Design and Contol of a Bi-diectional Resonant - Convete fo Automotive Engine/Battey Hybid Powe Geneatos Junsung Pak, Minho Kwon and Sewan Choi, IEEE Senio Membe Depatment of Electical and Infomation Engineeing Seoul National Univesity of Science and Technology E-mail: schoi@seoultech.ac.k Abstact In this pape a bidiectional - convete is poposed fo automotive engine/battey hybid powe geneatos. The two-stage bidiectional convete employing a fixed-fequency seies loaded esonant convete(src) is designed to be capable of opeating unde zeo-cuentswitching(zcs) tun on and tun off egadless of voltage and load vaiation, and hence its magnetic components and EMI filtes can be optimized. Also, a new autonomous and seamless bidiectional voltage contol method that combines two individual contolles fo low voltage side contol and high voltage side contol by intoducing a vaiable cuent limite is poposed to povide uninteupted powe to citical AC loads and educe the size of the bus capacito. Expeimental esults fom a 5 kw pototype ae povided to validate the poposed concept. Keywods hybid powe geneato, bidiectional - convete, seies loaded esonant convete, zeo cu-ent switching, seamless tansition I. INTRODUCTION Standby o emegency geneatos ae often used as backup powe supplies fo buildings, industial facilities, and powe plants in the event of a loss of utility powe [1]. In addition, emote powe geneation fo militay, industial, and pesonal use equies a eliable, compact, and lightweight powe geneation system. The diesel geneation system has been used as backup powe supplies o emote powe geneatos[]. Since the engine geneato may not be able to espond to sudden load changes, enegy stoage devices should be used along with the engine geneato to level out the eatic changes in powe balance between the geneation and load consumption[3][4]. Enegy stoage device is used along with a bidiectional - convete(b) in ode to match the voltage level and/o achieve efficient chaging and dischaging opeation[]. Fig. 1 shows an automotive engine/battey hybid powe geneation system. The B is located between the high voltage bus and the low voltage battey which is also connected to loads such as anti-lock bakes, electic powe steeing, heated seats, electonic ignition and HVAC in the vehicle. The -AC invete convets the powe to AC powe to supply the citical AC load in the vehicle such as boadcasting equipment of outside boadcast van and communications equipment of tactical vehicle. The AC- convete convets the AC powe fom the engine geneato to the powe, egulating the high voltage bus[5]. If the engine geneato is capable of supplying total demanded powe of AC and loads, the AC- convete will be able to egulate the high voltage bus, and the B will delive the powe fom the engine geneato to the low voltage side. If the engine geneato is shut down o total demanded powe of the AC and loads is geate than the maximum powe of the engine geneato, high side bus voltage will dop off to a voltage depending on the capacitances of the bus capacito. Then, the B is equied to take ove the egulation duty of the high voltage bus by changing ove fom V contol (battey chaging) to V H contol (battey dischaging) so that it should be able to delive powe fom the battey to the AC load. Theefoe, in ode to povide uninteupted powe to the citical AC loads and educe the size and cost of the bus capacito, the tansition fom V contol to V H contol of the B should be seamless and as shot as possible. This is a cucial pefomance of the B, especially, in the automotive application whee electolytic capacitos cannot be used due to limited lifespan and bulky natue[6]-[9]. So fa, bidiectional voltage contol methods with seamless mode tansition of the B have not been discussed. The B should povide galvanic isolation and high step up/down voltage convesion atio in the application whee the low voltage battey is used. Typical topology candidates with Fig. 1. Automotive engine/battey hybid powe geneation system 978-1-4799-048-/13/$31.00 013 IEEE 740
0 S H1, S 1 DT s= f 0.5T s S H, S 1 T s v Fig.. Poposed two-stage bidiectional - convete these equiements include half-bidge, full-bidge and pushpull PWM convetes [10][11], dual active bidge(dab) convetes [1][13], and esonant convetes [14]-[17]. The half-bidge, full-bidge and push-pull PWM convetes usually necessitate passive o active clamping on the low voltage side with inductos to clamp the suge voltage geneated by the leakage inductance of the tansfome. The active clamping technique makes the convete not only clamp the suge voltage, but achieve zeo-voltage-switching (ZVS) tun on of all switches. A dawback of the active clamped PWM convete is high switch tun off losses[18]. The DAB has a modula and symmetic stuctue and can achieve ZVS tun on without auxiliay components. Howeve, the DAB has limited ZVS ange and high ciculating cuents fo applications equiing wide voltage vaiation. The ipple cuent of the DAB convetes is high and especially poblematic in the low voltage application[19]. The bidiectional esonant - convete geneally sees diffeent esonant tanks in fowad and evese modes, espectively, esulting in diffeent voltage gains. This often makes it difficult to satisfy the equied voltage gain fo both modes of opeation[14][15]. The dual bidge SRC convete has lage cuent in the esonant tank compaed to the DAB convete[16]. A minimum cuent opeation fo the dual bidge SRC convete has been poposed with a complicated switching method[17]. The bidiectional CC esonant convete in [14] equies fou esonant components to be designed and theefoe has a challenging issue fo high volume manufactuing associated with esonant component toleances. In this pape, a two-stage B is poposed fo automotive engine/battey hybid powe geneatos. The poposed twostage B consists of a non-isolated convete and a fixed fequency SRC. The SRC is designed be capable of opeating unde ZCS tun on and tun off egadless of voltage and load vaiation in both fowad and evese opeation. A method of adjusting dead time of the SRC will be pesented to minimize the switch tun on losses associated with enegy stoed in MOSFET s output capacitances duing the ZCS tun on pocess. Also, a new autonomous and seamless bidiectional voltage contol stategy is poposed to povide uninteupted powe to the citical AC loads and educe the size of the bus capacito. II. PROPOSED BIDIRECTIONA - CONVERTER The poposed B consists of two powe convesion stages: a non-isolated convete and a fixed fequency SRC, as shown in Fig.. Since the SRC is opeated at fixed fequency and fixed duty all components can be designed with minimum voltage and cuent ating. The non-isolated convete is opeated to egulate eithe high side voltage V H o low side voltage V accoding to demanded load powe and availability of the engine geneato. Figs. 3 and 4 show key wavefoms and opeation states of the poposed SRC, espectively. Mode I i v C1 v C i SH1 i SH i S1 i S V S,on V i V i Nea ZCS tun-on v SH begins with -C esonance when switches S H1 and S ae tuned on at t 0. The angula esonant fequency of the esonant cicuit can be expessed as, ω = π f = 1 C whee esonant inductance and esonant capacitance can be detemined espectively by, V SH,on ZCS tun-on v S1 V S,off ZCS tun-on I,pk ZCS tun-on I m,pk t 0 t 1 t = kp + m m D d T s V S,ON Fig. 3. Key wavefoms of the poposed SRC ks ks n + n C C1 C 3 v SH1 v S (1) () = +. (3) It is seen fom Figs. 3 and 4 that low side cuent i (=i S ) at Mode I(t 0 -t 1 ) becomes puely sinusoidal if the on-time duty cycle is selected such that DT s = 0.5f. Then it can be expessed as, i m ISH,off = I m,pk Nea ZCS tun-off Nea ZCS tun-off ZCS tun-off ZCS tun-off V SH,on t 3 t 4 π I, i() t = sinωt (4) 741
V i Mode I (t 0~t 1) Mode II (t 1~t ) V i C 1 C C a C 1 a S H1 S H S H1 S H b b Also, voltage acoss m can be expessed as, di v () ( m t = n V + ks ) (5) dt Theefoe, fom eqns. (4) and (5) the magnetizing cuent at Mode I (t 0 -t 1 ) can be expessed using i m (t 0 ) = - i m (t 1 ) by, nπv nv nπ ksi, im() t = t + sinωt ωm m m The esonant cuent can then be obtained using eqns. (4) and (6) by, nπv nv nπksi, πi, i () t = t + sinωt. (7) ωm m m n Neglecting voltage oscillation afte tuning on of S, voltage acoss low side switch S 1 at Mode I (t 0 -t 1 ) is expessed as, (6) () di vs1 t = V + ks (8) dt The tun off voltage of low side switch can be obtained by, V i i kp m i m kp Tansfome n : 1 : 1 Tansfome m i m n : 1 : 1 Fig. 4. Key wavefoms of the poposed SRC πω I ks, S, off = V (9) It should be noted that V S,off should be geate than zeo fo the poposed opeation. Theefoe, fom eqns. (4) and (9) the seconday side leakage inductance should be limited such as, ks ks ks ks S 1 S S 1 S i C i C I, I, V V ks 4V < πω I (10), Switch S H1 is tuned off at t 1, and tun off cuent of the high side switch, I SH,off, becomes equal to peak magnetizing cuent I m,pk. Since m is made vey lage in the poposed SRC, I m,pk is vey small, esulting in negligible switch tun off losses. Duing Mode II, the output capacitos of S H1 and S H ae chaged and dischaged, espectively by I m,pk, as shown in Fig. 3. The chaging and dischaging opeation may not be completed at the end of Mode II if I m,pk is not sufficiently lage, which may lead to a non-zeo tun on v oltage of high and low side switches. The tun on voltages of the high and low side switches can be detemined espectively by, ni DT m, pk d s SH, on = SH ( ) = i ncossp + COSSs V v t V 4V πωksi ni D T, VS, on = vs 1( t) = nc + C Gain 30 40 m, pk d s OSSp OSSs (11) (1) Note that S H and S 1 ae tuned on with ZCS, but thee exists tun on losses of high and low side switches associated with enegy stoed in MOSFET s output capacitances as follows[0][1], 1.5 1.0 11.5 11.0 10.5 10.0 9.0 0 P = 0.5C V f. (13) SH, loss( on) OSSp SH, on s P = 0.5C V f. (14) S, loss( on) OSSs S, on s 9.5 10.0010 10.0005 10.0000 9.9995 Opeating fequency 1.67 X 10-4 f= 1 fs1 D 9.9990 40 45 50 55 60 Po=1 kw Po=3 kw Po=5 kw 50 60 70 80 90 100 110 f s1 (khz) Fig. 5. Voltage gain cuve chaging mode dischaging mode (P o=5 kw, V i=80 V, V =8 V, f s1=48 khz, n=5, =5.8 uh, C =1.88 uf) i SH oad incease v SH t Nea ZCS tun-on Nea ZCS tun-off i S ZCS tun-on oad incease v S ZCS tun-off Fig. 6. Switch voltage and cuent wavefoms of the poposed SRC high side switch low side switch t 74
Contolle G (s) Anti-windup Contolle G H (s) Contolle G I (s) PWM Geneato Vaiable cuent limite Anti-windup I B Fig. 7. Contol block diagam of the poposed battey chage Anti-windup Howeve, the tun on losses of the switches may be consideable in the high voltage application. The tun on loss P S,loss(on) of the low side switch is negligible since V S,on is small in this low voltage application, and the tun-on loss P SH,loss(on) of the high side switch is also small due to the twostage configuation. In the poposed SRC, P SH,loss(on) can futhe be educed by inceasing D d T s and, in tun, deceasing V S,on, as shown in Fig. 3. Howeve, inceasing D d T s may cause inceased cuent atings and undesied esonance, and hence it should popely be chosen. Theefoe, it is noted that both tun off and tun on switching losses of the poposed SRC is made negligible in this application. In the conventional fequency-contolled SRC, in geneal, esonant inductance should be made lage to educe the switching fequency ange. In the poposed SRC, on the contay, is chosen to be small since the SRC is not used fo egulation, esulting in vey small gain vaiation accoding to load vaiation in both chaging and dischaging modes, as shown in Fig. 5. Futhemoe, small leads to less sensitive to the esonant component toleances, eliminating the voltage egulation issues and satuation poblem of magnetic devices that was intoduced in the conventional fequency-contolled SRC[][3]. This also allows to be easily embedded in the tansfome. Also, the poposed SRC is able to achieve ZCS tun on and tun off of the switch without egad to voltage o load vaiation, as shown in Fig.6, by choosing the esonant fequency f as follows, 1 1 f = fs1 fs1 D = 1 D (15) III. PROPOSED CONTRO STRATEGY The high side bus is egulated to eithe 400V by the AC- convete o 380V by the B, espectively, accoding to condition of V H. The conventional contol of the B is in geneal ealized with two individual contolles of V contol fo battey chaging and V H contol fo battey dischaging, and theefoe may not be able to avoid lage tansient duing the tansition fom V contol to V H contol of the B. In this pape a new autonomous and seamless bidiectional voltage contol stategy, as shown in Fig. 7, is poposed to povide uninteupted powe to the citical AC loads and educe the size of the bus capacito. The two oute loop d voltage contolles fo V contol and V H contol ae combined by VC whose output I * B is automatically selected to be eithe I B,H, the output of the high side voltage contolle, o I B+, the positive limit of VC which vaies with the output of the low side voltage contolle. This makes it possible to shae inne loop cuent contolle, esulting in autonomous and seamless tansition fom V contol(chaging mode) to V H contol(dischaging mode), and vice vesa. The peak values of the positive and negative limit, I B-,pk and I B+,pk, of the VC ae detemined by, I P i B+, pk = IB, pk = (16) Vi Accoding to C-ate of the battey used, I B+,pk may be chosen smalle than eqn. (16). I B+ vaies with magnitude of V while I B- is always fixed at I B-,pk. The anti-windup is used to Powe [W] Cuent [A] 10K 5K 0K 400 395 390 385 380 375 9 8 7 6 5 4 40 0 0-0 Mode I Mode II Mode III 743 Fig. 8. Simulation wavefom of the poposed bidiectional voltage contol fo seamless tansition fom V contol to V H contol
Powe [W] Cuent [A] 10K 5K 0K 400 395 390 385 380 375 9 8 7 6 5 4 40 0 0-0 CC Mode I Mode II I B,CC Mode III Fig. 9. Simulation wavefom of the poposed bidiectional voltage contol fo seamless tansition fom V H contol to V contol pevent the satuation of the contolles. Fo the sake of simplicity it is assumed that the -load is constant and all the powe losses of the AC- convete, the -AC invete and the B in Fig. 1ae neglected. A. Tansition fom V contol to V H contol Figs. 8 shows PSIM simulation wavefoms fo illustation of the opeating pinciple of the poposed bidiectional contol stategy fo tansition fom V contol to V H contol. Mode I : Assume that the battey has aleady been fully chaged. The engine geneato is supplying the AC and loads duing this mode. V H is egulated to 400V by the AC- convete, and the efeence voltage V * H of the B is set at 380V. Since the high side voltage contolle G H (s) is satuated the efeence cuent I * B of the B is detemined by I B+ which is the same as I,. Mode II : This begins when the AC load inceases and the sum of the AC and loads is geate than P G,max, the maximum powe that can be poduced by the geneato. Then, the AC- convete is not able to egulate the bus, and V H dops off fom 400V, which makes I * B be changed to I B,H, as shown in Fig. 8. I * B deceases, changes its sign and continuously inceases. This means that the B stats to dischage the battey and egulate V H to 380V. As the battey voltage deceases, I B+ which is the output of the low side voltage contolle G (s) inceases up to I B+,pk. This is the end of the mode. CV Mode III : I * B is fixed at constant value since the AC load is constant. The B keeps dischaging the battey and egulating V H to 380V. I B+ is kept at I B+,pk. B. Tansition fom V H contol to V contol Figs. 9 shows PSIM simulation wavefoms fo illustation of the opeating pinciple of the poposed bidiectional contol stategy fo tansition fom V H contol to V contol. Mode I : This mode is identical to Mode III of Section III-A. The B is dischaging the battey and egulating V H to 380V. I * B is detemined by I B,H, and I B+ is the same as I B+,pk. Mode II : This mode begins when the AC load deceases and the sum of the AC and loads becomes smalle than P G,max. This makes the AC- convete be capable of egulating V H, ecoveing it back to 400V. Theefoe, I B(=I * B,H ) deceases and changes its sign, meaning that the B is able to egulate V to 8V, and continuously inceases until it eaches to I B+,pk. Now, I * B is detemined by I B+ (=I B+,pk ) since the high side voltage contolle G H (s) is satuated. Then, the B stats to chage the battey with constant cuent of I B,CC which is detemined by, I = I I (17) BCC, B+, pk oad, Mode III : When the battey voltage V gets close to V * the efeence cuent I * B which is detemined by I B+ stats to decease. Duing this mode the B chages the battey with constant voltage of V *. IV. EXPERIMENTA RESUTS A 5 kw pototype of the poposed B has been built unde the following system paametes. P o = 5 kw V H 340~440 V V = 4~3 V N P : N S = 5 : 1 f s1 = 48 khz f s = 0 khz C f = 110 μf C H = 45 μf C i = 100 μf C = 380 μf B = 1 mh f = 0.4 μh = 5.8 μh D d T s = 600 ns C 1 (=C )=0.94 μf Figs. 10 and 11 show key expeimental wavefoms of the chaging and dischaging modes at full load, espectively. As we can see fom Figs. 10, (c) and Figs. 11, (c) all switches of the SRC ae being tuned on and off with ZCS in both chaging and dischaging modes. In fact, all switches of the SRC ae always tuned on and off with ZCS without egad to voltage and load vaiations. Figs. 1 shows the expeimental wavefoms of the mode tansition. A 4 V/100 Ah lead acid battey was used at the low voltage side. Fig. 15 shows that the B is egulating V to chage the battey, and V H is egulated to 400 V by the AC- convete. When the engine geneato is shut down, V H dops but is ecoveed to 380 V since the B changes ove to V H contol to dischage the battey. The efficiency of the poposed B including gate dive and contol cicuit losses is measued by YOKOGAWA WT3000 and shown in Fig. 13. The maximum efficiencies ae 95.13 % at 1.3 kw in chaging mode and 95.08 % at 1.5 kw in 744
(c) Fig. 10. Expeimental wavefoms of the chaging mode inducto cuent IB, switch voltages VSB,1 and VSB, of the non-isolated convete pimay cuent Ipi, high side switch voltages VSH,1 and VSH, of the SRC (c) pimay cuent Ipi, low side switch voltages VS,1 and VS, of the SRC VS, [50V/div] VS,1 [50V/div] ZCS tun on & tun off Ipi [0A/div] [5μs/div] (c) Efficienty (%) Fig. 11. Expeimental wavefoms of the dischaging mode inducto cuent IB, switch voltages VSB,1 and VSB, of the non-isolated convete pimay cuent Ipi, high side switch voltages VSH,1 and VSH, of the SRC (c) pimay cuent Ipi, low side switch voltages VS,1 and VS, of the SRC Fig. 13. Measued efficiencies of the poposed B including gate dive and contol cicuit losses Fig. 1. Expeimental wavefoms of tansition fom V contol fo chaging to VH contol fo dischaging dischaging mode, espectively. Fig. 14 shows the photogaph of the poposed B pototype. V. CONCUSIONS This pape poposes a bidiectional - convete fo automotive engine/battey hybid powe geneatos. The featues of the poposed B ae as follows. The poposed topology peseves the advantages of the two-stage - convete: 1) The switching method is simple in that voltage egulation and mode tansition ae caied out only by the non-isolated convete; ) All components atings of the isolated convete ae optimized. Fig. 14. Photogaph of the poposed B pototype advantages: 1) The SRC has vey small gain vaiation accoding to load vaiation, and theefoe the poposed B can be designed fo wide voltage ange; ) The SRC is less sensitive to the esonant component toleances, and theefoe suitable fo high volume Small can be used since the poposed SRC is not used fo egulation, which leads to the following 745
manufactuing; 3) Small can be easily embedded in the tansfome. The poposed SRC is capable of achieving ZCS tun on and tun off egadless of voltage and load vaiation. A method of adjusting dead time of the SRC has been pesented to minimize the switch tun on losses associated with enegy stoed in MOSFET s output capacitances duing the ZCS tun on pocess. An autonomous and seamless bidiectional voltage contol method with a vaiable cuent limite has been poposed to povide uninteupted powe to citical AC loads and educe the size of the bus capacito. Expeimental esults fom a 5kW pototype wee povided to validate the poposed concept. The maximum efficiencies including gate dive and contol cicuit losses ae 95.13 % at 1.3 kw in chaging mode and 95.08 % at 1.5 kw in dischaging mode, espectively. REFERENCES [1] P. Famoui, W. R. Cawthone, N. Clak, S. Nandkuma, C. Atkinson, R. Atkinson, T. McDaniel, and S. Peteanu, Design and testing of a novel linea altenato and engine system fo emote electical powe geneation, in Poc. IEEE Powe Engineeing Society 1999 Winte Meeting, Jan. 31- Feb. 4, 1999, pp. 108-11. [] Z. Chen, and Y. Hu, A hybid geneation system using vaiable speed wind tubines and diesel units, in Poc. 003 IEEE Ind. Electon. Soc. Annu. Meeting Conf., Nov. -6, 003, pp. 79-734. [3] E. Muljadi, and T. Bialasiewicz, Hybid Powe System with a Contolled Enegy Stoage, in Poc. 003 IEEE Ind. Electon. Soc. Annu. Meeting Conf., Nov. -6, 003, pp. 196-1301. [4]. Wang, and D. ee oad-tacking Pefomance of an Autonomous SOFC-Based Hybid Powe Geneation Enegy Stoage System, IEEE Tans. Enegy Conves., vol. 5, pp. 18-139, Ma. 010. [5] D. Kim, S. Choi, oad Balancing with Mobile Base Stations in Tactical Infomation Communication Netwoks, in Poc. IEEE Wieless Commun. and Netwoking Conf., Ma. 8-31, 011, pp. 8-31. [6] H. Wen, X. Wen, J. iu, X. Guo, and F. Zhao, A ow-inductance High- Fequency Film Capacito fo Electic Vehicles, in Poc. Int. Conf. on Electical Machines and Systems, Oct. 8-11, 007, pp. 046-050. [7] Y. X. Qin, H. S. H. Chung, D. Y. in, and S. Y. R. Hui, Cuent souce ballast fo high powe lighting emitting diodes without electolytic capacito, in Poc. 008 IEEE Ind. Electon. Soc. Annu. Meeting Conf., Nov. 10-13, 008, pp. 1968 1973. [8] J. Kim and S. Sul, Resonant link bidiectional powe convete.ii. Application to bidiectional AC moto dive without electolytic capacito, IEEE Tans. Ind. Appl., vol. 10, pp. 485-493, Jul. 1995. [9] H. Chae, H. Moon, and J. ee, On-boad battey chage fo PHEV without high-voltage electolytic capacito, Electon. ett., vol. 46, pp. 1691-169, Dec. 010. [10]. Rongyuan, A. Potthast, N. Fohleke, and J. Bocke, Analysis and design of impoved isolated full-bidge bidiectional - convete, in Poc. 35th IEEE Annu. Powe Electon. Spec. Conf., Jun. 0-5, 004, pp. 51-56. [11] G. Ma, W Qu, G. Yu, Y. iu, N. iang, and W. i, A Zeo-Voltage- Switching Bidiectional Convete With State Analysis and Soft- Switching-Oiented Design Consideation, IEEE Tans. Ind. Electon., vol. 56, pp. 174-184, Jun. 009. [1] R. W. De Doncke, D. M. Divan, and M. H. Khealuwala, A thee-phase soft-switched high-powe density / convete fo high-powe applications, IEEE Tans. Ind. Appl., vol. 7, pp. 63-73, Jan. 1991. [13] F. Kisme, and J. W. Kola Efficiency-Optimized High-Cuent Dual Active Bidge Convete fo Automotive Applications, IEEE Tans. Ind. Electon., vol. 59, pp. 745-760, Jul. 01. [14] W. C, P. Rong, and Z u, Snubbeless Bidiectional - Convete With New CC Resonant Tank Featuing Minimized Switching oss, IEEE Tans. Ind. Electon., vol. 57, pp. 3075-3086, Sep. 010. [15] G. Pledl, M. Taue, and D. Buechel, Theoy of opeation, design pocedue and simulation of a bidiectional C esonant convete fo vehicula applications, in Poc. IEEE Vehicle Powe and Populs. Conf., Sept. 1-3, 010, pp.1-5. [16] X. i, and A. K. S. Bhat, Analysis and Design of High Fequency Isolated Dual-Bidge Seies Resonant / Convete, IEEE Tans. Powe Electon., vol. 5, pp. 850-86, Ap. 010. [17]. Coadini, D. Seltze, D. Bloomquist, R. Zane, D. Maksimovi c, and B. Jacobson, Minimum Cuent Opeation of Bidiectional Dual-Bidge Seies Resonant / Convetes, IEEE Tans. Powe Electon., vol. 7, pp. 366-376, Jul. 01. [18] D. Fu, F.C. ee, Y. iu, and M. Xu, Novel multi-element esonant convetes fo font-end dc/dc convetes, in Poc. 39th IEEE Annu. Powe Electon. Spec. Conf., Jun. 15-19, 008, pp.50-56. [19] H. Xiao, and S. Xie, A ZVS Bidiectional - Convete With Phase-Shift Plus PWM Contol Scheme, IEEE Tans. Powe Electon., vol. 3, pp. 813-83, Ma. 008. [0] K. iu, and F. C. Y. ee, Zeo-Voltage Switching Technique in / Convetes, IEEE Tans. Powe Electon., vol. 5, pp. 93 304, Jul. 1990. [1] A. Bambilla, E. Dallago, P. Noa and G. Sassone, Study and Implementation of a ow Conduction oss Zeo-Cuent Resonant Switch, IEEE Tans. Powe Electon., vol. 41, pp. 41 50, Ap. 1994. [] J. Pak, M. Kim, and S. Choi, Fixed fequency Seies loaded Resonant Convete based Battey Chage which is insensitive to Resonant Component Toleances, in Poc. 7th Int. Powe Electon. and Motion Contol Conf. Jun. -5, 01, pp. 918-9. [3] M. Z. Youssef, and P. K. Jain, A eview and pefomance evaluation of contol techniques in esonant convetes, in Poc. 004 IEEE Ind. Electon. Soc. Annu. Meeting Conf., Nov. -6, 004, pp. 15-1. [4] W. Zhang, D. Xu, X. i, R. Xie, H. i, D. Dong, C. Sun, and M. Chen. Seamless Tansfe Contol Stategy fo Fuel Cell Uninteuptible Powe Supply System, IEEE Tans. Powe Electon., vol. 8, pp. 717-79, Feb. 013. 746