A Family of Zero Current Switching Switched- Capacitor DC-DC Converters

Transcription

1 A Family of Zero Curren Swiching Swiched- Capacior DC-DC Converers Dong Cao Deparmen of Elecrical & Compuer Engineering Michigan Sae Universiy Eas Lansing, MI 48824, USA Fang Zheng Peng Deparmen of Elecrical & Compuer Engineering Michigan Sae Universiy Eas Lansing, MI 48824, USA Absrac This paper presens a new zero curren swiching (ZCS) echnique for a family of swiched-capacior dc-dc converers. Compared o he radiional ZCS swiched-capacior dc-dc converers by insering a magneic core in he circui, hese new ZCS swiched-capacior dc-dc converers employ he sray inducance presen in he circui as he resonan inducor and provide sof swiching for he devices. These ZCS swichedcapacior dc-dc converers do no uilize any addiional componens o minimize swiching loss and reduce he curren and volage spike, hus leading o high efficiency and reliable benefi over radiional swiched-capacior dc-dc converers. Moreover, he bulky capacior bank exising in radiional swiched-capacior circuis for high power high curren applicaion o achieve high efficiency was reduced significanly. Small size, low capaciance, low ESR, high curren raing and high emperaure raing ceramic capaciors can be employed. Therefore, by using proposed ZCS echnique, small size, high power densiy, high efficiency, high emperaure raing, and high curren raing swiched-capacior dc-dc converer could be buil. Simulaion and experimenal resuls are given o demonsrae he validiy and feaures of he sof swiching swiched-capacior dc-dc converers. I. INTRODUCTION Wih he echnological developmen of silicon carbide (SiC) and ceramic maerials, very high emperaure (250 C) SiC swiching devices and ceramic capaciors will be available. Bu he magneic cores become dysfuncional a very high emperaure. Therefore, magneic-less swichedcapacior dc-dc converers operaing a very high emperaures become possible and aracive wih he adopion of naural air cooling by eliminaing bulky hea sinks and magneic cores. There are hree main basic srucures of radiional swichedcapacior dc-dc converers ha is mos popular, Marx generaor ype swiched-capacior dc-dc volage muliplier shown in Fig. 1 [1-3], charge pump ype muli-level modular swiched-capacior dc-dc converer shown in Fig. 2 [4, 5], and generalized muli-level ype swiched-capacior dc-dc converer shown in Fig. 3 [6-9]. The derivaion circuis of generalized muli-level ype swiched-capacior dc-dc converer are also popular in auomoive applicaions [10-14]. Fig. 2. Fig. 3. Fig. 1. Swiched-capacior dc-dc volage muliplier. Mulilevel modular swiched-capacior dc-dc converer. Generalized muli-level swiched-capacior dc-dc converer. However, here are many common drawbacks in radiional swiched-capacior dc-dc converers for high power and high curren auomoive applicaion. A huge capacior bank wih high capaciance has o be uilized in order o /10/$ IEEE 1365

2 reduce he volage ripple of he capaciors and achieve high efficiency, which will undoubedly increase he size of he converer [7, 10, 13, 15]. Besides, wih he increase of curren raing, huge urn off curren leads o unneglecable swiching loss of he device. High volage overshoo is also caused by large urn off curren. Moreover, EMI problems caused by he di/d and dv/d generaed during he swiching ransien are undesirable in auomoive applicaions. In order o reduce he swiching loss, volage spikes, and EMI, several ZCS mehods have been proposed by insering an inducor in series wih he capacior [16-21]. Bu hese mehods require a relaively big resonan inducor (larger han 1 µh) which is no viable o be achieved by he circui sray inducance as claimed. By insering a magneic core in he swiched-capacior circui o achieve ZCS is a conradicion by iself. The swiched-capacior circui wih a magneic core is no a swiched-capacior circui anymore. Many good feaures of swiched-capacior will lose including good inegraion capabiliy, small size and high emperaure operaion. Also, o uilize he parasiic inducance in he circui, he swiching frequency has o be pushed o ens of megaherz by using hese mehods, which is no echnically feasible [22-24]. This paper presens a new ZCS sraegy for a family of swiched-capacior dc-dc converers ha is able o overcome he aforemenioned drawbacks of radiional swichedcapacior dc-dc converers wihou insering big magneic cores or increasing swiching frequency o megaherz level. This new sraegy can achieve he ZCS for all he swiches wihou losing any he good feaures of swiched-capacior circui compared o he radiional ZCS sraegy. This ZCS sraegy employs he disribued parasiic inducance in he circui resonaing wih he capaciors o provide zero curren ransiion o he swiching devices. So, he swiching loss is minimized, volage spike is reduced and EMI is limied. In case he sray inducance is no sufficienly large or equalized as expeced, small air core inducors (less han 100n) or layou PCB wires can be used o mee he requiremen of he sray inducance. By considering he influence of sray inducance, he power loss is only relaed o he conducion loss of capaciors and swiching devices wihou considering gae drive and conrol loss, which is differen from he radiional swiched-capacior circuis. Therefore, bulky capacior banks wih high capaciance o reduce volage ripple and achieve high efficiency are no longer needed, while small size MLCC capaciors wih low ESR and low capaciance can be adoped o increase power densiy and reduce he converer size. No exra componens are added in he presened sof swiching sraegy, hus making i reliable and low in cos. A 160 W ZCS swiched-capacior dc-dc muliplier is analyzed and simulaed o confirm he proposed ZCS sraegy. A 12 V inpu 480 W ZCS volage doubler prooype is also designed and buil o confirm he operaion, simulaion and experimen resuls are provided. II. PROPOSED ZCS SWITCHED-CAPACITOR DC-DC CONVERTER FAMILY Fig. 4, Fig. 5, and Fig. 6 show he proposed ZCS swichedcapacior family uilizing he disribued parasiic inducance exising in he circui. Fig. 4 shows he N-level ZCS swichedcapacior dc-dc volage muliplier. Fig. 5 shows he N-level ZCS muli-level modular swiched-capacior dc-dc converer (ZCS-MMSCC) which has already been discussed in deail in [25]. Fig. 6 shows he N-level ZCS generalized muli-level swiched capacior dc-dc converer. The parasiic inducance mainly includes he sray inducance due o he circui layou, MOSFETs package parasiic inducance and he capacior ESL. The sray inducance caused by circui layou is usually he dominan par. By designing he circui layou properly, he inducance needed for resonan can be achieved. In case he circui layou is no well designed or equalized as expeced, an air core inducor could be insered o achieve he prerequisie disribued sray inducance. Because resonan inducors are disribued in he circui, only small resonan inducance is needed for resonan. Therefore, ZCS of all he swiching devices can be achieved by he resonan of he capacior and he disribued sray inducance in he circui. Fig. 5. Fig. 6. Fig. 4. ZCS swiched-capacior dc-dc volage muliplier. ZCS mulilevel modular swiched-capacior dc-dc converer. ZCS generalized muli-level swiched-capacior dc-dc converer. III. OPERATION PRINCIPLE A. ZCS Swiched-Capacior DC-DC Volage Muliplier Fig. 7 shows he four-level ZCS swiched-capacior dc-dc volage muliplier as an example. Similar o he four-level ZCS-MMSCC, his circui also works as a four imes sep-up dc-dc converer. V represens he ideal inpu volage source. Load 1366

3 L S L S represens he equivalen sray inducance presen in he circui. L S, L S and L S are he equivalen sray inducance when he capacior is charged in parallel. L S, L S, L S and L S are he equivalen sray inducance beween each capacior when he capacior discharges in series. S P and S N are he same swiching devices conrolled complemenary a 50% duy cycle. C o C are he capaciors wih he average volage of inpu volage, while C has he average volage of four imes of inpu volage. L S does no have o be in he posiion drawn in Fig. 7, i could be disribued anywhere in series wih swiches or capaciors in he circui. Similar o he ZCS-MMSCC, he oal equivalen sray inducance is he sum of he connecion wire parasiic inducance, capacior parasiic inducance and he MOSFETs package parasiic inducance. Usually he connecion wire parasiic inducance is he major par of he sray inducance. For he analysis convenience, only one equivalen L S is used o represen he oal sray inducance presen in each parallel resonan loop. And one equivalen L S is used beween wo capaciors in he series resonan loop. _,, is he volage across he capacior C, C and C wih he inpu volage dc offse and a sinusoidal ripple. The volage ripple is deermined by he capacior curren and capaciance. _ is he volage across he capacior C, wih he dc offse four imes inpu volage and a volage ripple also deermined by he capacior curren and capaciance. The operaion of his circui can be described in wo saes shown in Fig. 9 and Fig. 10 wih differen swiches urned on. V GS _S P V GS _S N V DS _S P V DS _S N I_S P I_S N I_C 1,2,3 Fig. 7. Four-level ZCS swiched-capcior volage muliplier main circui. I_C 4 Fig. 8 shows he idealized waveform of proposed ZCS swiched-capacior dc-dc volage muliplier under seady-sae condiions. _ and _ are he gae signal of swich S P and S N wih 50% duy cycle. _ and _ are he drain source volage of he swich S P and S N. Acually, he drain source volage of differen S P and S N are differen in value bu similar in shape due o he characerisics of volage muliplier circui. _ and _ are he drain source curren of he swich S P and S N. All he swiches of S P or S N have he same curren waveforms. Assume inpu volage is an ideal volage source. By considering he sray inducance presen in he circui, when he swiches are urned on, he curren hrough he sray inducance, capaciors and he swich will begin o resonae from zero. By adjusing swiching frequency o he resonan frequency, he curren hrough swiches S P, S N and sray inducance will decrease o zero when he swiches are urned off. The half swiching period is a half sinusoidal waveform. Therefore, he ZCS of all he swiches is achieved in boh urn on and urn off. The capacior C C and C are charged in parallel in he half-period wih he sinusoidal curren waveform when S P is on. And hey are discharged in series wih he inpu volage source in anoher half-period also in he sinusoidal shape when S N is on. _,, are he curren hrough capacior C, C, and C, which is he sum of he curren hrough he swich wih he sinusoidal shape. When he capacior is charged, he curren is he posiive par; when he capacior discharges, he curren is negaive. The capacior C is charged when oher capaciors are in series wih inpu volage when S N is on. And i is discharged o he load when S P is on. _ is he curren hrough capacior C, which is a sinusoid waveform when S N is on When S P is on, he curren hrough C is he negaive dc load curren wih small ripple. V_C 1,2,3 V_C 4 Fig. 8. Fig. 9. Fig I o V in 4V in I II I II Ideal waveforms of four-level ZCS volage muliplier. Operaion modes of sae I when S P is on. Operaion modes of sae II when S N is on. 1367

4 1) Sae I [ 0, 1 ] Fig. 9 shows he sae when S P is urned on a while S N is off. During his sae C, C and C are charged by V. Fig. 11 show he hree simplified equivalen circuis of sae I. Fig. 11(a) shows he siuaion when V, L S, S P, C and S P form a resonan loop. Fig. 11(b) shows he siuaion when V, L S, S P, C and S P form a resonan loop. Fig. 11(c) shows he siuaion when V, L S, S P, C and S P form a resonan loop. Because of he presence of he sray inducance L S, before he swich is urned on, he curren hrough L S already decreases o zero. The curren hrough S P will increase from zero when he swich is urned on, so S P is urned on a zero curren. For he case shown in Fig. 11(a), afer L S and C resonae for half cycle, he curren hrough S P and S P falls o zero. Therefore S P and S P urn off a zero curren. Similarly, for he case shown in Fig. 11(b) and Fig. 11(c) he curren hrough S P, S P, S P and S P will realize zero curren urn on and urn off oo. So, ZCS is achieved on all he swiches. The required sray inducance value is he same for he hree circui and is easy o be achieved by he circui layou due o he symmery of he circui, assuming he capaciance are he same. vc 1 ( 1 ) = Vin +. (5) 4VinC1ω r The capacior volage ripple is: Δ vc 1 = (6) 4VinC1ω r The sae equaions of Fig. 11(b) and Fig. 11(c) are similar o he sae equaions of Fig. 11(a). The volage across C and C are he same as he volage across C. The volage ripples of C and C are also he same as. 2) Sae II [ 1, 2 ] Fig. 10 shows he sae when S N is urned on a while S P is off. During his sae, C is charged by he V C C and C in series. Assume he load is zero. Fig. 12 shows he simplified equivalen circuis of sae II. I shows he siuaion when V, L S, S N, C, L S, S N, C, L S, S N, C,L S, S N, and C form a resonan loop. Similar as he las sae, because of he presence of he L S, he curren hrough S N will also increase is value from zero in a resonan manner. The zero curren urn-on of S N can be achieved. Afer sray inducance L S, L S, L S and L S in series resonae wih capacior C, C, C and C in series for half cycle a, S N, S N, S N and S N will have a zero curren urn-off when he curren hrough hem decreases o zero. Hence, zero curren swiching can be achieved on hese swiches. (a) (b) (c) Fig. 11. Simplified equivalen circuis of sae I when S P is on. Wihou loss of generaliy, he following assumpions have been made for he analysis: all he swiches are ideal, i.e. no conducion resisance is considered; inpu volage source is ideal, i.e. consan and no inernal impedance; he capacior ESR is zero. Assuming C C C C, so in order o have he same resonan frequency, L S L S L S, Assume L S L S L S L S. The sae equaions of Fig. 11(a) are: dis 2 Vin = LS 2 + vc d 1 (1) dvc1 ils 2 = C1 (2) d The soluions are: is2( ) = sinωr (3) 4Vin vc 1 () = Vin cosωr (4) 4VinC1ω r Where V is he value inpu volage, L S is he value of sray inducance, ω is he resonan frequency equals o 1 L S C, and P is he oupu power. Afer half cycle, he capacior volage is charged o: Fig. 12. Simplified equivalen circuis of sae II S N is on. The sae equaions of Fig. 12 are: dils1 Vin + vc 1 + vc 2 + vc 3 = 4LS1 + vc d 4 (7) dvc i 4 LS1 = C4 (8) d The soluions are: π Po vc 4 () = 4Vin cosωr (9) 4VinC4ωr π Po il S1 () = sinωr (10) 4Vin Afer half cycle, he capacior volage is charged o π Po vc 4 ( 2) = 4Vin + (11) 4VinC4ωr The capacior volage ripple is: 1368

5 Po Δ vc 4 = (12) 4VinC4ωr If zero load is considered, he required sray inducance in he series resonan loop is he same as he parallel resonan loop shown in Fig. 11 which means L S L S L S L S L S L S L S. Afer considering he load effec wih a negaive dc offse in he capacior C curren. The required sray inducance of series resonan loop will be a lile bi smaller han he parallel resonan loop. Because he resonan frequency of a pure LC nework is differen wih he LCR nework. B. ZCS Volage Doubler Fig. 13(a) shows he wo-level ZCS generalized mulilevel swiched-capacior dc-dc converer as an example. This circui is called ZCS volage doubler in shor because he oupu volage is wice as much as he inpu. V represens he ideal inpu volage source. L S, L S L S and L S can be considered as he disribued sray inducance in series wih he swiches in he circui layou. S P and S N are he same swiching devices conrolled complemenary a 50% duy cycle. C and C are he capaciors wih he average volage he same as he inpu volage. Because of he symmery of he circui, he disribued sray inducance L S, L S L S and L S can be replaced wih an equivalen sray inducance L S in he inpu side shown in Fig. 13(b) for he analysis convenience. Only one equivalen sray inducance L S is needed o represen he oal sray inducance in wo resonan loop. π on and urn off. _ and _ are he curren hrough capacior C and C. The capacior C and C are charged in each half-period wih he sinusoidal curren waveform when S P or S N is on. And hey are always discharged in series wih load curren. So, he curren hrough he capacior C, and C, is he curren hrough he swich subracs he oupu curren. _ and _ are he volage across he capacior C and C. is he oupu volage wih he volage ripple half of he volage ripple of he capacior. Because of he 180 degree phase shif of he capacior volage ripple, he capacior volage ripple will cancel ou wih each oher. The operaion of he circui can be described in wo saes as shown in Fig. 15(a) and Fig. 15(b) wih differen swiches urned on. (a) Fig. 13. (b) ZCS volage doubler and is opology simplificaion. Fig. 14 shows he idealized waveform of proposed ZCS volage doubler under seady-sae condiions. _ and _ are he gae drive signal of swich S P and S N complemenary wih 50% duy cycle. _ o _ are he drain source volage of swich S P and S N. _ and _ are he drain source curren of he swich S P and S N. All he swiches of S P or S N have he same curren waveforms. Assume inpu volage is an ideal volage source. By considering he equivalen sray inducance in he inpu side, when he swiches are urned on, he curren hrough he sray inducance, capaciors and he swich will begin o resonae from zero. By adjusing swiching frequency o he resonan frequency, he curren hrough swiches S P, S N and sray inducance will decrease o zero when he swiches are urned off, which is he half period of he sinusoidal waveform. Therefore, he ZCS of all he swiches is achieved in boh urn Fig. 15. Fig. 14. Ideal waveforms of ZCS volage doubler. (a) (b) (a)operaion modes of sae I when S P is on. (b) Operaion modes of sae II when S N is on. 1369

6 IV. DESIGN GUIDELINES The 480 W ZCS volage doubler design procedure is shown here as an example. The specificaion of he prooype converer is V =12 V, V =24 V, P =480 W, f S =44.25 khz. A. Capaciance Capaciance value should be chosen according o he volage ripple of he capacior using he following equaion. C = (13) 2VinΔvCωr Because of he special srucure of he circui, he volage ripple across all he capaciors are he same. And he value of he volage ripple is deermined by he oupu power, inpu volage, capaciance and he resonan frequency. The capacior volage ripple should be chosen smaller han he inpu volage o preven he volage across he capacior from resonaing o he negaive region and lose he zero curren swiching. The oupu volage ripple is abou five imes smaller han he capacior volage ripple because of he 180 degrees phase shif operaion of he swiches. And he capacior volage ripple will cancel ou and he oupu volage is wo imes bigger han one capacior volage. The oupu ripple is chosen around 8% of oupu volage. So he capacior volage ripple is 40% of he capacior volage. According o he (13), he capaciance is chosen 47 μf in he simulaion. B. Sray inducance The circui layou should be designed carefully, in order o make he sray inducance of each equivalen circui equal. Assume all he sray inducance in he circui is equalized. And he required sray inducance can be saisfied by using proper inpu inducance. Required sray inducance for ZCS can be deermined by he resonan LCR nework. C. Swiching frequency Swiching frequency should be se he same as resonan frequency in order o promise he zero curren swiching. Usually, he sray inducance of he circui is already deermined when he circui layou is finished. The capaciance is also deermined by he required volage ripple. Assume he air core inducor is used for he inpu inducance, and he swiching frequency can be deermined by he inpu inducance value. If he inpu inducance is deermined, he swiching frequency can be wised by monioring he power device curren when he swich is urned off. The swiching frequency should be se exacly a he poin when he swich curren resonaes o zero when he swich is urned off. V. SIMULATION AND EXPERIMENT RESULTS A. ZCS Volage Muliplier Fig. 16 shows saber simulaion waveforms of a 160 W four-level ZCS volage muliplier, where Vp and Vn are he swich gae-source conrol volage, Vds_Sp and Vds_Sn are he swich drain-source volage, I_Sp and I_Sn are he swich drain-source curren. I_C1,2,3 is he curren hrough capacior C, C and C. I_C4 is he curren hrough capacior C. V_C1,2,3 is he volage across he capacior C, C and C. Vin is he inpu volage. Vo is he oupu volage or he volage across he capacior C. The inpu volage is 5 V. Swiching frequency is abou 70 khz. Capaciance is 47 μf and he value of he sray inducance L S L S L S 108 nh, L S = L S = L S = L S =98 nh. The series resonan sray inducance is smaller caused by he load effec. The simulaion resuls is consisen wih he heoreical analysis, which verifies he above analysis. Fig. 16. Simulaion resuls of 160 W ZCS volage muliplier. B. ZCS Volage Doubler Fig. 17 and Fig. 18 shows saber simulaion waveforms of a 480 W ZCS volage doubler, where Sp and Sn are he swich gae-source conrol volage, Vds_Sp1, Vds_Sn1, Vds_Sp2, Vds_Sn2 are he swich drain-source volage of swich S P, S N, S P and S N. I_Sp1 and I_Sn1 are he swich drain-source curren of swiches S P and S N. which is omied here. The curren hrough S P is he same as S P, he curren hrough S N is he same as S N. Iin is he curren hrough he inpu sray inducance L S. I_C1 and I_C2 are he curren hrough capacior C and C. V_C1 and V_C2 are he volage across he capacior C and C. Vin is he inpu volage. Vo is he oupu volage. The inpu volage is 12 V. Swiching frequency is abou 44 khz. Capaciance is 47 μf and sray inducance L S 165 nh. The simulaion resuls is consisen wih he heoreical analysis, which verifies he analysis. 1370

7 In he 480 W ZCS volage doubler prooype, he swiching devices are wo 30 V 180 A MOSFETs IPB009N03L from infineon conneced in parallel. Resonan capacior are en 100 V 4.7 µf MLCC capaciors C5750X7R2A475K from TDK conneced in parallel. Inpu capacior are welve 16 V 470 µf conducive polymer aluminum solid elecrolyic capaciors PLG1C471MDO1 from nichicon conneced in parallel. Gae drive volage is 7 V. The swiching frequency is abou 40 khz. The inpu sray inducance is around 200 nh. Fig. 19 and Fig. 20 show he experimen waveforms of he 480 W ZCS volage doubler prooype wih he pars menioned above. Fig. 19 shows he complemenary gae drive signals of S P and S N wih duy cycle abou 49% due o some dead ime. V GS _S P and V GS _S N are he complemenary gaesource conrol volage. Fig. 17. Simulaion resuls of 480 W ZCS volage doubler. Fig. 19. Gae drive signal of ZCS volage doubler. Fig. 20. Swich volage and inpu curren waveform of ZCS volage doubler. Fig. 18. Simulaion resuls of 480 W ZCS volage doubler. VI. CONCLUSION In his paper, a family of zero curren swiching swichedcapacior dc-dc converers is proposed. By eliminaing he bulky, lossy inducive componen wih a magneic core, he 1371

8 converer is able o operae a very high emperaures wih high efficiency. By using he proposed sof-swiching sraegy, swiching loss has been minimized and EMI has been resriced; he size of capaciors has been reduced, hus making he converer small and ligh. Owing o he uilizaion of disribued sray inducance or disribued air core insering echnique, he big inducor is avoided o achieve ZCS. Hence, he proposed ZCS swiched-capacior converer family shows grea poenial in high emperaure, high power fuure auomoive applicaions. REFERENCES [1] F. Ueno, T. Inoue, I. Ooa and I. A. H. I. Harada, "Power supply for elecroluminescence aiming inegraed circui," in Circuis and Sysems, ISCAS '92. Proceedings., 1992 IEEE Inernaional Symposium on, 1992, pp vol.4. [2] M. S. Makowski and D. Maksimovic, "Performance limis of swichedcapacior DC-DC converers," 1995, pp vol.2. [3] M. On-Cheong, W. Yue-Chung and A. 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