A novel phase-shift full-bridge converter with voltage-doubler and decoupling integrated magnetics in PV system

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1 BULLETIN OF THE POLISH ACADEMY OF SCIENCES TECHNICAL SCIENCES Vol. 56 No A novel phase-shif full-bridge converer wih volage-doubler and decoupling inegraed magneics in PV sysem Y. JIANG Z. CHEN 2 J. PAN X.I ZHAO and P. LEE Deparmen of Elecrical Engineering Shanhai Jiao Tong Universiy Shanghai P.R. China 2 Deparmen of Elecrical Engineering Anhui Universiy of Technology Ma Anshan P.R. China Absrac. A novel phase shif full bridge (PSFB) converer wih volage-doubler and decoupling inegraed magneics in phoovolaic (PV) sysems is proposed. Considering he demand ha he oupu volage is higher han he inpu volage in PV sysems he volage-doubler is added o achieve higher volage gain compared wih he radiional PSFB. In order o avoid curren oscillaion caused by he volage-doubler and obain he wide zero volage swiching (ZVS) ranges an exernal inducor is imposed on he circui. Especially o obain much higher power densiy he exernal inducor and ransformer are inegraed ino one magneic core. The operaion and volage gain of proposed converer are analyzed. Also in order o reveal he effecs he inegraed magneics gives o he converer he decoupling condiion and he expression of leakage inducor of inegraed magneics are obained in deail. Finally a 00 W prooype converer is made and he experimenal resuls are given o verify he analysis. Key words: inegraed magneics volage-doubler PSFB converer PV sysem.. Inroducion Using he phoovolaic (PV) power sysem as an alernaive energy resource has been widely discussed due o he rapid growh of power elecronics echniques [ 3].There are hree differen sysems widely used in PV applicaions he cenralized inverer sysem he sring inverer sysem and he module inegraed converer sysem [3 4].The muli-sring inverer is he furher developmen of he sring inverer where several srings are inerfaced wih heir own dc-dc converer o a common dc-ac inverer [5 9]. The main challenge is o develop a dc-dc converer ha can lif he low volage. A Phase-Shif Full-Bridge (PSFB) converer is widely used for high volage high power applicaions due o is advanages such as simple srucure and zero-volage swiching (ZVS) [0 5]. However full ZVS operaion can only be achieved in a limied load and inpu-volage range unless a relaively large inducance is provided in series wih he primary winding of he ransformer which can be implemened by adding an exernal inducor. Several converers achieve ZVS in all primary swiches over an exended load and inpu volage range by uilizing energy sored in he inducive componens of an auxiliary circui [6 20]. Unforunaely hese converers are no appropriae o achieve high power densiy high reliabiliy and low cos because of exra devices and/or complicaed conrol circuiry. In he modern power elecronics indusry he demand for inegraed magneics has become much sronger because of he following reasons [2 28]: ) The number of magneic componens can be reduced. 2) The size and cos of power elecronic circuis can be reduced. 3) Someimes a conrolled coupling beween magneic componens is required o achieve special funcions. In brief i is an effecive mehod o improve power densiy. When he PSFB converer is used in PV sysem as dc-dc converer i has wo main problems: ) The volage gain is higher i means ha he oupu volage is much higher han he inpu volage hough he high volage gain can be solved hrough he increasing of urns raio of high-frequency ransformer i decreases he power densiy due o he increasing of he volume of ransformer. 2) Due o he high volage gain he number of urns of secondary winding of ransformer is more han ha of primary winding of ransformer herefore he leakage inducor of ransformer used as resonan inducor o achieve wide ZVS range is no enough. In his paper in order o overcome above problems a novel PSFB converer wih volage-doubler and decoupling inegraed magneics is proposed. The volage-doubler is adoped o increase volage gain. In order o avoid curren oscillaion ha caused by he volage source parallel wih capaciors of volage-doubler direcly hrough ransformer an exernal inducor beween volage source and volage-doubler is se. Moreover he exernal inducor is also used as resonan inducor o achieve wide ZVS range herefore he problem ha only leakage inducor of ransformer is used o achieve wide ZVS range is no enough is solved. Especially in order o improve power densiy and save volume of magneics he exernal inducor and ransformer are inegraed ino one magneic core. The inegraed magneics are decoupled in order no o abjiangying@gmail.com 285

2 Y. Jiang Z. Chen J. Pan X.I Zhao and P. Lee influence he operaion of converer and he leakage inducor of inegraed magneics is also used as resonan inducor o achieve ZVS besides he exernal inducor. The paper sudies he operaion of he individual modes of he converer horoughly. The key feaures in he individual modes are also discussed in deail. The heoreical analyses are done o explain he converer operaions including he realizaion of ZVS and he calculaion of volage gain. Also he decoupling condiion of inegraed magneics is analyzed and he leakage inducor expression of inegraed magneics is obained. Experimenal resuls of a 00-W converer wih 48-V inpu and 380-V oupu are provided a he end of he paper o confirm he heoreical analysis. Gae Signals i pri S S 4 S 3 S 2 2. Operaional principles Figure shows he circui diagram of he convenional PSFB converer in order o increase volage gain and save volume of magneics convenional recifier circui is replaced by volagedoubler and resonan inducor and ransformer T are inegraed ino one magneic core he proposed converer is shown in Fig. 2. In Fig. 2 he winding of inducor is in he lef and righ legs and he winding of ransformer T is in he middle leg. The operaing waveforms of he proposed converer in he seady sae are shown in Fig. 3. In order o perform a mode analysis several assumpions are made as follows: ) Turns raio of ransformer T is n and includes leakage inducor. 2) Swiches S 4 are ideal excep for parasiic capaciors (C oss = C oss2 = C oss3 = C oss4 = C oss ) and inernal diodes (D = D 2 = D 3 = D 4 ). 3) The oupu volage V 0 is consan. 4) Volage doubler is ideal recifier capaciors C r and C r2 are idenical and each volage is V 0 /2 D r and D r2 are recifier diodes. V in S S 2 D Coss D C oss 2 2 A i pri D3 D4 S3 S4 C oss3 B C oss4 Lr T :n D r D r2 Fig.. Convenional PSFB converer L f C f R o V o V AB V S V 0 / Fig. 3. Operaing waveforms of he proposed converer As shown in Fig. 3 each swiching period is subdivided ino six modes and heir opological saes are shown in Fig. 4. From 0 o 5 since he primary curren i pri () and i Dr () are coninuous ha is he volage V s of secondary side of ransformer T is he volage of C r which means V s = V 0 /2. ) Mode ( 0 ). The inpu power is ransferred o he secondary side hrough S and S 4. D r is urned on and C r is charged by i Dr () herefore he volage V 0 /2n is refleced on he primary side of T and V in V 0 /2n is pu on ha is deermines he slope of he primary curren i pri () and i can be described as follows: V in i pri () = V in V o /2n ( 0 ). () 2) Mode 2 ( 2 ). When S is urned off C oss and C oss3 are charged and discharged by resonance wih respecively and hen he primary curren i pri () and he volage of C oss and C oss3 can be described as follows: i pri () = i pri ( )cosω( ) (2) Vin S S 2 D C C oss D2 oss 2 A i pri B D3 D4 S S 3 4 C oss3 C oss4 T :n i Dr V S i Dr2 D r C r D C r2 r 2 R o Vo v coss () = i pri ( ) Z sin ω( ) (3) v coss3 () = V in i pri ( ) Z sin ω( ) (4) Fig. 2. Proposed PSFB converer wih volage-doubler and decoupling inegraed magneics where ω = 2Coss Z = Lr 2C oss. 286 Bull. Pol. Ac.: Tech. 56(3) 2008

3 A novel phase-shif full-bridge converer wih volage-doubler and decoupling inegraed magneics in PV sysem c) d) e) f) Fig. 4. Equivalen circuis of he proposed converer for mode analysis: ( Mode ( Mode 2 (c) Mode 3 (d) Mode 4 (e) Mode 5 (f) Mode 6 3) Mode 3 ( 2 3 ). The volage of C oss3 is discharged o zero he ani-diode D 3 of swich S 3 is urned on naurally and hen he S 3 can be urned on o achieve ZVS. The primary curren i pri () can be described as follows: i pri () = i pri ( 2 ) + V o/2n ( 2 ). (5) 4) Mode 4 ( 3 4 ). S 4 is urned off C oss2 and C oss4 are discharged and charged by resonance wih respecively. Then he primary curreni pri () and he volage of C oss2 and C oss4 can be described as follows: i pri () = i pri ( 3 )cosω( 3 ) (6) v coss2 () = V in i pri ( 3 ) Z sin ω( 3 ) (7) v coss4 () = i pri ( 3 ) Z sin ω( 3 ) (8) Lr where ω = Z =. 2Coss 2C oss 5) Mode 5 ( 4 5 ). The volage of C oss2 is discharged o zero he ani-diode D 2 of swich S 2 is urned on naurally and hen he S 2 can be urned on o achieve ZVS. The primary curren i pri () can be described as follows: i pri () = i pri ( 4 ) + V in V o /2n ( 4 ). (9) 6) Mode 6 ( 5 6 ). The primary curreni pri () goes hough S 2 and S 3 D r2 is urned on and C r2 is charged by i Dr2 () herefore he volage V 0 /2n is refleced on he primary side of T and he analysis is similar wih mode. From mode 6 anoher circle is began which is similar wih mode o mode 5 analyzed above. 3. Analysis of volage gain Compared wih convenional PSFB which is widely used o sep down he inpu volage he proposed converer is used o lif inpu volage. In order o analyze he volage gain M (V o /V in ) he waveform of primary curren i pri is shown in Fig. 5a. In Fig. 5a when 0 i pri increases linearly as i + pri when T i pri decreases as i pri which is composed of four pars which are described in formula (2) (5) (6) (9) respecively ( T ). Compared wih mode 3 ( 2 3 ) and mode 5( 4 T ) he charging and discharging ime of mode 2( 2 ) and mode 4( 3 4 ) are insananeous and hen can be omied which are shown in Fig. 5b. In Fig. 5b i pri is described as i pri ( on off ) and i pri2 ( off T ) I max and I av are respecively he max value of i pri and he average value of i pri. I av can be described as follows: I av T = on 0 i + pri d + off on i pri d + T off i pri2 i + pri i pri and i pri2 can be described as follows: i + pri = V in V o /2n ( 0 ) i pri = i+ pri ( on) + V o/2n ( on ) i pri2 = i pri ( off) + Vin Vo/2n ( off ) d (0). () Bull. Pol. Ac.: Tech. 56(3)

4 Y. Jiang Z. Chen J. Pan X.I Zhao and P. Lee i /A I max I av i /A I max I av i pri DonT off 4 i p ri i i pri pri i pri 2 on T D T Doff 2T / us us off T / Fig. 5. Waveforms of primary curren: ( waveform of primary curren ( simplified waveform of primary curren Based on power conservaion I av also can be described as follows: I av = V o 2 V in R. (2) Based on (0) () (2) he volage gain M (V o /V in ) can be go as follows: M = V o V in = 4n + 2 D 2 4n 2 + 4f R D (3) where D on T = on 0 D off T = off on D off2 T = T off f = /T R is load D = D 2 = 2 D2 on + 2 D2 off2 + D ond off ( 2 D2 on + 2 D2 off + D ond off 2 D2 off2 2 D2 on + 2 D2 off2 + D ond off 2 D2 on + 2 D2 off + D ond off 2 D2 off2 ) 2. (4) From (3) and (4) i can be go ha volage gain M is decided by D D 2 urns raio n resonan inducor frequency f and load R. I means ha such parameers should be adjused ogeher o saisfy he volage gain M demanded. 4. Design of inegraed magneics 4.. Decoupling of inegraed magneics. The proposed PSFB converer is used o lif volage which means ha he number of urns of ransformer primary winding is less han ha of ransformer secondary winding. Furhermore he leakage inducor in primary winding is much smaller herefore he ZVS range is narrow when only he leakage inducor is used for resonance. In order o solve his problem an exernal inducor is added bu i increases volume which resuls in he decreasing of power densiy. In his paper he inegraed magneics which are shown in Fig. 6 are used o solve his problem. In Fig. 6a ransformer T and inducor are inegraed ino one EE magneic core N P and N S are respecively he number of urns of primary winding and secondary winding of ransformer T N L and N L2 are he number of urns of inducor R R 2 and R 22 are respecively he magneic resisance in middle leg lef leg and righ leg i P i s and i L are respecively he curren of primary winding secondary winding and inducor he ransformer winding is in he middle leg and he inducor winding is divided ino wo pars which are in lef and righ legs respecively ϕ TL and ϕ TL2 are respecively he fluxes in ransformer windings (middle leg) which are imposed by inducor winding (lef and righ legs) ϕ LT and ϕ LT2 are respecively he fluxes in inducor winding which are imposed by ransformer winding and he magneic circui is shown in Fig. 6b. In order o preven heir fluxes from coupling wih each oher which make i difficul o analyze he operaion of converer he inegraed magneics are decoupled. Fig. 6. Inegraed magneics: ( inegraed ransformer and inducor ( equivalen magneic circui 288 Bull. Pol. Ac.: Tech. 56(3) 2008

5 A novel phase-shif full-bridge converer wih volage-doubler and decoupling inegraed magneics in PV sysem Based on Fig. 6b he fluxes ϕ TL and φ TL2 can be described as follows: N L i L R 22 φ TL = R R 2 + R R 22 + R 2 R 22. (5) N L2 i L R 2 φ TL2 = R R 2 + R R 22 + R 2 R 22 The flux linkage ψ TL of ransformer T which is imposed by inducor is described as follows: 4.2. Leakage inducor of inegraed magneics. Compared wih convenional PSFB converer which adops leakage inducor of ransformer as resonan inducor he proposed PSFB converer s resonan inducor includes wo pars: () Inducor inegraed in magneics. (2) Leakage inducor of inegraed magneics. Therefore i is necessary o analyze he leakage inducor of inegraed magneics. ψ TL = (N P N S )(φ TL φ TL2 ) = N P i L N S i L R R 2 + R R 22 + R 2 R 22 (N L R 22 N L2 R 2 ). (6) The fluxes φ LT and φ LT2 can be described as follows: (N P i P N S i S )R 22 φ LT = R R 2 + R R 22 + R 2 R 22. (7) (N P i P N S i S )R 2 φ LT2 = R R 2 + R R 22 + R 2 R 22 The flux linkage ψ LT of inducor which is imposed by ransformer T is described as follows: ψ LT = N L φ LT N L2 φ LT2 = N P i P N S i S R R 2 + R R 22 + R 2 R 22 (N L R 22 N L2 R 2 ) (8) When ψ LT = ψ TL = 0 he inducor and ransformer T are decoupled he decoupling condiion can be go as follow from (6) and (8): R 2 R 22 = N L N L2. (9) In order o design i convenienly make air gaps of lef leg and righ leg be he same which means ha R 2 = R 22 and hen he condiion of decoupling is go from (9): N L = N L2. (20) Assuming ha B B 2 and B 22 are respecively he flux densiy of middle leg lef leg and righ leg hey can be described as follows: B = (N Pi P N S i S )(R 2 + R 22 ) (R R 2 + R R 22 + R 2 R 22 )S B 2 = i L(N L + N L2 ) (N P i P N S i S )R 22 (R 2 + R 22 )S 2 (R R 2 + R R 22 + R 2 R 22 )S 2 B 22 = i L(N L + N L2 ) (N P i P N S i S )R 2 + (R 2 + R 22 )S 22 (R R 2 + R R 22 + R 2 R 22 )S 22 (2) where S S 2 and S 22 are respecively he cross secion areas of middle leg lef leg and righ leg. The inegraed magneics are designed o make sure ha each leg is no sauraed according o (2). Fig. 7. Leakage flux of inegraed magneics: ( fron view of inegraed magneics ( op view of inegraed magneics The leakage fluxes of inegraed magneics are shown in Fig. 7 V L V P and V S are respecively he volage of inducor winding primary winding of ransformer T and secondary winding of ransformer T hey can be described as follows: d V L = N L d (φ L + φ ll + φ lsl + φ lsl2 ) V P = N P d d (φ T + φ lp + φ lps ) V S = N S d d ( φ T + φ ls φ lps + φ lsl φ lsl2 ) (22) where N L (N L = N L + N L2 ) is he number of urns of inducor φ T and φ L are respecively he fluxes of ransformer T and inducor. φ ll φ lp and φ ls are respecively he leakage fluxes of inducor winding primary winding and secondary winding of ransformer T φ lsl φ lsl2 and φ lps are respecively he leakage fluxes which goes hrough inducor winding in lef leg and secondary winding of ransformer T inducor winding in righ leg and secondary winding of ransformer T and primary winding and secondary winding of ransformer T and hey can be described as follows: Bull. Pol. Ac.: Tech. 56(3)

6 φ T = (N Pi P N S i S )(R 2 + R 22 ) (R R 2 + R R 22 + R 2 R 22 ) Y. Jiang Z. Chen J. Pan X.I Zhao and P. Lee The oal leakage inducor L l for resonance can be described as follows: φ L = N Li L R 2 + R 22 φ lsl = N Li L + N S i S φ lsl2 = N L2i L N S i S R lsl R lsl2 φ lps = N Pi P N S i S φ ll = N Li L φ lp = N Pi P φ ls = N Si S R ll R lp R ls (23) where R lijk is leakage magneic resisance according o is corresponding leakage flux φ lijk i = L S P j = L S P k = 2. Furher more in order o ge he expression of leakage inducor he formula (22) can be deduced as follows: V L V P V S = L L + L ll + L ll + L ll2 0 0 L P + L lp + L lps M ls M ls2 M lsp M SP M ll M ll2 M lps M PS L S + L ls + L lsp + L ls + L ls2 where NL 2 L L = L ll = N2 L R 2 + R 22 R ll L ll = N2 L 2R lsl L ll2 = N2 L 2R lsl2 M ll = N LN S 2R lsl M ll2 = N LN S 2R lsl2 ; L P = N 2 P (R 2 + R 22 ) R R 2 + R R 22 + R 2 R 22 L lp = N2 P R lp L lps = N2 P M lps = N PN S M PS = L S = N P N S (R 2 + R 22 ) R R 2 + R R 22 + R 2 R 22 ; N 2 S (R 2 + R 22 ) R R 2 + R R 22 + R 2 R 22 L ls = N2 S R ls L lsp = N2 S L ls = N2 S R lsl L ls2 = N2 S R lsl2 di L d di P d di S d M ls = N LN S R lsl M ls2 = N LN S R lsl2 M lsp = N PN S N P N S (R 2 + R 22 ) M SP = R R 2 + R R 22 + R 2 R 22. (24). (25) L l = L Ll + L TPl + N2 P NS 2 L TSl (26) where L Ll is oal leakage inducor of he inducor. L TPl andl TSl are respecively he oal leakage inducor of primary and secondary winding of ransformert and hey can be described as follows: L Ll = L ll + L ll + L ll2 + M ll M ll2 L TPl = L lp + L lps M lps. (27) L TSl = M ls M ls2 + L ls + L lsp + L ls + L ls2 M lsp Since leakage magneic resisance R lsl equaes o R lsl2 approximaely and hen M ll = M ll2 M ls = M ls2 he formula (27) can be simplified as follows: L Ll = L ll + L ll + L ll2 L TPl = L lp + L lps M lps. (28) L TSl = L ls + L lsp + L ls + L ls2 M lsp According o (28) L Ll is only composed of is self leakage inducors since he muual leakage inducors M ll and M ll2 beween inducor and ransformer T are couneraced by each oher i isn influenced by ransformer. The leakage inducor of ransformer T is composed of L TPl and L TSl since he muual leakage inducors M ls and M ls2 beween and ransformer T are couneraced by each oher i isn influenced by inducor. Therefore besides he fluxes beween inducor and ransformer T he leakage fluxes beween hem are also decoupled. The decoupling inegraed magneics can be seen as discree inducor and ransformer T and hen he leakage inducors can be measured by common shor experimen. 5. Experimenal resuls 5.. Decoupling of inegraed magneics. The parameers of inegraed magneics are shown as follows: he resonan inducor is = 2.5 uh he inducor of ransformer primary winding is L TP = 38 uh he inducor of ransformer secondary winding is L TS = 2.8 mh he leakage inducor of ransformer primary winding is L TPl = 2. uh he leakage inducor of ransformer secondary winding is L TSl = 42 uh he urns raio is N S : N P = 4.5 he air gaps of hree legs are he same are 0.4mm. L TPl and L TSl are measured by shor circui experimen since less han 0% of L TP compared wih L TPl L Ll is so small ha i can be omied. Based on (26) i can be calculaed ha L l = 4.2 uh. In order o es he decoupling of inegraed magneics a 5 V and 00 Khz sinusoidal volage source is imposed on inegraed magneics. When volage source is imposed on he primary winding of ransformer T he waveform of he volage of ransformer secondary side v s and inducor v l are shown 290 Bull. Pol. Ac.: Tech. 56(3) 2008

7 A novel phase-shif full-bridge converer wih volage-doubler and decoupling inegraed magneics in PV sysem in Fig. 8a. In Fig. 8a v s is 22.6 V according o urns raio and v l is zero approximaely i means ha he volages of ransformer and inducor don influence on each oher due o decoupling. When volage source is imposed on he inducor winding he waveform of he volage of ransformer secondary side v s and primary side v p are shown in Fig. 8b. In Fig. 8b if inducor and ransformer are coupled closely according o urns raio (N L : N P = L TP / = 3.3 and N L : N S = L TS / = 4.8) v p should be 6.5 V and v s should be 74 V from Fig. 8b i can be seen ha v p and v s are less han 0% of 6.5 V and 74 V herefore inducor and ransformer are decoupled wih each oher approximaely. when v AB becomes zero he leading swiches can achieve ZVS. Figure shows he waveforms of lagging swich i can be seen ha when gae signal v GS is on he volage of swich v DS has been decreased o zero and hen he lagging swich achieves ZVS. Figures 2 3 show he waveforms of v TS and he volage v Cr and v Cr2 of volage-doubler when v Cr is charged v TS equaes o v Cr when v Cr2 is charged v TS equaes o v Cr2 since V o = v Cr + v Cr2 he oupu volage V o doubled he v TS. Figure 4 shows he converer efficiencies under some load condiions. Figure 5 shows he phoograph of Prooype 00-W converer. Fig. 8. Waveforms of decoupling inegraed magneics: ( waveforms of v s and v l ( waveforms of v p and v s 5.2. PSFB converer. Based on he designed parameers a 00 khz 00 W 380 V prooype dc-dc power module wih an inpu volage range of 48 V has been consruced. The parameers are as follows: IRF385s and BYM36Cs are used as swiching devices and volage-double diodes volagedouble capaciors are seleced as 0. uf. The key experimenal waveforms are shown in Figs. 9 3 i can be seen ha all he waveforms agree well wih he heoreical analysis. Figure 9 shows he primary curren i pri wih differen. In Fig. 9a when = 7.3 uh he i pri decreases o zero before nex circle due o he small herefore he oscillaion of i pri is caused. In Fig. 9b and c wih he increasing of he i pri becomes coninuous he oscillaion of i pri is reduced and he ZVS range is widen. Figure 0 shows he waveform of v AB c) Fig. 9. Waveforms of i pri wih differen : ( = 7.3 uh ( = 2.5 uh (c) = 7.6 uh Bull. Pol. Ac.: Tech. 56(3)

8 Y. Jiang Z. Chen J. Pan X.I Zhao and P. Lee Fig. 0. Waveform of v AB Fig. 4. The converer efficiencies under a range of load condiions Fig.. Waveforms of lagging swich Fig. 5. Prooype 00-W converer 6. Conclusions Fig. 2. Waveform of v TS In his paper a novel PSFB converer wih volage-doubler and inegraed magneics in PV sysem is proposed. The volagedoubler is adoped o increase volage gain and an exernal inducor which is used no only o avoid curren oscillaion bu also as resonan inducor o achieve ZVS is added. Especially he exernal inducor and ransformer are inegraed ino one magneic core o improve power densiy. The operaional principles have been presened by he mode analysis and he design equaions for he achievemen of ZVS and he volage gain are derived. Moreover he decoupling condiion of inegraed magneics and he leakage inducor expression of inegraed magneics are obained. Based on he design of ZVS volage gain and inegraed magneics a prooype has been designed o prove he validiy of he proposed converer. The experimenal resuls of a 00 W prooype converer have been presened. The efficiency of he proposed converer is obained abou 93% a a raed condiion. The proposed converer is suiable for he muli-sring inverer as dc-dc converer in PV sysem requiring he high efficiency and high power densiy. REFERENCES Fig. 3. Waveforms of volage-doubler [] S.B. Kjær J.K. Pedersen and F. Blaabjerg Power inverer opologies for phoovolaic modules a review Proc. IEEE IAS 02 Conf (2002). 292 Bull. Pol. Ac.: Tech. 56(3) 2008

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