the utput current and the switching cycle perid. When the switch Q is turned ON, the charges flw int the capacitr C frm pwer surce V causing a gradual increase in capacitr vltage V C. And then, the switch Q is turned OFF and the charge stred in C during the charging prcess flws ut f capacitr C t utput filter capacitr C 2 and the lad that causes the capacitr vltage V C gradually decreases frm its maximum t its minimum. The amunt f charge flwing int capacitr C during the charging prcess shuld be equal t the amunt f charge flwing ut f C during the discharging prcess, and the amunt als shuld be equal t the amunt f charge flwing thugh the lad during ne switching cycle, i.e., ( C_ max V in () V V ) C_ min C = T (2) S 25 Engineering and Technlgy Publishing 9

3 nternatinal Jurnal f Electrnics and Electrical Engineering Vl. 3, N. 2, April, 25 where is the average utput current. The charging current C2 changes in a sinusidal manner with the resnant frequency f =/2π L r C ; hence, the amunt f charges flw int C during the charging prcess can als be expressed as V V ) C_ min C =2 C ( C_ max Lr C (3) The scillatin amplitude f resnant current C can therefre be derived frm (2) and (3) T S C (4) 2 L C And the vltage scillatin amplitude can be derived frm (2) and expressed as Δ C r V = V C_ max V = TS (5) C_ min Fr the inductr L, the amunt f charge flwing thugh it during the discharging prcess is als equal t the amunt f charge flwing ut the capacitr C. ts average current L can therefre be expressed as L d And the ripple current Δ L is related t the input vltage V 2, the switching cycle T S, and the duty rati, i.e., 2 L dt S L C (6) V (7) When the switch Q is turned OFF, the vltage acrss it is the difference between the utput vltage V and the capacitr vltage V C, and a vltage (V V ) is develped acrss the dide D. The current flwing thugh the dide D2 is the same as the inductr current L during the OFF state. ts average and maximum transient values therefre can be expressed as L /( d) and ( L +Δ L /2) respectively. When Q is turned ON, the vltage acrss D2 is the difference between the input vltage V and the utput vltage V. The current flwing thugh the dided is the same as the capacitr current C and the current flwing thugh the switch Q is the sum f the capacitr current and the inductr current, i.e., ( C + L ). Their average values can be derived frm (4), and (6) and expressed as fr D and ( + L /d) fr Q, respectively. The maximum current flwing thugh D is the same as C and the maximum value f the current flwing thugh Q is the value f [ C + L Δ L /2+V 2 /(2ωOL )]. The switches stress therefre can be expressed as V _ = V V C V V ds Q V R _ D= V V V R _ D2 = V V 2 (8) Based n the previus analysis, the scillatin amplitudes f resnant current and vltage can be calculated by the values f C and L r. n turn, the values f C and L r can be determined by the design requirements f the resnant current and vltage, and the value f L can be determined by the design requirements f its current ripple. The design prcess therefre can be divided int the fllwing steps: ) Determine the minimum and maximum values f the duty rati and the switching frequency (usually, the switching frequency is higher than 5kHz), and then calculate the resnant frequency accrding t the cnditin that the switch cnductin time shuld be lnger than half f a perid f resnant frequency, i.e., f (9) 2 L C 2) The value f the capacitr C can be calculated by (5), i.e., C = r max T V C s () where ΔV C is the design requirement f the vltage scillatin amplitude. and max is the maximum utput current. 3) The resnant inductr L r hence can be determined by the value f C and the resnant frequency, i.e., L r () 4 C 2 2 f 4) The value f inductr L can be determined by (7), i.e., L V2 L d max T (2) s where Δ L is the current flwing thugh L and d max is the maximum values f the duty rati. V. ANALYSS WTH CONVENTONAL METHOD The cnventinal methds like bst cnverter, switched capacitr, switched inductr cnverter circuits are analyzed. n bst cnverter the utput vltage is step-up 3 times f input vltage with duty cycle.68. While the switch Q is ON vltage acrss Q equal t input vltage, and the OFF state the inductr current flws thrugh the dide giving utput vltage equal t switch vltage. Fr this analysis it is assumed that the inductr current always remains flwing (cntinuus cnductin). The duty rati d is between and the utput vltage must always be higher than the input vltage in magnitude. n the SC circuit the utput vltage is step-up t 3 times f input vltage. The switchedcapacitr dc-dc cnverter, the energy is transferred by the capacitrs. By the high-frequency switching actins, the capacitrs will be cnnected in series r in parallel directly by the switches. There are six switches used fr getting 3 cnversin rati s that the switch stress is high and switch lsses als high. Because f high switch 25 Engineering and Technlgy Publishing 9

4 nternatinal Jurnal f Electrnics and Electrical Engineering Vl. 3, N. 2, April, 25 lsses the efficiency f the cnverter is reduced. Fr an utput/input vltage bst rati f N times (NX), the input current has t g thrugh N switching devices. n S cnverter circuit step-up the input vltage by 3 times f input vltage with.55 duty cycle. The efficiency f the cnverter is lw. T mitigate the pulsating current, vltage spike, and switching lss, resnant switchedcapacitr cnverters have been prpsed with additinal inductr t resnate with the capacitr. Yet, their practical ptential t reach high vltage gain has nt been extensively investigated. Sme cmbinatins f switched-capacitr and inductrs have been reprted fr large vltage cnversin rati, the easy integratin and light weight feature f switched-capacitr dc-dc cnverters disappears after intrducing relatively large inductrs. The bst cnverter having the input pwer f 25W and the utput pwer is 84. There is sme lsses due t turn OFF f switches s that it having 89% efficiency nly. The Switched nductr cnverter has the efficiency f 9.6%. This cnverter has lw switching lsses. The cnventinal SC cnverter has efficiency f 94%. The SC cnverter give cntinues utput vltage due t charging and discharging f Capacitr C. The prpsed SC cnverter cnnects nductr L parallel with Capacitr C s that the fluctuatin f utput vltage is reduced and imprves the efficiency. The SC cnverter efficiency is imprved abut 95-98%. The value f nductr, Capacitr, and Resistr are designed by using the abve derived equatins (9-2). The fllwing table shws the efficiency f cnventinal methd is cmpared with the prpsed SC cnverter. Because f using mre switches in SC cnverter the Output Vltage is 88V nly. Sl.n TABLE. COMPARSON WTH CONVENTONAL CONVERTER type Output Vltage Output Pwer Efficiency Duty Cycle The efficiency f the prpsed SC cnverter is % (5) By calculating the input pwer frm equatin (3) and utput pwer frm equatin (4) the efficiency f the cnverter is calculated. Frm the equatin (5) the efficiency f the SC cnverter is 98%. The efficiency f prpsed cnverter is cmpared with cnventinal methd is given by the abve Table. P P in V. SMULATON RESULT The Prpsed SC cnverter is simulated with nverter circuit and the utput wavefrms are shwn. n this simulatin the 3V is applied t the cnverter and the.55 duty cycle is given t the switch pulse and the 9V utput vltage btained. The cnversin rati f the cnverter is 3 and the utput current is 2A. The efficiency f the cnverter is calculated by using input pwer and utput pwer (5). The utput f the cnverter is given t the inverter circuit and it is cnverted int 23V AC utput. A simulatin circuit with parasitic cmpnents f the single input step-up has been built as shwn in Fig. 3. When the input pwers V is 3V, the lad is a 45Ω pure resistr, and the switch Q is perated at 2kHz switching frequency with duty rati.53, the utput vltage is 9V and sme simulatin wavefrms are shwn in Fig. 4 and Fig. 5 Accrdingly, a prttype circuit f the single input step-up cnverter has als been built t cnfirm the theretical analysis and simulatin results. With the simulatin parameters given in Table. TABLE. SMULATON PARAMETER nput Vltage Maximum utput Pwer 3V DC 25W 2 Bst Switched nductr Switching Frequency 2kHz Capacitr C 4.7µF Capacitr C2 µf 3 Switched Capacitr nductr L 95µH Resnant nductr Lr.3µH 4 SC Resistr R 45Ω The efficiency f the cnverter is calculated by using input pwer and utput pwer as fllws The input pwer f the cnverter is P V (3) i n The utput pwer f the cnverter is in in P (4) V The SC DC-DC cnverter simulatin circuit is cnnected with H-Bridge inverter. The utput f the inverter circuit are cnnect with LC filter and get the sinusidal utput wavefrm. The 3V input is given t the SC cnverter and it is step-up t 9V. The utput f SC cnverter is given t the H-Bridge inverter and cnverted int 23V AC utput vltage. During Turn ON perid the vltage acrss Capacitr and inductr is 3V. During Turn OFF perid Vltage 25 Engineering and Technlgy Publishing 92

5 nternatinal Jurnal f Electrnics and Electrical Engineering Vl. 3, N. 2, April, 25 acrss Capacitr is 3V and inductr is -3V. The switch Vltage during Turn ON is 3V and during urn OFF is V. Therefre the Vltage stress f the cnverter is reduced, switch lss als reduced. Because f this reduced Vltage stress and switch lss the Efficiency f the cnverter is increased cmpared with cnventinal methds. Figure 7. Output current f inverter V. CONCLUSON The High step up Switched Capacitr nductr dc-dc cnverter is prpsed in this paper. Frm the abve explanatins SC dc-dc cnverter give high step up and efficiency cmpared with cnventinal SC cnverter. The prpsed cnverters emply tw energy transfer cmpnents (ne SC and ne inductr) and d nt use the cascade methd like cnventinal SC/switched-inductr cnverters. The energy stred in the tw cmpnents bth directly cme frm input pwer surces and then directly been released t utput terminal. This design can meet the high efficiency requirement with a simple structure. A resnance methd is used in this paper t limit the current peak caused by the SC. Detailed analysis and design cnsideratins are als intrduced. Cmpared with traditinal switched-mde cnverters, the prpsed cnverters can prvide higher r lwer vltage gains and the switch stress is lwer. The SC cnverter vltage stress is high because f using mre number f switches. n SC cnverter used ne switch therefre vltage stress f the cnverter is reduced. The renewable energy surces can give mre efficient pwer by using SC dc-dc cnverter. Figure 3. Simulatin circuit f SC cnverter The utput Vltage f SC cnverter and nverter are shwn in the belw Diagram (Fig. 4, Fig. 5, Fig. 6, and Fig. 7). t shws that the utput vltage f cnverter is 9V and inverter is 23V. Figure 4. Output vltage f SC cnverter REFERENCES [] [2] [3] [4] [5] Figure 5. Output current f SC cnverter [6] [7] [8] [9] Figure 6. Output vltage f inverter 25 Engineering and Technlgy Publishing 93 B. W. Williams, Basic DC-t-DC cnverters, EEE Transactin n Pwer Electrnics, vl. 23, n., pp , Jan. 28. Y. Ren, M. Xu, J. Sun, and F. C. Lee, A family f high pwer density unregulated bus cnverters, EEE Transactin n Pwer Electrnics, vl. 2, n. 5, pp , 25. K. W. E. Cheng and P. D. Evans, Parallel-Mde extended-perid quasi resnant cnvertr, EEE Transactin n Pwer Electrnics, vl. 38, n. 5, pp , Sep. 99. C. K. Tse, S. C. Wng, and M. H. L. Chw, On lssless switched capacitr pwer cnverters, EEE Transactin n Pwer Electrnics, vl., n. 3, pp , May 995. J. M. Henry and J. W. Kimball, Switched-Capacitr cnverter state mdel generatr, EEE Transactin n Pwer Electrnics, vl. 27, n. 5, pp , May 22. K. W. E. Cheng, Zer-Current-Switching switched-capacitr cnverters, EEE Transactin n Pwer Electrnics and Applicatins, vl. 48, n. 5, pp , Sep. 2. E. H. smail, M. A. Al-Saffar, and A. J. Sabzali, A family f single switch PWM cnverters with high step-up cnversin rati, EEE Transactin n Circuits and System., Reg. Papers, vl. 55, n. 4, pp. 59-7, May 28. B. Axelrd, Y. Berkvich, and A. invici, Switched-Capacitr/ Switched-nductr structures fr getting transfrmerless hybrid DC DC PWM cnverters, EEE Transactin n Circuits and System., Reg. Papers, vl. 55, n. 2, pp , Mar. 28. A. A. Fardun and E. H. smail, Ultra step-up DC-DC cnvert with reduced switch stress, EEE Transactin n ndustrial and Applicatins, vl. 46, n. 5, pp , Sep./Oct. 2.

6 nternatinal Jurnal f Electrnics and Electrical Engineering Vl. 3, N. 2, April, 25 [] Y.-P. Hsieh, J.-F. Chen, T.-J. Liang, and L.-S. Yang, Nvel high step-up DC-DC cnverter with cupled-inductr and switchedcapacitr techniques fr a sustainable energy system, EEE Transactin n Pwer Electrnics, vl. 26, n. 2, pp , Dec. 2. [] J. C. Rsas-Car, J. M. Ramirez, F. Z. Peng, and A. Valderraban, A DC-DC multilevel bst cnverter, EEE Transactin n Pwer Electrnics, vl. 3, n., pp , 2. [2] O. Abutbul, A. Gherlitz, Y. Berkvich, and A. invici, Step-up switching-mde cnverter with high vltage gain using a switched capacitr circuit, EEE Transactin n Circuits and System. : Fundum. Thery Appl., vl. 5, n. 8, pp. 98-2, Aug. 23. [3] Y. Deng, Q. Rng, W. Li, Y. Zha, J. Shi, and X. He, Single- Switch high step-up cnverters with built-in transfrmer vltage multiplier cell, EEE Transactin n Pwer Electrnics, vl. 27, n. 8, pp , Aug. 22. [4] S.-M. Chen, T.-J. Liang, L.-S.Yang, and J.-F. Chen, Acascaded high stepup DC-DC cnverter with single switch fr micrsurce applicatins, EEE Transactin n Pwer Electrnics, vl. 26, n. 4, pp , Apr. 2. [5] K.-B. Park, G.-W. Mn, and M.-J. Yun, Nnislated high stepup stacked cnverter based n bst-integrated islated cnverter, EEE Transactin n Pwer Electrnics, vl. 26, n. 2, pp , Feb. 2. Maheshkumar. K was brn in 989 at Salem, ndia. He had finished schl in V.C. Bys Higher secndary schl, Salem, ndia in 26. He had cmpleted his Bachelr degree f electrical and electrnics engineering in Anna University Chennai, ndia 2. He cmpleted Master degree in the area f Pwer Electrnics and Drives in Anna University Chennai, ndia 24. He had wrked as an assistant Engineer in PVN Pwer Lines PVT LTD, Salem, ndia during 2 t 22. n that time he wrked in the varius High Vltage and Lw Vltage level Pwer cnsuming machineries and Equipment s like ACB, Relay, MCCB., etc. His research is based n the DC-DC fr Renewable energy surces. He had presented paper in varius natinal and nternatinal Cnferences and published the articles in that prceeding. Recently he had presented his research paper in Gvernment cllege f Engineering Salem, ndia. He is the student member f EEE and STE. Prf S. Ravivarman was brn in 984 at Salem, ndia. He had finished schl in Salem, ndia in 996. He had cmpleted his Bachelr degree f electrical and electrnics engineering in Anna University Chennai, ndia 26. He cmpleted Master degree in the area f Pwer Electrnics and Drives in Anna University Chennai, ndia 28. He had wrked as an Assistant Prfessr in Adiyaman Cllege f Technlgy, Hsur, ndia during 28 t 2. Nw he is wrking as an Assistant Prfessr in K.S. Rangasamy Cllege f Technlgy, Tiruchengde, ndia. His research is based n the DC-DC fr Renewable energy surces. He had presented paper in varius natinal and nternatinal Cnferences and published the articles in that prceeding. He is the member f EEE and STE. 25 Engineering and Technlgy Publishing 94