Hybrid Modulator for power converters in parallel topology

Transcription

1 Hybrid Modulator for powr convrtrs in paralll topology J. Mon, D. Gonzálz, J. Balclls, J. Gago, P. Bogónz Dpartant d Enginyria Elctrònica, Univrsitat Politècnica d Catalunya. Capus d rrassa rrassa, Spain. juan.on@upc.du bstract his papr prsnts a nw ixd odulator that cobins intrlaving and sprad-spctru tchniqus in ordr to achiv th lowst lvl of conductd EMI gnration. his odulator is addrssd to powr convrtrs in paralll arrangnt. h practical dtails of th hybrid odulator and controllr iplntation on a FPG ar xplaind. h charactristics of such odulator in trs of EMI rduction and convrtr prforanc ar thortically xplord and xprintally validatd in a four channl paralll buc convrtr oprating in closd loop. Kywords Intrlaving, frquncy odulation, EMI, EMC. I. IRODUCIO Switchd powr convrtrs ar opratd with constant switching frquncy undr hard switching rgi using Puls Width Modulation. In a gnral way, th odulator is th bloc that gnrats th switching pattrns fro th control signal gnratd by th convrtr controllr. hrfor, it is th bloc rsponsibl of th ain sourc of EMI. Sinc switching frquncy odulation (SFM) was introducd as EMI rduction tchniqu in switchd powr convrtrs a lot of wors hav bn publishd dvloping this ida [ ]. t prsnt, it is a wll stablishd tchniqu and a worthy altrnativ to th traditional filtring thods such as th buly EMI filtrs or snubbr ntwors in trs of attnuation, cost and siplicity of application. In part du to incras of using prograabl logic dvics in ordr to iplnt digital control systs [, 3], SFM-odulators ar digitally iplntd on a fild prograabl gat array (FPG) [0, ] or coplx prograabl logic dvic (CPD) [4]. hy hav bn applid to svral applications such as ho cooing applianc [0] or high prforanc powr supply [4]. Howvr, th application of SFM tchniqus in distributd or odular powr systs ad up of svral powr convrtrs has not bn dply studid yt. On th othr hand, so rcnt wors addrss th iplntation of ultiphas digital odulators in ordr to apply intrlaving in paralll ulticonvrtr arrangnt, [5, 6]. Howvr, th cobind application of intrlaving and SFM tchniqus is an opn rsarch fild. his papr prsnts a nw ixd odulator that cobins intrlaving and sprad-spctru tchniqus spcially intndd for conductd EMI supprssion. It should b ntiond that this ixd odulator could b applid not only to DC/DC convrtrs but to all ind of ulticonvrtrs arrangnts. thorough dscription of intrlaving can b found in [7-9]. his papr is organizd as follows. First of all, Sction II prsnts th thortical dvlopnt of th thr hybrid odulations that hav bn considrd. Sction III dscribs th practical iplntation usd to validat thortical dvlopnts. Sction IV suarizs ain rsults that validat th proposd approach. Finally, conclusions ar outlind in Sction V. II. HYBRID MODUOR HEORY Sprad Spctru Modulation in singl convrtr consists of odulating th switching priod around a cntral valu, c, according to a givn odulation profil. In ordr to cobin th intrlaving and sprad spctru odulation in ulticonvrtr arrangnt thr ar svral possibilitis. Fig. illustrats switching pattrns of a ultichannl hybrid odulator whn th priodic odulation profil is usd, whr i nots ach channl (i =, 2,..., ), α i is th dlay aong switching pattrns, q i (t), and ε,i is th puls position dlay insid th th switching cycl. Each switching pattrn contains switching cycls (). otic that ach switching pattrn has a priod qual to th priod of th odulation profil,. =,int gr > 0 () c Fig.. Gnric frquncy-odulatd switching pattrns. abl I suarizs th odulation charactristics of th thr odulation considrd in this papr: Constant Dlay with switching Frquncy Modulation (CDFM-), Constant Dlay c with switching

2 Frquncy Modulation (CDFM-c) and Variabl Dlay with switching Frquncy Modulation (VDFM). In all cass, a odulation on th switching priod is introducd according to a triangular odulation profil. On th othr hand, th valu of th duty cycl, D c, is always stablishd by th controllr. BE I CHRCERISICS OF DIFFERE MODUIOS Modulations ε,i,i τ,i α i CDFM- 0 i, c Δ i D c i CDFM-c 0 i, c Δ i D c i c VDFM, i c Δ i D c i 0 i In ordr to valuat th attnuation providd by th proposd odulations, a ti doain dscription of th switching pattrn, q i (t), ust b dtrind. Considring that a switching pattrn has a priod qual to th odulation profil priod,, th ti doain xprssion of ach of th, q i (t), can b writtn as (2) i Ci,n = Ci, 0 jt jt 2Ci,n q ( t ) = (2) whr C i,n ar th Fourir cofficints calculatd according to (3) C i,n = j 0 q ( t ) i ( ε,i H,i ) jt dt = j jτ,i jαi whr is th aplitud of ach pattrn, q i (t), and H,i is th starting ti of th th switching cycl of ach pattrn. Finally, th quivalnt sourc of nois, s(t), in a ulticonvrtr arrangnt with channls is dtrind by th addition of ach particular pattrn, q i (t), according to (4). s( t ) = q i ( t ) h odulation paratrs shown in abl II wr usd to copar ffcts of th proposd odulations. triangular odulation profil was usd in all cass and was st qual to. (3) (4). Constant Dlay with switching Frquncy Modulation (CDFM-) h intrlaving ffct is obtaind by introducing a dlay α i aong th switching pattrns, which is dtrind according to th odulation profil,. Considring th valus of abl I, th quivalnt sourc of nois in frquncy doain, S CDFM (w), can b xprssd by (5) S j j = D CDFM c ( w ) = F ( w) E ( w) = = jh qi ( t ) = Dc jh CDFM jdc ( w) jdc ( w nw ) ( w nw ) whr w is corrsponds to th odulation profil frquncy (6). 2π w = 2 πf = (6) otic that th absolut valu of E CDFM- (w) tas th valus givn by (7): 0 w ) = n = h n h h = 0,, 2, ECDFM (, Figur 2 illustrats th CDFM- ffct. his odulation lads to nrgy sprading of original haronics in sidbands. his spctru contains coponnts at frquncis nf only instad of nf if pur odulation (without intrlaving) wr applid [4]. For this rason, thr ar no coponnts at frquncis f c, 3f c and 5f c in th rsulting spctru shown in Fig. 2. (5) (7) Modulations o odulation CDFM- CDFM-c VDFM BE II MODUIO PRMEERS f c Δf c f [Hz] [Hz] [Hz] D c [%] Fig. 2. CDFM- vs. on odulatd. B. Constant Dlay c with switching Frquncy Modulation (CDFM-c) In this odulation, th dlay α i aong th switching pattrns is calculatd fro th cntral valu of switching cycl, c. h quivalnt sourc of nois in frquncy doain, S CDFMc (w), is xprssd by (8).

3 S j j = D CDFM c c ( w ) = F ( w) E ( w) jh qi( t ) = Dc jh CDFM c jdc jdc ( w) ( w nw ) ( w nw ) (8) h tr E CDFM-c (w) provids a nrgy sprad ffct that is illustratd in Fig. 3. Fro Fig. 3 haronic cancllation is noticd at frquncis nf c xcpt thos ultipl of f c. In coparison to CDFM-, an additional attnuation is obsrvd for all frquncis xcpt thos ultipl of f c. hrfor, a bttr prforanc than CDFM- is xpctd. Figur 4 shows th rsulting spctru of CDFM- c. Fig. 5 VDFM vs. on odulatd Figur 5 illustrats th VDFM ffct. h rsulting spctru contains only haronics of f c, which nrgy is sprad in sidbands. Sparation btwn sidbands is f. VDFM provids th bst rsults in trs of attnuation. h rsulting spctru of VDFM is quivalnt to a singl convrtr opratd at f c with sprad spctru frquncy odulation. III. HYBRID MODUOR IMPEMEIO h hybrid odulator and th digital control loop wr iplntd on a Spartan-3 FPG board fro Xilinx. Figur 6 shows th bloc diagra of an n-channls hybrid odulator. h input signal of th hybrid odulator is th nurical valu of th duty cycl, d, that cos fro th convrtr controllr odul. Output signals PWMi gos to th drivr of ach switching dvic. his ixd odulator can gnrat th thr abov ntiond odulations prsntd in Sction II. Fig. 3. Envlop of E CDFM-c (w). Fig. 4. CDFM-c vs. on odulatd. C. Variabl Dlay with switching Frquncy Modulation (VDFM) In VDFM thr is any dlay aong switching pattrns (α i =0). In this cas, a dlay on ach particular switching cycl, ε,i, is introducd according to abl I. h quivalnt nois pattrn in frquncy doain, S VDFM (ω), is xprssd by (9). S VDFM ( w ) = F jh qi( t ) = Dc ( w) j jdc j ( w nw ) (9) Fig. 6. Bloc diagra of Hybrid-Modulator. Each particular channl consists of two oduls, Switching Frquncy Modulator, (SFMi), and Digital Puls Width Modulator, (DPWMi). his structur is rpatd to obtain a ultichannl structur. h odul SFM gnrats th odulation on th switching priod and th duty cycl. Fro ths valus, odul DPWM finally gnrats th puls trains for th drivrs of th switching dvics. h odul Gn_Enabl anags all th channls of th ixd odulator by gnrating th dlay aong th switching pattrn of ach channl and thir nabl signals as wll.

4 . Gn_Enabl h basic structur in ordr to apply a shift dlay, α i, aong PWMi signals is basd in a shift rgistr [8, 9]. Howvr, this approach prsnts two drawbacs. First, all PWMi signals hav th sa switching priod. On th othr hand, this structur dos not allow to introduc dlays in th puls position in ach switching cycl, ε,i. Figur 7 shows th proposd structur in ordr to apply a shift dlay, α i. It is basd on th countr-coparator architctur. hs dlays ar obtaind by introducing variabl shift dlays aong th nabl signals for ach channl, En_PWMi. his iplntation allows having diffrnt switching priods for ach particular channl. Fig. 7. Bloc diagra of Gn_Enabl. B. SFM SFM odul, which bloc diagra is shown in Fig. 8, is intndd to odulat th instantanous switching priod,,i, of ach switching pattrn, as it is rquird by th odulations prsntd in Sction II. his has bn don by varying th aplitud of a sawtooth signal, as it illustratd in Fig. 9 whr th output signal of th odul ar shown. h valu of data_cmpr adjusts th duty cycl and Data_PR adjusts th instantanous switching priods,,i. h c signal is usd to synchroniz th updat of Data_CMPR and Data_PR signals at th bginning of ach switching cycl. otic that Data_CMPR is scald in ach switching cycl in ordr to p constant th ratio btwn its valu and th varying Data_PR. his rsults in a corrct gnration of th duty cycl valu that is st by th convrtr controllr on ach switching cycl. hr ar two ory blocs, MEM_CMPR and MEM_PR, that contains Data_CMPR scaling valus and,i valus, rspctivly. h valu rquird for Data_CMPR scaling for th currnt switching priod is containd in CMPR_aux signal. hir valus ar calculatd off-lin according to (0) and stord in th MEM_CMPR ory bloc. Rgarding MEM_PR ory bloc, it contains th nubr of cloc cycls rquird to gnrat ach instantanous switching priods,,i. hy ar calculatd off-lin according to ().,i CMPR_aux =, =, 2,..., (0) in { },i,i Data_PR =, =, 2,..., () cl h bloc Control Unit (CU) is a finit stat achin that gnrats all control signals ncssary for accssing MEM_CMPR and MEM_PR ory blocs. In th particular cas of odulation VDFM, only th initial puls position dlay for ach channl, ε,i, is introducd by th Gn_Enabl odul as a dlay btwn PWM pattrns. Howvr, th following puls position dlays ar introducd by th SFMi oduls by odifying th instantanous switching priod of ach channl, according to (2). his approach is illustratd by Fig. 0. Fig. 8. Bloc diagra of SFM.,i,i, =, 2,..., = ε ε =,i = =,i,,i ε,i,i ε,i,i =,,i,i,i, = (2) Fig. 0. PWM signals usd by VDFM. Fig. 9. Sprad Spctru PWM.

5 IV. EXPERIME RESUS h hybrid odulator dscribd in Sction III has bn validatd in a four channl paralll buc convrtr. Figur shows th bloc diagra of th xprintal plant. h oprating conditions of ultichannl buc convrtr ar suarizd in abl III. odulation profil, V (t), with a odulation frquncy f =0 Hz and a axiu frquncy dviation Δf c =60 Hz. h f paratr has bn chosn considring th Rsolution Bandwidth (RBW) of th EMI rcptor [4]. (a) Fig.. Bloc diagra of ultichannl buc convrtr. BE III MI FEURES OF MUICHE BUCK COVERER Input Voltag Output Voltag Powr Switching Frquncy 2 V DC.5 V DC 4 W 300 Hz h digital PID copnsator hav bn iplntd according to (3), whr d[n] is th duty cycl, [n] is th rror signal and 0, and 2 ar th discrt copnsator cofficints. d[ n] = d[ n ] [ n ] [ n ] [ n 2] (3) 0 2 h paratrs of th voltag PWM controllr ar suarizd in abl IV. h valu of sapl is rcalculatd on ach switching cycl of channl. In our application its valus rang fro 2.77 µs up to 4.6 µs. (b) Fig. 2 EMI asurnt st-up. (a) Bloc diagra. (b) Full viw st-up. Figur 3 shows th spctru obtaind whn th convrtrs wr opratd at constant frquncy. Figurs 4, 5 and 6 show th spctru corrsponding to th thr proposd odulations. BE IV PRMEERS OF HE VOGE PWM COROER K K K In ordr to valuat th odulation schs prsntd in Sction II, th conductd disturbancs up to 30 MHz and output voltag rippl ar prsntd. Masurnts of conductd disturbancs wr carrid out using a copliant in Ipdanc Stabilization twor (IS) as show in Fig. 2. h xprintal rsults hav bn obtaind for a cntral switching frquncy f c =300 Hz, a triangular Fig. 3 Conductd nois without frquncy odulation.

6 rang (up to th 4th haronic) th canclation ffct is clarly noticd. For highr frquncis, th cobination of canclation and nrgy sprad ffcts provids an attnuation of alost 5 db in all frquncy rang. chniqus basd on sprad spctru can lad to undsird sid ffcts on th convrtr prforanc. It has bn donstratd that powr fficincy is not clarly affctd [6]. h ost noticabl ffct will appar as an incras of th output voltag rippl [9]. h output voltag rippl without odulation nithr intrlaving is 8.4 V. Figurs 7 and 8 copar th output voltag rippl in all cass considrd. h odulation frquncy, f, is clarly rflctd in th output voltag whn CDFM-c or VDFM ar applid. his ffct is lss noticabl in CDFM- du to th dlay introducd aong switching pattrns. Fig. 4 Conductd nois of CDFM-. Fig. 5 Conductd nois of CDFM-c. Fig. 7 Output voltag rippl coparison: o odulation and CDFM- (Uppr trac: no odulatd ; lowr trac: CDFM-). Fig. 6 Conductd nois of VDFM. s it has bn donstratd in Sction II, th CDFM-c and VDFM provid th bst attnuation. h haronic canclation ffct of CDFM-c that is prdictd in Fig. 3 is clarly noticabl in Fig. 5. h bst attnuation is givn by VDFM. In th low frquncy Fig. 8 Output voltag rippl coparison: CDFM-c and VDFM (Uppr trac: CDFM-c ; lowr trac: VDFM). V. COCUSIO In this papr a hybrid odulator intndd to supprss th sourc of nois inhrnt to th opration of switchd

7 powr convrtrs is prsntd. his hybrid odulator iplnts thr cobinations of intrlaving and sprad spctru. h attnuation providd by such odulators wr thortically xplord and practically validatd in a four channls buc convrtr in paralll arrangnt and opratd in closd loop. EMI attnuation obtaind with ths tchniqus was asurd on th full bandwidth of conductd disturbancs. s a rfrnc to valuat attnuation, convrtrs wr opratd at constant frquncy and without intrlaving. Spcial attntion has bn paid to th influnc of such tchniqus on th output voltag rippl of th convrtr. h VDFM is th tchniqu that provids th bst trad-off btwn attnuation and convrtr prforanc dgradation in trs of output voltag rippl. CDFM-c shows siilar attnuation but with wors rsults in trs of output voltag rippl. It has bn donstratd that hybrid odulator is a viabl and worthy altrnativ or coplntary to convntional passiv EMI filtrs for conductd disturbancs attnuation purposs. It should b ntiond that th iplntation of ths tchniqus dos not rquir additional coponnts. CKOWEDGEME his rsarch is supportd by th Ministrio d Cincia Innovación in th fra of th projct EC REFERECES [] F. in and D. Y. Chn, Rduction of Powr Supply EMI Eission byswitching Frquncy Modulation, IEEE rans. Powr Elctron., vol. 9, no., pp , January 994. [2]. M. Stanovic, G. E. Vrghs, and D. J. Prrault, nalysis and Synthsis of Randoizd Modulation Schs for Powr Convrtrs, IEEE rans. Powr Elctron., vol. 0, no. 6, pp , ovbr 995. [3] K. K. s, H. S.-H. Chung, S. Y. Ron Hui, and H. C. So, Coparativ Study of Carrir-Frquncy Modulation chniqus for Conductd EMI Supprssion in PWM Convrtrs, IEEE rans. Ind. Elctron., vol. 49, no. 3, pp , Jun [4] J. Balclls,. Santolaria,. Orlandi, D. Gonzalz, and J. Gago, EMI Rduction in Switchd Powr Convrtrs Using Frquncy Modulation chniqus, IEEE rans. Elctroagn. Copat., vol. 47, no. 3, pp , ugust [5] S. Johnson and R. Zan, Custo Spctral Shaping for EMI Rduction in High-Frquncy Invrtrs and Ballasts, IEEE rans. Powr Elctron., vol. 20, no. 6, pp , ov [6] D. Gonzalz, J. Balclls,. Santolaria, J.-C. Buntl, J. Gago, D. Magnon, and S. Brhaut, Conductd EMI Rduction in Powr Convrtrs by Mans of Priodic Switching Frquncy Modulation, IEEE rans. Powr Elctron., vol. 22, no. 6, pp , ovbr [7] S. Kaboli, J. Mahdavi, and. gah, pplication of Rando PWM chniqu for Rducing th Conductd Elctroagntic Eissions in ctiv Filtrs, IEEE rans. Ind. Elctron., vol. 54, no. 4, pp , ugust [8] D. Gonzalz, J.. Bialasiwicz, J. Balclls, and J. Gago, Wavlt-Basd Prforanc Evaluation of Powr Convrtrs Oprating With Modulatd Switching Frquncy, IEEE rans. Ind. Elctron., vol. 55, no. 8, pp , ugust [9]. Santolaria, Effcts of Switching Frquncy Modulation on th Powr Convrtr s Output Voltag, IEEE rans. Ind. Elctron., vol. 56, no. 7, pp , July [0].. Barragan, D. avarro, J. cro, I. Urriza, and J. M. Burdio, FPG Iplntation of a Switching Frquncy Modulation Circuit for EMI Rduction in Rsonant Invrtrs for Induction Hating ppli- ancs, IEEE rans. Ind. Elctron., vol. 55, no., pp. 20, January [] G. Dousoy, M. Shoyaa, and. inoiya, FPG-Basd Sprad-Spctru Schs for Conductd-ois Mitigation in DC-DC Powr Convrtrs: Dsign, Iplntation, and Exprintal Invstigation, IEEE rans. Ind. Elctron., vol. 58, no. 2, pp , Fbruary 20. [2] E. Monasson,. Idhajin, M. Cirsta, I. Bahri,. isan, and M. aouar, FPGs in Industrial Control pplications, IEEE rans. Ind. Inforatics, vol. 7, no. 2, pp , May 20. [3] E. Monasson,. Idhajin, and M. aouar, FPG-basd Controllrs, IEEE Industrial Elctronics Magazin, vol. 5, no., pp. 4 26, March 20. [4] O. rscass, G. Wi,. Prodic, and W. ung, n EMI Rduction chniqu for Digitally Controlld SMPS, IEEE rans. Powr Elctron., vol. 22, no. 4, pp , July [5] R. Foly, R. Kavanagh, W. Marnan, and M. Egan, Multiphas Digital Pulswidth Modulator, IEEE rans. Powr Elctron., vol. 2, no. 3, pp , May [6] M. Scharrr, M. Halton,. Scanlan, and K. Rinn, FPG-Basd Multi- Phas Digital Puls Width Modulator with Dual-Edg odulation, in pplid Powr Elctronics Confrnc and Exposition (PEC), 200 wnty-fifth nnual IEEE, Fbruary 200, pp [7] C. Chang and M.. Knights, Intrlaving chniqu in Distributd Powr Convrsion Systs, IEEE rans. Circuits Syst. I, vol. 42, no. 5, pp , May 995. [8] S. Ozri, D. Shilovitz, S. Singr, and. Martinz-Salaro, h Mathatical Foundation of Distributd Intrlavd Systs, IEEE rans. Circuits Syst. I, vol. 54, no. 3, pp , March [9] P. Zul, O. Garcia, J.. Olivr, and J.. Cobos, Diffrntial- Mod EMI Rduction in a Multiphas DCM Flybac Convrtr, IEEE rans. Powr Elctron., vol. 24, no. 8, pp , ugust [9]. d Castro, G. Glz-d Rivra, O. Garcia, P. Zul, and. Risgo, Coparison of Phas-shiftrs for Multiphas Powr Convrtrs, IEE Journal of Rsarch, vol. 57, no., pp , March 20.