A Four Quadrants HF AC Chopper with no Deadtime

Transcription

1 Four Quadrans HF hopper wih no Deadime Sam enyaakov,*, Yakir Hadad, and Noam Diamansein Power Elecronics Laboraory, Deparmen of Elecrical and ompuer Engineering engurion Universiy of he Negev, P.O. ox, eersheva 0, SREL. Phone: 9; Fax: 999; Websie: ompulie sysems(000) LTD, Hanagar S., Hod Hasharon, SRELl, Tel: 9 9, Fax: 9 9 Websie: bsrac four quadran HF hopper is described, analyzed and veried experimenally. The main advanage of he proposed opology is he abiliy o handle reacive loads wihou he need for a deadime beween swiches. This is accomplished by dynamically configuring he chopper as posiive or negaive uck or ackward oos converers corresponding o he momenary polariies of he inpu volage and oupu filer inducor curren. 00W breadboard uni was buil o es he proposed concep. The experimenal resuls conform o he expeced behavior of proposed chopper. SW Figure. basic HF chopper SW O V O Keywords chopper, high frequency converer swiching deadime, power facor correcion (PF), Field Programmable Gae rray (FPG).. NTRODUTON HF hoppers are useful in applicaions ha require a conrollable linefrequency volage ha is lower han he mains volage. The simples design of a HF chopper (Fig. ) includes wo bidirecional swiches ha are driven a a consan duy cycle and an, O filer o reduce he HF ripple a he oupu []. Thn imporan feaure of he HF is ha, for linear loads, he HF hopper will comply naurally wih he limis for harmonic curren emissions (EN000). The HF hopper design of Fig. poses a pracical problem ha needs o be addressed especially high chopping frequency is desired. The problem sems from he need o provide a deadime beween he operaions of he wo swiches o preven shoo hrough. The inducor curren inerrupions during he deadime need o be absorbed by a snubber o avoid dangerous volage spike. This will reduce he overall efficiency of he HF hopper. way o avoid his problem is o configure he chopper as a uck converer (swich plus diode) for each half cycle []. This will avoid he curren inerrupion (save he forward recovery of he diode) when he curren commuaes beween he swich and diode. However, his soluion is no suiable for reacive loads (Fig. ) in which four quadran operaion is required. n his case he diodes need o be swiched oo. This, inadverenly, brings back he deadime problem []. * orresponding auhor. This research was suppored by THE SREL SENE FOUNDTON (gran No. /0) and by he Paul vanier ener for Roboics and Producion managemen. T T T T Figure. Oupu volage and curren for a reacive load. The objecive of his work was o develop a four quadran HF hopper ha does no suffer from he deadime problem.. PROPOSED HOPPER a. General Descripion. The generic opology of he proposed chopper (Fig. ) includes wo swichdiode assemblies (SD) and an oupu filer, O. Each SD can be configured as a diode or swich. To provide four quadrans operaion, wihou he need for a dead ime, he SDs are configured, a any given insance, as a swich and a freewheeling diode in four dferen chopping opologies (Fig. ). n he followings we define he polariy of he inpu volage wih respec o he common (boom) line of Fig. and he posiive curren direcion is aken when he curren is flowing from he inpu o he oupu. For a posiive inpu volage and a posiive curren (corresponding o he siuaion of duraion T in Fig. ) he SDs are configured as a uck converer for a posiive inpu volage (Fig. a). For a negaive volage and a posiive curren 009/0/$ EEE.

2 (as in T of Fig. ) he SDs are configured as a ackward oos converer where he load is acing as a source and he line as a load (Fig. b). Figs. c and d correspond o he remaining combinaions of volagecurren polariies. To obain a consisen aenuaion facor (=/), over he four quadrans, he duy cycle of he swiches (D) should be: D uck = () Doos = () where D uck and D oos are he swich duy cycle of he uck and ackward oos configuraion. The duy cycle rules () and () assume ha he operaion is in he oninuous onducing Mode (M). s shown below, M can be assured even for ligh loads. Hence, operaion of he proposed chopper is idenical o choppers ha are implemened wih wo bidirecional swiches []. However, in presen case he commuaion of he inducor curren from he chopping swich o he caching diode is smooh and no snubber is required o handle an inerrupion in he inducor curren pah associaed wih a deadime, as would be he case when wo swiches are used. The SDs can be implemened by series (as shown in Fig. ) or parallel conneced swiches and diodes. The diodes need o be fas diodes o reduce he losses associaed wih he reverse recovery. The swiches could be MOSFETs or GTs as here is no need for bidirecional conducion of he swiches. in OMP SD D E F G OMP LOG RUT Figure. Proposed HF hopper OMP Vc Vsaw SD O V O a b Figure. Sysem configuraion for dferen inpu volage and oupu inducor curren polariies. onfiguraions a, b, c, d correspond o periods T, T, T, T (Fig. ) respecively. n a ypical applicaion (Fig. ) he proposed chopper will include he SDs an inpu volage polariy sense, an inducorcurren polariy sense, a PWM modulaor and a logic circui ha generae he correc gae drives per he volage and curren polariies. b. Possible onrol Sraegies. Two dferen conrol approaches can be considered wih regard o he duy cycle generaion: a free running or a clocked drive. The laer can be accomplished by applying wo D ype flipflops ha lock, a he beginning of each swiching cycle, he polariy signals corresponding o he volage and curren direcions. n his case, a change in he polariy of he volage or curren wihin a swiching period will ake effec in he following swiching cycle. This implies ha he inducor curren drops o zero wihin he swiching cycle, i will say zero (save reverse recovery effecs) ill he nex cycle. Tha is, he sysems will operae in DM. However, he polariy signals of he volage and curren are no locked a he beginning of each swiching cycle, he chopper will respond o a polariy change wihin he swiching cycle. n his case he chopper will no ener DM bu raher, he inducor curren will wobble beween posiive and negaive values. Namely, as soon as he curren will drop o zero, and in fac change polariy due o he reverse diode currens, he configuraion will change and he curren will coninue o increase in he reversed direcion. This laer mode of operaion, denoed as free running mode, is demonsraed by considering he case of a posiive inpu volage. n his siuaion he four connecions, shown in Fig., are possible. should be noed ha connecions (e) and (f) are for he on duy sae while connecions (g) and (h) are for he off duy sae. f he chopper is allowed o reconnec wihin he swiching cycle (no locking D flipflops) hen he expeced inducor curren waveform for ligh load will behave as shown in Fig.. onsequenly, in his operaional opion, () and () will hold for low loads oo, minimizing he oupu volage disorions. should be noed ha he reconfiguraion beween he uck and ackward oos opologies is aken place a c d

3 virually zero curren, so he deadime inerrupions pose no problem. The crierion for he borderline beween he M and he bipolar operaion is idenical o he borderline beween M and DM. Tha is, for a resisive load R L : D L R O L = () ( D)T S where T S is he swiching period c. Ripple urren and Ripple lage onsideraions. n mos pracical cases he oupu volage ripple will be relaively small. Hence, he high frequency oupu inducor curren ripple can be esimaed by assuming consan oupu volage. Tha is: f g e h L V O () = ( D)T S () LO where V O () is he low frequency oupu volage. Or: L () = D( D)T S () where () is he inpu volage. Hence, maximum inducor curren ripple is expeced when =0. and : Figure. Duy cycle command (upper race) and inducor curren (lower race) a ligh load. Periods e, f, g, h, correspond he configuraions in Fig.. V L O = T S () O For reacive loads, and under he assumpion of small ripple, a firs order esimae of he oupu volage ripple can sill be obained by () excep ha O needs o be replaced by Oeq, he equivalen oupu capaciance. n his case, one has o firs calculae he effecive oupu capaciance Oeq for he swiching frequency range: () () V O = 0. () The magniude of he oupu volage ripple depends on he naure of he load. For a resisive load he oupu volage ripple V O is like he case of a buck converer: e f Figure. Possible configuraion wihin a swiching cycle for a posiive inpu volage. g h Oeq = π fs Xp jπf s O where X P is he equivalen parallel reacance of he load and f s =/T s. d. npuurren Harmonics. The low frequency componen of he inpu curren inav is he low frequency inducor curren sampled during he on ime of he series SD (Fig. ). Tha is: () inav = D TS (9) n he free running mode, he average volage fed o he inducor will be proporional of he inpu volage and assuming a sinusoidal inpu waveform, he inducor curren will be sinusoidal. On he oher hand, in he locked duy cycle mode an oupu volage disorion is expeced a low oupu curren levels when he converer eners DM. One can hus conclude ha even for low oupu currens, he free running mode will heoreically produce an inpu curren of very low disorion for a sinusoidal inpu volage.

4 D D L o.mh in V in in.uf S R g VRf S Rg R g V Rf o.uf Rg D c V f Vf D c R HPL0 HPL0 HPL0 HPL0 V cc VRf VRf R R R R u D E F G FPG PLEV,9, omp V V R u R R u R9 R0 V R dd R R D v R D v V R R omp V V cc R u 0.0u 0 9 U (PWM REGULTOR) R R R R9 V cc R R R R 0 Figure. asic circui diagram of experimenal four quadrans HF chopper.. EXPERMENTL low power laboraory breadboard was consruced and esed o very he Four Quadran hopper concep experimenally. The experimenal chopper (Fig. ) was buil around GT swiches (S S ), fas diodes (D D ) floaing drivers and a Field Programmable Gae rray (FPG). Diodes (D c, D c, D v, D v ) and associaed comparaors were used o sense inpu volage polariy and inducor curren direcion. The uni was operaed a a swiching frequency of khz and was esed up o a 0Vac inpu volage range and a power levels of up o 00W. The oupu filer componens were: =.mh; O =. µf. Operaion was in he free running mode ha is, he chopper was allowed o change configuraion wihin a swiching cycle (relevan o ligh load condiions). The operaion was auomaically conrolled by he FPG. The ruh able of he programmed logic uni is given in Table. Examples of he experimenal resuls are illusraed in Figs. 0. Fig depics he chopping volage and inducor curren under no load condiions save he oupu filer. This plo demonsraes he free running mode operaion (Fig. ). Fig. 9 shows he chopped volage beween he wo SDs and he

5 inducor curren a no load condiion. veries he fac ha he proposed HF chopper keeps he sysem in M even a low curren levels. Fig. 0 depics four quadrans operaion wih an inducive load (approximaely 0 0 lag of load curren wih respec o load volage). The Efficiency of he experimenal sysem was found o be 9%. Table. Truh Table of programmable logic. D E F G = 0 = 0 = PWM < 0 > 0 L L > 0 < 0 Figure 9. Measured inpu (upper race) and oupu (lower race) volages under no load condiions. 00V/div. Time scale: ms/div. V. DSUSSON ND ONLUSSONS four quadran HF hopper was described, analyzed and veried experimenally. The main advanage of he proposed opology is he abiliy o handle reacive loads wihou he need for a deadime beween swiches. This is accomplished by dynamically configuring he chopper as posiive or negaive uck or ackward oos converers corresponding o he momenary polariies of he inpu volage and oupu filer inducor curren. 00W breadboard uni was buil o es he proposed concep. The experimenal resuls conform o he expeced behavior of proposed chopper. The planned applicaions of proposed HF hopper are dimmers for sage lighing o replace SR based choppers ha generae unaccepable line curren harmonics. Figure 0. Measured (from op o boom) inpu volage, oupu volage (00V/div), inpu curren and load curren (/div). Time scale: ms/div. REFERENES Figure. Operaion under no load condiion. Upper race: Duy cycle command. Middle race: chopped volage (mid poin beween he SDs), 00V/div. wer race: inducor curren, 0./div. Time scale: 0 µs/div. [] S.. K. ha, "Digially conrolled muliplepulsewidhmodulaed chopper for power conrol," NT. J. Elecron., 9, vol., no., pp.. [] N.. hmed, K. mei, and M. Sakui, " new configuraion of SinglePhase symmerical PWM chopper volage conroller," EEE Trans. nd. Elecron., vol., no., pp. 99, Oc [] G. H. hoe,. K. Wallace, M. H. Park, "n improved PWM echnique for choppers," EEE Trans. Power Elecron., vol., no., pp. 9 0, Oc. 99. []. H. Kwon,. D. Min, and J. H. Kim, "Novel opologies of choppers," Proc. ns. Elec. Eng. Elec. Power pplica., vol., no., pp. 0, July 99.