An Isolated Bi-Directional Buck Boost Converter with Fly Back Snubber

Transcription

1 IJTE - Interntionl Journl of cience Technoloy & Enineerin Volue 2 Issue 1 April 216 IN (online): X An Isolted Bi-irectionl Buc Boost Converter with Fly Bc nubber Mr.R.VELMURUGAN Assistnt Professor eprtent of Electronics & Couniction Enineerin Christin Collee Of Enineerin & Technoloy. indiul Tilndu Indi A.CHANRAEKHAR PG cholr eprtent of Electronics & Couniction Enineerin Christin Collee Of Enineerin & Technoloy. indiul Tilndu Indi Abstrct In renewble C systes bi-directionl C-C converters re used for hih volte nd hih power pplictions. One such isolted bi-directionl full bride buc boost converter with flybc snubber tht hs sinificnt volte spie clpin cpbility is proposed in this project.. An isolted bidirectionl full-bride dc dc converter with hih conversion rtio, hih output power, nd soft strt-up cpbility is lso proposed. The use of cpcitor, diode nd flybc converter cn clp the volte spie cused by the current difference between the current-fed inductor nd lee inductnce of the isoltion trnsforer nd cn reduce the current flowin throuh the ctive switches t the current-fed side. The siulted odel of the conventionl converter without flybc snubber,proposed converter with flybc snubber s well s odifiction of the proposed ethod with RC snubber is developed in MATLAB softwre for both buc nd boost odes. Keywords: Buc Boost, Flybc nubber I. INTROUCTION Over the pst decde buc-boost converters hve becoe n iportnt reserch topic with jor focus on volte spie reduction. The jor concerns of these studies include reducin switchin loss, reducin volte nd current stresses, nd reducin conduction loss due to circultion current. A ore severe issue is due to lee inductnce of the isoltion trnsforer, which will result in hih volte spie durin switchin trnsition. Additionlly, the current freewheelin due to the lee inductnce will increse conduction loss nd reduce effective duty cycle. everl pproches hve been suested to llevite volte spie few re stted below, Pre-chrin lee inductnce, Active clp circuit etc. T. Reinn nd G. Berer(28) hs proposed novel control principle of bi-directionl C-C power conversion is n lterntive pproch to pre-chre the lee inductnce to rise its current level up to tht of the current-fed inductor, which cn reduce their current difference nd, in turn, reduce volte spie hs been proposed. However, since the current level vries with lod condition, it is hrd to tune the switchin tiin dir to tch these two currents..yujin nd P.N. Enjeti(29) hs proposed newsoft switchin technique for bi-directionl power flow full-bride C-C converter is tht n ctive couttion principle to control the current of lee inductnce. however, clpin circuits re dditionlly required. Pssive nd ctive clpin circuits hve been proposed to suppress the volte spies due to the current difference between the current-fed inductor nd lee inductnce of the isoltion trnsforer. An ctive clpin circuit hs been proposed to suppress volte spie due to the current difference by controllin the current of lee inductnce. But its resonnt current increses the current stress on switches. Hu Bi nd Chris Mi(28) hs described rective power eliintion nd increse syste efficiency of isolted bidirectionl dul-ctive bride dc-dc converters usin novel dul-phse-shift control sttes tht novel dul-phse-shift (P) control strtey for dul-ctive-bride isolted bidirectionl dc dc converter. This P control consists of phse shift between the priry nd secondry voltes of the isoltion trnsforer, nd phse shift between the te sinls of the dionl switches of ech H-bride. It shows tht the P control hs excellent dynic nd sttic perfornce copred to trditionl phse-shift control (sinle phse shift). In this pper, the concept of rective power is defined nd the correspondin equtions re derived for isolted bidirectionl dc dc converters. It is shown tht the rective power in trditionl phse-shift control is inherent, nd is the in fctor contributin to lre pe current nd lre syste loss.the P control cn eliinte rective power in isolted bidirectionl dc dc converters. In ddition, the P control cn decrese the pe inrush current nd stedy-stte current, iprove syste efficiency, increse syste power cpbility (by 33%), nd iniize the output cpcitnce s copred to the trditionl phse-shift control. The soft-switchin rne nd the influence of short-tie-scle fctors, such s dedbnd nd syste-level sfe opertion re, re lso discussed in detil. Under certin opertion conditions, dedbnd copenstion cn be ipleented esily in the P control without current sensor. Hu Bi nd. Gries(28) hs described the short-tie-scle trnsient processes in hih-volte nd hih-power isolted bidirectionl C-C converters is tht the effect of dedbnd nd the influence of phse-shift error. It lso discusses the enery All rihts reserved by 43

2 An Isolted Bi-irectionl Buc Boost Converter with Fly Bc nubber (IJTE/ Volue 2 / Issue 1 / 73) flow durin the dedbnd nd introduces definition of enery dedbnd to describe the condition durin stedy stte nd trnsients where no enery flows fro source to lod or lod to source, but only fro the lee inductnce to lod nd sources. Chunhon Zho nd ion. Round(28) hs proposed n isolted three-port bidirectionl C-C converter with decoupled power flow neent is tht the iniu overll syste losses, nin the power flow between the ports, utiliztion of the duty cycle control for optiizin the syste behvior cobined with the phse-shift control between the hihfrequency c voltes enerted by the full-bride cells. Controllin the power flow independently is ipleented throuh the use of decouplin networ.this converter is suitble for ultiple volte electricl systes where store eleent is required such s in renewble enery enertion systes powered by solr nd fuel cells. R. Hun nd. K. Mzuder(28) hs described soft-switchin schee for n isolted C/C converter with pulstin C output for three-phse hih frequency-lin PWM converter is detiled nlysis of soft-switchin echnis bsed on zero-volte-zero-current-switchin (ZVZC) principle for the front-end isolted dc/dc converter of n isolted three-phse rectifier-type hih-frequency-lin bidirectionl power converter. H. Xio nd. Xie(28) hs desined ZV bidirectionl dc-dc converter with phse-shift plus PWM control schee is presents current-volte-fed bidirectionl dc dc converter, which refers to current-fed inverter t low volte side nd volte-fed inverter t hih volte side, cn relize zero volte switchin (ZV) for the switches with the use of phse-shift (P) technoloy. W. Qu nd Y. Liu(29) hs described zero-volte-switchin bidirectionl C-C converter with stte nlysis nd softswitchin-oriented desin considertion is tht the converter chieved zero-volte switchin (ZV) for the entire in switches nd zero-current switchin for the rectifier diodes in the lre-lod rne. These fetures reduce switchin loss, volte nd current stresses, nd diode reverse-recovery effect. K. Wn nd C. Y. Lin(1998) hs described bi-directionl C to C Converters for Fuel Cell ystes is tht the need of bidirectionl dc to dc converter for fuel cell syste. Vrious cobintions of current-fed nd volte-fed converters re explored for the ppliction of different volte levels. With preliinry study, puttin current-fed on low-volte side nd volte-fed on hih-volte side indicted hiher efficiency thn the other wy round. Two low-side circuit topoloies were then selected for hrdwre ipleenttion. One is the L-type hlf-bride current-fed converter nd the other is full-bride current-fed converter. The hih-side circuit topoloy is fixed with full bride volte-fed converter. Two systes were built nd tested to full power. The results indicte tht the cobintion with the full-bride converter on the low-volte side is ore efficient thn the cobintion with the L-type hlf-bride converter on the low-volte side for both chrin nd dischrin odes.the in drwbc is L-type converter under dischrin is inefficient due to pssive clp circuit nd reltively hih device conduction drop. Circuit Confiurtion The proposed isolted bidirectionl full-bride dc dc converter with fly bc snubber is shown in Fi.3.2. The converter is operted with two odes: buc ode nd boost ode. It consists of current-fed switch bride, fly bc snubber t the lowvolte side, nd volte-fed bride t the hih-volte side. Inductor L perfors output filterin when power flows fro the hih-volte side to the btteries, which is denoted s buc ode. On the other hnd, it wors in boost ode when power is trnsferred fro the btteries to the hih-volte side. Furtherore, clp brnch cpcitor C C nd diode C re used to bsorb the current difference between current-fed inductor L nd lee inductnce L ll nd L lh of isoltion trnsforer T x durin switchin couttion. The fly bc snubber cn be independently controlled to reulte V c to the desired vlue, which is just slihtly hiher thn V AB. Fi. 1: Proposed circuit dir All rihts reserved by 44

3 An Isolted Bi-irectionl Buc Boost Converter with Fly Bc nubber (IJTE/ Volue 2 / Issue 1 / 73) Thus, the volte stress of switches M1 M4 cn be liited to low level. The jor erits of the proposed converter confiurtion include no spie current circultin throuh the power switches nd clpin the volte cross switches M1 M4, iprovin syste relibility sinificntly. Note tht hih spie current cn result in chre irtion, over current density, nd extr netic force, which will deteriorte in MOFET crrier density, chnnel width, nd wire bondin nd, in turn, increse its conduction resistnce. II. CIRCUIT OPERATION A bidirectionl dc dc converter hs two types of conversions: step-up conversion (boost ode) nd step-down conversion (buc ode). In boost ode, switches M1 M4 re controlled, nd the body diodes of switches M5 M8 re used s rectifier. In buc ode, switches M5 M8 re controlled, nd the body diodes of switches M1 M4 operte s rectifier. To siplify the stedystte nlysis, severl ssuptions re de, which re s follows. 1) All coponents re idel. The trnsforer is treted s n idel trnsforer ssocited with lee inductnce. 2) Inductor L is lre enouh to eep current i L constnt over switchin period. 3) Clpin cpcitor CC is uch lrer thn prsitic cpcitnce of switches M1 M8. In boost ode, switches M1 M4 re operted lie boost converter, where switch pirs (M1, M2 ) nd (M3, M4 ) re turned ON to store enery in L. At the hih-volte side, the body diodes of switches M5 M8 will conduct to trnsfer power to V HV. When switch pir (M1, M2) or (M3, M4 ) is switched to (M1, M4) or (M2, M3 ), the current difference i C (= i L i P ) will chre cpcitor C C, nd then, rise i p up to i l. The clp brnch is inly used to liit the trnsient volte iposed on the current-fed side switches. Moreover, the fly bc converter cn be controlled to chre the hih-volte-side cpcitor to void over current. The clp brnch nd the fly bc snubber re ctivted durin both strt-up nd reulr boost opertion odes. A non phse-shift PWM is used to control the circuit to chieve sooth trnsition fro strt-up to reulr boost opertion ode. A detiled description of hlf-switchin cycle opertion is shown s follows. Mode 1 [t t < t 1 ] In this ode, ll of the four switches M1 M4 re turned ON. Inductor L is chred by V LV, inductor current i L increses linerly t slope of V LV /L, nd the priry windin of the trnsforer is short-circuited. The equivlent circuit is shown in Fi.3.3. Fi. 2: Mode 1 (M1-M4 ON nd L chred) Mode 2 [t 1 t < t 2 ] At t 1, M1 nd M4 rein conductin, while M2 nd M3 re turned OFF. Clpin diode C conducts until the current difference (i L (t2 ) i P (t2 )) drops to zero t t = t 2. Moreover, the body diodes of switch pir (M5, M8) re conductin to trnsfer power. urin this intervl, the current difference (i L (t) ip (t)) flows into clpin cpcitor C C. The equivlent circuit is shown in Fi.3.4. All rihts reserved by 45

4 An Isolted Bi-irectionl Buc Boost Converter with Fly Bc nubber (IJTE/ Volue 2 / Issue 1 / 73) Fi. 3: Mode 2 (M2 -M3 -OFF,5-8 Power trnsfer nd c conducts) Mode 3 [t 2 t < t 3 ] At t 2, clpin diode c stops conductin, nd the flybc snubber strts to operte. At this tie, clpin cpcitor C c is dischrin, nd flybc inductor is storin enery. witches M1 nd M4 still sty in the ON stte, while M2 nd M3 rein OFF. The body diodes of switch pir (M5, M8 ) rein ON to trnsfer power. The equivlent circuit is shown in Fi.3.5. Fi. 4: Mode 3(c OFF, Cc dischres nd flybc stores enery) Mode 4 [t 3 t<t 4 ] At t 3, the enery stored in flybc inductor is trnsferred to the hih-volte side. Over this intervl, the flybc snubber will operte independently to reulte V C to V C (R). On the other hnd, switches M1 nd M4 nd diodes 5 nd 8 re still conductin to trnsfer power fro V LV to V HV.The equivlent circuit is shown in Fi.3.6. Fi. 5: Mode 4(flybc trnsfer enery to HV side) Mode 5 [t 4 t < t 5 ] At t 4, cpcitor volte V C hs been reulted to V C (R), nd the snubber is idle. Over this intervl, the in power ste is still trnsferrin power fro V LV to V HV. It stops t t 5 nd copletes hlf-switchin cycle opertion. The equivlent circuit is shown in Fi.3.7. All rihts reserved by 46

5 iscrete, Ts = 5e-5 s + - v Volte Mesureent1 powerui Input Volte Output Volte 1 2 Pulse Genertor1 Pulse Genertor Rely cope v cope Volte Mesureent An Isolted Bi-irectionl Buc Boost Converter with Fly Bc nubber (IJTE/ Volue 2 / Issue 1 / 73) Fi. 6: Mode 5 (Vc reulted nd snubber becoes idle) The opertion wvefors of step-up conversion re shown in Fi.3.8. III. IMULATION REULT AN ICUION The siultion is done for both buc nd boost odes of opertion for the proposed circuit,hrdwre prototype s well s for the odifiction of proposed circuit. MATLAB version 7.11 is used for the siultion. Fi. 7: Proposed circuit siultion dir dir In boost ode, switches M1 M4 re operted lie boost converter, where switch pirs (M1, M2 ) nd (M3, M4 ) re turned ON to store enery in L. At the hih-volte side, the body diodes of switches M5 M8 will conduct to trnsfer power to V HV. When switch pir (M1, M2) or (M3, M4 ) is switched to (M1, M4) or (M2, M3 ), the current difference i C (= i L i P ) will chre cpcitor C C, nd then, rise i p up to i l. The clp brnch is inly used to liit the trnsient volte iposed on the current-fed side switches. Moreover, the fly bc converter cn be controlled to chre the hih-volte-side cpcitor to void over current. The clp brnch nd the fly bc snubber re ctivted durin both strt-up nd reulr boost opertion odes. A non phse-shift PWM is used to control the circuit to chieve sooth trnsition fro strt-up to reulr boost opertion ode Tie Tie Fi. 8: Input nd Output wvefors All rihts reserved by 47

6 An Isolted Bi-irectionl Buc Boost Converter with Fly Bc nubber (IJTE/ Volue 2 / Issue 1 / 73) x x Tie x 1-3 Fi. 9: witchin pulse wvefors IV. CONCLUION This project hs presented n isolted bidirectionl full-bride buc boost converter with flybc snubber for hih-power pplictions. The flybc snubber cn llevite the volte spie cused by the current difference between the current-fed inductor nd lee inductnce of the isoltion trnsforer, nd cn reduce the current flowin throuh the ctive switches t the current-fed side. ince the current does not circulte throuh the full-bride switches, their current stresses cn be reduced drticlly under hevy-lod condition, thus iprovin syste relibility sinificntly. REFERENCE [1] H.Bi ndc.mi, Eliinte rective power nd increse syste efficiency of isolted bidirectionl dul-ctive-bride C-C converters usin novel dulphse-shift control, IEEE Trns. Power Electron., vol. 23, no. 6, pp , ec. 28. [2] B. Bi, C. Mi, nd. Gries, The short-tie-scle trnsient processes in hih-volte nd hih-power isolted bidirectionl C-C converters, IEEE Trns. Power Electron., vol. 23, no. 6, pp , Nov. 28. [3] C. Zho,.. Round, nd J.W.Kolr, An isolted three-port bidirectionl C-C converter with decoupled power flow neent, IEEE Trns. Power Electron., vol. 23, no. 5, pp , ep. 28. [4] R. Hun nd. K. Mzuder, A soft-switchin schee for n isolted C/C converter with pulstin C output for three-phse hih frequency-lin PWM converter, IEEE Trns. Power Electron., vol. 24, no. 1, pp , Oct. 29. [5] H. Xio nd. Xie, A ZV bidirectionl dc-dc converter with phsed shift plus PWM control schee, IEEE Trns. Power Electron., vol. 23, no. 2, pp , Mr. 28. [6] G. M, W. Qu, nd Y. Liu, A zero-volte-switchin bidirectionl C-C converter with stte nlysis nd soft-switchin-oriented desin considertion, IEEE Trns. Ind. Electron., vol. 56, no. 6, pp , Jun. 29. [7] F. Kriser nd J. W. Kolr, Accurte sll-sinl odel for the diitl control of n utootive bidirectionl dul ctive bride, IEEE Trns. Power Electron., vol. 24, no. 12, pp , ec. 29. [8] F. Brone, A lihtweiht inverter for off-rid nd rid-connected systes, in Proc. Photovoltic pec. Conf., 1994, vol. 1, pp [9] T. Reinn,. zeponi, nd G. Berer, A novel control principle of bi-directionl C-C power conversion, in Proc. Power Electron. pec. Conf., 1997, vol. 2, pp All rihts reserved by 48