PASSIVE PFC FOR FLYBACK CONVERTORS

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1 PASSIE PFC FOR FLYBACK COERORS Parviz Par and Keyue M Sedley Dep f Elecrical and Cpuer Engineering Universiy f Califrnia, Irvine Irvine, Califrnia 9697 Absrac A new passive Pwer Facr Crrecr (PFC) based n alley Fill (F) is prpsed fr an ff-line Flyback cnverer By adding an exra winding which is agneically cupled he Flyback ransfrer and elecrically cupled he F, higher Pwer Facr (PF) and lwer al Harnic Disrin (HD) can be achieved he prpsed circui uses a high frequency inducr, lw vlage capacirs ha perae a a vlage slighly higher hen he half f he peak line vlage, and a lw sress swich fr DC/DC cnversin Since i is passive an acive swich fr PFC funcins is n necessary he paper describes he prpsed circui in deail fllwed by experienal resuls I IRODUCIO Cnveninal dide recifiers draw inpu curren in shr pulses raher hen sh sine waves, which causes harnics disrin and lw pwer facr his pulsed inpu curren pllues he pwer syses, inerfere neighburing appliance, and ipse high vlage and curren sress he DC/DC cnverers Many agencies have se inernainal sandards regulae he inpu curren f elecrnic prducs In rder fulfil he sandards, nuerus Pwer Facr Crrecin (PFC) ehds have been prpsed in recen years Pwer facr iprveen circuis can be achieved by acive and passive eans A ypical acive w sage PFC circui uses a bs cnverer fllwed by a DC/DC cnverer regulae he upu vlage wih a DC link a higher vlage han he peak f he AC supply he acive PFC circui is enirely saisfacry fr harnics cpliance bu he design cplexiy and cs f he addiinal circuiry is fen unaccepable in lw pwer applicains he single-sage acive PFC inegraes w pwer sages in ne, bu he high swich sress and he use f high vlage capacir are se f he drawbacks he passive PFC circuis perae a he line frequency and use capacirs and inducrs in a lw pass r band pass cnfigurain his sluin ffers a rade-ff beween he cs and perfrance Unfrunaely, he physical size and weigh f his filer akes i unaracive fr cpac sluins Anher way achieve passive pwer facr iprveen is by a circui called alley Fill, which sly used in he elecrnic ballas as PFC In his paper, a new single-sage Flyback cnverer suiable fr lw pwer applicain wih Iprved alley Fill (IF) as pwer facr crrecr is inrduced he new cnverer uses an exra winding ha is agneically cupled he Flyback ransfrer and elecrically cupled he alley Fill capacirs A high frequency inducr is eplyed suppress he charging spikes a he peaks f he curren wave and achieve lwer al harnic disrin (HD) Secin II prvides a review f varius cnveninal passive PFC ehds he principle f he prpsed circui is given in Secin III, Secin I illusraes he experienal resuls Furher iprveen wih experien resuls has been shwn in Secin, Secin I discuses he upu vlage ripples and finally cnclusins are given in Secin II II REIEW OF PASSIE PFC MEHODS A frequenly used passive PFC is a LC-newrk, which wrks a he line frequency and has been hrughly described in lieraure here are any pssible psiins fr placing he capacirs and inducrs, as discussed in [], [] An exensin has been shwn in [], by adding an exra capacir and ne dide, which is, called LCD recifier he iprveen leads saller inducance and cnsequenly saller agneic cre and causes he equipen change he class fr D A accrding he E Sandards [4] he her passive PFC sluin is he cnveninal alley Fill which is frequenly used in elecrnic ballas applicains he circui cnains w capacirs and hree dides he w elecrlyic capacirs are charged in series arund he line peak a half f he peak line vlage As lng as he line vlage reains abve single capacir vlage, he line feeds he lad direcly When he line vlage falls belw he single capacir vlage, he bridge recifier dides are reversely biased, and alley Fill s dides cnduc and he capacirs are cnneced in parallel feed he lad Figure shws a cnveninal alley Filled circui and is wavefrs, he spike a he peak f inpu

2 curren is a resul f charging he capacirs a he peak line vlage his spike and he crss ver disrin are refleced AC side as alernaing curren pulses and assciaed harnics iprve he basic alley Fill circui, an inducr can be added in frn f bridge r charging leg sh u he peak f inpu curren due he abrup charging f he w capacirs [5] Hwever, he penaly is again he addiin f a line frequency inducr Anher sluin has been presened in [6] reduce he charging curren spike by insering a resisr R in he b elecrde f C (see figure, dashed cpnens) and adding a vlage dubler exending he inpu curren cnducin angle A higher pwer facr and lwer HD can be achieved, bu he drawback is lwer efficiency, due lsses a he resisr R he lsses can be slighly reduced if resisr R is insered in he dide D branch insead A resnan based iprveen f alley Fill circui was repred in [7] fr ligh ballas applicains where a resnan curren was injeced in he alley Fill circui iprve he inpu curren wavefr i g DC-bus g C C 4 C D D g g/ D Lad Fig he riginal alley Fill and is wavefrs he bjecive f his paper is develp an iprved valley fill ehd fr a PWM cnverer (ie Flyback) achieve lw inpu disrin and high pwer facr a a lw cs he advanage f he prpsed circui is ha i uses lw vlage capacirs ha perae a a vlage slighly ver he half f inpu vlage and high frequency inducr addiinal swich is needed perfr PFC funcin and n addiinal vlage and curren sresses are added he DC/DC cnverer swich herefre i is a cs-effecive sluin and prvides less sress ver he DC/DC cnverer he parallel cbinain f capacirs als can prvide he hld-up vlage DC/DC cnverer during he ie when inpu vlage is lw III R C HE PROPOSED CIRCUI he funcinal diagra f he prpsed circui is shwn in Figure he cnverer peraes under bh lw (line) and high (swiching) frequency he circui cnains w elecrlyic capacirs (C, C), hree dides (D, D and D ), an inducr (L ) and an exra winding ( ), which is agneically cupled he Flyback ransfrer and elecrically cupled valley fill capacirs L and cnneced in series wih he capacirs in charging pah sh u he peaking f inpu curren he inducr L peraes a he high frequency, which eans sall size and relaively lw cs In he fllwing analysis, i is assued ha he swich and dides are ideal g i g _ C D D D C Q D 4 C RL L L DC--bus _ Fig he prpsed circui fr Flyback cnverer he perain f he Flyback cnverer is well knwn s i is n repeaed here I is assued ha he cnverer peraes beynd he bundary cndiin (CCM and DCM), hus he upu vlage is given by: DC bus D D n = () where is upu vlage, DC-bus is priary vlage, D is duy cycle and n is Flyback ransfrers urns rai / he perain cnsiss f w des in a half f a line cycle g M M M Fighe peraing des in half f a line cycle Operaing de M : 0 < g < he inpu vlage sars fr zer crssing f he inpu vlage Since g he recifier dides are reversebiased, he valley fill capacirs (C, C) are cnneced via D and D in parallel prvide energy he lad During his de here is n inpu curren drawn fr he AC surce by he cnverer While swich Q cnducs, energy fr he Fs capacirs charges he priary inducance L l, and we have:

3 = DC bus c () During ha inerval here is n curren hrugh, because dide D 4 is reverse-biased (see figure 4) he upu vlage is given by he fllwing equain: D c D n = () where is Capacir vlage When he agniude f he inpu vlage increases abve, he line direcly supplies energy he Flyback When ransisr Q is n, he priary winding inducance f ransfrer is charged by he inpu vlage DC-bus = g g Ll C RL _ C C C R L Fig6 Mde, g > and Q is n Fig4 Mde, c> g and Q is n When swich Q is ff, he dide D 4 cnducs and he sred energy ransfers he lad If (4) g * c = (5) By cbining () and (5), cndiin (4) beces: D c g (6) D c Under his cndiin, here is n curren hrugh If: g c (7) he curren sars flw hrugh and L and charges C and C Figure 5 shws he equivalen circui C L C C D 4 R L Fig5 Mde, swich Q is ff and g> C he vlage sress acrss swich Q during de is given by: Q = c n where Q is vlage acrss swich, is capacir vlage, is upu vlage and n is he urns rai / Operaing de M : g > he sred energy ransfers he upu when ransisr Q is ff and dide D 4 cnducs here is n curren hrugh if: (4) g c he capacirs are being charged hrugh (see figure 7) when: (8) g D c D C c L g g D C D 4 (9) C RL Fig7 Mde, < g < and Q is ff and C, C charge hrugh and L Equain (9) shws ha he exra winding pulls curren fr inpu charge he capacirs In cnras, he riginal alley Fill charges he capacirs nly a he peak f inpu vlage Figure 8 shws he hereically curren wavefrs hrugh he capacirs (I c ) and charging leg (I D ) f riginal ally Fill circui he crrespnden currens fr he Iprved alley Fill wih exra winding (prpsed circui) are shwn in figure 9 I c I D M M Fig8 I c and I D fr en riginal alley Fill

4 easured currens hrugh he alley Fill capacir I c and charging leg I D wih / = I c I D M M Fig9 I c and I D fr he prpsed circui By adjusing he urns rai beween he w windings and, he vlage acrss he capacirs can be cnrlled In his case, he capacirs vlage is slighly higher han half f he peak line vlage; as a resul, he curren peak is reduced If he winding is high such ha he capacir vlage is uch higher han a half f he peak inpu vlage he nncnducin angle will be larger which resuls in higher HD he nn-cnducin angle is direcly relaed he capacir vlage and inpu vlage and can be expressed as fllws: c = g Sinα (0) Eq () shws α as a funcin f / and duy cycle D Sin = D D α () where α is he nn-cnducin angle f inpu curren An ipran ne is ha i is necessary have bh and L in he charging pah prvides an early charging f capacirs, and acs as an exra vlage surce, while L sh u he curren he using f L als resuls in a lwer upu ripple he axiu vlage sress acrss swich Q ccurs during his de is given by: Q = g n () where Q is vlage acrss swich, g inpu vlage, upu vlage and n is / Equain () shws ha he new circui desn cause addiinal sress he swich, hus he swich sress will be he sae as ha f a regular Flyback I EXPERIMEAL RESULS he prpsed circui f figure has been pryped and esed in he labrary he prype is designed fr a 50kHz Flyback wih fllwing cpnen daa: C, C = 50µF, C =00µF, / =[0, 05 and ], L =00 µ H, P u =50W he line vlage is 0 ac, 60 Hz Efficiency easured n a 50 W pwer supply is nly slighly (%) less hen he Flyback cnverer wih cnveninal dide recifiers Figure 0 shws he GD() GD() M M Fig0 he easured I c and I D fr he prpsed circui ):I c (A/div), ):I D (A/div) Hriznal scale (5 s/div) As figure 0 shws he capacirs are charged up shly when Mde sars and here is n spike a he peak Figures - shw he experienal wavefrs f DC-bus vlage, inpu vlage and inpu curren, easured a clsed lp wih a differen urns rai / (GD) Fig ) dc-bus (50/div),, )inpu vlage (00/div), and )inpu curren (A/div), wih / =0 and Clsed lp, HD=4% Hriznal scale (5 s/div) (GD) ` Fig ) dc-bus (50/div), )inpu vlage (00/div), and )inpu curren (A/div), wih / =05 and Clsed lp, HD=8% Hriznal scale (5 s/div) 4

5 (GD) Fig5 ) dc-bus (50/div), )inpu vlage (00/div), and )inpu curren (A/div), wih / = and Clsed lp, HD=% Hriznal scale (5 s/div) Fig ) dc-bus (50/div), )inpu vlage (00/div), and )inpu curren (A/div), wih / = and Clsed lp, HD=% Hriznal scale (5 s/div) he resuls shw hw varying he / rai can cnrl he DC-bus vlage and AC line curren and cnsequenly iprves he inpu curren shape fr saisfy he harnics sandard Figure 4 shws he easured harnics f inpu curren cpared wih E class D % f Inpu Curren E Class D he easured harnics f he prpsed Circui nh Harnics Fig4 Inpu curren and is harnics cpering he E Class D a / = FURHER IMPROME furher iprve he prpsed circui, a vlage dubler accrding [6] can be applied (See figure, dashed capacirs C and C 4 ) he exra curren pah, creaed by w sall capacirs, causes he curren sar a zer crssing, and exend he cnducin angle, which resuls in lwer HD Figure 5 shws he inpu curren wih a vlage dubbler he easured HD have been reduced % I OUPU OLAGE RIPPLE Curren prgraed cnrl schee has been used fr he experiens Figure 6 shws he inducr curren wavefr I L, f a curren-de cnverer being cnrlled by an errr vlage e he inducr curren rises wih a slpe and falls wih a slpe i L () e i L (0) D s s Fig6 Inducr curren f a CMC he slpes and fr a Flyback cnverer are given by: = L g and p = L * n where g is inpu vlage, L p is he ransfrers priary inducance, is he upu vlage, n is urns rai f ransfrers, D is duy cycle and s is swiching perid his cnrller is unsable when cnverer seadysae duy cycle D is graer han 05 I can be sabilised by adding an arificial rap he sensed swich curren wavefr he arificial rap can als be adjused reduce he upu vlage ripple he ripple a he inpu vlage will be fund in he sensed swich curren he arificial rap shuld fulfil he fllwing relainship: c where is he falling slpe f he inducr and c is he arificial slpe P (GD) c guaranees curren lp sabiliy a duy cycle greaer han 50%, and c is fr he bes pssible inpu ripple rejecin 5

6 Figure 7 shws he inducr curren wavefr and he arificial slpe I shws ha any ransien I caused by inpu vlage perurbain decreases wih ie by adding a prper arificial slpe i L () Figure 0 shws he easured upu vlage, is ripple and inpu curren wih a uned arificial slpe c =08 As shwn he upu ripple is reduced very lw value wihu affecing he inpu curren shape e i L (0) i i 0 c D s s Fig 7 inducr curren and he arificial slpe Figure 8 shws graphically, hw a ransien perurbain is daped u in exacly ne cycle when c = i L () i 0 e i L (0) c = D s s Fig 8 inducr curren and he arificial slpe when c= When adjus he arificial rap he value in beween / and, he effec f he inpu ripple ay be iniized Figure 9 shws he prpsed circui easured upu vlage and is ripple wihu arificial slpe GD () GD () Fig9 upu vlage and is ripple wavefr wihu arificial slpe )u (0/div), )u (500/div) ac cupled Hriznal scale (5 s/div) GD() GD() GD() Fig0 upu vlage and is ripple wavefr wih uned arificial slpe and inpu curren )u (0/div), )u (500/div) ac cupled, )I in (A/div)Hriznal scale (5 s/div) ie II COCLUSIO A lw-cs passive pwer facr crrecr ehd is inrduced ha cbines alley Fill wih a Flyback cnverer by adding an exra winding his yields a cs-effecive sluin and cpliance wih he harnics sandard can be achieved I is suiable fr lw pwer and lw cs Experienal resuls have shwn an iprveen in pwer facr and HD f inpu curren he upu vlage ripple can be reduced an accepable level by adjusing he arificial slpe f he curren cnrl lp III ACKOWLEDGME he auhrs wuld like hank he ebers f he Pwer Elecrnic Lab f Universiy f Califrnia, Irvine fr any valuable discussins REFERECES [] A Prasad, P Zigas, S Manias A vel Passive Waveshaping Mehd fr Single-Phase Did Recifiers IEEE ransacin n Indusrial Elecrnics, OL 7, O 6, Deceber 990, P5-0 [] R Redl, L Balgh Pwer-Facr Crrecin in Bridge and lage-dubler Recifier Circuis wih Inducr and Capacirs APEC 95, P446-7 [] R Redl An Ecnical Single-Phase Passive Pwer- Facr-Crreced Recifier: plgy, Operain, Exensins, and Design fr cpliance APEC 98, P [4] Liis fr Harnic Curren E , English versin [5] Ji Spangler, Anup K Behara Elecrnic Flurescen Ballas using a Pwer Facr Crrecin echniques fr Lads Greaer hen 00 Was APEC 9, P9-9 [6] K Ki Su Iprved alley-fill Passive Curren Shaper PCIM 97, P4-50 6

7 [7] Yng-Sik Yun, Gyun Chae and Gyu-Hyeng Ch A Uniy Pwer Facr Elecrnic Ballas fr Flurescen Lap having Iprved alley Fill and alley Bs Cnverer PEPSC 97, P5-9 7

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The Buck Resonant Converter EE646 Pwer Elecrnics Chaper 6 ecure Dr. Sam Abdel-Rahman The Buck Resnan Cnverer Replacg he swich by he resnan-ype swich, ba a quasi-resnan PWM buck cnverer can be shwn ha here are fur mdes f pera under