A Bidirecional Three-Phase Push-Pull Converer Wih Dual Asymmeral PWM Mehod Minho Kwon, Junsung Par, Sewan Choi, IEEE Senior Member Deparmen of Elecral and Informaion Engineering Seoul Naional Universiy of Science and Technology Seoul, Korea E-mail: schoi@seoulech.ac.r Absrac This paper proposes a new bidirecional hree-phase push-pull converer ha has he simples srucure and achieves ZVS of swhes. The proposed dual asymmeral PWM (DAPWM) echnique offers no only power flow conrol or oupu volage conrol bu reduced circulaing curren by maching he primary volage wih he secondary volage referred o he primary. A bidirecional mode change is easy o implemen since swhing paerns for boh forward and reverse operaions are idenal and he power flow is deermined by he difference in he wo duy cycles. Experimenal resuls from a 5W prooype are provided o validae he proposed concep. I. INTRODUCTION The hree-phase DC-DC converer has presened good performance in he high power applaions where high deve sresses are faced when implemened wih he single-phase DC-DC converer. Generally, he hree-phase DC-DC converer has several advanages over is single-phase counerpar; easy MOSFETs selecion due o reduced curren raing, reducion of he inpu and oupu filers volume due o increased effecive swhing frequency by a facor of hree, and reducion in ransformer size due o beer ransformer uilizaion. The hree-phase curren-fed converer proposed so far can be classified by primary-side configuraion ino hree bas opologies: full bridge [1], L-ype half bridge []-[4], and push-pull [5]. A simple acive-clamp circui [1] was inroduced ino he hree-phase curren-fed converer in order o achieve ZVS of swhes as well as alleviae volage spies, bu swhing frequency of he acive-clamp swh is six imes higher han ha of main swhes, whh limis he swhing frequency of he overall sysem. The hree-phase curren-fed converer based on L-ype half-bridge opology was inroduced in []. Acive-clamp circuis were applied o he hree-phase L-ype half-bridge converer in [] and [4]. Besides reduced oal number of swhes compared o he hree-phase full-bridge converer proposed in [1], a major advanage of he hree-phase L-ype half-bridge converer is ha he swhing frequency of clamp swhes is he same as ha of main swhes, and herefore, higher power densiy can be achieved by furher increasing he swhing frequency of he overall sysem. However, curren unbalance associaed wih hree inducors could be a challenging issue, especially when he power raing is increased, and herefore some conrol means needs o be provided for balancing he phase currens [5]. A hree-phase curren-fed push pull converer was inroduced in [6], and an acive clamping echnique has been applied o he hree-phase curren-fed push-pull converer [7] in order o achieve ZVS urn ON of swhes as well as clamping of he surge volage. The hree-phase push pull converer has he simples srucure in ha only one inducor and a hree-phase ransformer are used, and hence he unbalance associaed wih hree phase currens is alleviaed. In his paper, a new bidirecional hree-phase push-pull converer wih acive clamping is proposed. The proposed converer achieves boh ZVS urn ON of swhes and clamping of surge volage. The proposed DAPWM echnique offers no only power flow conrol or oupu volage conrol bu reduced circulaing curren by maching he primary volage wih he secondary volage referred o he primary owing o he use of wo independen duy cycle conrols on each side. A bidirecional mode change is easy o implemen since swhing paerns for forward and reverse operaions are he same and he power flow is deermined by he difference in he wo duy cycles. The gae signal generaion of he DAPWM mehod can easily be implemened in digial sysem such as a general PWM mehod. II. DESCRIPTION OF PROPOSED CONVERTER The proposed converer is basally a hree-phase currenfed push pull converer, as shown in Fig. 1. The low volage side (LVS) of he proposed converer includes a hree-phase swh bridge consising of six swhes ~S L6, a clamp capacior C C, and an inpu filer inducor L f whh is operaed a hree imes he swhing frequency. The high volage side V L S L a I L b c S L6 L f i a i b i c N P1 N P N P no 1 : N N S1 N S N S i x i y i z S H x y z S H6 Figure 1. Proposed bidirecional hree-phase push-pull converer 978-1-4799-7-/1/$1. 1 IEEE 161
(HVS) of he proposed converer is a hree-phase swh bridge consising of six swhes ~S H6. The hree-phase windings of he ransformer are configured in Y Y connecion. The neural poin of he hree-phase primary winding is conneced o he inpu source hrough he inpu inducor. Noe ha a hree-leg core mus be used for proper operaion of he proposed converer. A. Swhing Mehod Fig. shows he swhing paern of he proposed DAPWM mehod for a phase of he converer. I has wo conrol variables, D L and D H, for boh forward(boos) and reverse(buc) operaion. Duy cycles, D L and 1-D L, of he op and boom swhes of he LVS are used o mainain consan capacior volage under varying LVS volage condiion. The volage across C C is deermined by he following equaion: V V L =. (1) DL In he meanwhile, duy cycles, D H and 1-D H, of he op and boom swhes of he HVS are used o conrol he power flow beween he LVS and HVS. The direcion of power flow is deermined by relaive lengh of he wo duy cycles: D L < D H for boos operaion and D L > D H for buc operaion. The hree swh pairs are inerleaved wih 1 phase shif, whh leads o an increased effecive swhing frequency resuling in smaller inpu-curren ripple. B. Operaing Principles In his secion he operaing principles of he boos and buc operaions of he proposed converer are described in deail. The ey waveforms of he proposed converer wih DAPWM for boos operaion are shown in Fig.. The boos operaion has six operaing modes wihin an operaing cycle, and he operaion saes of he six operaing modes are shown in Fig. 4. Fig. 5 shows simplified equivalen circuis of each mode for deailed circui analysis. For he sae of simpliy, i is assumed ha he volage across C C and he curren hrough he L f are consan during he swhing period T S, and leaage inducances of each phase are L. Mode I [ - 1 ]: Before, swhes,,,, and are being urned ON. A swhes and are urned OFF, and swhes and are urned ON, whh causes changes in he volages across he leaage inducors and he volage can be obained from Fig. 5. Thus, he slopes of he phase currens flowing hrough he leaage inducors can be expressed as follows: dia d N = = () d d NL dib ( N) =. () d NL If capacior volage is regulaed o /N, he slopes of each curren flowing hrough he leaage inducors are zero, meaning all he phase curren are consan in his mode. During his mode he power is ransferred from LVS o HVS. A HVS he curren flows only hrough and alhough swh is being urned ON. Noe ha is urned ON under ZVS condiion and he ZVS curren is he same as phase curren i a = I L /. Mode II [ 1 - ]: A 1, swh is urned OFF, and S L6 is urned ON under ZVS condiion. I can be seen from Fig. 5 ha i c sars o increase wih he slope whh is deermined by: d + N =. (4) d NL As i c increases phase currens i a and i b decrease wih he slopes deermined, respecively, by: dia N = (5) d NL dib N =. (6) d NL Mode III [ - ]: A, swh is urned OFF, and S H6 is urned ON under ZVS condiion. The slopes of he phase currens can be obained from Fig. 5(c) as follows: dia ( N) = (7) d NL dib d + N = =. (8) d d NL All he phase currens are consan if capacior volage is regulaed o /N. This is he power ransfer mode such as Mode I. A HVS he curren flows only hrough and S H6. During his mode and are urned OFF, and S L and S H are urned ON. Noe ha S L is urned ON under ZVS condiion, and S H and are urned ON and OFF under ZCS condiion, respecively. The phase currens mainain conan even hough he volages across he leaage inducor change. Mode IV [ - 4 ]: A, swh is urned OFF, and is urned ON under ZVS condiion. I can be seen from Fig. 5(d) T S T S Figure. Swhing paern of he DAPWM. boos operaion. buc operaion. 16
Mode I ( 1) Mode II ( 1 ) Mode III ( ) SL SH SL SH SL SH L1 L1 L1 L L ib NP NS L L ib NP NS L L ib NP NS Mode IV ( 4) Mode V ( 4 5) Mode VI ( 5 6) SL SH SL SH SL SH L1 L1 L1 L L L L ib NP NS L ib NP NS L ib NP NS Figure. Operaion modes of he proposed converer(boos operaion). v L v L1 v L1 1 S L6 1 S L NP v L NS NP v L v L NS S H Mode I Mode II i c S H6 i a i b T S NP v L v L1 v L NS v L1 v L NP v L NS v i I,on (c) Mode III v L (d) Mode IV v L1 v i v i v i I,on 1 4 5 ha he volages of he leaage inducors. Thus, he slopes of phase currens are obained as follows: dia + N = (9) d NL dib N = (1) d NL I,on Figure 4. Key waveforms of he proposed converer wih DAPWM (boos operaion). 6 NP v L1 v L NS d + N =. (11) d NL Mode V [ 4-5 ]: A 4, swh is urned OFF, and is urned ON under ZVS condiion. From Fig. 5(e), he slopes of phase currens can be obained as follows: dia ( N) = (1) d NL dib d N = =. (1) d d NL v L v L (e) Mode V (f) Mode VI Figure 5. Equvalen circui for each mode(boos operaion). NP NS 16
Mode I ( 1) Mode II (1 ) Mode III ( ) SL SH SL SH SL SH L1 L1 L1 L L L L ib NP NS L ib NP NS L ib NP NS Mode IV ( 4) Mode V (4 5) Mode VI (5 6) SL SH SL SH SL SH L1 L1 L1 L L L L ib NP NS L ib NP NS L ib NP NS Figure 6. Operaion modes of he proposed converer(buc operaion). 1 S L6 1 S L sar o decrease or increase, respecively, wih he slopes deermined as follows: dia + N = (14) d NL v i v i v i v i I,on I,on S H6 i c This is also he power ransfer mode such as Mode I and Mode III. During his mode S L6 and S H6 are urned OFF, and and are urned ON. Noe ha is urned ON wih ZVS, and and S H6 are urned ON and OFF under ZCS condiion, respecively. Mode VI [ 5-6 ]: A 5, swh S L is urned OFF, and is urned ON under ZVS condiion. Then he phase currens S H I,on 1 4 5 i T b S Figure 7. Key waveforms of he proposed converer wih DAPWM (buc operaion). i a 6 dib + N = (15) d NL d N =. (16) d NL When S H is urned OFF, he phase currens sop decreasing or increasing, and he converer eners ino he power ransfer operaion. This mode ends when and are urned OFF. This is he end of one complee cycle. In he buc operaion he proposed converer wih DAPWM mehod has six operaing modes wihin an operaing cycle, and he operaion saes of he six operaing modes are shown in Fig. 7. Deailed explanaion of operaing modes is omied here since he operaing principle of he buc mode is very similar o he boos mode. I is noed ha all he swhes are urned on wih ZVS in he buc mode. C. Power Equaion Fig. 8 shows waveforms of he winding volage and curren for obaining power equaion of he proposed converer assuming N =. The power equaion of DAPWM mehod can be obained by he inegraion of he insananeous power over one swhing period. π PO = v ( ) ( ) xo ω ix ω dω π (1) where v xo is he insananeous volage across N S1 and he secondary curren i x is Nvan vxo ix( ω) = ω + i () x (14) N ωl where i x ()=. The power equaion can be obained from (1) and (14) by, 164
πd L Power flow conroller v an v xo Nv an -v xo πd L π(d L - ) πd H π(d H - ) πd H ω ω ω Conroller PI HVS volage compensaor PI I L PI Lf curren compensaor CC volage compensaor 1 D L V V L Feed forward compensaor D H D L PWM PWM Generaor S H6 S L6 i x Po(p.u.).5 1.5 1.5 -.5-1 -1.5 - Figure 8. Waveforms of winding volage and curren for obaining power equaion. -.5 1.8.6 DH Figure 9. Power flow versus D L and D H..4. (N + ) PO = ( DH DL ). (15) ωl If = N, he power equaion can be rewrien as follows: 5NV P = ( D D ). (16) O H L ωl The normalized power equaion can be expressed as follows: 5 PO = ( DH DL ) (17) where 1p.u. = N V /ωl. Using (17) he power flow of he proposed converer as a funcion of D L and D H is ploed as shown in Fig. 9. D. Conrol sraegy Fig. 1 shows he conrol bloc diagram of he proposed converer for bidirecional operaion while regulaing he HVS volage. The proposed converer has conrol variables, D L and D H, and herefore i needs wo conrollers: One is he power flow conroller ha regulaes he HVS volage using an average curren-mode conrol. The oher is he clamp..4 DL.6.8 1 π ω Figure 1. Conrol bloc diagram of he proposed converer for bidirecional operaion. capacior volage conroller ha regulaes under varying he LVS volage condiion. In order o minimize he curren sress of boh ransformer and swhes, he reference value of is deermined as follows: * =. (18) N Noe ha he clamp capacior volage conroller includes a feed forward compensaor whose oupu D L is he nominal value of D L and deermined from (1) by: D L V =. (19) VL I is also noed ha D H is sum of he oupu of he power flow conroller and D L whh is he oupu of conroller. III. EXPERIMENTAL RESULTS To verify he operaing principle of he proposed converer, a 5W prooype was buil according o he following specifaion: P o = 5W = 8V V L = 8V f s = 5Hz L f = μh L = μh C C = 18μH Figs. 11 and 1 show he experimenal waveforms of he boos and buc operaions of he proposed converer, respecively. I can be seen ha swhes are urned ON under ZVS condiion. Fig 1 shows he primary phase curren waveforms showing inerleaving operaion. The measured effiencies for boos and buc modes are shown in Fig. 14. The effiency was measured using Yoogawa WT. The maximum effiencies of he boos and buc modes are 95.7% a W and 96.9% a.5w, respecively. IV. CONCLUSIONS In his paper, a new bidirecional hree-phase push-pull converer wih acive clamping has been proposed. The proposed converer achieves no only clamping of surge volage bu ZVS urn on of swhes. The proposed DAPWM echnique offers no only power flow conrol or oupu volage conrol bu reduced circulaing curren. A bidirecional mode change is easy o implemen since swhing paerns for forward and reverse operaions are he same. A 5W prooype of he proposed converer has been buil and esed o verify he validiy of he proposed operaion. The maximum effiencies in forward and reverse mode are 95.7% a W 165
V [1V/div] V [1V/div] V [1V/div] V [1V/div] i a [A/div] i a [A/div] V [1V/div] V [1V/div] V [1V/div] V [1V/div] i x [A/div] i x [A/div] Figure 11. Experimenal waveforms of swh volages and curren(boos operaion). LVS. HVS. Figure 1. Experimenal waveforms of swh volages and curren(buc operaion). LVS. HVS. i b [A/div] i a [A/div] i c [A/div] Effiency (%) i a [A/div] i c [A/div] i b [A/div] Oupu Power (W) Figure 14. Measured effiency as a funcion of he oupu power a V L = 8V. and 96.9% a.5w, respecively. Furher experimenal resuls associaed wih bidirecional mode change will be provided in he final paper. REFERENCES Figure 1. Experimenal waveforms of he primary phase currens. boos operaion. buc operaion. [1] H. Cha, J. Choi. P.N. Enjei, A Three-Phase Curren-Fed DC/DC Converer Wih Acive Clamp for Low-DC Renewable Energy Sources, IEEE Trans. Power Elecron., vol., no. 6, pp. 784 79, Nov. 8. [] S. V. G. Oliveira and I. Barbi, A Three-Phase Sep-Up DC DC Converer Wih a Three-Phase High-Frequency Transformer for DC Renewable Power Source Applaions, IEEE Trans. Ind. Elecron., vol. 58, no. 8, pp. 567 58, Aug. 11. [] H. Cha, J. Choi, and B. Han, A newhree-phase inerleaved isolaed boos converer wih acive clamp for fuel cells, in Proc. IEEE Power Elecron. Spec. Conf. (PESC), Jun. 8, pp. 171 176. [4] C. Yoon and S. Choi, A muli-phase dc dc converers using a boos half bridge cell for high volage and high power applaions, in Proc. IEEE In. Power Elecron. Moion Conrol Conf. (IPEMC), May 9, pp. 78 786. [5] Z. Wang and H. Li, Three-phase bidirecional DC-DC converer wih enhanced curren sharing capabiliy, in Proc. IEEE Energy Convers. Congr. Expo (ECCE), Alana, GA, Sep. 1, pp. 1116 11. [6] R. L. Andersen and I. Barbi, A hree-phase curren-fed push-pull dc-dc converer, IEEE Trans. Power Elecron., vol. 4, no., pp. 58 68, Feb. 9. [7] S. Lee, J. Par. S. Choi, A hree-phase curren-fed push-pull DC-DC converer wih acive clamp for fuel cell applaions, IEEE Trans. Power Elecron., vol. 6, no. 8, pp. 66 77, Aug. 11. [8] M. H. Kheraluwala, D. W. Novony, and D. M. Divan, Design consideraions for high power high frequency ransformers, in IEEE Power Elecron. Spec. Conf. (PESC), 199, pp. 74 74. [9] H. J. Chiu and L. W. Lin, A bidirecional DC-DC converer for fuel cell elecr vehle driving sysems, IEEE Trans. Power Elecron., vol. 1, no. 4, pp. 95 958, Jul. 6. [1] S. Inoue and H. Aagi, A bidirecional DC-DC converer for an energy sorage sysem wih galvan isolaion, IEEE Trans. Power Elecron., vol., no. 6, pp. 99 6, Nov. 7. 166
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