Design of a Three-Phase Unity Power Factor Single-Stage Telecom Rectifier

Transcription

1 Design of a Three-Phase Uniy Power Facor Single-Sage Telecom Recifier Bünyamin Tamyürek Deparmen of Elecrical Engineering, Eskisehir Osmangazi Universiy, Eskisehir, Turkey bamyurek@ogu.edu.r Absrac This paper presens he design and implemenaion of a hree-phase uniy power facor single-sage recifier. The main use of he converer is expeced o be in he elecommunicaions indusry where i supplies consan DC volage o he elecom nework and charges he high capaciy baeries while providing uniy power facor o he uiliy. The converer is based on he flyback opology operaing in disconinuous curren mode (DCM). A fas dynamic response, low cos, small size, and a very simple conrol are he furher viable benefis of he converer. The sudy includes finding an opimum ransformer design wih he lowes leakage inducance and he selecion of componens wih he lowes parasiic effecs for high efficiency and good performance. Afer he design is verified using he Simulink and PLECs models of he converer, a full-scale prooype was implemened o evaluae he performance of he design. Finally, experimenal resuls demonsrae ha converer works successfully and mee he design expecaions. 1. Inroducion The harmonics drawn from he uiliy lines due o disored curren waveforms and low power facor caused by hese currens are imporan power qualiy problems [1-4]. The common approach for he soluion of hese problems is o use wo-sage power conversion schemes. The wo-sage schemes employ a power-facor correcion sage where harmonic currens are eliminaed and anoher cascaded sage such as a DC-DC converer for generaing regulaed oupu wih fas dynamic response and isolaion. However, he cascaded converers increase he complexiy of he sysem, and so he cos and he size of he produc. For his reason, major research has been carried ou for he developmen of less complex single-sage sysems which provide he same performance as heir wo-sage counerpars [5-9]. Mos manufacurers are sill looking for realizaion of alernaive sysems ha improve on he specificaions of he producs available oday, bu also offer lower cos, smaller size, and simpler conrol requiremens wih superior dynamic response. Sudies have showed ha he flyback based converer opologies sill have he mos poenial o achieve hese demands [10-13]. However, he research so far has considered he flyback opology being more feasible in low power applicaions. In his sudy, we propose a design ha demonsraes he pracicabiliy of single-sage flyback based PFC sysems in high power applicaions. The circui opology of he proposed conversion sysem is shown in Fig. 1. The converer is based on flyback opology operaed in disconinuous curren mode (DCM). Flyback opology offers he lowes componen coun and isolaion. Operaion in DCM mode offers many advanages such as eliminaion of urn-on swiching losses ha allows higher swiching speeds for IGBTs, eliminaion of half-plane zero in he feedback loop ha allows a robus and sable conrol, and lasly very fas dynamic response. The main disadvanage of operaion in DCM is he disconinuous curren waveforms wih high peaks boh a he inpu and a he oupu of he converer. For his reason, a lowpass filer a he inpu and a capaciive smoohing filer a he oupu, as shown in Fig. 1, are needed o remove he high frequency componens of he curren and o reduce EMI. Moreover, boh of hese filers especially he capacior a he oupu should have high RMS ripple curren capaciy. v an v bn v cn i a i b i c L a L b L c Can a C bn b C n c cn i bp S 1 S 2 i cp S 3 i am i a1 i a2 i as i bs i cs D1 D2 D3 D4 D5 D6 Fig. 1. The circui opology of he proposed converer Anoher challenging design problem in high-power flyback based converers is o minimize he parasiics especially he leakage inducance in he ransformer and he parasiic inducances along he pahs hrough which he energy ransfer occurs. Energy ransfer from inpu o he oupu suffers significanly especially during curren ransfers ha occur a swich urn-offs [9, 14-15]. Even so, a carefully designed flyback ransformer wound on a disribued-air gapped ferrie core wih aller window area and using sandwiched winding echniques are considered as effecive soluions o he leakage inducance problem. The work presened in reference [9] has implemened such a converer and obained resuls ha could be used as proof of concep. Now, in his work, major developmens and design improvemens have been made o bring he idea from a concep ino a commercially viable produc. As menioned above, he main design improvemens include he following: All of he curren carrying power lines are ransferred o he prined circui board (PCB) insead of bus bars. Low-profile screw ype IGBT and diode packages such as SOT 227 are used o shoren he curren pahs and herefore o reduce he parasiic inducances. Smaller sized componens wih reduced curren raings are used in parallel insead of large single componen in order o S idc C o Io V o I-311

2 reduce parasiics. For example, Schoky diodes will be paralleled and many small value capaciors will be paralleled o make he oupu capacior. Secondary sides of he flyback ransformers are conneced as Dela for wo reasons: zero sequence currens canno flow o oupu, and i allows lower urns raio of he ransformers which reduces he volage sress across he primary side swiches. Disribued air gap in he core, aller window area, and sandwiched windings wih wide copper srips. 2. Basic Operaional Principles of he Converer The waveforms shown in Fig. 2 are he heoreical volage and curren waveforms over he posiive half-cycle of one phase of he converer shown in Fig. 1. These waveforms will be used o explain he basic operaional principles of he converer. The is he line-o-neural inpu volage, is he insananeous flyback ransformer primary winding curren which is also he unfilered converer inpu curren, is he insananeous average of, which is he curren o be drawn from he uiliy line. As shown in Fig. 2, he peak of inpu curren depends on he applied volage and he duy raio of he swich. If he duy raio is fixed, hen all he peaks will change according o he volage. Because he applied volage changes sinusoidally a he inpu, he peaks of he curren will also change sinusoidally, as indicaed by he dashed line in Fig. 2. This peak envelop is he sign of fac ha he moving average of he riangular pulse rain (he inpu curren) will also be sinusoidal, which is shown by he icker line in Fig. 2 as. The moving average of his curren waveform can be wrien as ( ) = sin. I is imporan o noe ha his averaged curren is in phase wih he inpu volage. This is how he converer achieves uniy power facor. Fig. 3 shows he waveforms of primary curren and secondary side curren refleced o he primary side over a swiching period when he inpu volage is a is peak. The sum of hese wo currens gives he flyback ransformer magneizing curren =( ). As indicaed in Fig. 3, we have assumed ha he change in he inpu volage during swich on ime is negligible and herefore he increase in he magneizing curren is linear. As shown in Fig. 3, a small dead ime region can be added every ime afer he secondary curren is brough o zero o guaranee DCM operaion under abnormal condiions. v an i a (V o 2VD ) DTs i as Ts Vˆ an v p T s Fig. 2. The heoreical waveforms of he inpu volage ( ), he flyback ransformer primary winding curren ( ), and is insananeous average ( ) The converer is operaed wih a fixed swiching frequency. The waveform of in Fig. 2 indicaes a duy raio of he swich a 50%. The hree swiches a he primary side of he converer are operaed simulaneously using he same gae pulse. Because of DCM operaion, every ime he swiches are urned on, he primary curren sars from zero and increases almos linearly o a maximum. During his mode, energy is sored in he magneizing inducance of he flyback ransformer, no curren flows o he secondary side due o hree-phase recifiers a he oupu, during his ime he load power is supplied by he oupu capacior. When he swiches are urned off, all of he energy sored in he magneizing inducances of each phase is ransferred o he oupu hrough he flyback ransformer secondary windings and he hree-phase recifier. The capacior smoohes he ripple a he oupu volage caused by he recified curren pulses. 3. Analysis of he Converer Performing he analysis only for he posiive half-cycle of he inpu volage as shown in Fig. 2 is adequae o drive all of he necessary design equaions. Moreover, we will assume ha all he componens are ideal and converer operaes in DCM mode and in periodic seady-sae. Also assume a pure sinusoidal volage ( ) = sin is applied o he phase a of he converer. Fig. 3. The waveforms of he ransformer primary volage ( ), ransformer primary curren ( ) and secondary curren ( ) refleced o he primary side DT s Fig. 4. The waveforms of ransformer primary curren ( ) over a swiching cycle and is cycle based average ( ) Fig. 4 shows he primary curren and is cycle based average. The average of he primary curren a his specific ime (when is a is peak) gives he magniude of he sinusoidal curren drawn from he uiliy line, which is. Therefore, he area of he riangular in Fig. 4 gives his maximum. = 1 2 (1) The peak of he primary winding curren in (1) is found using equaion (2), where is peak inpu volage, is duy raio of he swich, is he magneizing inducance of he flyback ransformer, is he swiching frequency. Î ap T s Î a = (2) I-312

3 Equaion (3) gives he inpu real power per phase. = 1 2 (3) Using (1), (2), and (3), duy raio of he swich can be derived as given by (4). = 2 (4) The parameers,, and in (4) are no specified and should be deermined for a given and. This is he sep where a good design opimizaion is required. Selecion of hese parameers grealy affecs he performance, size and he efficiency of he converer. Afer an opimum design is obained, we go o he nex imporan design sep which is he design of he flyback ransformer. The main crierion in he design of he ransformer is o achieve he lowes possible leakage inducance. Equaions (5) hrough (9) are used o deermine he opimum core area, he number of primary urns 1, and he air gap lengh. Moreover, equaing he vol-second area across he magneizing inducance gives he value of he urns raio of he flyback ransformer. From Fig. 3, and assuming operaion a he boundary of coninuous curren mode (CCM), he equaion for he urns raio becomes, 1 = 2 (1 )( +2 ) (5) where is he diode volage and is he average oupu volage. = 1 =2 (6) = (7) = 1 2 (8) = 1 2 (9) Equaion (6) gives he maximum flux linkage. Using (7), (8) and (9) in a spreadshee program, an opimum core size, he number of primary urns, he magneizing inducance value, and finally he air gap lengh are deermined. Because he inpu volage range is very wide, as shown in Table 1, he range duy raio will also be wide. Using (4), his range is found beween 33.74% and 67.76% for a magneizing inducance of 150 H. Saying wihin his range is a design objecive since anyhing beyond his range would make i difficul o obain he desired performance from he converer. Therefore, he value of he magneizing inducance was seleced based on his crierion. Table 1. The inpu and oupu specificaions of he converer Oupu volage range V Nominal oupu volage 48 V Maximum oupu curren 50 A Oupu power W Oupu volage ripple (pk-pk) less han 100 mv Inpu volage range V THD of he inpu curren less han 5% Power facor uniy Efficiency 90% Table 2. The summary of design parameers Parameers Value Swiching frequency 30 khz Magneizing inducance 150 H Duy raio % Flux linkage 5 Wb Primary number of urns 1 18 Secondary number of urns 2 2 Core area 785 mm 2 Air gap lengh 2.13 mm Swich volage 852 V The flyback ransformer design is he mos rigorous par of his projec. Fig 5 shows he core assembly and he finished ransformer. The U shaped core pieces made from Ferrie maerial is used o minimize he core losses a 30 khz. Besides minimizing he losses, i is very imporan o obain he lowes possible leakage inducance. To achieve his objecive, he following was done in he design of he ransformer. 4. Design of he Converer Power Sage This secion presens he design of he converer based on he mahemaical analysis performed in he previous secion. The Mahcad sofware was used o deermine he design parameers. The program uses he specificaions given in Table 1 as he inpu daa and provides resuls by simulaneously solving he equaions derived in he analysis secion. An opimum design, which is given in Table 2, is obained by evaluaing hese resuls. The following paragraphs will discuss he crieria for he opimum design. The firs sep in he design process is o specify he swiching frequency. I is seleced as 30 khz since his value is high enough o allow small size of magneic componens and low enough o allow he use of new generaion high speed discree IGBTs. Nex, we need o find he duy raio of he swich. Fig. 5. The flyback ransformer core assembly (lef), he finished hree-phase flyback ransformer (righ) Firs of all, insead of using a single large air gap, which is 2.13 mm, we disribued he gap along he legs. As shown in Fig. 5, here are five air gaps along each leg. Besides providing he same magneic properies and he energy sorage requiremens, he disribued air gap mehod significanly minimizes fringing and also conribues o he low leakage in he ransformer. Second, we pu he U pieces face o face o obain a aller window area. In a aller window, escaping of flux from he upper and lower reurns of he core sides is quie less. Then, I-313

4 insead of using round conducors for windings, hinner bu wider copper foils are used o minimize he space beween he urns where he high leakage flux is generally presen. Finally, secondary winding is sandwiched beween he wo primary halves in order o reduce o peak magneic field inensiy in he window; his echnique significanly reduces he leakage inducance. A finished hree-phase flyback ransformer which provides he all design crieria is shown in Fig. 5. The oal leakage inducance of he ransformer is measured as less han 1%. Lasly, as seen from Fig. 5, even he leads of he windings are made using wide copper srips o minimize parasiic inducance beween he ransformer and he PCB connecion poins. The EMI filers a he inpu use 300 H inducors wound on an iron powdered oroidal core and 3 F meal film EMI suppression capaciors. These componens produce a corner frequency of 5.3 khz. As shown in Fig. 1, a bipolar swich is needed for he converer. From he analysis, i can be found ha he swich will see maximum 852 V when swiching ransien volages are ignored. To build he bipolar swich, one 1200 V high speed IGBT and 4 fas recovery diodes are used. Especially in flyback applicaions, he ransien over volages are always presen and hey are expeced o be very high in magniude due o he fas urn off of he IGBT. For ha reason, using 1200 V device here seems risky, bu a passive volage clamp circui will be used o proec he swiches agains ransien over volages. The clamp will be designed o fix he maximum swich volage always below 1000 V o ensure he safey of he devices. SOT 227 package ype devices will be used in order o shoren he pahs for he curren flow and herefore o minimize he parasiic inducances. The hree-phase recifier a he oupu sage is consruced using 150 V Schoky diodes in SOT 227 package. Each package has wo diodes in parallel. The low on sae volage of Schoky will conribue o he efficiency and again he paralleling is expeced o reduce parasiics. As saed earlier, he curren waveform a he oupu is highly disconinuous and has high RMS o average raio. From he simulaion sudies, i was found ha a nominal condiions when he average oupu curren is 50 A, he RMS of he DC bus curren is 114 A and he RMS of he ripple curren flowing ino oupu capacior is 103 A. Therefore, 20 pieces of 200 V and 470 F elecrolyic capaciors wih 6.45 A coninuous curren raing, which is based on 30 khz ripple frequency and 55ºC ambien emperaure, are conneced in parallel o handle 103 A. Table 3 liss he main semiconducors and he passive componens used in he power sage of he converer. Table 3. The lis of he componens used in he power sage Par descripion IGBT Fred diode Schoky diode Oupu capacior Manufacurer par number IXYS IXEN 6020D1 IXYS DSEI 2x61-12B IXYS DSS 2x A Kendeil K _PM0CB 5. Design of he Conrol Sysem The mos aracive characerisic of his converer is he very simple conrol requiremens. As seen in he Simulink model of he conroller sysem shown in Fig. 6, only a single-loop volage-mode conrol echnique is enough o do he conrol job. The same PWM pulse is applied o he hree swiches of he hree-phase converer. The conroller here is capable of regulaing a consan oupu volage wih excellen dynamics. Fig. 7 shows he deails of he PLECs model of he power sage ha is shown as a block in Fig. 6. Simulaion was used o deermine he conroller parameers based on he dynamic response of he oupu. Since he PLECs model provides a real represenaion of he power sage during simulaions, he mahemaical model was no needed for conrol developmen. The conrol algorihm was hen implemened in a microconroller. For his job, we used 16-bi dspic30f2020 digial conroller from Microchip Technology Inc. Vo_ref /2500 Power 1/500 abc 500 W PI 1 %V_in Fig. 6. Simulink model of he conrol sysem Fig. 7. The PLECs model of he power sage 6. Experimenal Resuls Power Circui Fig. 8 shows he experimenal seup of he converer sysem and he es arrangemen. To monior and evaluae he sysem performance, we used precision meers such as a 3193 HIOKI power analyzer ha has 0.1% reading accuracy, and a TPS2024 Tekronix scope o capure waveform informaion. Fig. 9 shows he experimenal waveforms of he volage and he curren drawn from he uiliy line of one phase. Fig. 10 is he screen copy of he power analyzer and liss all he imporan inpu and oupu parameers, where 1,2,3 reads he uiliy line-o-neural volages, 1,2,3 reads he uiliy line currens, 123 and 123 are he oal hree-phase real and apparen power, respecively. Then, in he same screen, 4 reads he average oupu volage, 4 is he average oupu curren, and 4 is he real power measured a he oupu sage. Finally, 1 is he power facor, 1 is he power facor angle (phase shif beween he volage and he curren), 1 is he THD of he uiliy volage, 1 is he THD of he uiliy curren, and 1 reads he overall efficiency of he converer. The curren waveform in Fig. 9 clearly demonsraes he capabiliy of he converer in realizaion of sinusoidal curren wih very low disorion plus a power facor very close o uniy. As also shown in Fig. 10, he THD of he curren waveform is 1.75%, which is well below wha regulaions sae [1], and he power facor is The 3.53º phase shif here is due o he inpu EMI filer and i is no because of he converer operaion. Finally, he efficiency of he converer is measured as 86.85%, which is around 3% less han he design objecive of 90%. 0.1 >= g123 Vabc r_load PLECS Circui vo ic_rms iap idc van ia I-314

5 auhor also would like o hank Arda Yesil, N. Niha Ozurk, and A. Ihsan Yalap for heir grea help in he projec. 9. References Fig. 8. The experimenal seup of he implemened converer Fig. 9. The experimenal waveforms of he uiliy volage (purple) and he curren (green waveform) Fig. 10. The experimenal resuls of he converer 7. Conclusions This paper has presened he design and he experimenal verificaion of a hree-phase high power qualiy single-sage elecom recifier. The main objecive was o implemen a commercially compeiive soluion o mulisage and complex converer srucures in he recifier applicaions. In he design process of he converer, advanced design ools and echniques were employed o achieve he hough design objecives. In conclusion, he es resuls demonsrae ha he converer saisfacorily achieves he inpu curren harmonic and he power facor requiremens. Bu, he overall efficiency is measured a lile lower han expeced. However, he disinc advanages such as low cos, nearly zero harmonic emission o he uiliy lines, a power facor close o uniy, small size, and very simple conrol requiremens make he opology aracive for commercializaion. 8. Acknowledgemens This projec is suppored by he Scienific Research Projec Fund of Eskisehir Osmangazi Universiy (PN ). The [1] IEEE Recommended Pracices and Requiremens for Harmonic Conrol in Elecric Power Sysems, IEEE Sd [2] Limis for Harmonic Curren Emissions, IEC , [3] A. R. Prasad, P. D. Ziogas and S. Manias, An acive power facor correcion echnique for hree phase diode recifiers, IEEE Transacions on Power Elecronics, Vol. 6, No.1, pp , January [4] R. Erickson, M. Madigan, and S. Singer, Design of a simple high-power-facor recifier based on he flyback converer, IEEE Applied Power Elecronics Conference Proceedings, pp , [5] R. Y. Igarashi and I. Takahashi, Uniy power facor hreephase recifier using a single swiching device, IEEE Indusry App. Sociey Annual Meeing, pp , [6] J. W. Kolar, H. Erl, and F. C. Zach, A novel hree-phase single-swich disconinuous-mode ac-dc buck-boos converer wih high-qualiy inpu curren waveforms and isolaed oupu, IEEE Trans. on Power Elec., Vol. 9, pp , March [7] H. Mao, F. C. Lee, D. Boroyevich, and S. Hii, Review of high-performance hree-phase power facor correcion circuis, IEEE Transacions on Indusrial Elecronics, Vol. 44, pp , Augus [8] Y. T. Feng, G. L. Tsai, and Y. Y. Tzou, Digial Conrol of a Single-Sage Single-Swich Flyback PFC AC/DC Converer wih Fas Dynamic Response, in Proc. IEEE Power Elecron. Spec. Conf., vol. 2, pp , [9] B. Tamyurek, D. A. Torrey, A High Power-Qualiy, Three-Phase Uiliy Inerface, IEEE Applied Power Elecronics Conference. and Exposiion, Vol. 2, pp , [10] V. N. She, A High Power Facor Forward Flyback Converer wih Inpu Curren Waveshaping, Inernaional Conference on Power Elecronics, Drives and Energy Sysems, pp. 1-6, Dec [11] K. Sangsun, N. E. Prasad, A Parallel-Conneced Single Phase Power Facor Correcion Approach Wih Improved Efficiency, IEEE Transacions on Power Elec., Vol. 19, No. 1, pp , January [12] D. G. Lamar, A. Fernández, M. Arias, M. Rodríguez, J. Sebasián, and M. M. Hernando, A Uniy Power Facor Correcion Preregulaor Wih Fas Dynamic Response Based on a Low-Cos Microconroller, IEEE Transacions on Power Elec., Vol. 23, No.2, pp , March [13] D. G. Lamar, A. Fernandez, M. Arias, M. Rodriguez, J. Sebasian, and M. M. Hernando, Limiaions of he Flyback Power Facor Correcor as a One-Sage Power Supply, IEEE Power Elecronics Specialiss Conference, pp , June [14] L. Dixon, The effecs of leakage inducance on mulioupu flyback circuis, Unirode Power Supply Design Seminar, SEM-500. [15] K. H. Liu, Effecs of leakage inducance on he cross regulaion in disconinuous-mode flyback converer, Proceedings of 4h Inernaional Conference on High Frequency Power Conversion, pp , May I-315