An Improved Zero-lage-Transiion Technique in a Single-Phase Acive Power Facor Correcion Circui Suriya Kaewarsa School of Elecrical Engineering, Rajamangala Universiy of Technology Isan Sakon Nakhon Campus, Sakon Nakhon, Thailand Absrac This paper presens an improved Zero-lage-Transiion Technique (ZVT- Technique) in a single-phase acive power facor correcion circui based on a dc-dc boos converer opology and operaed in a coninuous-inducor-curren mode wih fixed-swiching frequency conrol. An addiional circui for reducing he urn-off swiching loss of he auxiliary swiching circui was applied. Experimenal work was carried ou wih a circui operaed a 220 V rms inpu volage, 400 V dc oupu volage, 500 W oupu power and 40 khz swiching frequency. The es resuls showed ha he efficiency was improved from 95 o 97% wih he proposed circuiry, while he power facor was consan. Keywords: Boos converer, dc-dc converer, power facor correcion, sofswiching, boos converer opology, coninuous-inducor-curren mode. Inroducion In recen years, he number of recifiers conneced o uiliies has increased rapidly, mainly due o he growing use of compuers. Therefore, he problems caused by he harmonic currens become more imporan. Inernaional regulaions governing he amoun of harmonic currens (e.g. IEC1000-3-2) became mandaory and acive power facor correcion (PFC) circui became ineviable for he ac-dc converers. Generally, he soluion for harmonic reducion and PFC are classified ino passive approach and acive approach. The passive approach offers he advanages of high reliabiliy, high power handling capabiliy and easy o design and mainain. However, he operaion of passive compensaion sysem is srongly dependen on he power sysem and does no achieve high power facor. While he passive approach remains he bes choice in many high power applicaions, he acive approach dominaes he low o medium power applicaions due o heir exraordinary performance (uniy power facor and efficiency approach o 100%), regulaion capabiliies and 207 high power densiy. Wih he power handling capabiliy of power semiconducor devices being exended o megawas, he acive power elecronic sysems end o replace mos of he passive power processing devices (Akagi 1994; Bose 1992; McEachern 1990). Today s harmonic and PFC echnique o improve disorion are sill under developmen. Power supply indusries are undergoing he change of adoping more and more PFC echniques in all off-line power supplies. Moreover, wih he residenial and defense indusries coninuously demanding for even higher power densiy, swiching mode power supply operaing a high frequency is required because a high swiching frequency, he size and weigh of circui componens can be remarkably reduced. However, wih he increasing of swiching frequency, he swiching loss becomes inolerable, resuling in very low conversion efficiency (Gegner and Lee 1994). Sof-swiching echniques have been widely used in reducing he swiching losses and EMI noises of swiching mode power converer. Sof-swiching echniques, especially zero-volage-ransiion (ZVT) have become more and more popular in he power
Vac supplies indusries. The boos PFC converer employing he ZVT echnique was firs inroduced by Hua e al. (1994) showed in Fig. 1. This converer provides ZVS condiion for he main swich wihou increasing volage sress of he acive swiches. However, i has a disadvanage such as he auxiliary swiching circui is urned-off wih hard-swiching which deerioraes he overall efficiency and increase EMI noises (Kim, e al. 2000). This paper proposes an improved ZVT PWM boos PFC converer using addiional circui. The proposed converer achieves zero volage or zero curren urn-on and urn-off for he acive swiches as well as he sofswiching for he passive swiches. A 500 W, 40 khz ZVT PWM boos PFC converer prooype has been implemened o verify he improved performance of he proposed converer. 1 2 3 4 L Fig. 1. Convenional ZVT PWM boos PFC converer Circui escripion and Operaion Lr 1 ZVT Circui Co RL By insering addiional circui, all of he swiches, including auxiliary swiches, are only urned-on and off a sof-swiching. The proposed converer has eigh operaing modes. The ideal waveform and equivalen circui of each mode are shown in Figs. 3 and 4, respecively. To analyze he seady sae operaion, all componens and devices are assumed o be ideal and he boos inducor ( L ) and oupu capacior ( C o ) are assumed o be large enough o rea as a curren source and a volage source, respecively (Kaewarsa, e al. 2004). VGS VGS VS I VS ILr V I T IL 0 1 2 3 4 5 6 7 0 The power sage of he proposed converer is shown in Fig. 2. The addiional circuiry of he converer is consised of a diode ( 2 ) and wo capaciors ( C 1, C 2 ). The converer operaes in a coninuous curren mode wih fixed frequency. Vac 1 2 3 4 L s1 Fig. 2. Proposed ZVT PWM boos PFC converer Lr 1 C1 2 Addiional Circui Co RL 208 Fig. 3. Theoreical waveform of he proposed converer Mode of Operaion The operaions of each mode are explained as follows: Mode 1 [ 0 1 ]: Prior o = 0, he main swich S 1 and he auxiliary swich S 2 are urned-off, and main diode is conducing. A = 0, S 2 is urned-on, he resonan inducor curren I Lr linearly ramp up unil i reaches I in a 1, where main diode is urned-off wih sof-swiching. The volage and curren expressions ha govern his circui mode are given by:
V I o Lr = L r (1) V = V Lr = V o. (2) Mode 2 [ 1 2 ]: A 1, he resonan inducor curren I Lr reaches I in, L r and C r begins o resonae. The resonan capacior volage V is equal o V o. The volage and curren expressions are given by: V I o Lr = I in + sinωn ( 1 ) Zn (3) V = V o cosωn ( 1 ) (4) where Z n = L r 1 ωn =. C r L r C r Mode 3 [ 2 3 ]: When V reaches zero he body diode of he main swich conducs providing a freewheeling way for L r curren. A his insan, main swich S 1 can be urned-on a zero volage. The curren I is given by: I = + = Z. n Z n (5) Mode 4 [ 3 4 ]: The auxiliary swich S 2 is urned-off wich near ZVS a = 3. The energy sored in he resonan inducor L r is ransferred o he capacior C 1 and C 2. Then he volage polariy of he capacior C 1 is reversed o negaive. uring his period, he ILr I s1 (a) Mode 1 I V ILr 1 1 2 2 s1 (b) Mode 2 Is1 1 (c) Mode 3 Lr s1 (d) Mode 4 (e) Mode 5 (f) Mode 6 (g) Mode 7 2 (h) Mode 8 Fig. 4. Equivalen circui of each operaion mode capacior C 1 is acing as a urn-off snubber of he auxiliary swich. The energy sored in he capacior C 2 will be recycled and used o suppress he urn-off volage spike of he main swich S 1. The volage and curren expressions of his mode are given by: I Lr = I Lr ( 2 )cosωn ( 3 ) (6) ILr ILr I s1 1 Lr s1 s1 1 C1 1 2 2 C1 1 2 2 IO s1 1 2 209
where VC1 = ZnI Lr ( 2 )sinωn( 3 ) (7) L r 1 Z n = ωn =. C1 + L r (C1 + ) Mode 5 [ 4 5]: uring his period, he inducor L is charged by he inpu dc volage source V in while he main swich S 1 coninues o be urned-on and he auxiliary swich S 2 is urned off. Mode 6 [ 5 6 ]: A 5, he main swich S 1 begins o urn-off, he inducor L charges he resonan capacior C r and he volage across he capacior increases. The curren L r equals zero and he volage across C r is given by: I I V in L = =. (8) Mode 7 [ 6 7 ]: When he increasing volage across C r is greaer hen ( V o + V C 1 ), he capacior C 1 begins o discharge hrough he diode 2. This discharge of C 1 can slow down he rising volage slope of he rising volage across C r or he main swich S 1. Therefore, he capacior is performing as a urned-off snubber for he main swich o suppress he urned- off volage spike and he urned-off volage slope of he main swich S 1. The volage across C r is given by: V = V o + V C1 (9) Mode 8 [ 7 0 ]: This sage begins when he diode is urned-on under ZVS. The operaion of he circui a his sage is idenical o he normal urned off operaion of a PWM boos converer. I ends a he momen ha S 2 is urned on o begin a new swiching cycle. elay Time To ensure proper operaion of he ZVT sof-swiching boos PFC converer, a minimum delay ime ( T ) of he auxiliary swich S 2 is required. This delay ime ( T ) mus saisfy he following condiion: I in L r π T + Lr (10) 2 esign Procedure In he design of a boos PFC converer, he required inpu power facor and he oal harmonic disorion (TH) of he line curren under specified ranges of line volage is he major design goal. This design procedure of he proposed ZVT PWM boos PFC converer is summarized as follows: Swiching Frequency ( f s ) eerminaion of swiching frequency plays a mos imporan role in he design of he power converer. There are many facors influence is proper selecion. However, he deerminaion of swiching frequency is sill a compromise beween heoreical analysis and pracical implemenaion. Peak Inducor Curren ( I L ) According o he design raing of he boos PFC converer, he converer was designed o operae in a coninuous conducion mode, herefore, he peak inducor curren is deermined by: s I 1 V L η = V dc I o = P o (11) 2 P I o L = 2 η (12) V s where η is he converer efficiency. Minimum uy Raio ( min ) The minimum duy raio occurs when he inpu volage ges he maximum and his is equal o: Vin(max) min = (13) 210
Primary Inpu Inducor ( L ) The primary inpu inducor mus saisfy a consrain governing o mee he requiremen on maximum allowable ripple curren. The inpu inducor ( L ) is given by: T s = where 1 f s Oupu Capacior ( C o ) Vin(min)minTs L = (14) is he inpu ripple curren and The selecion of he oupu capacior depends on he oupu ripple volage ( ) as follows: P o Co 2 ωs (15) where ωs = 2 πfline elay Time ( T ) The on-ime of auxiliary swich ( S 2 ) mus be shorer han one enh of he swiching period. 1 T = Ts (16) 10 Curren Sress Facor ( a ) The curren sress facor of he auxiliary swich is defined as ILr( pk ) a = (17) I in(max) I is greaer han one ( 1 a 1. 5) and is desired o be as small as possible. This facor can be used for he selecion of he auxiliary swich. Resonan Capacior ( C r ) The resonan capacior ( C r ) can be expressed as ( a 1) 2 I in(max) T C r = (18) π V 1+ ( a 1) o 2 Resonan Inducor ( L r ) The resonan inducor is given by L = T r. (19) π 1+ ( a 1) (max) 2 Addiional Capacior ( C 1, C 2 ) To guaranee a sof-swiching of he auxiliary swich, he required capaciance C 1 should be seleced according o he expression: L [ ] 2 r I in(min) + V o L r / C r C1 < 2 (20) V o where C 2 < C1. The specificaions of he prooype boos PFC converer are given in Table 1. Table 1. Specificaions of he boos PFC converer Oupu power ( P o ) Oupu dc volage ( V o ) Inpu ac volage ( V in ) Swiching frequency ( f s ) Oupu volage ripple ( Inpu curren ripple ( 500 W 400 V 176-264 V rms 40 khz ) 5 % ) 20 % Esimaed efficiency (η) 95% Experimenal Resuls A 500 W, 40 khz prooype of he proposed ZVT PWM boos PFC converer, as shown in Fig.2, has been buil in he laboraory o experimenally verify he analysis. The major parameers and componens are given in Table 2. 211
Table 2. Componens used in prooype Componen Value/Model Swiches ( S 1, ) IRFP450 iode ( 1 2 MUR8100E Boos inducor ( L ) 2 mh Resonan capacior ( C r ) 1.8 nf Resonan Inducor ( L r ) 80 µh Oupu capacior ( C o ) 220 µf Capacior C 1 4.7 nf Capacior C 2 1.5 nf Conroller chip UC3855AN Fig. 6. Experimenal resuls of he inpu volage and curren for he convenional ZVT PWM boos PFC converer, = 5ms/div For comparison, a convenional ZVT boos PFC converer wih he same specificaions is also buil. POWER CONVERTER AUXILIARY CIRCUIT AC LINE NOISE FILTER CO LOA Rs CURRENT SENSE WAVEFORM INPUT GATE RIVE CIRCUIT CONTROLLER UC3855AN LTAGE SENSE Fig. 7. Experimenal resuls of he inpu volage and curren for he proposed ZVT PWM boos PFC converer, = 5ms/div Fig. 5. Block diagram of an experimenal circui Fig. 5 shows he block diagram of an experimenal circui. I consiss of a noise filer, a diode bridge, a power converer, auxiliary circuis, gae drive circuis and a conroller chip. A noise filer is used o reduce noise componens in he inpu side. An auxiliary circui is used o sofen swiching configuraion. And a gae drive circui splis a gae signal of he conroller ino wo, where one is main circui and oher is for he auxiliary circui. Is swiching frequency is consan. 212 Fig. 8. Experimenal resuls of he oupu volage and curren for he proposed ZVT PWM boos PFC converer, = 5 ms/div Fig. 6 and Fig. 7 show he waveforms of he inpu line volage and line curren for he convenional converer and he proposed converer. The line curren is in phase wih he
line volage and i is nearly sinusoidal. The power facor of boh converers are almos uniy (0.992) and oal harmonic disorion (TH) is 2.82%. Fig. 8 shows he waveforms of he oupu volage and curren for he proposed converer. Fig. 11. Curren and volage waveforms of S 2 for he convenional ZVT PWM boos PFC converer, = 1µs/div Fig. 9. Curren and volage waveforms of S 1 for he convenional ZVT PWM boos PFC converer, = 5µs/div Fig. 12. Curren and volage waveforms of S 2 for he proposed ZVT PWM boos PFC converer, = 1µs/div 98 96 Fig. 10. Curren and volage waveforms of S 1 for he proposed ZVT PWM boos PFC converer, = 5µs/div Figs. 9 and 10 show he waveforms of he main swich S 1 for he convenional converer and he proposed converer. As can be seen in hese figures, S 1 urns-on and urns-off under zero volage condiion. Efficiency (%) 94 92 90 88 86 improved ZVT convenional ZVT 100 W 200 W 300 W 400 W 500 W Oupu Power Fig. 13. Efficiency comparison beween boh converers 213
Fig. 11 shows he waveforms of he auxiliary swich S 2 for he convenional ZVT PWM boos PFC converer and he auxiliary swich is urned-on wih ZCS and urned-off wih hard-swiching. Fig. 12 shows he waveforms of he auxiliary swich S 2 for he proposed ZVT PWM boos PFC converer. As can be seen Fig. 12, he auxiliary swich S 2 is urned-on wih ZCS and urned-off near ZVS. Thus he swiching loss of S 2 is reduced. Fig.13 shows he efficiency measuremens of he improved ZVT and he convenional ZVT PWM boos PFC converer (Hua, e al.1994). The measured efficiency a 500 W of he proposed ZVT PWM boos PFC converer is 97% as compared wih he convenional ZVT PWM boos PFC converer which has an efficiency of 95 %. Conclusion In his paper, an improved ZVT PWM boos PFC converer was proposed. The swiching loss of he auxiliary swich are minimized by using an addiional circui applied o he auxiliary swich. Besides he main swich ZVS urned-on and urned-off, and he auxiliary swich ZCS urned-on and urnedoff near ZVS. Since he acive swich is urnedon and urned-off sofly, he swiching losses are reduced and he higher efficiency of he sysem is achieved. A prooype of a 500W/40 khz sysem was implemened o experimenally verify he improved performance. Acknowledgmen The auhor acknowledges he financial suppor from he Rajamangala Universiy of Technology Isan, Sakon Nakhon Campus, Sakon Nakhon, Thailand, during a period of his work. References Akagi, H. 1994. Trends in acive power line condiioners. IEEE Trans. Power Elecronics 9: 263-8. Bose, B.K. 1992. Power elecronics - a echnology review. Proc. IEEE In. Conf. Power Elecronics (PESC 92), pp. 1303-34. Gegner, J.P.; and Lee, C.Q. 1994. Zero-volage -ransiion converers using an inducor feedback echnique. Proc. IEEE In. Conf. Power Elecronics (PESC 94), pp. 590-6. Hua, G.; Leu, C. S.; Jiang, Y.; and Lee, F. C. 1994. Novel zero-volage-ransiion PWM converer. IEEE Trans. Power Elecronics 9: 213-9. Kaewarsa, S.; Krongkisiri, W.; Prapanavara, C.; and Yangyuen, U. 2004. An improved ZVT-PWM C-C boos converer using addiional circui. Proc. IEEE In. Conf. TENCON 2004, pp. 201-4. Kim, T.W.; Kim, H.S.; and Ahn, H.W. 2000. An improved ZVT PWM boos converer. Proc. IEEE In. Conf. Power Elecronics (PESC 00), pp. 615-9. McEachern, W. 1990. Power elecronics in he 1990 s. Proc. IEEE In. Conf. Indusrial Elecronics (IECON 90), pp. 839-43. 214