A Novel Phase Shifted DC-DC Converter with Adaptive Soft Switching to Improve Efficiency under wide Load Range

Transcription

1 ntenatonal Electcal Engneeng Jounal (EEJ) Vol. 6 (05) No.3, pp A Novel Phase Shfted DC-DC Convete wth Adaptve Soft Swtchng to mpove Effcency unde wde Load Range Sudha Bansal, Lalt Mohan San bansal.sudha@gmal.com Abstact Ths pape pesents a novel dc-dc convete wth adaptve soft swtchng as a means to acheve ZVS opeaton fo all the swtches. t adopts phase shft modulaton featues fo constant fequency opeaton and adaptve soft swtchng at low load. To accomplsh ths task two loops ae employed; nne cuent contol loop s to check the loadng condton and tun on of auxlay swtch accodngly. Oute contol loop s used to mpove the dynamc pefomance of DC-DC convete by achevng a obust output voltage aganst load dstubances. Ths pape also pesents the pefomance of vaous contolles. A kw/00khz dc/dc convete s smulated and analyzed. Pefomance of the poposed topology s evaluated at dffeent loads.e. statc and dynamc load (DC moto). An effcency compason of the convete wth a epoted topology has also been caed out. ndex Tems DC-DC convete; phase-shfted; esonant tank; evese ecovey; esonant convete; Soft swtchng.. NTRODUCTON DC-DC conveson technology has been developng vey apdly, and DC-DC convetes have been wdely used n ndustal applcatons such as dc moto dves, compute systems and communcaton equpment. The output voltage of pulse wdth modulaton (PWM) based DC-DC convetes can be contolled by changng the duty cycle. n geneal, to mnmze the sze and weght of pulse wdth modulated (PWM) convetes, t s equed that the swtchng fequency must be nceased []- []. Howeve, nceasng the swtchng fequency leads to substantal swtchng losses, whch causes deteoaton n system effcency. Theefoe, the swtchng losses should be educed n the case of hgh swtchng fequency opeaton. Vaous types of esonant convetes have been epoted to decease the swtchng losses dung the tansent states [3] - [5]. Numeous soft swtchng technques fo the swtchng powe convetes have been poposed [6] - [9]. These technques educe the swtchng losses, thus enablng hgh fequency opeaton and also educe the oveall system sze. Among many new technques poposed fo hgh fequency powe conveson to educe the swtchng loss n tadtonal PWM convetes, the phase- shfted zeo-voltage full-bdge pulse wdth modulaton (ZVS FB- PWM) convetes ae most desable snce they educe swtchng loss consdeably wthout the penalty of a sgnfcant ncease n conducton loss [0] - []. Fo powe levels up to 3 kw, the full-bdge convetes employ MOSFET swtches and use Phase-Shft Modulaton (PSM) to egulate the output voltage. The FB ZVS phase-shft DC-DC convete s pefeed due to ts emakable featues. n most of these convetes, zeo voltage swtchng (ZVS) s acheved by placng a snubbe capacto acoss each of the swtches and ethe by nsetng an nducto n sees wth the tansfome o by nsetng an nducto n paallel to the powe tansfome. These benefts can be summazed as: ZVS fo all the bdge tansstos, educton of the conducton losses as compaed wth quas-esonant convetes, educton of the electomagnetc nose, utlzaton of the devce output capactance and tansfome leakage nductance, fxed-fequency opeaton[3] - [4]. Howeve, thee ae some dawbacks as hgh cculatng cuents, loss of duty cycle, ZVS s lost fo lght loads.e. naow ZVS ange and load-dependent dc chaactestcs, also, t undegoes vaous nfluences by ngng between the paastc capacto of ectfyng dodes and the leakage nductance, whch cause swtchng losses and swtchng nose. Snce LLC esonant convete can offe wde zeo voltage swtchng egon and hghe conveson effcency, t ecently has been wdely adopted n the desgn of font end powe supply whee output voltage s elatvely hgh and output load cuent s elatvely low. The poblem of naow ZVS ange at lght load cuent s addessed n ths pape. Fo ths an L-C- L esonant ccut, wth an auxlay actve swtch s employed. The man contbuton of ths pape s to popose a smple adaptve soft swtchng convete to acheve ZVS opeaton fo all the swtches. t adopts phase shft modulaton featues fo constant fequency opeaton and adaptve soft swtchng at low load. ZVS of actve swtches n the laggng leg can be acheved fom zeo- to full-load condton. n ths pape the opeaton of poposed full bdge phase-shfted convete and then steady state analyss of the convete s dscussed n 8

2 D ntenatonal Electcal Engneeng Jounal (EEJ) Vol. 6 (05) No.3, pp C s C s3 chapte. Chapte explans the desgn of contolle. The pefomance C s4 at dffeent loadng condton (statc and dc D 5 moto load) s analyzed n chapte V.. Q Q Vg, Vg3,4 Vab a D D Q C C Q4 Q3 Q4 D 3 D 4 C 3 L C La C 4 Q Q3 Ca D R D R t 0 t t t 3 t 4 t 5 t 6 t 7 t 8 t9 Fg.. An adaptve soft swtchng convete and ts Steady state wavefom. NSGHT NTO THE OPERATNG PRNCPLE AND CRCUT DESCRPTON Fg. shows the schematc of full bdge adaptve soft swtchng convete and ts steady state wavefoms. The pmay sze contans fve swtches Q Q 4 & Q a. The phase shfted full bdge s fomed by the swtches Q Q 4 wth the output paastc capactos C C 4, ant- paallel dodes D D 4. Resonant ccut s fomed by esonant nducto L, esonant capacto C, paallel nducto L a n sees wth an actve swtch Q a. D & D ae the output ectfe dodes, L o s the output flte nducto and C o s output flte capacto. V o s the output voltage eflected to pmay, V s the nput voltage, Q = (L /C ) / /R L, R o = V o /Po, ω = ω s /ω, ω s the angula esonant fequency, ω = πf = (L /C ) /, ω s s the angula swtchng fequency of convete, ω s = πf s. The duty cycle of auxlay swtch Q a s kept low and contol pulse gven to the auxlay swtch depends upon the load cuent. The detals of ths cuent contolle ae dscussed n chapte. The opeaton of the convete fo heavy load attans ZVS fo all swtches but unde lght load, the load cuent s low, 0 Q Q4 L0 C0 R0 the ZVS of the laggng-leg swtches s lost as the enegy stoed n the leakage nductance of the tansfome s nsuffcent to dschage the swtch and tansfome capactances. Thus, the opeaton of the convete fo lght load s dscussed hee. The pulse wdth gven to swtch Q a depends upon the load cuent when the cuent educes, pulse duaton nceases. nductance n the ccut nceases wth tun on of Q a, so as to obtan suffcent enegy to dschage the swtch and tansfome capactances and hence ZVS condton at low load s obtaned. Unde steady state opeaton, eght opeatng states n each half swtchng cycle ae dscussed. To smplfy the analyss, few assumptons made ae as follows: All actve swtches and dodes ae deal. nductos, capactos and tansfomes used n the ccut ae deal. The output flte nducto, L o s lage enough so that the pple cuent s neglected. The output flte capactance, C o s lage enough so that the output voltage s constant The opeaton s dvded nto ten ntevals n one cycle. Mode (t 0 -t ) : Po to t 0 swtches Q & Q 4 ae conductng and powe s tansfeed fom nput to the load though swtches, and ectfe dode D R. At t= t 0, swtch Q tuns off wth ZVS as the capacto C blocks the sudden se of the voltage acoss the swtch. Now n ths mode flow of pmay cuent chages the output capactance C of Q and dschages capacto C of Q. At t=t, the voltage of C deceases to zeo and the body dode D conducts natually. Ths mode conssts of only chage and dschage opeatons, t lasts a shot tme nteval (fom t 0 to t ). Hence the dead tme should be suffcent enough to enable ths opeaton. n ths nteval the load cuent flows though the tansfome seconday wndng. Hence nductve enegy povded to chage/ dschage the capacto comes fom the leakage and output nducto. V C t d t 0 t V C V Fg. : Chage/dschage Opeaton of Capacto t t td ( C C4 ) () 0 p Mode (t - t ): At t= t, capacto C s completely dschaged hence dode D stats conductng. Now pmay cuent feewheels though D, Q 4. The pmay cuent deceases fom P-PK to P wth slope V o /L o. Auxlay swtch Q a stats conductng n ths duaton and auxlay nducto L a eneges by the auxlay cuent. Snce L a << L o, hence most of the cuent passes though L a and stoes the 83

3 ntenatonal Electcal Engneeng Jounal (EEJ) Vol. 6 (05) No.3, pp enegy n the nducto. The auxlay cuent flowng though the swtch s gven by a ( t) a ( t) ( t t) () Le Whee, a ( t ) s the ntal cuent flowng at t. The voltage acoss the swtch s vds cos[ ( t t)] (3) Whee, / C ( L L ) s the esonant fequency, e a and C e = C 3 + C Mode 3 (t - t 3 ) : Ths mode stats wth the tun off of the swtch Q 4, pmay cuent flows though C 3 & C 4. The capacto C 4 begns to chage by the pmay cuent and when voltage acoss C 4 becomes hghe than the total voltage dop value of the nductances, ectfe dode D R tuns on and stats conductng and hence the seconday wndng of the tansfomes s shot ccuted. Pmay voltage changes fom 0 to V n. The enegy equed to chage the capacto C 4 and dschage the capacto C 3 s povded by leakage and auxlay nducto. ( L La ) p ( C4 C3) V (4) Whee, v ds3 s the voltage acoss the swtch Q 3. Mode 4 (t 3 - t 4 ) : At the end of the mode 3, C 3 gets completely dschaged, hence dode D 3 stats conductng. Pmay cuent falls apdly wth the slope of V /L e. Dode D 3 and Q conducts dung the tme nteval t 3 -t 4 and Q 3, Q conduct dung the tme nteval t 4 -t 5. At the end of ths mode the pmay cuent eaches to a magntude P. d ( t) d & a( t t3) vds( t t3) (5) dt Le dt Le Whee, L e = L lk + L Mode 5 (t 4 t 5 ): Swtches Q 3 & Q conduct. The powe s tansfeed fom nput to the output ccut by the ectfe dode DR. The cuent ses n the ccut and t eaches to P at the end of ths mode. PK d ' p ' ( Llk Lo ) V & dv0 ' V0 ' o Co p (6) dt dt R0 Fom t 6 t 0: same cycle epeats fo the next half cycle. n summay snce the stoed enegy n the auxlay nducto s utlzed addtonally n laggng leg swtchng tanston, all swtchng devces n the full bdge nvete of the poposed convete tun on & off wth ZVS condton fom no load to full load. n ode to analyze the pefomance of the convete n swtchng tanston peod can be expessed as: dp( t) ( L La ) p( t). dt 0 dt C Refe equaton 3, at t=t 3, v ds3 = V and t d = (t 3 -t ) (7). cos[ ( t t)].sn[ ( t t)] Ce. Hence, t d =. Ce..tan (8) C e p A. Zeo Voltage Condton Due to the nfluence of enegy stoed n the output flte nducto, ZVS s acheved by the leadng leg swtches Q & Q 4 fo wde ange of load. Fo the laggng leg swtches the ctcal cuent s equed to attan ZVS depends on the enegy stoed n the nductve ccut. Fo the patcula value of nductance the ctcal cuent equed to supply suffcent nductve enegy to ensue ZVS can be detemned. The ctcal cuent equed fo the convete to attan ZVS wthout havng any auxlay nductance s gven by, C t p, mn. Llk V Wth the ncopoaton of auxlay nducto the equed cuent wll be, C t p, mn, a. Le V On compang, p, mn, a Llk o p,mn, a L e. Llk p,mn L e p,mn Snce, L e = L lk + L a, hence the value of auxlay nducto equed to ncease the ZVS ange depends on the value of a L lk L a a. ; Whee, a = p,mn, a p,mn A. The Cuent Rpple The effectve duty cycle d eff s the ato of the voltage pulse duaton fom +V o V appeang at the tansfome seconday wndng n a swtchng cycle. The DC voltage conveson ato of the convete dectly depends upon the effectve duty cycle. Vo Ns. d, the effectve duty cycle s gven by, eff V N eff p d = d o - d, whee, d o s the ognal duty cycle of the convete & d s duty cycle loss and s gven by, p p d TS. Llk B. Dead Tme The dead-tme between the laggng leg swtches s one fouth of the esonant peod (T R /4), whch s calculated by utlzng the tansfome leakage nductance and the total output paastc capactance of the laggng leg swtches. The dead-tme equement fo MOSFETs s shot whle GBTs eque lage dead-tme due to the tal cuent. (9) 84

4 ntenatonal Electcal Engneeng Jounal (EEJ) Vol. 6 (05) No.3, pp Hence, the dead-tme equement of the ccut must be detemned based on the swtchng devce chaactestcs.. CONTROLLERS DESGN A dual loop contolle s desgned fo the system. A. nne Loop Fo adaptve contol of swtch Q a a cuent contolle s desgned. The pncple behnd the opeaton of ths contolle s that t wll dect the swtch only n the case of cuent falls to the 0% of ated cuent. Ths swtch emans nopeatve n the case of hgh load cuent. t wll help n gettng zeo voltage condton fom zeo to the ated load condton. Swtchng Pulse To Sa V V ef DC/DC CONVERTER Swtchng Pulse to P/ Fuzzy + Φ - Contolle Swtchng Pulse o + - Contol Ccut Contolle ated + - Load V ef + to Q a Fg. 3. nne Cuent Contol loop & Oute Voltage contolled loop + - contolles.e. P and fuzzy contolles ae dscussed and H(s) Powe Ccut Vo Voltage Senso B. Oute Loop To obtan the output voltage egulaton vaous contolles can be used. Hee n ths pape two types of late on the pefomance of the poposed convete usng these contolles ae analyzed. ) P contolle: n ode to desgn a P contolle, the lneazed model of the convete has to be detemned. n ths, the output voltage s compaed wth the efeence to geneate the eo sgnal and ths sgnal s gven to the P contolle to obtan the desed phase- shft fo the actve swtches. These swtches ae gven phase shfted pulse to contol the output voltage. The value of popotonal contolle, k p and ntegal contolle, k ae taken as 0. and 0 and ae fnely tuned theeafte. ) Fuzzy logc contolle : P contolle s smple to mplement and easy to desgn, but ts pefomance geneally depend on the wokng pont, so that the pesence of paastc elements, tme-vayng loads and vaable supply voltages can make selecton of the contol paametes dffcult, whch ensue a pope behavo n any opeatng condtons. Achevng lage-sgnal stablty often calls fo a educton of the useful bandwdth, so affectng convete pefomance. Fuzzy contol s appled to contol dc dc convetes because of ts smplcty, ease of desgn and ease of mplementaton. Fuzzy contolles ae well suted to nonlnea tme-vaant systems and do not need an exact mathematcal model fo the system beng contolled. The fuzzy logc contolle detemnes the opeatng condton fom the measued values and selects the appopate contol actons usng the ule base ceated fom the expet knowledge. The contol wll wok based on two nput sets: the output voltage eo, e(k) = V ef - V dc (k) (0) and the change n eo vaatons de(k) = e(k) - e(k-l)) () Whch ae sampled at evey T sv = 5µs. The k s the actual samplng sequence. The basc contol stuctue of a fuzzy logc system and ts membeshp functon fo eo, change n eo and output ae shown n Fgue 4-(d). The FLC has thee functonal blocks fo calculaton and two databases. The functonal blocks n FLC ae: ) fuzzfe; ) ule evaluato; and 3) defuzzfe. The two databases ae Rule base and Database. Fuzzy logc uses lngustc vaables nstead of numecal vaables. The pocess of convetng a numecal vaable (eal numbe) nto a lngustc vaable (fuzzy numbe) s called fuzzfcaton. Fo a gven csp nput, fuzzfe fnds the degee of membeshp n evey lngustc vaable. Snce, thee ae only two ovelappng membeshps n ths specfc case, all lngustc vaables except two wll have zeo membeshp. n FLC, the equvalent tem s ules and they ae lngustc n natue. A fuzzy logc contolle so desgned s used to contol the convete by sendng the desed contol sgnal to the PWM sgnal geneato. 85

5 Degee of membeshp ntenatonal Electcal Engneeng Jounal (EEJ) Vol. 6 (05) No.3, pp zeo ps psm psl pm pml pl pvl pel output (c) (d) Fg. 4. ntenal stuctue of FLC Membeshp functon plot fo eo, (c) Membeshp functon plot fo change n eo and (d) Membeshp functon plot fo output (c) Fg.6. Wth P Contolle, Wth Fuzzy Contolle &(c) Cuent of the DC/DC convete at 0% of load, when sudden load s nceased to 0% of full load V. RESULTS AND DSCUSSON The smulaton of the kw, 00/50 Volt, 00 khz full bdge phase- shfted DC/DC convete ccut s caed out. The systems tansent pefomance s evaluated on applyng sudden load changes and the esults so obtaned ae analysed n tems of steady state eo, peak oveshoot, settlng tme. Hee two types of contolles.e. P and fuzzy contolles ae dscussed and the pefomance of the poposed convete usng these contolles ae analyzed. B. At full load and 50% of load The convete s ntally full loaded and then the load s educed suddenly to 50% of full load at t = 0.06 sec. The output voltage and cuent ae measued wth ths sudden change at t = 0. sec load s agan nceased suddenly to full load. Fg. 5. Tansfome voltage and cuent wavefom at the pmay of the nvete A. At 0% of full -load to 0% of full -load: n ths convete s ntally loaded wth 0% of the full load and then load s suddenly deceased to 0% of full -load at t=0.06 sec by step decease n load. The output voltage and cuent wavefom fo P Contolle and Fuzzy contolle ae shown n fg.6. Fg. 6 (d). Output Voltage and Cuent of the DC/DC convete at 00% load, When Sudden load s educed to 50% load at t =0.06 Sec & agan nceased at t=0. sec. C. At dffeent values of Load nductance, keepng esstve load constant: The behavo of convete ccut wth dffeent values of nductve load s obseved. The effect of nductance vaaton on output voltage s shown n fg.7. Fg. 7. The output Voltage at dffeent load condtons D. Zeo voltage Swtchng: All the actve swtches n the convete tuns on and off at zeo voltage, so as to mnmze swtchng losses. The voltage acoss dan to souce at 5% of load and at full load s shown n fg. 8 & espectvely. 86

6 ntenatonal Electcal Engneeng Jounal (EEJ) Vol. 6 (05) No.3, pp Fg. 8 & V ds and Gate pulse at 5% of load & at 00% of load TABLE. PERFORMANCE COMPARSON BETWEEN FUZZY AND P CONTROLLER S. No. Peak oveshoot Settlng tme (Sec) P contolle Fuzzy Contolle V. CONCLUSON % Steady state eo Ths pape has pesented two dffeent contolles P and fuzzy contolle to mpove the dynamc esponse of the DC/DC boost convete aganst the load vaaton. t has been obseved that the system s stable fom 5% of load to full load. The system shows excellent pefomance when DC moto load s appled. The system s also vefed on fequent change of load. The smulaton esult shows that the pefomance of convete wth fuzzy contolle ensues the tght egulaton of output voltage effectvely unde the load uncetanty. The effcency of the convete at dffeent loadng condtons s also measued and mpovement n effcency s found.. [5]. Hua G., Lee F. C., Jovanovc M. M., An mpoved Full-Bdge Zeo- Voltage- Swtched PWM Convete Usng a Satuable nducto, EEE Tansacton on Powe Electoncs 993, vol. 8, ssue 4, pp [6]. Sun J., Hamada S., Yoshtsugn J., Guo B., Nakaaka M., Zeo Voltage Soft Commutaton PWM DC-DC Convete wth Satuable Reacto Swtch-Cascaded Dode Rectfe, EEE Tansacton on Ccuts System 998, vol. 45, ssue 4, pp [7]. Redl R., Balogh L., Edwads D. W., Optmum ZVS Full-Bdge DC/DC Convene wth PWM Phase-Shft Contol: Analyss, Desgn Consdeatons, and Expemental Results, Poceedngs of EEE APEC confeence 994, pp [8]. Valtchev S., Bages B.V., KW/50 khz Full Bdge Zeo Voltage Swtched Phase Shft DC-DC Convete wth mpoved Effcency, Poceedngs of NTELEC confeence 995, pp [9]. Koo G., Moon G., and Youn M.Y., New zeo-voltage swtchng phase-shft full-bdge convete wth low conducton losses, EEE Tansacton of ndustal Electoncs 005, vol. 5, pp [0]. A. K. Rathoe, A. K. S. Bhat and R. Ougant, A compason of soft swtched dc-dc convetes fo fuel cell to utlty nteface applcaton, EEJ Tansactons on ndusty Applcatons, vol. 8, no. 4, pp , 008. []. A. K. Rathoe, A. K. S. Bhat and R. Ougant Small sgnal modelng and closed loop contol desgn of ZVS cuent-fed half-bdge L-L type dc/dc convete wth actve-clamp," ntenatonal Jounal on Compute and Electcal Engneeng, vol., no. 6, Dec 00, pp []. Wu X., Zhang J., Xe X., and n Z., Analyss and optmal desgn consdeatons fo an mpoved full bdge ZVS dc-dc convete wth hgh effcency, EEE Tansactons on Powe Electoncs 006, vol., ssue 5, pp [3]. Song T., Wang H., Chung H., Tapuh S., and onovc A., A hgh-voltage ZVZCS dc dc convete wth low voltage stess, EEE Tansactons on Powe Electoncs 008, vol. 3, ssue 6, pp [4]. Joseph X.F., slam N., Kuma S.P., Domnc D.A. and Pabha D.M.M. S.R., Desgn and Smulaton of a P contolled Soft Swtched Font end Convete fo Swtched Reluctance Moto, ntenatonal Jounal of Compute Applcatons 0, vol. 34, ssue 0. [5]. S. Sunsth Lz Joseph and M. Satha, Compason of Fuzzy PD Contolle wth Conventonal PD Contolle n Contollng the Speed of a Bushless DC Moto, ntenatonal Electcal Engneeng Jounal (EEJ),VOL_5 NO_, 5 JAN, 05 REFERENCES []. A. K. Rathoe, A. K. S. Bhat and R. Ougant Analyss, desgn and expemental esults of wde ange ZVS actve-clamped L-L type cuent-fed dc-dc convete fo fuel cell to utlty nteface applcaton, EEE Tansactons on ndustal Electoncs, vol 59, ssue, Jan 0, pp []. A. K. Rathoe, "nteleaved soft-swtched actve-clamped L-L type cuent-fed half-bdge dc-dc convete," ntenatonal Jounal on Hydogen Enegy(Elseve), vol. 34, ssue 4, Dec 009, pp [3]. Hua G.and Lee F. C., Soft-swtchng technques n PWM convetes, EEE Tansacton of ndustal Electoncs 995; vol. 4, ssue 6, pp [4]. Watson R.and Lee F. C., A soft-swtched, full-bdge boost convete employng an actve- clamp ccut, Poceedngs of EEE PESC confeence 996 pp