A novel single-stage constant-wattage high-power-factor electronic ballast

A Novel Single-Stage Constant-WattageHigh-Power-Factor Electronic BallastJ.Marcos Alonso,Member,IEEE,Antonio J.Calleja,Associate Member,IEEE,Emilio L´o pez,Member,IEEE, Javier Ribas,Student Member,IEEE,and Manuel Rico-Secades,Member,IEEEAbstract—A novel single-stage high-power-factor electronicballast is presented in this paper.The ballast is obtained from the integration of a buck–boost converter and a half-bridge LC resonant inverter.The ballast features lamp power regulation against line voltagefluctuations together with high power factor and dimming capability.The steady-state analysis of the ballast is performed and a low-frequency model of the input stage is derived.A design example,including closed-loop circuitry,is also presented.Finally,some experimental results from a laboratory prototype are shown.Index Terms—Constant-wattage feature,fluorescent lamps, high-frequency operation,power-factor correction,single-stage ballast.I.I NTRODUCTIOND ISCHARGE lamps are a source of light in which light isproduced by the radiant energy generated from a gas discharge.Most gas discharge lamps must be operated in series with a current-limiting device.This auxiliary,commonly called ballast,limits the current to the value for which each lamp is designed.It also provides the required starting and operating voltages.Fig.1shows two traditional ballasts used to supply dis-charge lamps.The simplest ballast is shown in Fig.1(a);it consists of an electromagnetic inductance placed in series with the lamp.The only function of this ballast is to limit the current delivered to the lamp.Normally,a capacitor is placed across the line input,in order to both increase the input power factor and decrease the input current under starting and operating conditions.Although this resulting ballast is economical and small,it presents the main shortcoming of little regulation forfluctuations in line voltage.For example,a5%change in line voltage would cause a10%change in lamp wattage [1].Therefore,this ballast is not recommended where line fluctuations exceed5%.Fig.1(b)shows the so-called constant-wattage autotrans-former(CWA).This ballast consists of a high-reactance au-totransformer with a capacitor in series with the e of the capacitor allows the lamp to operate with better wattage stability when the line voltagefluctuates.For example,a5% change in line voltage would result in only a2%change in lamp wattage.This ballast is used when the line voltage is expected to vary more than5%[1].Manuscript received July11,1998;revised April16,1999.Abstract published on the Internet August20,1999.The authors are with DIEECS—Tecnolog´ıa Electr´o nica,Universidad de Oviedo,33204Gij´o n,Spain(e-mail:marcos@ate.uniovi.es).Publisher Item Identifier S0278-0046(99)08480-4.(a)(b)Fig.1.Traditional ballasts for discharge lamps.(a)Inductive ballast.(b)CWA.Although electromagnetic ballasts present great simplicityand low cost,they have to operate at line frequency,thusshowing high volume and weight,as well as low efficiency.Therefore,high-frequency(HF)electronic ballasts are beingused nowadays to supply discharge pared withtraditional electromagnetic ballasts,electronic ballasts canprovide higher efficiency,output power control(dimming),high-quality lighting,longer lamp life,and lower volume[1],[10].The introduction of recent regulations for harmonic currentemissions from electronic equipment connected to the mains,such as IEC-1000-3-2[2],has imposed a new requirementto electronic ballast.It is necessary to implement electronicballast with high power factor,typically,over0.9,and withlow total harmonic distortion,typically,below30%.Theprecise limits for each harmonic can be obtained from[2].With the harmonic content requirements introduced by theregulations,the typical passive solutions to improve the inputpower factor can hardly be employed.This makes necessarythe use of active solutions and,consequently,an importantincrease in the ballast cost results.Fig.2(a)shows a typicalelectronic solution to obtain a high-input power factor by usingan upstream power-factor-correction(PFC)stage and an HFinverter.The PFC stage generates a dc voltage level at theinput of the HF inverter,assuring a high-input power factor. 0278–0046/99$10.00©1999IEEE(a)(b)Fig.2.High-power-factor electronic ballasts.(a)Two-stage ballast.(b) Low-cost single-stage ballast.This stage also regulates the dc-bus voltage against line voltage fluctuations,thus providing constant-wattage operation,as in the CWA ballast.In spite of its good features,this arrangement presents a high cost,due to the two-stage configuration,which makes it necessary to duplicate both components and control circuitry.Cost is one of the main drawbacks of electronic ballasts when compared with electromagnetic ballasts.Therefore,it is very important to reduce the overall cost of electronic ballasts to make them competitive.Fig.2(b)shows a single-stage electronic ballast,where both PFC stage and HF inverter have been integrated in a single-stage ballast.This new technique of integrating several power stages into a single stage is pro-voking a great deal of interest,in particular,in implementing low-and medium-power ballasts[3]–[7].In this paper,a new single-stage high-power-factor elec-tronic ballast is presented.The ballast is obtained from the integration of the buck–boost converter and the half-bridge inverter.The operation of the buck–boost converter in dis-continuous conduction mode(DCM)provides unity power factor with both constant frequency and duty cycle.The buck–boost topology in DCM assures high power factor,main-taining relatively low voltage stress across the switches when compared with the boost PFC topology.Also,using a very simple control circuit,the output voltage of the buck–boost converter can be regulated against line voltagefluctuations, thus providing constant wattage in the lamp.The resulting topology is a low-cost single-stage constant-wattage high-power-factor electronic ballast.The results from a laboratory prototype supplied from a wide input voltage range(180–260 V(a)(b)Fig.3.Derivation of the single-stage ballast.(a)Two-stage configuration.(b)Proposed single-stageballast.Fig.4.Equivalent circuits of the proposed ballast during one cycle of operation.As can be seen in Fig.5,the buck–boost semistage is op-erated in DCM in order to provide an average input current proportional to the sinusoidal input voltage,thus achieving high-input power factor.The half-bridge semistage is operated at a switching frequency above the resonant frequency,thusthe resonant currentis lagged and zero-voltage-switching (ZVS)is provided for the turn-on of transistor Q1,whereas transistor Q2is turned on with zero current,as can be seen inFig.5.V oltage and current waveforms of the proposed ballast.Fig.5.Also,Fig.5shows how the duty cycle of transistor Q2can be modified by adjusting its turn-on instantwithin the timeintervaland 0.5.If the converter is operatedwith a duty cycle below this minimum value,a new operating mode appears and thevoltage(1).Mode III:Q1OFF ,Q2ON,.For both modes,equations are thefollowing:(4).Mode V:Q1ON ,Q2OFF,.For both modes,equations are thefollowing:(7)(10)is the duty cycle of transistor Q2,100%efficiency for the buck–boost semistage,the steady-statevoltageand(21)per-unit inductorcurrent(22)inductor currentphaseare the normalized frequency and load,respec-tively.The following base values have beenused:(24)In order to determine the operating point of the buck–boostsemistage,the inverter input resistance must be obtained.Thisresistance can be calculated asfollows:andincreasesand.For the buck–boost semistage,it is also important to deter-mine the duty-cycle range of operation,which,in turn,definesthe admissible variation of the inputvoltageto0.5,allowing the regulation of the output voltage.The nominalduty cycle must be selected between the minimum value and0.5.The selection of the nominal duty cycle provides also therange of regulation above and below the nominal point.Sincethe bulk capacitor voltage is proportional to the duty cycle,the total regulation range is givenbyandfor the higher values ofthe normalized switchingfrequency.In the previous analysis,a complete study of the ballast op-eration has been performed,and results are given by(21)–(29).At closed-loop operation,voltage(a)(b)Fig.6.(a)Normalized input resistance of the half-bridge semistage.(b) Minimum duty cycle of the buck–boost semistage.and the minimum duty cycle for each dimming level can be obtained.IV.L OW-F REQUENCY M ODELThe low-frequency model of the proposed ballast is shown in Fig.7.The input of the buck–boost semistage is modeled as a lossfreeresistor(30)The input power is transferred to the output by the currentsource.Then,the instantaneous value of the outputcurrent source willbe(32)Fig.7.Low-frequency model of the buck–boostsemistage.being the dc value in the followingexpression:(38)withFollowing the same procedure,the transfer function between the output voltage and the instantaneous line peak voltage can be obtained from(34)(40)with/50Hz,and afluorescent lamp PLC-26W fromPhilips is used.The lamp is tested at HF(around25kHz)andthe following data aremeasured:)is0.375;with this value,the minimum busvoltageVmHwill be obtained for the highvalues of the input voltages.The study of the ballast operatingwith duty cycle lower than the minimum value in order toincrease the regulation range represents an interesting subjectfor future work.Regarding the buck–boost semistage,the design includesthe reactiveelementsmHparameter iscalculated asfollows:).Below this value,the CCM operation mode begins toappear and the input power factor begins to decrease.Thecapacitance(53)(a)(b) Fig.8.(a)Electric diagram of the implemented regulator.(b)Bode diagrams. The attenuation of the control circuit should also be con-sidered.The peak-to-peak value of the sawtooth oscillator is(54)following expression:(a)(b)Fig.9.(a)Simplified control circuit.(b)Detailed electric diagram of the laboratory prototype.Fig.10.Measured main voltage and current (90V/div,0.15A/div,4ms/div).Fig.11.Measured lamp voltage and current waveforms (60V/div,0.8A/div,10 s/div).The power stage has been implemented following the elec-tric diagram of Fig.3(b).Transistors Q1and Q 2are MOSFET IRF840and all diodes,including the main rectifier,are BA157.The cores usedforare E25/N27and dc blockingcapacitanceand 24W.Themeasured efficiency was around 85%.Finally,Fig.12illustrates the time response of the out-put voltage at closed-loop operation for a step-up and step-down transient in the peak line voltage.An HP-6812power source/analyzer programmed with a 500-V/s slew rate was used.As can be seen,the time constant is quite low,about 500ms,as expected for this kind of converter.However,the response of the lamp luminous flux is still slower and no variation is observed during the line voltagetransients.Fig.12.Response of voltage V O at closed-loop operation for a step-up and step-down of peak line voltage V g (50V/div,500ms/div).VII.C ONCLUSIONA new single-stage high-power-factor electronic ballast has been presented in this paper.The ballast is generated from the integration of a buck–boost converter and a half-bridge LC resonant inverter.The buck–boost converter is used to provide unity power factor and the resonant inverter ignites and supplies the lamp at the nominal operating point.The steady-state analysis of the ballast has been presented and a low-frequency model of the input stage is ing the results of the performed analysis,a design procedure for a 24-W fluorescent lamp is performed.Some experimental results from a laboratory prototype are presented.The ballast features lamp power regulation against line voltage fluctuations together with high power factor and dimming capability.The dimming feature can be implemented in two ways.A first solution would be the use of the duty cycle as control variable in order to change the lamp power;this will probably provide a very small dimming range and also disturb the lamp power regulation against line voltage variations.The second solution would be the use of the switching frequency as control variable;in this case,the different duty-cycle ranges at each dimming level should be calculated using (29)in order to maintain the line regulation.R EFERENCES[1]IES Lighting Handbook ,Illuminating Engineering Society of NorthAmerica,New York,NY,1984.[2]Standards on Electromagnetic Compatibility (EMC),Part 3,Section 2:Limits for Harmonic Current Emissions ,IEC 1000-3-2(1995-03),Apr.1995.[3]M.Madigan,R.Erickson,and E.Ismail,“Integrated high quality rectifierregulators,”in Proc.IEEE PESC’92,1992,pp.1043–1051.[4]T.F.Wu and T.H.Yu,“Off-line applications with single-stage convert-ers,”IEEE Trans.Ind.Electron.,vol.44,pp.638–647,Oct.1997.[5] E.Deng and S.Cuk,“Single stage,high power factor,lamp ballast,”inProc.IEEE APEC’94,1994,pp.441–449.[6] C.Blanco,J.M.Alonso,E.L´o pez,A.J.Calleja,and M.Rico,“Asingle-stage fluorescent lamp ballast with high power factor,”in Proc.IEEE APEC’96,1996,pp.616–621.[7]J.M.Alonso,A.J.Calleja,E.L´o pez,J.Ribas,F.J.Ferrero,and M.Rico,“Analysis and experimental results of a single-stage high-power-factor1158IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS,VOL.46,NO.6,DECEMBER1999 electronic ballast based onflyback converter,”in Proc.IEEE APEC’98,1998,pp.1142–1148.[8]P.R.K.Chetty,“Modeling and design of switching regulators,”IEEETrans.Aerosp.Electron.Syst.,vol.AES-18,pp.333–334,May1982.[9]J.M.Alonso,A.J.Calleja,F.J.Ferrero,E.L´o pez,J.Ribas,and M.Rico,“Single-stage constant-wattage high-power-factor electronic ballast withdimming capability,”in Proc.IEEE PESC’98,1998,pp.2021–2027.[10]M.K.Kazimierczuk and W.Szaraniec,“Electronic ballast forfluores-cent lamps,”IEEE Trans.Power Electron.,vol.8,pp.386–395,Oct.1993.[11]R.L.Steigerwald,“A comparison of half-bridge resonant convertertopologies,”IEEE Trans.Ind.Electron.,vol.35,pp.174–182,Apr.1998.[12]M.K.Kazimierczuk,W.Szaraniec,and S.Wang,“Analysis of parallelresonant converter at high Q L,”IEEE Trans.Aerosp.Electron.Syst.,vol.27,pp.35–50,Jan.1992.[13]M.K.Kazimierczuk and D.Czarkowski,Resonant Power Converters.New York:Wiley,1995.J.Marcos Alonso(S’94–A’96–M’98)was born in Gij´o n,Spain,in1967.He received the M.Sc.and Ph.D.degrees in electrical engineering from the University of Oviedo,Gij´o n,Spain,in1990and 1994,respectively.In1990,he joined the Electrical and Electronic Department,University of Oviedo,where he is cur-rently an Associate Professor.His research interests include high-frequency electronic ballasts,discharge lamp modeling,power-factor-correction topologies, high-frequency switching converters,and industrial controlsystems.Antonio J.Calleja(S’97-A’99)was born in Le´o n,Spain,in1964.He received the B.Sc.and M.Sc.de-grees from the University of Oviedo,Gij´o n,Spain,in1985and1987,respectively.Since1995,he has been an Associate Professor atthe University of Oviedo.His research interests areswitching-mode power supplies,high-power-factorrectifiers,and high-frequency electronicballasts.Emilio L´o pez(M’97)was born in Oviedo,Spain,in1965.He received the M.Sc.degree in electricalengineering from the University of Oviedo,Gij´o n,Spain,in1992.Since1993,he has been an Assistant Professor atthe University of Oviedo.His research interestsinclude industrial and power high-frequencyelectronic ballasts,discharge lamp modeling,high-frequency switching converters,power-factor-correction converters,and industrial controlsystems.Javier Ribas(S’97)was born in Milwaukee,WI,in1971.He received the M.Sc.degree from the Universityof Oviedo,Gij´o n,Spain,in1995.Since1996,he has been an Associate Professor atthe University of Oviedo.His research interests areelectronic lighting systems,switching-mode powersupplies,and high-power-factorrectifiers.Manuel Rico-Secades(M’89)was born in Oviedo,Spain,in1961.He received the M.Sc.and Ph.D.degrees in electrical engineering from the Univer-sity of Oviedo,Gij´o n,Spain,in1986and1989,respectively.Since1986,he has been with the Electrical andElectronic Department,University of Oviedo,wherehe is currently a Full Professor.His research in-terests include industrial and power electronics,inparticular,resonant converters,electronics ballasts,dc-to-dc converters,and industrial control.Dr.Rico-Secades is a member of the Illuminating Engineering Society ofNorth America and European Power Electronics Society.。