A Novel ZVS-ZCS Bidirecional DC-DC Converer For Fuel Cell And Baery Applicaion V.V.SUBRAHMANYA KUMAR BHAJANA Research scholar, EEE deparmen Bharah Universiy Chennai, India kumarbvvs@yahoo.co.in S.RAMA REDDY Professor, EEE Deparmen. Jerusalem College of engineering Chennai, India srrvicory@yahoo.co.in Absrac A new ZVS-ZCS bidirecional DC-DC converer is proposed, which provides high oupu volages 80v-180v. Wih proposed ZVS-ZCS concep, he MATLAB simulaion resuls of he applicaion o a fuel cell and baery applicaion have been obained and compared wih hose of ZVS bidirecional and applicaions in order o show he excellen performance of he proposed concep. In addiion o his experimenal seup has been developed. The experimenal resuls are compared wih he simulaion resuls. Keywords-componen; ZVS,ZCS,TDR,DC-DC converer. I. INTRODUCTION In recen years, he area of bidirecional DC-DC converers is improving he fuel cell economy, auomobile companies are developing alernaive baery operaed vehicles. In addiion, a major change in he elecrical sysem of he vehicles is on he horizon by going for a 40 o 300V DC from 12/24v DC sysems. The main reasons for swiching over o 12v/24v o 300v are o mee he increased elecrical demands of cell vehicles, o lower he curren drawn from he baery, and o implemen addiional safey and comfor feaures, also o reduce he mechanical and hydraulic componens, and o improve he design flexibiliy of he vehicles. In hybrid/fuel cell vehicles, he main goals are o have a high efficien, small size, rugged and low cos bidirecional DC-DC converer. In hybrid/fuel cell vehicles, a power condiioning uni such as novel bidirecional DC-DC converer o mach he fuel cell volage wih he baery pack may also required. In cerain condiions, a fas response required o supply load, converer o give bidirecional power o ha vehicle sysem wihou any disurbance. I is able o operae a adverse environmenal condiions. The power semiconducor devices (MOSFET, IGBT, ec) and packaging of he individual unis and he sysem inegraion play a major role in hybrid/fuel cell vehicles. The proposed converer sysem should be efficien o improve he range of performance of he baery operaed vehicles. In addiion o he power semiconducor devices, conrollers, here are several oher componens such as inducors, capaciors, isolaion ransformer form a major porion of he proposed sysem. The sof swiching converers have he advanage of lower swiching losses and higher operaing volage. Hence he proposed sof swiching echniques ZVS/ZCS were needed. The proposed sysem wih wo inegraed funcion is ha DC/AC and AC/DC conversion, wih low losses and wih minimum use of capaciors need o be developed. This paper presens a novel ZVS-ZCS bi-direcional DC- DC converer. The new converer is based on a dual half-bridge opology wih an auxiliary circui in primary side. I has he advanages like low EMI, low swiching sresses, low swiching losses compared wih ZVS bi-direcional DC-DC converer. The ZCS opology removes he urn-off curren ail of he main swich. The ZCS operaion is obained by boh forcing he primary curren owards zero and delaying is raise, or by reseing he primary curren before he corresponding swich urned off. The ZVS-ZCS bi-direcional DC-DC converer has been simulaed and developed for recificaion and inversion operaions in boh buck and boos. The operaing modes of he proposed converer are described in he following secion. The obained resuls shows ha he proposed converer can be a good soluion for fuel cell vehicle sysems, where volage booss and efficiency are key issues. The simulaions were conduced wih he swiching frequencies of 10 KHz. The curren waveforms a he DC-AC sages are observed o be conformiy wih he heoreical esimaes. II POWER STAGE DESCRIPTION AND OPERATION A. power sage descripion The proposed bi-direcional DC-DC converer for fuel cell and baery applicaions is shown in Fig. 2. In he ZVS bidirecional DC-DC converer[1] low-volage side half-bridge wih MOSFETS and high volage side half bridge wih IGB were developed. Where as in he proposed ZVS-ZCS bidirecional DC-DC converer, dual half-bridges are developed using MOSFE wih an auxiliary circui in he low volage side. The auxiliary circui used in his converer has been adaped from [6] and i can also be used in full-bridge opologies, bu his will be he scope of fuure work. In proposed ZVS-ZCS bidirecional DC-DC converer he auxiliary circui is composed of one resonan inducor L a, one auxiliary swich S a, and also diode D a, so ha he zero curren swiching (ZCS) in main swiches S 1 & S 2 can be obained. Swich S a is urned on under zero curren swiching (ZCS) condiion. When power flows from he low volage side o high volage side, he circui works in ZCS condiion o urned off and ZVS condiion o urned on of a main swiches S 1, S 2 12
in boos mode. In he oher direcion of power flow, he circui operaes in ZVS condiion (buck mode). The ransformer is used o provide isolaion and volage maching. The leakage inducance of he ransformer is uilized as an inerface and energy ransfer elemen beween wo half-bridges. The wo volage source half-bridges each generaes a square wave volage applied o he primary and secondary of he ransformer, respecively. The major draw back of his converer is TDR penaly because auxiliary circui used in primary side. The TDR of he [1] ZVS bidirecional DC-DC converer is calculaed as TDR = 2V dc. I ac. (2 devices) = 4 P o, where P o is he oupu power. The TDR of he proposed ZVS- ZCS bidirecional DC-DC converer is calculaed as TDR P = 2Vdc. Iac. (3 devices) = 6 P o, Where P o is again he oupu power. The TDR has been increased for he proposed converer and he ZVS bidirecional DC-DC converer is no same oupu power. The main advanage of proposed circui is he curren sresses are reduced for he low volage side main swiches S 1 and S 2 and high efficiency is achieved due o ZCS condiion. PEDS2009 ransformer curren i r of each mode can be calculaed as follows: Fig. 2. Proposed ZVS-ZCS bidirecional DC-DC converer Mode I: i r = (v 1 +v 4 )θ / ω L s + i r (0) (1) Mode II: i r = (v 1 -v 3 ) (θ -φ1) / ω L s + i r (φ1) (2) Mode III: i r = 0 (3) Mode IV: i r = - (v 2 +v 3 ) (θ -π) / ω L s + i r (π) (4) Mode V: i r = - (v 2 +v 4 ) (θ -π-φ) / ω L s + i r (π+φ1) (5) Mode VI: i r = 0 (6) The curren iniial condiions can be solved using he boundary condiions of i r (0) = i r (π)=0 (7) i r (φ1) = -i r (π+φ1) (8) Furher, he oupu power can be found o be Fig.1. ZVS bidirecional DC-DC converer B. Descripion of operaing sages Fig. 2. illusraes he proposed converer opology and he commuaion waveforms in boos mode. ZCS is achieved by auxiliary circui used in one half-bridge, operaing he wo half-bridges wih a phase shif. The circui operaion ha is significan for he developmen of he sae space model. Fig. 2 is he proposed circui. Fig. 3 presens he volage and curren waveforms of he ransformer during one swiching period. In fuel cell applicaions, when power flows from he low volage side o high volage side, he circui works in boos mode o keep he high volage a a desired high value before fuel cell can generae power. In oher direcion of power flow, he circui works in buck mode o absorb regeneraed energy. Based on he waveforms in Fig. 3, here are six operaion modes in one swiching cycle, and he T s is he period of swiching frequency, V dc is he inpu volage in boos mode. The oupu power can be regulaed by phase shif angle ø 1, duy cycle and swiching frequency ω. If duy cycle assumed o 50% hen he oupu power equaion can be simplified as P o = x0 / T s = V 2 dc / ωl s [(ø2- π) ø1/ π)] (9) Because of he asymmery propery of dual half-bridges, he operaion principles of boos mode and buck mode are no he same, polariy of he phase shif angle is also no same. 1. Boos mode: The inerval of Fig. 3. describes he various sages of operaion during swiching period in boos mode. The converer operaion is repeiive in he swiching cycle. One complee cycle is divided ino six seps. To aid in undersanding each sep, a se of corresponding annoaed circui diagrams is given in Fig. 4(a,b,c,d,e,f) wih a brief descripion. 13
Fig. 4(c). hird sage(φ 3 o π) Fig. 3. Volage and curren waveforms of ransformer during boos mode Firs sage (0 o φ1): swich S 1 sars o conduc. Due o he resonan capacior C r1, he volage across S 1 is becomes zero. During his sage C 1, C 4 are charged, C 2, C 3 are discharged. Fourh sage (φ2 o 2π): when S 2 is urned on, C 2 & C 3 are charged, C 3 & C 4 discharged. This sage finishes when S is urned-on. Fig. 4(d) fourh sage(π oφ 4) Fig. 4(a) firs sage(0 o φ1) Second sage (φ 1 oπ): S 1 is sill urn on sae. During his sage C 1, C 4 are charged, energy sored in C 2, C 3 are ransferred o he load. When i r reaches a φ 3, S a is gaed o urn off S 1. This sage finishes when S 1 is urned off. Fifh sage (2π o 3π): A his sage S 2 is sill in urn on sae. During his sage C 2, C 3 are charged, energy sored in C 1, C 4 are ransferred o he load. When i r reaches a 3π, S a is urned on o urn-off he S 2. This sage finishes when S 2 is urned off. Fig.4(b) second sage(φ 1 o φ 3) Third sage (π o φ2): a his sage S a is urn on, remaining swiches are in off sae. During his sage energy sored in C 1,C 4 are ransferred o he load. C 3, C 2 are charged. Fig. 4(e) fifh sage( 3π o φ5) Sixh sage (3π o φ5): a his sage S a is urned on, remaining swiches S 1 &S 2 are in off sae. During his sage energy sored in C 2, C 3 ransferred o he load. C 1, C 4 are charged. 14
v = i P C + P i C (17) 2 (1 ) / ( / ) 1 1 1 r p p [ ( 3 4 s 1) / S 0 ( 3 4) / )](1 2) / S v = v + v v P R + C d v + v d P C 3 + [ ir ( v3+ v 4 vs)/ Rs C 0d( v 3+ v 4) d] P 2/ Cs (18) 2. Buck mode: Fig.4(f) sixh sage( 3π o φ5) Because of he auxiliary circui in one half-bridge he wo sides are asymmerical, he operaion principles in buck mode are similar o hose in boos mode excep mode III & mode VI. Due o he reversed power-flow direcion, he phase of he V S2 is leading han V P1. The inducor curren L S is reversed. The buck mode only operaes under ZVS condiion. This mode of operaion can be divided ino four seps. In his mode he swiches in S 3 &S 4 are urned on and urned off a zero volage due o he resonan capaciors C r3, C r4.body diodes of he swiches S 1 & S 2 acs as recificaion. Mode I: i r = (v 3 +v 4 )θ / ω L s + i r (0) (10) Mode II: i r = (v 3 -v 2 ) (θ -φ1) / ω L s + i r (φ1) (11) Mode III: i r = - (v 1 +v 4 ) (θ -π) / ω L s + i r (π) (12) Mode IV: i r = (- v 2 +v 4 ) (θ -π-φ) / ω L s + i r (π+φ1) (13) III. STATE SPACE MATHEMATICAL MODEL The sae variables of he proposed converer [1] are chosen o be he inducor currens i 1, i 2, ransformer curren i r and he capacior volages v 1, v 2, v 3 and v 4 [1] ha sae variables vary slowly wih ime, also does i 1,i 2 if enough large inducance and small inducances are seleced, while he sae variable i r varies quickly wih ime. To analyze he behavior of he fas variable i r, he oher slow sae variables can be reaed as dc consans. From secion II, we know ha he converer is operaed as dual acive half-bridges and here are six operaion modes during one swiching cycle. Wih he help of swiching funcions, he sae equaion of he slow sae variables is described by [( r ( 3 4 s) / S 0 ( 3 4) / )](1 2) / S v = i + v + v v R + C d v + v d P C 4 + [ ( v3+ v 4 vs)/ Rs C 0d( v3+ v 4) d] P 2/ Cs (19) Where C p = C1=C2 and C s = C3=C4. These equaions describe all he operaion modes of one swiching cycle in Fig. 3.The nex sep is o calculae he inegraion of fas variable i r in [0, ø 1],[ ø 1, π],[π,ø 2],[ø 2,ø 3, ], [ø 3,2π],respecively based on (1)(2)(3)(4)(5)(6). Then subsiue he above resuls and swich funcions P 1 and P 2 in o (14)(15)(16)(17)(18)(19) o calculae he move averages of he slow variables shown in (20) + φ 2 iavg 1 = ( id 1 )/ ; iavg a = ( a id)/ π + + v1avg = ( v1d)/ ; v 2avg = ( i2d)/ + + vavg 3 = ( vd 3 )/ iavg ; 1 = ( i1)/ (20) The sae space model of proposed converer wih ZCS condiion is derived. We shall now demonsrae he normal operaion of he ZVS- ZCS bidirecional DC-DC converer hrough simulaion using MATLAB/Simulink. The simulaion resuls are shown in Fig. 3, 5(a, b)and Fig. 6. 1 i = [ v i1 R P ( v1+ v2)] / L (14) 1 dc b dc 1/ [ 1 ( 1 2 i = L v ir S v v )] a a b b a (15) 1 1 1 v = P ( i / C ) + P ( i / C ) 1 (16) Fig.5a. Transformer primary and secondary side volages in boos mode 15
IV SIMULATION RESULTS The deailed circui model is buil using Malab/Simulink. The simulaed resuls are compared wih ZVS-bidirecional DC- DC converer o show he performance of proposed converer. 1. Boos mode: The following parameers are seleced according o a 400W for fuel cell and baery applicaions. V b =12V, R b =1Ω, D = 45%, f s =10 khz, L s = 380 µh, L a = 4.96µH, C P1 = C S1 = 20mF, C 0 = 150mF, R L = 0.5Ω.V o = 80V The simulaions revealed modes of operaion where he primary side swiches operae under ZVS, ZCS condiions. The simulaion resuls were shown in Fig. 3, 5(a,b). Swiching frequency: f s = 10kHz Maximum duy cycle: D max = 0.5 Transformer urns raio: N1:N2 = 1:2 The 80W converer which was esed in he laboraory was designed wih a oupu volage 80V and was driven from a half-bridge wih an auxiliary circui. The oscillograms in Fig. 7b shows primary side and secondary side volages in boos mode, and Fig. 7c shows he driving pulses o he swiches S 1,S a and he ransformer curren (i r ) which shows ha ZCS sae in boos mode. The converer did no behave as expeced due o he circui layou and componen selecion. The raed inpu volage is 12V and oupu volage 80 V / 80W is due o a 1:2 urns raio for he ransformer. Insead of using IGB in secondary side [1],IRF 840 MOSFE are used in secondary side. An addiional advanage of he auxiliary circui is ha swiching losses of S 1 &S 2 is reduced. Fig. 5b. DC oupu volage 2. Buck mode: Similarly, he buck mode can also be simulaed using same parameers as boos mode. Simulaions of he proposed converer waveforms are presened in Fig. 6. Shown are he primary side and secondary side volages (VP1, V S2 ). The simulaions revealed modes of operaion where he primary side swiches operae under ZVS condiion. Fig. 7a. Experimenal seup Fig driving pulses Fig. 7b. Primary side and Secondary side volages in boos mode Fig. 6. Transformer primary and secondary volages in buck mode V Experimenal Resuls An experimenal seup of he proposed converer has been buil o verify he principle of operaion. I was operaed wih boh boos mode wih a ZVS-ZCS and buck mode wih he ZVS echnique. The experimenal seup is picured in Fig. 7a. The specificaions are as follows. Raed oupu power: P O = 80W Inpu volage: V in = 12V Oupu volage: V O = 80V Fig. 7c. Driving pulses S a& S 1 and Transformer curren i r 16
VI CONCLUSION A novel ZVS-ZCS bi-direcional DC-DC converer has been presened in his paper. The operaion, sae space mahemaical model and experimenal resuls were illusraed. Simulaion resuls are compared wih he experimenal resuls o verify he operaion principle. I is shown ha ZVS-ZCS in one direcion of power flow is achieved in boos mode wih no swiching losses involved and oher direcion of power flow involves ZVS wih no swiching losses. Due o he simulaneous boos conversion and inversion provided by he low volage side half bridge, curren sresses on he swiching devices and ransformer are reduced by swiching an auxiliary swich in primary side i.e. ZCS condiion. The advanages of he proposed circui are, curren sresses are reduced, high efficiency, which is achieved due o he ZCS operaion. The drawbacks of his proposed converer is cos is incremen due o he auxiliary circui componens and decreased oupu power. This proposed converer for medium power applicaions like fuel cell and baery, wih high power densiy. Excellen dynamic performance is obained because of he auxiliary circui used in he half bridge. ACKNOWLEDGMENT The auhors wishes o hank Mr Uday kumar for his help in fabricaion a he iniial sages. We are also graeful o Mr. Srinivas Rao Kurei for his simulaion assisance in his work and Mr.K.Rama Lingeswara Prasad his assisance. REFERENCES [1] Fang Z.Peng,Hui Li,Gui-Jia,Jack S.Lawler, A new ZVS bidirecional dcdc converers for fuel cell and baery applicaion, IEEE Trans. Power Elecro., vol. 19,No. 1,Jan 2004,pp 54-65. [2] H.L.Chan, K.Cheng, and D.Suano, An exended load range ZCS-ZVS bidirecional phase shif dc-dc converer, in proc. 8h In.conf.Power Elecron. Variable speed drives, 2000, pp 74-79. [3] Manu Jain, M.Daniele, and Praveen K.Jain, A bidirecional dc-dc converer opology for low power applicaion, IEEE Trans. Power Elecro.,vol. 15, No.4,July 2000,pp 595-606 [4] Fang Z.Peng,Hui Li, modeling of a new ZVS bidirecional dc-dc converer, IEEE Trans. Power Elecron, vol. 40, No. 1, Jan 2004, pp 272-283. [5] H.Chung e al., A ZCS bidirecional flyback dc-dc converer, IEEE Trans. Power Elecron, vol. 19,No. 6, Nov 2004, pp 1426-1434. [6] R.Mendes Finzi Neo,F.Lessa Tofoli, and Luis carlos de Freias, A High power-facor half-bridge doubler boos converer wihou commuaion losses, IEEE Trans.Power Elecron, vol. 52, No. 5, Oc 2005, pp 1278-1285. [7] L.C.Freias, D. F. Cruz, and V.J. Farias, A novel ZCS-ZVS PWM dc-dc converer for high swiching frequency: analysis,simulaion and experimenal resuls, in proc.ieee APEC 93,San Diego,CA,1993, pp 693-699. [8] F.Carichhi, F.Crescimbini, F.G.Capponi, and L.Solero, Sudy of bidirecional buck-boos converer opologies for applicaion in elecrical vehicle moor drives, in proc. IEEE applied power elecronics specialiss conf. Expo, 1998, pp. 287-293. [9] S.Hamada e al., A novel zero-volage and zero-curren swiching PWM dc-dc converer wih reduced conducion losses, IEEE Trans. Power elecron., vol. 17, pp. 413-419, May 2002. [10] Z.R.Marinez and B.Ray, Bidirecional dc/dc power conversion using consan frequency muli-resonan opology, in Proc. APEC 94, 1994, pp. 991-997.\ [11] D.Makasimovic, S.Cuk, A general approach o synhesis and analysis of quasi-resonan converers, IEEE Trans.Power Elecron., vol. 6,No. 1,Jan 1991, pp. 127-140. PEDS2009 [12] R. L. Lin, Fred C.Lee, Novel zero-curren swiching-zero-volage swiching converers, in proc. IEEE PESC 96, pp. 438-442. [13] R. W. DeDonker, D. M. Divan, and M.H.Kheraluwala, A Three-phase sof-swiched high power densiy dc-dc converer for high power applicaions, IEEE Trans. Ind.Applica.,vol. 27,pp.. 63-73,Jan./Feb.1991. V.V.SUBRAHMANYA KUMAR BHAJANA received his B.E. degree in Elecronics and Communicaion Engineering from Saphagiri College of Engineering, Dharmapuri, Tamilnadu, India (Universiy Of Madras), in 2000 and here afer, he did his M.E degree in Power Elecronics and Drives from he P.S.N.A College of engineering and Technology, Dindigul, Tamilnadu, India under Anna Universiy, Chennai in he year 2005. He is presenly a research scholar a Bharah Universiy Chennai, India. His key area of ineres is Power Elecronics engineering, which includes sof swiching DC - DC converers and heir applicaions. S.RAMA REDDY is professor of elecrical deparmen, Jerusalem engineering college, Chennai, amilnadu, India. He obained his L.E.E. from S.M.V.M.ployechnic, Tanuku, A.P, A.M.I..E. in elecrical engineering from insiuion of engineers (India), M.E. in Power Sysems from Anna Universiy. He has published over 20 echnical papers in naional and inernaional conference proceedings/journals. He has secured A.M.I.E. insiuion gold medal for obaining highes marks. He has secured Aimo bes projec award and Vijaya Rana Award. He has worked in Taa Consuling Engineers, Banglore and Anna Universiy, Chennai. He has eaching experience of 12 years. His research ineres is in he areas of resonan converers, VLSI, and solid sae drives. He is life member of insiuion of engineers (India), Indian sociey for echnical educaion, sysem sociey of India and sociey of power engineers. He is a fellow of insiuion of elecronics and elecommunicaion engineers ( India). He has published ex books on power elecronics and solid sae circuis. 17