A New Low-Stress Buck-Boost Converter for Universal-Input PFC Applications

Transcription

1 A New Low-Stre Buck-Boot Converter for Univeral-nput PFC Application -LQJXDQ&KHQ'UDJDQDNLPYLüDQG5EHUW(ULFNQ Colorado Power Electronic Center Deparent of Electrical and Computer Engineering Univerity of Colorado at Boulder Boulder, CO 89-5, USA Abtrt n converter for power-ftor-correction (PFC), univeral-input capability (ability to operate from any AC line voltage, world-wide) come with a heavy price in term of component tree and loe, ize of component, and retriction on the output DC voltage. A new two-witch topology i propoed to offer very ignificant performance improvement over the ingle-witch buck-boot converter (including flybk, SEPC, and Cuk topologie) and conventional two-witch buck-boot caded converter. he propoed converter ha buck-boot converion charteritic, witch conduction loe comparable to the boot converter, no inruh current problem, and potential for maller inductor ize compared to the boot converter. g L D Q C Q g D a) L Q Q D L C D C. NODUCON t i well known that boot topology i highly effective in PFC application, provided that the dc output voltage i cloe to, but lightly greater than the peak AC input voltage []. n univeral-input application, with the S input line voltage in the 9-5 range, the output voltage ha to be et to about 5. At low line (9 rm ), the witch conduction loe are high becaue the input S current ha the larget value, and the larget tep-up converion i required. he inductor ha to be overized for large S current at low line input, and for the highet volt-econd applied throughout the input-line range. A a reult, a boot converter deigned for univeral-input PFC application i heavily overized compared to a converter deigned for a narrow range of input line voltage. Furthermore, becaue of the large energy torage filter capitor at the output, the boot converter ha inruh current problem that can only be mitigated uing additional component. n univeral-input PFC application, the capability of providing both tep-up and tep-down converion i attrtive becaue the output DC voltage can be et to any value. However, conventional ingle-witch buck-boot topologie, including the plain buck-boot, flybk, SEPC, and Cuk converter [, ] have greatly increaed component tree, component ize, and reduced efficiency compared to the boot converter. g b) Fig.. Caded two-witch buck-boot topologie: a) boot-buckcaded, b) buck-boot-caded L Q Q C D Fig.. Boot nterleaved Buck-Boot Converter (BoBB). he boot and the buck converter are known to have the potential for highet efficiency and lowet component tree if their converion charteritic meet the input/output pecification. Baed on thi obervation, our objective wa to contruct a converter topology with two independently controllabe witche uch that it can operate a a buck or a a boot in portion of the AC line cycle. Such two-witch topologie could offer higher efficiency, reduced ize, and ability to arbitrarily chooe the DC output voltage. L D C hi work i upported by Philip earch, Briarcliff anor, NY, through Colorado Power Electronic Center

2 i L L D ABLE i L BASC FUNONS N BOOS AND BUCK ODES Q i Q i L i Q L C Q L C L i L C C Boot ode Buck ode Q tive alway off Q alway on tive /( d ) d L d d o L / o / o C g. OPEANG ODES AND SEADY-SAE CHAACESCS OF HE BOOS NELEAED BUCK-BOOS CONEE D Fig.. Operating mode of BoBB: boot, buck. wo imple example illutrated in Fig. and are the conventional cade connection of the buck and the boot converter [, 5]. hee converter can operate a a boot when Q i alway on, and a a buck when Q i alway off. n continuou conduction mode, the overall voltage converion ratio i: d d ) () ( where d and d are the duty ratio of Q and Q repectively. We have found that other two-witch topologie with buckboot charteritic are poible by adopting the converter ynthei approh decribed in [6]. One of thee new DC- DC converter i the Boot nterleaved Buck-Boot (BoBB) converter hown in Fig.. Operating mode and baic teady-tate charteritic of thi converter are decribed in Section. Operation of the BoBB converter a a low-harmonic rectifier i dicued in Section. he reult for tranitor and inductor conduction loe are derived in thi ection. Comparion in term of component tree, component conduction loe and magnetic ize among the new two-witch topology and boot, ingle-witch buck-boot, and cade connection of buck and boot converter are preented in Section. Section decribe a prototype of the new converter operating a a PFC rectifier with univeral-line input. Experimental reult are provided for both high-line and low-line input. he propoed Boot-nterleaved Buck-Boot (BoBB) converter i hown in Fig.. Unlike the caded topologie, the boot witch cell (Q and D ) i interleaved with the buck witch cell (Q and D ). n continuou conduction mode (CC), the converter ha the following overall voltage converion ratio: d + d ) () ( d f Q i alway on, the converter operate in boot mode, which i hown in Fig.. he average voltage on C i zero. n thi mode, the input current i divided through L and L. A a reult, the total S current in L and L i maller than the current in a ingle inductor. f Q i alway off, the converter operate in the buck mode a hown in Fig.. L and C form a low-frequency filter. he average current through L and C i zero and the voltage on C i equal to the difference between the input and the output voltage. he inductor L in the buck mode take the ame role a the inductor in the imple buck converter. he baic teady-tate reult for both mode of operation are ummarized in ABLE.. OPEAON OF HE BOBB CONEE AS AN DEAL ECFE n thi ection, we analyze operation of the BoBB converter a a low-harmonic rectifier. Expreion for S current of both tranitor and inductor, and volt-econd of inductor are derived o that conduction loe and magnetic ize can be evaluated. n PFC application, the rectified input voltage i: v g in( ϖ t) ()

3 t i deired that the output voltage i regulated at a contant voltage and that the input current i g i proportional to the input voltage: vg ig () where the emulated reitance i contant for a given output power. Fig. how the waveform of the input and the output voltage in one half of a line period, for the cae when the output voltage i choen to be lower than the peak of the input voltage. he converter operate in boot or buck mode cording to the condition of the input and the output DC voltage. n the following analyi, CC operation i aumed. A. Boot mode n the time period [, t m ], hown in Fig., the input voltage i lower than the output voltage, the boot witch cell (Q, D ) i tive, and the buck cell (Q, D ) i intive (Q i alway on). n quai teady-tate operation, the duty ratio of the tranitor a function of time are: d d he average inductor current are: i L il When Q i conducting, it current i the um of the two inductor current. n the buck mode, Q i alway off, and the current through L equal to a mall current ripple. herefore, the S current of Q and L are found from (5) and (6) in the boot mode. he reult are given by (7) and (8) repectively: Q, rm [ d ( i + i ) ] e ( L L e dt (5) (6) (7) ) boot d, d / t m ( L, rm ) he volt-econd applied to L and L during a witching period are the ame a the volt-econd applied to the inductor in a imple boot converter, and are given by v d v g ( in where i the witching period. B. Buck mode d ( ω t)) n the time period [t m, /], where i the line period, the intantaneou input voltage i greater than the output voltage, the buck cell become tive and the boot cell goe intive (Q i alway off). L and C form a low frequency filter between the input and the output. hey have inignificant effect in quai teady-tate operation. he duty ratio of Q and Q can be expreed a: d d( t) he inductor current are: i L t m / d Boot Buck Boot Fig.. ctified input voltage and DC output voltage waveform, duty ratio of the boot and the buck cell in the BoBB converter operated a a low-harmonic rectifier. (8) (9) () il () t t

4 ABLE COPONEN S CUEN A LOW LNE AND HGH LNE in,rm () Q,rm (A) Q,rm (A) L,rm (A) L,rm (A).5.5 ranitor() Conduction Loe Compared to Boot Converter BoBB and boot-buckcaded ingle-witch buck-boot buck-bootcaded.5 o, P o W ABLE COPASON OF SWCH OLAGE SESSES Q Q D D Boot o o nductor() Conduction Loe Compared to Boot Converter o() BoBB ingle-witch buck-boot buck-bootcaded boot-buckcaded Single-witch buck-boot + o + o he duty ratio of Q and Q during one half of a line cycle are plotted in Fig.. he tranition between the boot and buck mode are continuou. Both Q and L are conducting current in both boot and buck mode, and the S current are found from (5), (6), and (): Q, rm L, rm Buck-boot-caded o o Boot-buck-caded o BoBB o 8 o : output DC voltage, : input peak voltage o / [ d( il + il ) ] bootdt + [ dil ] e dt + / in ( ωt) dt + eo / buck () ω in ( t) () in () i the load reitance. he volt-econd applied to L during a witching period are the ame a thoe on the inductor of a imple buck converter: v ( d ) ( ) () he volt-econd applied to L are cloe to zero in the buck mode. A an example, the component S current are evaluated and hown in ABLE for two different line.. PEFOANCE COPASONS n thi ection, the BoBB converter i compared to the boot, the ingle-witch buck-boot, and caded buck-boot topologie in term of witch voltage tree, conduction loe, and ize of magnetic. All reult are obtained under the aumption that the converter operate in continuou conduction mode (CC). A. Switch voltage tree Fig. 5. Wort-cae tranitor conduction loe comparion wort-cae inductor conduction loe comparion he comparion of wort-cae witch voltage tree i ummarized in able. he output voltage o in the boot converter mut be greater than the maximum peak input voltage, while in all buck-boot converter, the output voltage can be arbitrarily et to any value. All two-witch topologie, including the BoBB converter, have lower voltage tree than the ingle-witch buck-boot converter, o(v)

5 . v in9rm inrm in5rm. v in9rm inrm in5rm. v in9rm inrm in5rm adian adian adian (c) Fig. 6. he volt-econd applied to the inductor boot, ingle-witch buck-boot, (c) two-witch buck-boot and have almot the ame voltage tre a the boot converter (at the expene of more witching device). B. ranitor conduction loe n thi comparion, we aume that all device have the ame on-reitance, and o we compare the total tranitor S current defined a the um of the quare of the individual tranitor S current. n prtice, for the ame die ize, the on-reitance for the tranitor in ingle-witch buck-boot converter would be higher becaue of the higher voltage rating. he wort cae for witch conduction loe occur at the minimum line input (9rm). Switch conduction loe for all buck-boot topologie are found a function of the DC output voltage and normalized to the witch conduction loe in a boot converter operating with fixed DC output voltage equal to 5. he reult are hown in Fig. 5. he propoed converter and the bootbuck-caded converter have the total tranitor conduction loe very cloe to the boot converter, and much maller loe than in the ingle-witch buck-boot or the buck-bootcaded converter. For example, at output, the tranitor conduction loe in the ingle-witch buck-boot converter and the buck-boot-caded converter are.78 and.5 time of the tranitor conduction loe in the new topology. voltage, the lo can be a low a 5% of the inductor conduction lo in the boot converter.. olt-econd applied to the inductor he volt-econd applied to the inductor in the inglewitch buck-boot converter are given by (5). For a twowitch buck-boot converter, an inductor can play the role a part of a low-frequency filter in one of the mode. n thi cae, the volt-econd applied during a witching cycle are almot zero. When the input voltage i lower than the output voltage, the inductor operate a in a boot converter and the volt-econd applied follow from (9). When the input voltage i greater than the output voltage, the inductor operate a in a buck converter, and the volt-econd applied follow from (). v + in ω t (5) he total volt-econd applied to the inductor for the boot, ingle-witch buck-boot and two-witch buck-boot converter are plotted in Fig 6. a function of time over one half of the line cycle. hree curve are hown, baed on different rm input voltage and for a fixed witching C. Comparion of magnetic L f Q L D Wort-cae inductor copper loe and volt-econd applied to inductor are two ftor that determine the inductor ize. C f L C C Q D. nductor conduction loe he wort-cae inductor copper lo alo occur at the minimum AC line input. he reult for copper loe a function of the dc output voltage, normalized to the copper loe in the boot converter with fixed o 5, are hown in Fig. 5. Again, the ame reitance i aumed for all inductor, o that total S current are compared. he new converter ha ignificantly lower loe than the other buckboot topologie; and by proper election of the output DC Current Shaping oltage Compenator control Dual PW Driver Controller Fig. 7. Experimental BoBB converter, L.mH, L mh, C.5uF, C 5uF, fkhz, o

6 ax(d ).9 d + control d control - v control control t -+ o / Fig. 8. Duty ratio a function of control, control in half line cycle Fig. 9. ctified input voltage and control voltage control : rm low-line input, rm high-line input. Ch: /div, Ch: 5m/div Efficiency in,rm Fig.. Efficiency v line input Fig.. ctified input voltage and input line current: rm low-line input, rm high-line input Ch: /div, Ch:.5A/div

7 frequency of KHz. For ingle-witch and two-witch buck-boot converter, the output voltage i et to 5, while the boot dc output voltage i 5. he peak voltecond applied to the inductor for all two-witch buckboot converter ha the mallet value of.8e - (v), compared to.8e - (v) for all ingle-witch buck-boot converter, and.5e - (v) for the boot converter. A a reult of low inductor conduction loe and low peak volt-econd applied, the BoBB topology ha the potential for maller inductor ize compared to other buck-boot topologie and the boot converter.. EXPEENAL ESULS An experimental prototype (Fig. 7) ha been built to verify feaibility of the propoed converter. L and L are elected o that the converter operate in CC in both boot and buck mode at full load. A ingle control voltage control i ued to produce the witch control ignal with the duty ratio d for the witch Q and d for the witch Q a hown in Fig. 8. he teady tate value of control a a function of time i hown in Fig. 8. he control voltage i the input to a dual PW circuit that output drive ignal for Q and Q. he experimental waveform of control i hown in Fig. 9. Average current control i applied to hieve PFC operation. Experimental waveform are hown in Fig 9. he output power i W. n Fig., the input line voltage ha low rm value rm and the converter operate in the boot mode alway. he efficiency i 9.8% and the total current harmonic ditortion i.9%. he waveform of Fig. are for high input (rm) and converter work in the boot and buck mode in different part of the line period. he efficiency i 9.8% and the total current harmonic ditortion i.6%. Fig. how the rectifier efficiency a a function of the input line S voltage. Efficiency of over 9% i hieved throughout the line voltage range (9rm-6rm).. CONCLUSONS A new two-witch topology, named Boot nterleaved Buck-Boot (BoBB) converter, ha been propoed for univeral-input PFC application. he new converter ha advantage of low voltage tree, low witch and inductor conduction loe, potential for mall inductor ize, and the ability to et the output dc voltage arbitrarily. Experimental reult are provided to verify the validity of the new topology. High efficiency (over 9% throughout the whole line voltage range), and low current harmonic ditortion at both high and low line input are demontrated. EFEENCES []. Erickon, Fundamental of Power Electronic, Kluwer 997, ch7. [] D.S.L. Simonetti, J.Sebatian, F.S.do i and J.Uceda,"Deign criteria for SEPC and CUK converter a power ftor preregulator in dicontinuou conduction mode," EEE ECON9, 99, pp8-88. [].Erickon,.adigan, and S.Singer," Deign of a imple high power ftor rectifier baed on the flybk converter," EEE APEC9, 99, pp [] O. Lopez, L. icuna,. Catilla, J. ata and. Lopez, "Slidingmode-control deign of a high-power-ftor buck-boot rectifier," EEE ran. ndu. Elec., ol. 6, No., June 999, pp.6-6. [5].C.Ghanem, K. Al-Haad, and G.oy," A new control trategy to hieve inuoidal line in a cade buck-boot converter," EEE ran. ndu. Elec., ol., pp. -9, ay 996. [6] D.Zhou, "Synthei of PW Dc-to-Dc Power Converter, Ph.D. thei, California ntitute of echnology, October 995