Analysis and performance of novel and highly efficient electronic ballast operating at unity-power-factor

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1 Sādhanā Vol. 33, Par 5, Ocober 008, pp Prined in India Analysis and performance of novel and highly efficien elecronic ballas operaing a uniypowerfacor V B BORGHATE, H M SURYAWANSHI and G A DHOMANE Elecrical Engineering Deparmen, Visvesvaraya Naional Insiue of Technology, Souh Ambazari Road, Nagpur vijay borghae@rediffmail.com; hms 1963@rediffmail.com; g dhomane@rediffmail.com Absrac. This paper presens he elecronic ballas, in which he coupling inducors are used o injec he curren o he dcbus capaciors, o boos he dcbus volage and o filer ou he ripples from inpu line curren. The curren injecion coupling inducor injecs is sored energy o he dcbus capaciors in every swiching half cycle. Whereas, he boos coupling inducor keeps he dcbus volage always above he peak of ac inpu volage. Therefore, he proposed ballas mainains uniypowerfacor and high efficiency wih ripplefree inpu curren over wide range of inpu line volage in case of wors regulaion. A symmerical halfbridge inverer is used o drive he fluorescen lamps. The experimenal resuls of he laboraory prooype ballas for 36 W fluorescen lamps operaing a 50 khz are presened. Keywords. Couplinginducor; powerfacorcorrecion; uniypowerfacor; zerovolageswiching. 1. Inroducion High frequency (HF) elecronic ballass (EB) are used now widely o replace he fluorescen lamps, because hese ballass have he addiional feaures like no flickering or sroboscopic effec, silen operaion, high efficiency, highpowerfacor (HPF), insan sar, low harmonic disorions (THD), and low EMI. In he basic circui of elecronic ballas, he power conversion akes place in wo seps as 50 Hz acodc and dcohf ac. Owing o use of unconrolled recifier wih large elecrolyic capacior, he inpu line curren of elecronic ballas conains significan harmonics, and herefore, resuls in poor inpu power facor. To achieve he HPF wih low THD specified by IEC Sandards on EMC, addiional powerfacorcorrecion (PFC) circui is required. Therefore, large inpu LC filer is added, resuling in wosage opology (Almeida e al 1998; 000). In such circuis, he dc volage is mainained above he double value of inpu peak volage, which resuled in high volage sress on he power swiches, reducion in efficiency and reliabiliy besides increase in cos. The repored efficiency, power facor and THD in hese papers are up o 89%, 0 99 and 17% respecively. By inegraing he convenional PFC circui wih he inverer swiches resuled in singlesage opology (Brumai e al 005; De e al 1998; Do & Kwon 003) in which he repored values of efficiency, 53

2 54 V B Borghae, H M Suryawanshi and G A Dhomane HF diode bridge recifier HF Volage generaing circui C d V d Resonan Inverer F. Lamp HF Curren injecing circui PFC Circui Figure 1. Schemaic diagram of proposed circui. power facor and THD are up o 90%, 0 99 and 10% respecively. Bu problem of high dclink volage was unsolved. This problem has been overcome by using unconvenional PFC circui in he singlesage elecronic ballas (Kazimierczuck e al 1993; Lin & Chen 1998; Spangler & Benera 1991). The dclink volage is kep slighly above he peak of inpu ac volage o achieve he same effecs, resuled in main advanage of low sress on he swiches. The repored efficiency, power facor and THD are 85 94%, and % respecively. Borghae e al 006, repored operaion of singlesage elecronic ballas for fluorescen lamp. However, only performance of inpu line parameer is invesigaed. In his paper, he analysis, performance and design of componens of a singlesage elecronic ballas based on unconvenional PFC circui and symmerical halfbridge inverer is presened in deail. The deailed experimenal resuls along wih characerisics of fluorescen lamp are also presened. Is schemaic diagram is shown in figure 1. The boos coupling inducor is used as a HF volage generaing circui, and is conneced beween he ac inpu volage source and he dclink capacior. This circui generaes he HF volage of magniude inversely proporional o he insananeous value of he inpu ac volage. Therefore, he dclink capaciors are always charged o he insananeous value of inpu ac volage plus HF generaed volage. This resuls in ripple free consan dclink volage over he enire inpu ac cycle. To mainain he energy of he dclink capaciors, anoher coupling inducor is used as a HF curren injecing circui, which injecs he energy in every half swiching cycle. As such no addiional filer circui is required for his proposed circui, bu due o nonideal componens, a coupling inducor of small value is used a he inpu of he circui o filer ou he harmonics. The main advanage of his opology is ha, over he wide range of inpu volage, he power facor is mainained a uniy wih ripple free inpu curren. I requires low value of dcbus elecrolyic capaciors and no need of dcblocking capaciors in he inverer oupu circui. Due o low componens coun, he circui is cos effecive wih high reliabiliy. The ripple free perfecly sinusoidal HF curren flows hrough he fluorescen lamps; herefore, prolongs he lamp life.. Operaion of proposed circui The proposed elecronic ballas and is equivalen circuis are shown in figures and 3 respecively. The PFC circui consiss of filer capaciors C 1 C, curren injecing coupling inducor L j and boos coupling inducor L b. The wo idenical inducors L 1 L of L j injec heir sored energy equally o he dcbus capaciors C d1 C d besides inpu acsource during

3 Analysis and performance of efficien ballas 55 i Lr1 i Lr C 1 D 1 D 3 S 1 D s1 Cd1 L 1 v m L r L r1 FL 1 L j L f L b L D 4 D v m C d C r C r1 C S D s FL Figure. Circui of proposed elecronic ballas for wo parallelconneced fluorescen lamps. he some par of he half swiching cycle, and resoreback heir energy during anoher ime period of he same half swiching cycle. The values of hese inducors are small compared o he boos inducor used in he PFC circuis of (De e al 1998, Almeida e al 1998) and selfleakage inducances of coupling inducor in (Do & Kwon 003). The capaciors C 1 and C are idenical and sufficienly large, mainain he consan volage across hem a d during he whole swiching cycle, since he swiching frequency f s is very large as compared o inpu line frequency f. These capaciors ac as he filers for he inducor currens i L1 and i L. The coupling inducor L b a he oupu of recifier is used o boos he dcbus volage V d and o filer ou he HF ripples. As shown in figure 3, like a ransformer, L b has wo ideal windings (w 1 and w ) and a magneizing inducance L m. The w 1 and w carry he equal currens, whereas L m carries he difference of he currens (i 1 i ). The L m can be referred o he eiher side of L b, whichever side carries he higher curren. The required value of magneizing inducance, in his proposed opology, is very less compared o (Do & Kwon 003); herefore he possibiliy of sauraion of core is minimized. The high frequency volage v m induced in L b, as in Almeida e al (1998), helps o boos he dcbus volage V d always above he peak value of inpu acvolage V p, which ensures he disconinuous curren mode (DCM) operaion of boos converer (i Cd1 i Cd ) during he enire cycle of acmains. The V d can be mainained less han 400 V dc in case of 30 V applicaions. A his volage, rms value of MOSFETs curren is lower, resuls in higher efficiency han oher opologies; whereas, he convenional boos circui requires V d greaer han wice of V p. In he proposed ballas, no addiional wave shaper is required, bu he componens used are no ideal ones, herefore a L m C 1 v C1 L v 1 L1 i L1 i L L v L C vc D 1 D 3 D 4 D i m i 1 i i m v m i w1 w 1 i L w v m L m S 1 i w S i S1 D S1 i Cd1 Cd1 i ZL Z L i S i Cd D C d S V d V d Figure 3. Equivalen circui diagram of proposed elecronic circui.

4 56 V B Borghae, H M Suryawanshi and G A Dhomane small filer coupling inducor (L f ) is used a he inpu of circui o achieve he ripple free inpu line curren. The inverer oupu circui consiss of parallelconneced wo seriesparallel resonan circuis. I is represened by equivalen impedance Z L. To achieve he inheren zerovolageswiching (ZVS) of swiches, he swiching frequency is o be kep slighly greaer han he naural resonance frequency f 0. The duy raio d is kep a 0 5 for symmerical PWM. The above discussion is summarized as follows: L 1 = L,C 1 = C,C d1 = C d, (1) i w1 = i w,i m = i 1 i,i L = i L1 i L,i L1 = i L = i L /, v w1 = v w = v m, = v C1 v C,v C1 = v C = d = 0 5, v L1 = v L,V d1 = V d = V d /,V d >V p. () 3. Modes of operaion The proposed circui goes hrough eigh differen modes in an every swiching ime period T s (1/f s ) under seadysae condiion. Bu, only firsfour differen modes in a half swiching cycle are explained here. The remaining four modes of he nex half cycle are equivalen o hese firsfour modes. The equivalen circui diagrams of differen modes and is idealized key waveforms are shown in figures 4 and 5 respecively. Prior o sar of mode1, he currens i L1 freewheels hrough S, L m, D, acmains, C 1 and L 1 a I L /, whereas i L freewheels hrough S,L m, D, C and L. The diodes D 1, D 3 and D 4 and MOSFET S 1 are off. The DC bus capacior curren I Cd1 is zero, whereas C d is supplying curren o he resonan circui hrough S a I ZL. 3.1 Mode1 ( 0 1 ) As shown in figure 4a, a 0, he swich S is urned off and he diodes D S1 and D 1 sar conducing as soon as volage across he swich S 1 falls o zero. The inducors L 1 and L ransfer heir sored energy hrough D S1 o C d1 and C d along wih acmains hrough D 1 during his mode. This mode ends a 1, when inducor currens i L1 and i L decrease o zero. 3. Mode ( 1 ) The diode D S1 urns off a 1, since i L becomes zero, and swich S 1 urns on as shown in figure 4b. Thus, inheren ZVS of S 1 is achieved. The inducors L 1 and L resore heir energy from L m hrough S 1 during his mode. Therefore, he currens i L1 and i L coninue o vary as in mode1, bu opposie in direcion. This mode ends a, when charging curren I Cd1 decreases o zero. 3.3 Mode3 ( 3 ) This mode is similar o mode excep ha C d1 also sars supplying energy o Z L as shown in figure 4c. A he end of his mode a 3, he currens i L1 and i L reach o heir peak values and he curren i Cd of anoher dc bus capacior decreases linearly o zero.

5 Analysis and performance of efficien ballas 57 C 1 w 1 D 1 D 3 L 1 S 1 D S1 C d1 Z l L D 4 D C d S D S C w (a) Mode1 L m L m C 1 w 1 D 1 D 3 L 1 S 1 D S1 C d1 Z l L D 4 D C d S D S C w (b) Mode L m C 1 w 1 D 1 D 3 L 1 S 1 D S1 C d1 Z l L D 4 D C d S D S C w (c) Mode3 L m C 1 w 1 D 1 D 3 L 1 S 1 D S1 C d1 Z l L D 4 D C d S D S C w (d) Mode4 Figure 4. Operaing modes. 3.4 Mode4 ( 3 4 ) As shown in figure 4d, diode D urns off a 3, as curren i Cd is zero. The L m is greaer han L 1 and L, herefore, he currens i L1 and i L clamp a heir respecive peak values as on 3, and he addiional energy of L m is reurned o he ac source during his mode. This mode ends a 4, when energy of L m is exhaused. Similar operaion akes place in anoher four modes during he nex half swiching ime period.

6 58 V B Borghae, H M Suryawanshi and G A Dhomane v S1 V d i S1 i S i L I L v m 0.5(V d ) 0.5 v L 0.5V d 0.5V d i 1 i I L I L i Cd1 IZL i Cd I ZL 8 0.5I L T c T d T p T p Figure 5. Idealized key waveforms. 0.5T s 0.5T s 4. Analysis of circui 4.1 Analysis of modes During modes 1 o 3, he volages and currens of boos and injecing inducors are v m = V d v L1 = V d (1 d) (3) (4) i L1 () = I L V d (1 d) L 1 ( 0 ) (5)

7 he inpu curren is Analysis and performance of efficien ballas 59 i m = i L, and (6) = i 1 i L / = i i L /. (7) As shown in figure 5, he curren i 1 increases linearly from 0 (a 0 ) o maximum value I L (a 3 ), whereas he curren i decreases linearly from I L (a 0 )o0(a 3 )as i 1 () = 0 I L ( 3 0 ) ( 0), and (8) i () = I L I L ( 3 0 ) ( 0). (9) Therefore, from (7) o (9), he insananeous average value of inpu curren during he ime period ( 0 3 ) is he sum of he average values of i 1 and i L /, During mode 4, av = i 1 av (i L /) av = I L / 0 = I L /. (10) v L1 () = v L () = 0, v m () = v C1 = d = 0 5 (11) i 1 = i m = i L =I L, (1) = I L /. (13) From (10) and (13), i is seen ha he inpu curren mainains consan value a I L / during he whole swiching cycle. 4. Calculaions for L and inpu curren By applying an equal area crieria o he v L1 and v m during one swiching period, and defining he inducor curren linearly decreasing and increasing ime periods ( 0 o 3 ) and ( 4 o 7 )as T d and T c respecively, For v L1 : V d (1 d) T d = V d (1 d) T c. (14) For v m : V d (T d T c ) = d [(d T s T d ) (d T s T c )]. (15) Solving above wo equaions for T d and T c,gives d T s d T s T d =, and T c =. (16) V d (1 d) V d (1 d) The inducor curren i L1 given by (5) is zero a T d / and T c / respecively, since i varies linearly. Therefore, he maximum value of sum of inducor currens is, I L = d T s L 1. (17)

8 530 V B Borghae, H M Suryawanshi and G A Dhomane From (10) and (11) and aking L 1 = L = L, he inpu curren is = I L = d T s L. (18) where, is he insananeous value of inpu volage during ha swiching period. From (18), i is eviden ha he inpu curren varies wih he inpu volage a given value of curren injecing inducors L 1 and L, duy raio d, and swiching frequency f s (1/T s ); and i does no conain any oher componens han fundamenal. The inpu acvolage is () = V p sin πf, (19) where, f is he frequency of ac mains. Therefore, he inpu ac curren is, from (18), () = d T s V p L sin πf = I p sin πf, (0) Where, peak value of inpu curren is I p = d T s V p L. From (0), i is eviden ha he proposed ballas operaes a uniypowerfacor. The inpu power is, π P i = 1 () () d(ω) = V pi p = d T s Vp π 0 4L Therefore, he value of inducors, L = L 1 = L is given by, = d T s V L. (1) L = d T s V = ηt s V, () P i 8P o where P o,ηand V are he raed oupu power of he fluorescen lamp, efficiency of he ballas a raed oupu and raed rms inpu ac volage respecively. 4.3 Calculaions for L m and dcbus volage V d The inducance L m carries he fla op curren of value I L during he freewheeling ime period, T p = T s (T d or T c ) = T s (1 V d ) a duy raio d = 0 5, which varies wih he insananeous inpu volage over he half cycle of ac mains from maximum T s / (approximaely) a he valley poin of pulsaing recified ac inpu o minimum a he peak of i. Therefore, he minimum value of L m is calculaed as follows, L m min = v m maxt s. (3) I L From equaions (11), (17) and (3) L m min = dv p dv d = L. (4) f s I L f s I L From (17) and (4), he dcbus volage is V d = L m L V p. (5) Tha is o mainain he dcbus volage V d above he peak value of ac inpu volage V p a duy raio 0 5, he magneizing inducance L m should be greaer han he injecing inducors L 1 and L.

9 5. Design example Analysis and performance of efficien ballas 531 The specificaions of ballas are as follows; Raed inpu volage, V = 30 V (rms), 50 Hz Operaing inpu volage range = V (rms) Raing of fluorescen lamps, P 0 = 36 = 7 W Swiching frequency, f s = 50 khz. Based on he above specificaion and analysis, he inducors and capaciors are calculaed as; assuming he expeced efficiency of he ballas o be 93% a raed oupu power and 0 5 duy raio, he value of curren injecing inducors a 30 V is, L 1 = L = 1 7 mh, The capaciors C 1 and C are fixed a 0 1 μf/400 V (polypropylene). For mainaining he sufficien ligh inensiy L 1 = L = 1 mh and L m = 1 1 mh are seleced. The small value of inpu coupling inducor L f of 100 μh is used furher o minimize he HF swiching ripples. The DC link capaciors C d1 and C d are seleced as μf/400 V (elecrolyic). A swiching frequency f s = 50 khz, he parameers of resonan circui are C r = 10 nf (polypropylene), L r = 1 35 mh, f 0 = khz, Z 0 = 369, and R FL = 313. Diodes (D 1 D 4 ): UF 5408 and MOSFETs (S 1 S ): IRF Experimenal resuls A prooype of proposed elecronic ballas circui is buil and esed in he laboraory. The experimenal ac inpu line volage ( ), curren ( ) and dc link volage (V d ) waveforms a nominal volage 30 V are shown in figure 6. This figure shows ha he proposed ballas operaes a uniy power facor, for which he dclink volage (V d ) is jus above he peak value (V p ) of ac inpu volage. The experimenal waveform of HF generaed volage (v m ) in he coupling inducor L b is given in figure 7. I may be observed ha he value of v m is large a zero crossing and small a peak of he ac inpu volage. Therefore, he V d is mainained consan even a he valley of he inpu volage. Figures 8a and b give he volage (v Lj ) and curren (i Lj ) waveforms of he curren injecing inducor L j near peak and zero value of he ac inpu volage respecively. The L j injecs is sored energy o he dclink capacior in every half swiching cycle, when i Lj falls from is peak value (posiive or negaive) o zero. The proposed PFC circui produces he HF volage of consan magniude (v rin ) shown in figure 9, Figure 6. Experimenal inpu volage ( ) and curren ( ) and dclink volage (V d ) waveforms a 30 V: (100 V/div, 0 4 A/div, 10 ms/div).

10 53 V B Borghae, H M Suryawanshi and G A Dhomane v m Figure 7. Experimenal waveforms of inpu volage ( ) and HF generaed volage (v m ) in L b : (100 V/div, 5 ms/div). Figure 8. Experimenal waveforms of volage (v L ) and curren (i L ) of L j a (a) Near peak of AC inpu volage: (100 V/div, 0 A/div; 5 μs/div.), (b) Near valley of AC inpu volage: (50 V/div, 0 A/div; 5 μs/div.). b) over he inpu 50 Hz cycle, a he inpu of he diode bridge recifier ensures he conducion of bridge a he valley poin of he inpu volage. The swich volage (v s ) and curren (i s ) waveforms shown in figure 10 indicae is ZVS operaion. Figure 11 gives he oupu waveforms of he elecronic ballas circui. Figure 11a indicaes ha he HF fluorescen lamps volage (v FL ) and curren (i FL ) are sinusoidal wih minimum v rin Figure 9. Experimenal waveforms recifier inpu volage (vrin) and inpu volage (vi): (100,V/div; 5 ms/div).

11 Analysis and performance of efficien ballas 533 Figure 10. Experimenal swich volage (v S ) and curren (i S ) waveforms. (100 V/div, 1 A/div, 10 μs/div). Figure 11. (a) Experimenal fluorescen lamp volage (v FL ) and curren (i FL ) a 50 khz: (50 V/div, 0 5 A/div; 5 μs/div) and (b) VI characerisic: (Xaxis: 0 5 A/div; Y axis: 50 V/div). ripples, whereas is VI characerisic is shown in figure 11b. These lamp resuls a HF are compared wih he lamp resuls given in figure 1 a supply frequency (50 Hz). I is seen ha he fluorescen lamp behaves as a nonlinear impedance a low frequency, whereas resisive load a HF. The envelope of lamp curren (i FL ) of 50 khz given in figure 13 is fla. The cres facor of lamp curren is 1 4. Therefore, he elecronic ballas helps o prolong he lifeime of he fluorescen lamps. The experimenal resuls are also obained by changing he inpu volage a 180 V, 00 V and 50 V wih swiching frequency 50 khz and duy raio 0 5. As shown in figure 14, he proposed ballas mainains he power facor a uniy wih wide variaion in inpu volage. Experimenally i is seen ha, wih wide variaion in inpu volage, he efficiency of he ballas lies beween % and he THD is no more han 3 % saisfying sandards specified by IEC Figure 1. (a) Experimenal fluorescen lamp volage (v FL ) and curren (i FL ) a 50 Hz: (50 V/div, 0 5 A/div; 5 ms/div) and (b) VI characerisic: (Xaxis: 0 5 A/div; Y axis: 50 V/div).

12 534 V B Borghae, H M Suryawanshi and G A Dhomane 0 Figure 13. Envelope of lamp curren (i FL ) a 50 khz (0 A/div). I is also observed ha incase of failure of one lamp, he dclink volage V d increases from 350 V o 464 V, lamp curren increases from 0 51Ao0 695 A and swich curren decreases from 43Ao1 97 A. Whereas, he inpu power facor is mainained a uniy. 7. Conclusion In his paper, ripplefree singlesage elecronic ballas based on novel PFC circui along wih he symmerical half bridge inverer opology was proposed. The coupling inducor conneced (a) (b) ii (c) Figure 14. Experimenal inpu volage ( ) and curren ( ) waveforms a (a) 180 V, (b) 00 V, (c) 50 V: (100 V/div, 0 A/div, 10 ms/div).

13 Analysis and performance of efficien ballas 535 afer he recifier helps o boos he dclink volage above he peak of inpu volage and also reduces he HF swiching ripples. Two smaller dclink capaciors are required as compared o single large capacior wih no addiional dc blocking capaciors in he inverer circui. Based on he design, he laboraory prooype is buil and esed for ( 36 W) fluorescen lamps operaing a 50 khz wih mains 30 V, 50 Hz. The proposed singlesage elecronic ballas works a UPF wih high efficiency and low THD over wide range of inpu volage. Therefore, his opology is more useful in he sysem where wide flucuaion in he volage akes place. References Almeida M Co, Simonei D S L, Vieira J L F 1998 Highpowerfacor elecronic ballas operaing in criical conducion mode. IEEE Trans. power Elecron. 13: Almeida M Co, Simonei D S L, Vieira J L F 000 Highpowerfacor elecronic ballas based on a single power processing sage. IEEE Trans. Ind. Elecron. 47: Borghae V B, Suryawanshi H M, Rameke M R, Renge M M 006 Elecronic ballas wih uniy power facor based on curren injecion echnique. 37 h IEEE Inernaional Power Elecronics Specialis Conference PESC06, Jeju, Corea, Brumai M, Almeida M Co, Simonei D S L, Vieira J L F 005 Single sage selfoscillaing HPF elecronic ballas. IEEE Trans. Ind. Appl. 41: De Oliveira R, Brioschi, Vieira J L F 1998 High power facor elecronic ballas wih consan DClink volage. IEEE Trans. Power Elecron. 13: Do H L, Kwon B H 003 Singlesage linecoupled halfbridge ballas wih uniy power facor and ripplefree inpu curren using coupled inducor. IEEE Trans. Ind. Elecron. 50: Kazimierczuk M K, Szaraniec W 1993 Elecronic ballas for fluorescen lamp. IEEE Trans. Power Elecron. 8: Lin C S, Chen C L 1998 Singleswich sofswiching elecronic ballas wih high inpu power facor. IEE Proc. Elecr. Power Appl. 145: Spangler J, Behera A K 1991 Power facor correcion echniques used for fluorescen lamp ballas. in Conf. Rec. IEEEIAS Annaul Meeing