A Comparative Study of Soft-Switched CCM Boost Rectifiers and Interleaved Variable-Frequency DCM Boost Rectifier

Transcription

1 A Comparaive udy of ofwiched CCM Boos Recifiers and Inerleaved ariablefrequency CM Boos Recifier Brian T. Irving, Yungaek Jang, and Milan M. Jovanović ela Producs Corporaion Power Elecronics aboraory P.O. Box avis rive Research Triangle Park, NC Absrac In his paper hree singlephase, highpowerfacor recifier implemenaions were evaluaed on a comparaive basis. pecifically, a zerovolageswiching coninuousconducionmode boos recifier, a zerocurrenzerovolageswiching coninuousconducionmode boos recifier, and an inerleaved variablefrequency disconinuousconducionmode boos recifier were compared wih respec o heir efficiencies, compliance wih he EN specificaions, complexiy, and coss. The comparisons were done for he singlephase inpu volage of 90 rms 264 rms and for kw oupupower range. I. INTROUCTI In highpower offline power supplies, a coninuousconducionmode (CCM) boos recifier is he preferred opology for implemening he fronend converer wih acive inpucurren shaping. However, since he dcoupu volage of he boos converer mus be higher han he peak inpu volage, he oupu volage of he boos inpucurren shaper is relaively high. ue o he high oupu volage, he converer requires he use of a highvolage, fasrecovery boos recifier. A high swiching frequencies, fasrecovery recifiers produce significan reverserecoveryrelaed losses when swiched under hard swiching condiions [1]. These losses can be significanly reduced and, herefore, a high efficiency can be mainained even a high swiching frequencies by employing a sofswiching echnique [2][7]. All of he proposed opologies in [2][7] use addiional componens o form an acive snubber circui ha conrols he urnoff di/d rae of he boos recifier. The main feaures of he acive approaches inroduced in [2][6] is ha besides sof swiching of he boos recifier hey also offer sof swiching of he boos swich. In addiion, he approaches described in [4][7] offer sof swiching of he auxiliary swich ogeher wih he boos swich. Anoher mehod of achieving high efficiency while using highvolage, fasrecovery recifiers is o operae he boos converer a he boundary of disconinuousconducionmode (CM) and CCM. The reverserecoveryrelaed losses are hen eliminaed because here is no sored charge in he boos recifier a urnon. Addiionally, zerovolage urnon of he boos swich can be easily achieved. However, boundary operaion requires addiional inpucurren filering and produces peak currens which are a leas wo imes he inpu curren averaged over a swiching cycle. This is generally undesirable for highpower powerfacorcorrecion (PFC) applicaions. The drawbacks of he boundary operaing boos converer can be alleviaed if wo or more converers are inerleaved. Inerleaving reduces he inpuripple curren and peak inpu curren while reaining he benefis of sofswiching of boh boos recifier and swich, as inroduced in [8][9]. pecifically, an inerleaving scheme uilizing volagemode conrol was inroduced in [8] and an inerleaving scheme uilizing hyseresis conrol was inroduced in [9]. However, he inerleaving of variablefrequency PFC boos converers, in general, requires a relaively complex inerleaving circui. In his paper, an inerleaving echnique ha uilizes currenmode conrol is proposed for he variablefrequency, boundaryoperaing PFC boos converer. This echnique, hough suiable for muliple converers, was developed for wo converers which have a maser relaionship. pecifically, he maser operaes a he boundary of CM/CCM, while he always operaes in CM, bu very close o he boundary. The proposed inerleaving circui was evaluaed and compared o wo CCM singlephase, high powerfacor recifier implemenaions wih respec o heir efficiencies, compliance wih he EN specificaions, complexiy and coss. pecifically, he CM/CCM boos inerleaved converer is compared wih he zerovolageswiching (Z) CCM boos recifier described in [5], and he zerocurrenzerovolage swiching (ZCZ) CCM boos recifier describe in [7]. II. BRIEF REIEW OF EAUATE TOPOOGIE A. Z CCM Boos Recifier [5] The firs evaluaed opology, he Z CCM boos recifier which employs an acive snubber for reverserecoveryloss reducion, is shown in Fig. 1. The circui in Fig. 1 uses a snubber inducor, which is conneced in series wih he

2 IN C Fig. 1 chemaic diagram of Z CCM boos recifier [5] boos swich and recifier, o conrol he di/d rae of he recifier when boos swich is urned on. In addiion, he series connecion of auxiliary swich 1, clamp capacior C C is used o discharge he energy sored in inducor o he oupu afer is urned off. uring his period, he energy sored in inducor flows hrough he body diode of auxiliary swich 1. Therefore, auxiliary swich 1 can be urned on wih Z. Before auxiliary swich 1 urned off, he curren direcion of was changed o achieve he charge balance of C C. As a resul, he energy sored in inducor is also used o discharge he oupu capaciance of boos swich prior o he swich urnon, hus eliminaing is capaciive urnon swiching loss of. iode C is employed o eliminae he parasiic ringing beween he juncion capaciance of recifier and he snubber inducor by clamping he anode of o ground. B. ZCZ CCM Boos Recifier [7] The second evaluaed opology, he boos converer wih he ZCZ swich cell, is shown in Fig. 2. The circui in Fig. 2 also uses snubber inducor, which is conneced in series wih main swich and recifier, o conrol he di/d rae of he recifier. Along wih, and, auxiliary swich 1, clamp capacior C C, and clamp diode C form a ZCZ cell as indicaed by he dashed line in Fig. 2. The circui shown in Fig. 2 improves he performance of he CCM boos converer by eliminaing he swiching losses wih a ZCZ swich cell. The ZCZ cell reduces he reverserecoveryrelaed losses of he recifier and provides sof swiching of he main and auxiliary swiches. pecifically, he main swich in he proposed ZCZ cell urns off wih ZC, making he IGBT 1 C C C C F R O a good choice, whereas he auxiliary swich urns on wih Z. In addiion, because he proper operaion of he ZC Z swich cell requires ha he conducion period of he main swich and he auxiliary swich overlap, he proposed swich cell is no suscepible o failures due o accidenal ransien overlapping of he main and auxiliary swich gae drives. Finally, he complexiy and cos of he converers using he proposed echnique is furher reduced because he proposed ZCZ swich cell requires a simple nonisolaed (direc) gae drive for boh swiches. C. Inerleaved ariablefrequency CM Boos Recifier The hird evaluaed opology, wo inerleaved boos converers which share a common error volage configured wih a maser, currenmode conrol circui, is shown in Fig. 3. ince he boos recifiers operae a he boundary of CM/CCM here are no reverserecovery relaed losses and hence no need for acive or passive snubber componens as in [1][7]. Therefore, in he circui in Fig. 3, he design challenge is shifed from he power sage o he conrol circui o achieve sofswiching of he boos diode and swich. III. IMPEMENTATI OF INTEREAING CTRO CIRCUIT Inerleaving of muliple parallel conneced converers requires boh good curren sharing and precise conrol of he inerleaving insan. To achieve good inerleaving of wo parallel conneced boos converers, he peak inpu curren of each should be 180 degrees ouofphase. Generally, his means ha one converer mus urnon a he halfperiod insan of he oherconverer s swiching inerval for proper synchronizaion. However when he swiching frequency is variable, he halfperiod insan becomes variable, making synchronizaion difficul. Curren sharing in currenmodeconrolled converers can be achieved by applying a common error volage o each converer. Generally, in currenmode conrol, he urnoff of he swich occurs a he insan when he sensed swich i1 i2 MO IN C C C 1 C F R O IN EA INTEREAING CIRCUIT MO2 i1 i2 2 EA C F R O Fig. 2 chemaic diagram of ZCZ CCM boos recifier [7]. Fig. 3 chemaic diagram of inerleaved, variablefrequency CM boos recifier wih currenmode conrol.

3 curren a he inpu of he modulaor becomes equal o error volage EA. For consanfrequency conrol, he urnon insan of he swich is iniiaed by he conroller clock. For variablefrequency conrol, which is required for he CM/CCM operaion, he swich is urned on shorly afer he inducor curren falls o zero. If he componen values of he inerleaved converers operaing wih variablefrequency were idenical, each and every converer would operae a he CM/CCM boundary, as illusraed in Fig. 4(a) for he case of wo inerleaved converers. However, in pracice, componens of inerleaved converers are no likely o be he same due o he componen olerances. As a resul, he operaion of he individual converers in an inerleaved scheme would no be he same. To illusrae he effec of he componen mismaching on he operaion of he variablefrequency inerleaved converers, Figs. 4(b) and 4(c) show he inducor curren waveforms of wo inerleaved converers wih mismached boos inducances, i.e., for 1 > 2. As can be seen from Figs. 4(b) and 4(c), because of he difference in he boosinducor values, he upslope and downslope of he inducor curren i 1 and i 2 are differen. Namely, since 1 > 2, he slope of module #1 is less seep han he corresponding slopes of module #2. As a resul, for he same line and load condiions, module #1 requires a lower frequency han module #2 o operae a he CM/CCM boundary. Therefore, if power sage componens of variablefrequency inerleaved converers are mismached, i is no possible o operae all individual converers a he CM/CCM boundary. As shown in Fig. 4(b), if module #2 is made o operae a he CM/CCM boundary, module #1 has o operae in CCM since module #2 achieves he CM/CCM operaion a a higher frequency han module #1. On he oher hand, if module #1 is made o operae a he CM/CCM boundary, module #2 has o operae in CM, as shown in Fig. 4(c). Therefore, in a design which eliminaes reverserecovery losses by no allowing operaion in CCM, only one converer can operae a he CM/CCM boundary, whereas all he ohers operae in CM. As a resul, Z of he swiches in all converers bu one is los, unless he conrol circui is sophisicaed enough o wai for he charge in he oupu of he main swich o resonae wih he boos inducance o zero. One mehod of achieving inerleaving beween muliple converers operaing wih variable frequency and curren mode conrol is o design a conrol circui which imposes a maser/ relaionship beween converers. A. Maser/lave Inerleaving Approach Inerleaving currenmode conrolled converers which have a maser relaionship generally means ha he urnon is conrolled by he maser, whereas for boh maser and, urnoff is conrolled by he individual converer. ince he maser is chosen as he converer which operaes a he boundary of CM/CCM, seps mus be aken o ensure ha he reaches CM before he maser reaches is half i 1 i 2, 1=2 i pk 1 2 i 1 i 2 i 1 i 2 i pk 1 2, 1>2 I 2 I 1 Fig. 4 General swiching waveforms of wo inerleaved variablefrequency CM/CCM boos recifiers operaing wih currenmode conrol for a) converers wih idenical powersage componens ( 1 = 2); b) converers wih mismached powersage componens ( 1> 2) and module #2 wih CM/CCM operaion; c) converers wih mismached powersage componens ( 1> 2) and wih module #1 wih CM/CCM operaion. period insan. This can be achieved if he curren loop gain of each converer are mismached, eiher by implemening differen value inducors (i.e., M > ), which is generally undesirable from a manufacuring poin of view, or by adjusing he curren sensing gain. However, i should be noed ha if he gain of he curren loops are mismached, he peak of he individual inducor currens will also be mismached. This hen affecs he currensharing accuracy of he wo converers. I 2 I 1, 1>2 i pk 1 2 (a) (b) (c) I 1 I 2

4 Figure 5 illusraes he general swiching waveforms of wo inerleaved currenmode conrolled converers which have a maser relaionship. For simpliciy, he slope of he inducor currens are he same while he slope of he sensed swich curren of each are differen. However, here is nohing o preven he slope of he inducor currens (i.e. he value of inducors and M ) from becoming mismached. When gae of maser G (maser) is high, maser inducor curren i M ramps up, and he volage across maser auxiliary winding auxmaser is IN /N. Maser currensense volage maser C is proporional o i, unil i reaches he level of M conrol volage C. G (maser) hen goes low, diode M urns on, auxmaser changes insananeously o ( O IN ) N, and i M is delivered o he oupu, while swich M urns off and maser C becomes zero. When i M becomes slighly negaive, G (maser) becomes high again compleing one full swiching cycle. The halfperiod insan is hen deermined iniiaing urnon of gae G (). lave inducor curren i ramps i i M IN G (maser) (o IN )/N auxmaser 0 IN /N im maser C C i (o IN )/N aux 0 IN /N G () A A i M N:1 M M auxmaser i C in N:1 aux maser C C Ts/2 c c Fig. 5 General schemaic and swiching waveforms of wo inerleaved, currenmode conrolled boos converers wih maser relaionship. M (a) (b) Ts/2 C F R O up, auxiliary volage aux is equal o IN /N and currensense volage C follows i wih a slope maser 10% greaer han C. When C reaches C, G () urns off, diode urns on, aux insananeously changes o ( O IN )/N and i decreases as i sources curren o he oupu. When i decreases o zero, he oupu capaciance of resonaes wih and C IN unil he halfperiod insan of he previous swiching cycle of he maser is reached, signaling he insan of G () urnon and he end of is swiching cycle. While inducor is disconinuous, he volage across he auxiliary winding flucuaes beween ( O IN )/N and IN /N as he oupu capaciance of he swich rings wih and C IN. B. eermining HalfPeriod Insan of Maser A soluion o deermining he halfperiod insan of wo inerleaved, parallel conneced boos converers operaing wih currenmode conrol is o uilize he properies of similar riangles. In general, riangles are said o be similar when heir corresponding angles are equal. Figures 6 and 7 are used o faciliae he explanaion of he proposed inerleaving circui. Figure 6 is a block diagram represenaion of he proposed inerleaving circui. Is corresponding waveforms are depiced in Fig. 7. To deermine he halfperiod insan of he maser, informaion from he maser s previous swiching cycle is used. ince he inpu volage IN is nearly consan for a swiching cycle, i is reasonable o approximae ha he swiching frequency is nearly consan for several swiching cycles. A volage ramp is generaed wih a consan slope using a curren source and capacior. RAMP is hen rese a he end of a swich cycle by a pulsed rese (i.e., a pulse of a very shor duraion). This creaes a sawooh waveform RAMP whose slope is independen of line and load condiions, and whose peak PK is a funcion of he maser s swiching frequency. Two peak deecors, peak1 and peak2, are used o sore PK. The oupu of each are divided by wo and rese 180 degrees ouofphase. The halved oupus of he peak deecors are hen compared o RAMP. The oupu is a volage waveform Ts/2 which operaes wih a 50% duy cycle and is synchronized o G maser. The halfperiod insan is reached when Ts/2 ransiions from high o low (i.e., when RAMP reaches half he peak of he previous swiching cycle) due o a propery of similar riangles (i.e., a riangle whose peak is onehalf ha of anoher riangle which i is similar o has a base which is also onehalf ha of he oher riangle). This mehod of deermining he insan of urnon can be generalized for N converers. In he case of N converers, he 1/Nperiod insan mus be deermined o achieve proper inerleaving, which again can be achieved using N peak deecors whose oupus are divided by N and compared agains a single RAMP.

5 aux Gae of Maser G (maser) PulsedRese 1/2 Ts 1/2 Ts Pulsed Rese RAMP ramp PK Peak eec #1 (peak1) Peak eec #2 (peak2) peak 1, 1/2 peak 1 PK 1/2 PK Hold/ Rese Hold/ Rese peak 2, PK 1/2 peak 2 CAMP 1 2 _ Compare 1 2 ramp, 1/2 peak 1, and 1/2 peak 2 Ts / 2 PK 1/2 PK OR clamped aux OR ach G () lave urnon Fig. 6 Block diagram represenaion of proposed inerleaving circui. Though he halfperiod insan is deermined, Z of he main swich is no guaraneed unless he urns on when he charge in he oupu of he swich is zero. By clamping he volage derived from he auxiliary winding clamped aux, ORing i wih Ts/2 and assuming ha he resonan period is shor, Z urn on of 2 is achieved. I is hen necessary o lach he converer in he onsae unil he end of he onime. I. EXPERIMENTA REUT To verify he operaion and performance of he proposed inerleaving circui, wo 600W (385/ 1.6A), universal line volage (90264 RM ) boundary operaing PFC boos converers were inerleaved as in Fig. 3. The conrol circui was implemened using he variablefrequency powerfacor Fig. 7 Proposed inerleaving conrol circui waveforms. conroller inegraed circui MC33262 and sandard analog devices and logic gaes. The measured linevolage and unfilered inpu curren waveforms a lowline (in = 90 RM ) and fullload (1.2kW) are shown in Fig. 8. I can be seen from Fig. 8 ha he inpuripple curren has been reduced o slighly less han 50% of he inpu curren averaged over a swiching cycle. Figure 9 shows he individually measured inducor currens i, i M and he sum i i M which is he resuling inpuripple curren. From Fig. 9 i can be seen ha he maser always operaes a he boundary of CM/CCM and ha he operaes very close o he boundary of CM/CCM. The slighly mismached peakinducor currens are a resul of mismached maser and curren loop gains. By mismaching he curren loop gains, he dead ime of he swiching cycle can be furher minimized. The proposed inerleaving echnique resuls in very good inerleaving qualiy a low line and full load. However, as he swiching frequency increases (i.e., high line and ligh load),

6 Fig. 8 Unfilered inpu curren (lower waveform, 10 A/div) and inpu volage (upper waveform, 50 /div) waveforms of inerleaved variablefrequency CM boos recifier a in = 90 RM, O = 385, P O = 1.2 kw. i was found ha he inerleaving qualiy degrades due o he effecs of he pulsed rese, which prevens RAMP from spanning he enire swiching cycle, and he ampliude of RAMP, which is inversely proporional o he swiching frequency (i.e., RAMP decreases below 1). Consequenly, inerleaving was removed for highline, lighload condiions since inerleaving is no crucial in his range.. COMPARI OF CCM. CM TECHNIQUE The performance of he hree experimenal powerfacorcorrecion boos converers were evaluaed for a 1.2 kw (385 / 3.12 A) oupu power and universalline ( RM ) inpu range. The power sage componens which were i M i uilized for he hree experimenal circuis are described in Table I. The conrol circuis for he CCM boos converers wih Z (Fig. 1) and ZCZ (Fig. 2) were implemened wih an averagecurren mode PFC conroller UC3854. The inpu harmonic currens of hese recifiers were measured and compared wih he harmonic curren limis of he EN regulaion. The resuls show ha he TH and PF of all hree experimenal boos recifiers a he full load condiion are less han 10% and higher han 99%, respecively. The TH and all harmonic currens of he hree opologies well mee he EN regulaion over he enire inpu volage and oupu power range. Figure 10 shows he measured efficiencies of he experimenal converers. As can be seen from Fig. 10, all hree experimenal circuis show good efficiency over he enire inpu volage and oupu power range. I should be noed ha for evaluaion purposes, he same inpu filer was used for all hree experimenal circuis. However, he inpuripple curren for he inerleaved variablefrequency CM boos converer is slighly less han 50% of he inpu curren averaged over one swiching cycle as compared o he sofswiched CCM boos, whose inpuripple curren is less han 15%. Therefore, he inerleaved booss require addiional inpucurren filering o aenuae he inpuripple curren o he same level as he oher opologies. To accoun for he addiional loss, he inerleaved converer efficiency daa a low line shown in Fig. 9 should be reduced by 12%. Generally, he inerleaved variablefrequency CM boos recifier has a comparable efficiency wih he wo sofswiched CCM boos recifiers. However, he inerleaved circui is more complex han he Z and ZCZ boos recifiers since i requires more componens o implemen he power sage, as well as he conrol circui. EFFICIENCY [%] ac ac i M i Inerleaved F CM boos CCM boos w/ ZCZ snubber CCM boos w/ Z snubber OUTPUT POWER [W] Fig. 9 Measured inducor currens a full load, in = 90 RM. Fig. 10 Measured efficiencies of experimenal recifiers.

7 TABE I Power age Componens for Z CCM, ZCZ CCM, and Inerleaved ariablefrequency CM Boos Converers Componens Z CCM Boos recifier ZCZ CCM Boos Recifier Inerleaved ariablefrequency CM Boos Recifier Boos wich IXFK48N50B (MOFET) IXGK50N60B (IGBT) 4 x IRFP460 (MOFET) Auxiliary wich 1 IRFP460 (MOFET) IRFP460 (MOFET) NE Oupu iode 2 x RHRP x RHRP x RHRP3015 Clamp iode C RHRP3060 RHRP3060 NE Clamp Capacior C C 6.8 µf / µf / 100 NE Boos Inducor nubber Inducor = 0.5 mh (four mh inducors in series). Core = oroidal core (Koolµ 77071A7), wire = 45 urns of magne wire (AWG #12). = 3.3 µh, Core = oroidal core (Koolµ A7), wire = 12 urns of magne wire (AWG #12) = 0.5 mh (four mh inducors in series). Core = oroidal core (Koolµ A7), wire = 45 urns of magne wire (AWG #12). = 3.3 µh, Core = oroidal core (Koolµ 77312A7), wire = 12 urns of magne wire (AWG #12) = 2 x 79 µh (one inducor for each CM boos power sage) Core = oroidal core (Koolµ 77256A7), wire = 48 urns of iz wire (srands = 435 wire size = AWG #40). Oupu Capacior C F µf / µf / µf / 450 Required Aenuaion of Approximaely 91 db a 80 khz Approximaely 91 db a 80 khz Approximaely 97 db a 50 khz MEMI Filer Complexiy of Conrol Two ariablefrequency Conrol wih Average Curren Mode Conrol (Moderae) Average Curren Mode Conrol (Moderae) Circui Inerleaving Circui (Complex) wiching Frequency f 80 khz 80 khz 50 khz 460 khz NE I. CCUI An inerleaving echnique for he variablefrequency, CM PFC boos recifier which uilizes currenmode conrol is described. A comparison is made agains a Z CCM boos recifier and a ZCZ CCM boos recifier wih respec o heir efficiencies, compliance wih he EN specificaions, complexiy, and coss. The comparisons were done for he universal inpu volage range 90 RM o 264 RM and for he load range 0 W 1.2 kw. I was found ha he efficiency of he inerleaved variablefrequency CM boos recifier is similar o he efficiency of he wo sofswiched CCM boos recifiers. However, he inerleaved boos converer requires significanly more complex conrol circui, as well as more componens o implemen he power sage. REFERENCE [1] Y. Khersonsky, M. Robinson,. Guierrez, New fas recovery diode echnology cus circui losses, improves reliabiliy,'' Power Conversion & Inelligen Moion (PCIM) Magazine, pp , May [2] R. rei,. Tollik, High efficiency elecom recifier using a novel sofswiched boosbased inpu curren shaper,'' Inernaional Telecommunicaion Energy Conf. (INTEEC) Proc., pp , Oc [3] G. Hua, C.. eu, F.C. ee, Novel zerovolageransiion PWM converers,'' IEEE Power Elecronics pecialiss Conf. (PEC) Rec., pp , June [4] J. Basse, New, zero volage swiching, high frequency boos converer opology for power facor correcion,'' Inernaional Telecommunicaion Energy Conf. (INTEEC) Proc., pp , Oc [1] M.M. Jovanović, A echnique for reducing recifier reverserecoveryrelaed losses in highvolage, highpower boos converers, IEEE Applied Power Elecronics Conf. (APEC) Proc., pp , Mar [6] C.M.C. uare, I. Barbi, A new family of ZPWM aciveclamping dcodc boos converers: analysis, design, and experimenaion," Inernaional Telecommunicaion Energy Conf. (INTEEC) Proc., pp , Oc [7] Y. Jang, M.M. Jovanović, A new echnique for reducing swiching losses in pulsewidhmodulaed boos converer, IEEE Power Elecronics pecialiss Conf. (PEC) Proc., pp , June [8] M.. Elmore, Inpu Curren Ripple Cancellaion in ynchronized, Parallel Conneced Criically Coninuous Boos Converers, IEEE Applied Power Elecronics Conf. (APEC) Proc., pp , Mar [9] J.W. Kolar, G.R. Kamah, N. Mohan, F.C. Zach, elfadjusing Inpu Curren Ripple Cancellaion of Coupled Parallel Conneced HyseresisConrolled Boos Power Facor Correcors, IEEE Power Elecronics pecialiss Conf. (PEC) Proc., pp , June 1995.