BI-DIRECTIONAL EDGE-RESONANT SWITCHED CAPACITOR CELL-ASSISTED SOFT-SWITCHING PWM DC DC CONVERTER FOR RENEWABLE ENERGY APPLICATIONS

Transcription

1 BI-DIRECTIONAL EDGE-RESONANT SWITCHED CAPACITOR CELL-ASSISTED SOFT-SWITCHING PWM DC DC CONVERTER FOR RENEWABLE ENERGY APPLICATIONS 1 SARITHA THOMAS, 2 RABIYA RASHEED 1 Student, 2 Assstant Professor E-mal: sthomasvadyan@yahoo.com, rebyarasheed@yahoo.co.n Abstract- Ths paper presents a soft-swtchng pulse wdth modulaton (PWM) non-solated b-drectonal dc dc converter embeddng an edge-resonant swtched capactor (ER-SWC) cell. The conceptual dc dc converter treated heren can acheve hgh-frequency zero-current soft-swtchng turn-on and zero-voltage soft-swtchng turn-off operatons n the actve swtches. Those advantageous propertes enable a wde range of soft-swtchng operatons together wth a hgh-voltage stepup converson rato wth a reduced current stress. Crcut desgn gudelne based on the soft-swtchng range s ntroduced; then, a theoretcal analyss s carred out for nvestgatng the step up voltage converson rato. Keywords- B-drectonal DC-DC converter, Edge-Resonance, pulse wdth modulaton (PWM), soft-swtchng, swtched capactor, zero-current soft-swtchng (ZCS), zero-voltage soft-swtchng (ZVS). I. INTRODUCTION BIDIRECTIONAL dc-dc converters (BDC) have recently receved a lot of attenton due to the ncreasng need to systems wth the capablty of bdrectonal energy transfer between two dc buses. Apart from tradtonal applcaton n dc motor drves, new applcatons of BDC nclude energy storage n renewable energy systems, fuel cell energy systems and unnterruptble power supples (UPS). The fluctuaton nature of most renewable energy resources, lke wnd and solar, makes them unsutable for standalone operaton as the sole source of power. A common soluton to overcome ths problem s to use an energy storage devce besdes the renewable energy resource to compensate for these fluctuatons and mantan a smooth and contnuous power flow to the load. As the most common and economcal energy storage devces are batteres and supercapactors. A dc-dc converter s always requred to allow energy exchange between storage devce and the rest of system. Such a converter must have bdrectonal power flow capablty wth flexble control n all operatng modes. To charge and dscharge the storage element, the bdrectonal DC- DC converter s used. Fg.1 shows the block dagram of a PV system.in the presence of sunlght the output of the PV panel s gven to a DC-DC converter, whch s a boost converter. The output voltage of the DC-DC converter acts as the nput to the nverter. The DC s converted to AC and t s gven to the load. A storage element, here a battery s connected to the system through a bdrectonal converter. The output of the boost converter acts a source to charge the battery. At ths tme the B-drectonal converter acts as a buck converter. Durng nght there s no sunlght, therefore the output of DC-DC converter s zero. The battery act as the source, and hence the battery dscharges and gve supply to the load. At that tme BDC act as a boost converter. Here a non-solated b-drectonal edge resonant swtched capactor cell asssted soft swtchng DC-DC converter for renewable energy applcaton s proposed. Fgure 1: Block Dagram of PV system In the soft-swtchng PWM b-drectonal dc dc converter wth the ER-SWC cell, a wde range of soft-swtchng operatons can be acheved under the condton of DCM/crtcal conducton mode (CRM) n the nput dc current wthout any crculatng current, whle the current stresses n the power devces and the passve components can also be mtgated owng to the edge resonance wthn the swtchng cell. II. PROPOSED TOPOLOGY The proposed converter s a b-drectonal edge resonant swtched capactor cell asssted soft swtchng PWM DC-DC converter. The crcut confguraton of the ER-SWC soft-swtchng PWM boost DC-DC converter shown n Fg.2. 54

2 The ER-SWC cell conssts of three actve swtches S, S ands, two dodes D andd, a resonant capactorc, and a resonant nductor L. Ths converter works n two modes of operaton.e. n buck or boost. When the swtches S and S are on, the converter act as a boost converter. At that tme S s off. When S s on, the converter works as a buck converter. Durng that tme S and S s off. Fgure 2: Proposed Topology A. Operaton Prncple. Boost Mode In ths mode the DC-DC converter acts as a boost converter. The gate pulse s gven to S and S, keepng S off. The mode transtons wth the smplfed equvalent crcuts are shown n Fg.3. Fgure 3: The mode transtons wth the smplfed equvalent crcuts durng boost mode The crcut operaton durng one swtchng cycle s dvded nto the fve submodes, as descrbed n the followng. Mode 1 [t t < t,],( S, S, ZCS turn-on mode): The nductor current, s zero, and the actve swtches S,and S, are smultaneously turned ON at t,.then, and the swtch currents and rse gradually from the zero ntal value wth the edge resonance by L and C. Thereby, ZCS turn-on commutaton can be acheved n S and S.Durng ths mode, s wrtten as (t) = sn (ω t t ) (1) 55 where Z=L /C and ω =1/L C The resonant capactor C s dscharged by n ths nterval. Mode 2 [t t < t ], (nductve energy storng mode): The resonant capactor C s completely dscharged at t ; then, the dodes D and D are forward-based. The begnnng tme D of ths sub mode and ts nductor current can be determned from (1) as t =t +.cos ( ) (2) = (t ) = ( ) (3) Durng ths nterval, rses lnearly as expressed by (t)= (t-t )+ I (4) The nductor current I s equally shared by the two branches S D and S D. Mode 3 [t t < t ], (S, S ZVS turn-off mode): The two actve swtches S and S are turned OFF smultaneously at t.then, the edge resonance begns agan n the ER-SWC cell, and the voltages across S and S ncrease gradually by the effect of C.Thereby, ZVS turn-off commutaton can be acheved n S and S. The nductor current at t can be defned from (4) as I = (t ) == (t -t )+ I (5) where t = t + DT and D denotes the duty cycle of S and S as defned by D (6) Durng ths mode, s defned by I (t)= I snω (t t ) + tan ( )(7) where I represents the peak value of, as expressed by I =I + ( ) (8) Ths operaton mode contnues untl the capactor voltage V equals the output voltage V at t. Mode 4 [t t<t ], (nductor energy releasng mode): The resonant capactor voltage V rses up to the output voltage at t ; then, the conducton nterval of D and D s termnated. The begnnng tme t of the submode and the correspondng nductor current can be defned from (7) as t = t + sn + tan ( ) (9) = ( t )= I ( ) (10) The nductor current s forward to the load va D and thereby, the nput voltage V s boosted to the output voltage V. Durng ths nterval, s expressed by (t)= (t-t )+ I (11)

3 The nductor current gradually decreases and naturally reaches to the zero level at t. Accordngly, occurrence of the reverse recoverng current n the output freewheelng dode D can be mtgated. Mode 5 [ t t < t ], (nductor current dscontnuous Mode): Inductor current reduces to zero level after t,whch s determned from (11) by t =t + (12) The load current flows through the output capactor C n ths submode; then, the nductor current keeps the zero level untl the next swtchng cycle starts at t.. Buck Mode In ths mode the DC-DC converter acts as a buck converter. The gate pulse s gven to S3, keepng S1 and S2 off. The mode transtons wth the smplfed equvalent crcuts are shown n Fg.4. III. ANALYSIS OF VOLTAGE CONVERSION RATIO The analyss of the b-drectonal converter s done by consderng ts boost mode operaton. The nductor current and voltage waveforms of the ER-SWC softswtchng PWM dc dc converter n boost mode are llustrated and compared wth those of the conventonal hard-swtchng PWM boost dc dc converter n DCM under the condton of the same duty cycle n Fg.5. The postve voltage second area S n fg.5. Fgure 5: Current and voltage waveforms of nput nductor L r n DCM of conventonal and ER-SWC dc dc converters n boost mode under the same duty cycle condton. Fgure 4:Operaton mode and equvalent crcut as buck mode Mode 1 [0 t < DT],(S3 s on):durng ths nterval S s on, the ER-SWC cell s not conductng, because S and S are off and also D and D are reverse based. The nput provdes energy to the load as well as to the nductor. The voltage across the nductor can be represented as V =V -V (13) Mode 2 [DT t < T],(S3 s off):in ths nterval swtch S3 s off. The nductor dscharges through load. The nductor current flows through Lr - R0 -S2 -S1 V = -V (14) As a result, the negatve ampltude of V n Fg. 5 s extended much more than that of the conventonal type, then a larger output voltagev,.e., hgher voltage converson rato can be obtaned n the ER- SWC dc dc converter n boost mode. The voltage converson rato (M = Vo/Vn) of the ER-SWC boost dc dc converter n DCM can be determned from the nput and output power balance. By assumng the tme orgn to = 0 n Fg. 5 for smplcty, the tme ntegratons of the nductor current n each submode are defned by S =. dt=c V (15) S =. dt = (DT t. ) + I (DT t ) (16) S =. dt=c V (17) S =. dt= ( ) (18) S =. dt=0 (19) Therefore, the average nput current ı can be obtaned by ı=. dt= S (20) Neglectng the power losses n the ER-SWC boost dc dc converter, the power balances between the dc 56

4 power source V and the load V can be establshed as V ı= (21) The nput power V ı can be expressed from (15) (21) as V ı= ( ) (D. T) + D I T + 2C V (22) where D T = t2 t1. Furthermore, deformaton of (21) wth (22) yelds the equaton regardng the voltage converson rato M as M -(1+2C R f )M IV. D T( M + 2M- D T=0 (23) DESIGN GUIDELINE OF CIRCUIT PARAMETERS The crcut parameters of L and C n the ER-SWC cell should be based on both of the maxmum output power P, wth the maxmum duty cycle D and the mnmum output power Po,mn wth the mnmum duty cycle Dmn V. SIMULATION RESULTS Smulaton s done n MATLAB/SIMULINK software. Fgure 6: Smulaton model when the converter operates as Boost converter The determnaton of the zero crossng tme of,t4= DmaxT, the maxmum output power Po,max can be expressed as P, =V ı. (24) Where ırepresents the average current of at Po = Po,max and ths value can be obtaned from (1), (4), (7), and (11); then, Lr,max means ts maxmum value Then, the mnmum output power Po,mn can be gven by P, =V ı=, 1 + (25) where ı, denotes the mnmum value of the resonant nductor average current ı Fgure 7: Smulaton model when the converter operates as Buck converter Fg.8 shows the waveforms of g, V, V, V, I, V, I, V and I and Fg.9 shows the waveforms of g, V, V, V, I, V,and I. Deformaton of (25) yelds the parameter of the resonant capactor Cr as expressed by C = ( ), (26) The parameter of Lr should meet the condton ndcated as follows L 1 C f sn + + (27) TABLE I Crcut parameters Fgure 8: Wave forms durng Boost mode 57

5 CONCLUSION (a) (b) Fgure 9: Wave forms durng Buck mode The B-Drectonal converter plays an mportant role n renewable energy applcatons. The proposed nonsolated b-drectonal edge resonant swtched capactor cell asssted soft swtchng DC-DC converter can work n ether boost mode or buck mode. Ths converter can acheve hgh-frequency zero-current soft-swtchng turn-on and zero-voltage soft-swtchng turn-off operatons n the actve swtches. As a result a wde range of soft-swtchng operatons together wth a hgh-voltage step-up converson rato wth a reduced current stress. ACKNOWLEDGMENT Intally, I would lke to thank, the God Almghty for showng hs blessngs on me for successful completon of ths work. Also I would lke to thanks teachers frends and parents. REFERENCES [1] T. Mshma and M. Nakaoka, Analyss, Desgn, and Performance Evaluatons of an Edge-Resonant Swtched Capactor Cell-Asssted Soft-Swtchng PWM Boost DC DC Converter and Its Interleaved Topology, IEEE Tran. Power Electron, VOL. 28, NO. 7, July 2013 [2] Y. P. Hseh, J. F. Chen, T. J. Lang, and L. S. Yang, A novel hgh step-up DC-DC converter for a mcrogrd system, IEEE Trans. Power Electron., vol. 26, no. 4, pp , Apr [3] R. J.Wa and R. Y.Duan, Hgh step-up converter wth coupled-nductor, IEEE Trans. Power Electron., vol. 20, no. 5, pp , Sep [4] E. C. Das, L. C. G. Fretas, E. A. A. Coelho, J. B. Vera, Jr., and L. C. de Fretas, Novel true zero current turn-on and turn-off converters famly: Analyss and expermental results, IET Power Electron., vol. 3, no. 1, pp , [5] S. H. Park, G. R. Cha, Y. C. Jung, and C. Y.Won, Desgn and applcaton for PV generaton system usng a softswtchng boost converter wth SARC, IEEE Trans. Ind. Electron., vol. 57, no. 2, pp , Feb [6] H.-L. Do, A soft-swtchng DC/DC converter wth hgh voltage gan, IEEE Trans. Power Electron., vol. 25, no. 5, pp , May 2010 [7] P. Das and G. Moschopoulos, A comparatve study of zero-current transton PWM converters, IEEE Trans. Ind. Electron., vol. 54, no. 3, pp , Jun [8] K.-H. Lu and F. C. Lee, Zero-voltage swtchng technque n DC/DC converters, IEEE Trans. Power Electron., vol. 5, no. 3, pp , Jul [9] I. Aksoy, H. Bodur, and A. F. Bakan, A new ZVT-ZCS- PWM dc-dc converter, IEEE Trans. Power Electron., vol. 25, no. 8, pp , Aug [10] C. M. Sten, J. Pnhero, and H. L. Hey, A ZCT auxlary commutaton crcut for nterleaved boost converters operatng n crtcal conducton mode, IEEE Trans. Power Electron., vol. 17, no. 6, pp , Nov [11] K. Yao, X. Ruan, X. Mao, and Z. Ye, Reducng storage capactor of a DCM boost PFC converter, IEEE Trans. Power. Electron., vol. 27, no. 1, pp , Jan [12] K. Yao, X. Ruan, X. Mao, and Z. Ye, Varable-duty-cycle control to acheve hgh nput power factor for DCM boost PFC converter, IEEE Trans. Ind. Electron., vol. 58, no. 5, pp , May 2011 [13] T. Mshma and M. Nakaoka, A new famly of ZCS-PWM dc-dc converter wth clampng dodes-asssted actve edgeresonant cell, n Proc. Int. Conf. Electr. Mach. Syst., Oct. 2010, pp [14] T. Mshma, Y. Takeuch, and M. Nakaoka, A new hgh step-up softswtchng PWM boost dc-dc converter wth edge-resonant swtched capactor cell, n Proc. 8th Int. Conf. Power Electron., Jun. 2011, pp [15] T. Mshma, Y. Takeuch, and M. Nakaoka, Practcal performance evaluatons of a soft-swtchng PWM boost DC-DC converter wth hgh effcency and hgh scalablty edge resonant swtched capactor modular, n Proc. 3rd IEEE Energy Convers. Congr. Expo., Sep. 2011, pp [16] Y. Takeuch, T. Mshma, and M. Nakaoka, New evaluatons on soft commutaton range of a soft-swtchng PWM boost DC-DC converter wth edge-resonant swtched capactor modular, n Proc. 9th IEEE Int. Conf. Power Electron. Drve Syst., Dec. 2011, pp