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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 21, NO. 4, JULY 2006 959

Programmable PFC Based Hybrid Multipulse PowerRectifier for Ultra Clean Power ApplicationLuiz Carlos Gomes de Freitas, Member, IEEE, Marcelo G. Simões, Senior Member, IEEE,

Carlos Alberto Canesin, Member, IEEE, and Luiz Carlos de Freitas, Member, IEEE

Abstract—A novel hybrid three-phase rectifier is proposed.It is capable to achieve high input power factor (PF) and lowtotal harmonic input currents distortion (THD ). The proposedhybrid high power rectifier is composed by a standard three-phasesix-pulse diode rectifier (Graetz bridge) with a parallel connectionof single-phase Sepic rectifiers in each three-phase rectifier leg.Such topology results in a structure capable of programming theinput current waveform and providing conditions for obtaininghigh input power factor and low harmonic current distortion. Inorder to validate the proposed hybrid rectifier, this work describesits principles, with detailed operation, simulation, experimentalresults, and discussions on power rating of the required Sepicconverters as related to the desired total harmonic current distor-tion. It is demonstrated that only a fraction of the output poweris processed through the Sepic converters, making the proposedsolution economically viable for very high power installations,with fast investment payback. Moreover, retrofitting to existinginstallations is also feasible since the parallel path can be easilycontrolled by integration with the existing dc-link. A prototypehas been implemented in the laboratory and it was fully demon-strated to both operate with excellent performance and be feasiblyimplemented in higher power applications.

I. INTRODUCTION

I N ORDER to improve the distribution of electrical energyand to provide agreement with the power quality standards,

special rectifier structures have been currently used as front endenergy processors. But three-phase diode-bridge rectifiers con-tinue to be very popular in several industrial and rural applica-tions, where an intermediate dc link provides energy for otherelectronic circuits. However, such standard diode-bridge recti-fiers do not meet harmonic current content restrictions, as im-posed by several international standards such as IEC 61000 andIEEE 519 [1]–[6]. Thus, expensive and bulky passive filters orcomplex power factor correction (PFC) and active filter struc-tures must be installed to compensate the inherent harmonic cur-rent distortion. Therefore, in the past few years there has beena tremendous interest in achieving low harmonic current distor-tion in three-phase ac to dc converters, motivating the develop-ment of several front-end multipulse rectifier solutions [7]–[11].

Multipulse rectifiers have been typically applied in three-phase applications for mitigation of the input current harmonic

Manuscript received January 26, 2005; revised June 13, 2005. This work wassupported by CAPES, FAPEMIG, CNPq, FAPESP, and the National ScienceFoundation. Recommended by Associate Editor F. Z. Peng.

L. C. G. de Freitas and L. C. de Freitas are with the Faculty of Electrical Engi-neering (FEELT), Federal University of Uberlandia (UFU), Uberlandia 38400-902, Brazil.

M. G. Simões is with the Engineering Division, Colorado School of Mines(CSM), Golden, CO 80401-1887 USA (e-mail: [email protected]).

C. A. Canesin is with the Faculty of Engineering, São Paulo State University(UNESP), São Paulo 15385-000, Brazil.

Digital Object Identifier 10.1109/TPEL.2006.876859

content. However, these converters need magnetic circuits suchas multiphase transformers, interphase transformers, currentbalancing transformers, or harmonic blocking transformers,resulting in customized equipments which are complex, heavy,bulky, and expensive [12]–[16]. In addition, elimination ofinterphase transformers is particularly desirable when thereis preexisting harmonic voltage content in the three-phasepower source. Such harmonic voltages cause fluctuations inthe dc output voltage, leading to further design complexities[12]–[14], [17].

A simplified transformer concept for multipulse rectifier ap-plication was proposed in order to improve current sharing be-tween two rectifiers [18] and eliminate the use of an interphasetransformer. However, to compose the input line current wave-form, a power transformer with a rating of 1.16 (whereis the nominal value of output power) was necessary. Such a de-vice contributes for increased cost, weight, and size of the struc-ture. In the same context, in [19] the authors proposed an activemultipulse rectifier system using Boost converters to shape theinput line current to sinusoidal waveform and to improve cur-rent sharing, without the use of an interphase transformer. Inthis case, a controlled dc output voltage is achieved through theuse of two Boost converters processing 50% of the output power

and, a power transformer with a rating of 0.6169 ,limiting its application and increasing the cost, weight, and sizeof the proposed structure.

A novel approach that overcomes such disadvantages ispresented in this paper. The authors propose a new structurecomposed of a single-phase Sepic rectifier associated in parallelwith each leg of a three-phase six-pulse diode rectifier resultingin a programmable input line current waveform structure.Thus, controlled rectifiers operating in parallel to a standardthree-phase diode rectifier are proposed in contrast to expen-sive and complex schemes. The overall converter behaves asa current source controlled with a suitable strategy, i.e., theimposition of a suitable input line current waveform in orderto provide low THD (total harmonic distortion of current)and high input power factor. The system is a programmablePFC based hybrid multipulse power rectifier (PFC–HMPR)deploying Sepic converters. The proposed structure is depictedin Fig. 1. It is a very compact structure and somewhat easy toimplement when compared to the expensive and complex mul-tipulse schemes. The proposed system is capable of providingultra clean power without using multiphase transformers,interphase transformers, current balancing transformers, or har-monic blocking transformers. This new topology is describedand analyzed in the next section.

It is important to emphasize that the proposed hybrid multi-pulse power rectifier deploying Sepic rectifiers in parallel to

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Fig. 1. New three-phase PFC hybrid multipulse power rectifier (PFC-HMPR).

each leg of such a standard six-pulse diode rectifier does notneed connection to the neutral point. Standard operation of theSepic rectifiers is achieved when they are interconnected. Al-though it might be advisable connect the Sepic rectifiers to theneutral point for improved performance in conditions where har-monics may want to circulate in the neutral, but the applicationof the proposed structure does not depend on whether or notthere is any neutral point available. The authors are investigatingtowards detailed design guidelines for this proposed structure onimprovements of installations with corresponding neutral har-monic circulation issues improvements.

II. FUNDAMENTAL PRINCIPLES

Fig. 1 shows the PFC–HMPR which is composed by a stan-dard three-phase six-pulse diode rectifier, indicated in the blockdiagram as Rect—1, and single-phase Sepic rectifiers associ-ated in parallel to each diode-bridge rectifier leg. It should beobserved that non-isolated Boost rectifiers are not capable of im-posing input current waveform when operating in parallel con-nection such as indicated in Fig. 1. Thus, the proposed systemhas single-phase Sepic rectifiers, which have been observed tohave the capabilities to impose a desirable input line currentwaveform.

Fig. 2 shows the principle of constructing an input line currentthrough two components and , obtained when the

PFC–HMPR topology operates as a conventional three-phase12-pulse rectifier, which is the focus of this paper.

The current reference is the main controller of the overallcharacteristic of the final input line current waveform, as ana-lyzed in Section IV. The proposed PFC-HMPR allows the im-provement of the input line current by reducing its THD.It is important to notice that, only a fraction of the total output

Fig. 2. Theoretical waveforms for the case of 12-pulse in the line input current.

Fig. 3. Theoretical waveforms for programmable THD in the input linecurrent.

power is required to flow through the Sepic parallel circuits, sup-porting a competitive economic impact. It was experimentallyobserved that for the PFC-HMPR operating as a conventional12-pulse rectifier, just about 20% of the total output power isprocessed by the Sepic rectifiers and a less than 14% inthe input line current can be achieved. Besides, one can observethat a variety of harmonic content restrictions imposed by IEEEstd 519–1992 can be easily meet by the PFC-HMPR presentedin this paper, as one can see in Fig. 3. For example, if a controlledwaveform as indicated in Fig. 3(b) is imposed through the Sepicparallel rectifiers, the input line current , will be built of thecombination of and with a very low (around 5%).In this case, the Sepic converters will supply about 45% of therated power. In conclusion, the proposed PFC–HMPR is ableto operate with a programmable of the input line current

depending on the desired application conditions. Thus,


DE FREITAS et al.: PROGRAMMABLE PFC BASED HYBRID MULTIPULSE POWER RECTIFIER 961

this flexibility is a very good characteristic of the proposed hy-brid power rectifier system when compared to other multipulserectifier structures.

Depending on the kind of application, the proposed hybridrectifier can operate in accordance to the harmonic contentrestrictions of the input line current with the Sepic rectifiersprocessing just the minimum power. Therefore, the wholestructure presents reduced cost, volume and, higher efficiencywhen compared to other multipulse schemes that use multi-phase transformers and interphase transformers, saving energyand attending the IEEE Std. 519–1992 as well. Moreover,the economical benefits of this new topology are extremelyvaluable for high power installations, because around 33%maximum value of rated power will be processed in the parallelcircuits (Sepic rectifiers), in order to reduce the to a verylow value (around 5%). This feature allows higher efficiencyand payback in a very short time for the investment. Moreover,when used in retrofitting applications, the available total ratedpower will increase to 133% of the original output power,with obvious improvements on power quality. In this paper,the authors show the proposed PFC-HMPR operating as aconventional 12-pulse rectifier. The imposition of a sinusoidalinput current waveform is under progress and will be reportedin the future.

III. MOTIVATION TO USE A SEPIC CONVERTER

Boost converters have been traditionally used as front-endwave shaping systems but, in order to be applied as parallelpath of three-phase six-pulse diode bridge rectifier, non-iso-lated Boost converters are not suitable because during the pe-riod of time where the input line voltage of the three-phasepower source is higher than the dc output voltage, the Boostcurrent keep increasing even when the switch is open. In fact,when the Boost switch is open and the freewheeling diode is for-ward biased and connecting the path between Rect-2 and Rect-1,the Boost current flows through the diodes of the three-phasesix-pulse rectifier bridge (Rect-1) and its control is lost, eventu-ally impeding the desired current waveform composition. Thisis the main reason that non-isolated Boost converters are notsuitable for being associated in parallel for the proposed multi-pulse hybrid power rectifier.

On the other hand, Sepic converters behave naturally as aninput current source, allowing that the waveform of the inputcurrent can be imposed with a suitable control strategy. In con-trast to the Boost converter behavior, when the switch isopened ( : 1, 2, 3), the series capacitor of the Sepic converterassures, at any operating conditions, the isolation of those cir-cuits and correspondent decrease of the current flow through theinput inductor. Thus, the imposition of the input current doesnot strongly depend on the level of the output voltage (dclink voltage).

It should be emphasized that for isolated Boost convertersfed through single-phase transformers, there is galvanic iso-lation, as shown in Fig. 4. As a result, such structure is ableto replace Sepic converters, but with the obvious drawbacks(volume, weight and cost) of requiring extra magnetic devices.The authors discuss in [20] the implementation with Boost con-verters, as shown in Fig. 4. The Boost current is confined tothe secondary winding circuit and the dc link voltage is kept

Fig. 4. New three phase PFC hybrid power rectifier (PFC–HPR) deployingboost converters fed through single-phase isolating transformers.

Fig. 5. Proposed control strategy for 12-pulse input line current waveform.

with average value approximately equal to the peak line voltagevalue approximately. This structure is able to replace the Sepicconverters because it can be assured that Boost current will beforced to return through the Boost circuit instead of the three-phase six-pulse rectifier bridge. Hence, the control of the Boostcurrent is no longer lost resulting that the desired input line cur-rent waveform can be achieved. It is important to emphasizethat, even using single-phase isolating transformers, the pro-posed PFC-HMPR deploying Boost converters is still more at-tractive than the multipulse rectifier structures presented in [18]and [19], as described in [20].

IV. PROPOSED CONTROL STRATEGY

The main control circuit objective is to impose the input linecurrent at low THD and high input power factor for the pro-posed PFC–HMPR. Therefore, the control strategy must focuson establishing the best relationship between the input current

1 of the standard three-phase six-pulse diode bridge recti-fier(Rect-1), and the input current 2 of the controlled Sepic



Fig. 6. Simulated 3-kW PFC hybrid multipulse power rectifier (PFC-HMPR): (a) PWM 12-pulse control circuit and (b) power circuit.

rectifiers (Rect-2), in order to achieve a desirable input line cur-rent THD. As example, if a twelve pulses ac current waveformis desired, the control strategy of the controlled Sepic rectifiers(Rect-2) can be established as shown in the diagram of Fig. 5.

In order to compose the waveform of the input line current, a sample of the input line-to-neutral voltage must

be rectified and compared with dc voltage levels in order to gen-erate a synchronized square wave to impose the inputSepic current depicted in Fig. 2. The voltage is thereference current waveform and can be supplied either by analogor digital devices. It was found that, when operating as a con-

ventional 12-pulse rectifier, the lowest input line current THD isachieved when the magnitude of the current (Rect-2) is 33%of the magnitude of the current (Rect-1). Therefore, thereference voltage must be multiplied by a fraction of thecurrent of Rect-1 providing a reference signal equal to

, where k is equal to of the dc cur-rent through the output inductor filter of the three-phasesix-pulse diode rectifier (Rect-1) for the minimum THD .

In order to generate a PWM reference signal, a sawtoothvoltage waveform is added to the multiplier circuit signal. Fi-nally, the PWM reference signal must be compared with the cur-



TABLE IDESIGNED PARAMETERS AND USED SEMICONDUCTORS

Fig. 7. Input currents i (Sepic)—simulation result.

Fig. 8. Input current i (six-pulse diode rectifier)—simulation result.

rent flowing through the inductor of Sepic converter (Rect-2)to generate the gate-drive signal for switch . Hence, the cur-rent through the inductor will follow the imposed referencethrough a very simple PWM control strategy [21], [22].

A. Simulation Results

In order to analyze the operation of the proposed PFC-HMPR,a digital simulation was performed and then compared with ex-perimental results. Table I shows the system specifications. A12-pulse PWM control strategy was applied in order to controlthe proposed structure, imposing 12-pulse waveform in the lineinput currents. Thus, the proposed control shown in Fig. 5 wasimplemented, and used for simulation analysis. An open loopcontrol strategy, following the principles depicted in Fig. 6 wasimplemented in PSPICE.

The simulation results for the input line current compositionare portrayed in Figs. 7 and 8. Fig. 7 shows the input current

from the controlled Sepic rectifier, considering highly dcinductive filters ( and ).

Fig. 9. Sinusoidal input voltage waveform and 12-pulse line input currentwaveform (i )–line a–simulation result.

Fig. 10. Frequency spectrum of the input line current—simulation result.

Fig. 11. Output voltage (dc link)—simulation result.

Fig. 9 shows the simulation of input voltage and current wave-forms where it can be observed that a 12-pulse input currentwaveform was imposed in the input line current, resulting in aTHD near to 13.7%, for nominal output power. Fig. 10 showsthe frequency spectrum of the input line current , for ratedload. The ripple voltage over the average nominal output voltageis depicted on Fig. 11.

The simulation studies supported the best relationship be-tween the magnitudes of current magnitude and cur-rent to be about 33%. This relationship gives the lowest

of 13.55% for a 12-pulse waveform in the line input cur-rent, as shown in Fig. 12. Fig. 13 shows the power rating ofRect-2 in relation to the total output power. Therefore, one can



Fig. 12. THD of the line input current versus relation (I =I ) in %.

Fig. 13. THD of the line input current versus relation (P =P ) in %.

observe that, processing only 15.29% of the total output power,less than 14% of THD in the line input current is achieved.

B. Experimental Results

After careful simulation study and analysis, a 3-kW three-phase PFC non-isolated multipulse hybrid power rectifier(PFC–HMPR) prototype was implemented and evaluated inlaboratory, in order to validate the proposed structure. Theexperimental setup was built using analog and digital gatecircuitry. Fig. 14 shows the electrical diagram of the imple-mented prototype and details of the electronic circuit used inthe experimental setup to compose the input current of line A. Itshould be noticed that all implemented parameters and devicesare the same from Table I. As one can observe in Fig. 14, asample of the input voltage is rectified and compared with twodc voltages levels for the pulse generator circuit.

The outputs of the comparators are connected to an OR gateresulting a pulsed output voltage with width equal to 3 radand amplitude equal to the comparator supply voltage, and thereference current waveform is obtained. Therefore, the refer-ence current signal is filtered and reduced to unity value in orderto be applied to the input of the signal multiplier circuit. Thesignal multiplier circuit also receives a current signal of thesix-pulse diode rectifier in order to generate a signalproportional to 1/3 of the current . As a result, the ref-erence current signal to be imposed at the Sepic rectifiers is ob-tained at the output of the multiplier circuit.

Finally, the PWM reference generator circuit receives thesignal from multiplier circuit and, with a sawtooth waveform,

Fig. 14. Implemented prototype: PFC three-phase 3-kW hybrid rectifier.

Fig. 15. Input current I (Sepic) 4.7 A/div: Experimental Result.

provides the PWM reference current signal that is comparedwith the current through the inductor of Sepic rectifiers. There-fore, the driving command to the main Sepic switch is providedthrough the gate drive circuit.

The experimental results are shown from Figs. 15 –18. Theyare related to phase A of the power system, corroborating thebehavior of the analyzed simulation results; the other phaseshave similar performance.

Figs. 15–16 show the currents from the controlled Sepic rec-tifier and uncontrolled six-pulse diode bridge rectifier, respec-tively. These currents are responsible to perform the 12-pulsewaveform in the input line current. The experimental line input



Fig. 16. Input current I (six-pulse diode rectifier) 4.7 A/div: experimentalresult.

Fig. 17. Input line current I 4.7 A/div: Experimental Result.

Fig. 18. Frequency spectrum of the input line current I : experimentalresult.

current is shown in Fig. 17, providing conditions to obtain a lowTHD value as expected.

The experimental input line current frequency spectrum isshown in Fig. 18, where an experimental THD of 14.7% wasachieved, resulting in an input power factor (PF) equal 0.989,for rated load. It was verified that the power rating of the par-allel Sepic rectifiers (Rect-2) was about 21% of the total outputpower, which is a very close match to the results obtained in thesimulation analysis.

V. CONCLUSION

This paper introduced a novel three-phase hybrid power rec-tifier capable of achieving nearly unity input power factor withprogrammable input line current THD . The paper presentedcomprehensive analysis, evaluation and design of a system com-posed of single-phase Sepic rectifiers connected to each leg of astandard uncontrolled three-phase six-pulse diode rectifier. Theparallel converters power rating is only a small fraction of thetotal output power supporting a competitive economic impact.Additional analyses were presented to determine the amount ofpower processed by the controlled rectifiers, in order to obtaina given (and desirable) total harmonic distortion in the inputline current . It was verified that for less than15% only 21% of the rated output power had to be processed bythe Sepic rectifiers. Therefore, this proposed structure is recom-mended for high power installations, and retrofitting to existinginstallations is feasible since the parallel path can be easily con-trolled by integration with the existing dc-link. The proposedstructure provided a multipulse ac input line current withoutphase-shift transformers, with simplified design and reducedcost. In addition to the converter analysis and simulation results,experimental results from a 3-kW prototype were presented, inorder to validate the proposed structure and control strategy. Theauthors are working on further developments towards a fullydigital programmable control (using DSP and FPGA devices)for the proposed converter.

REFERENCES

[1] D. A. Paice and R. J. Spreadbury, “Calculating and controlling har-monics caused by power converters,” in Proc. IEEE Ind. Appl. Soc.Annu. Meeting (IAS’89), 1989, pp. 456–463.

[2] D. E. Rice, “A detailed analysis of six-pulse converter harmonic cur-rents,” IEEE Trans. Ind. Appl., vol. 30, no. 2, pp. 294–304, Mar./Apr.1994.

[3] W. F. Ray;, R. M. Davis;, and I. D. Weatherhogg, “The three-phasebridge rectifier with capacitive load,” in Proc. 3rd Int. Conf. PowerElectron. Variable-Speed Drivers, 1988, pp. 153–156.

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[7] G. Spiazzi and F. C. Lee, “Implementation of single-phase boostpower-factor-correction circuits in three-phase applications,” IEEETrans. Ind. Electron., vol. 44, no. 3, pp. 365–371, Jun. 1997.

[8] J. Hahn, P. N. Enjeti, and I. J. Pitel, “A new three-phase power-factorcorrection (PFC) scheme using two single-phase PFC modules,” IEEETrans. Ind. Appl., vol. 38, no. 1, pp. 123–130, Jan./Feb. 2002.

[9] S. Srianthumrong and H. Akagi, “A medium-voltage transformerlessac/dc power conversion system consisting of a diode rectifier and ashunt hybrid filter,” IEEE Tran. Ind. Appl., vol. 39, no. 3, pp. 874–882,May/Jun. 2003.

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[16] M. Kang, B. O. Woo, and P. N. Enjeti, “Autoconnected-elec-tronic-transformer-based multipulse rectifiers for utility interface ofpower electronics systems,” IEEE Trans. Ind. Appl., vol. 35, no. 3, pp.646–656, May/Jun. 1999.

[17] D. A. Rendusara, A. V. Jouanne, P. N. Enjeti, and D. A. Paice, “De-sign considerations for 12-pulse diode rectifier system operating undervoltage unbalance and pre-existing voltage distortion with some correc-tive measures,” in Proc. IEEE Ind. Appl. Soc. Annu. Meeting (IAS’95),1995, pp. 2549–2556.

[18] S. Martinius, B. Halimi, and P. A. Dahono, “A transformer connec-tion for multipulse rectifier applications,” in Proc. Power Syst. Technol.(POWERCON’02), 2002, pp. 1021–1024.

[19] J. Hahn and P. N. Enjeti, “A wide input range active multi-pulsethree-phase rectifier for utility interface of power electronics con-verters,” in Proc. IEEE-Ind. Appl. Soc. Annu. Meeting (IAS’02), 2002,pp. 2514–2519.

[20] L. C. Gomes de Freitas, E. A. A. Coelho, A. P. Finazzi, M. G. Simoes,C. A. Canesin, and L. C. de Freitas, “Programmable PFC based hybridmultipulse power rectifier for utility interface of power electronic con-verters,” in Proc. IEEE Power Electron. Spec. Conf. (PESC’05), 2005,pp. 2237–2243.

[21] L. H. S. C. Barreto, J. B. Vieira, Jr., E. A. A. Coelho, V. J. Farias,and L. C. de Freitas, “The bang-bang hysteresis current waveshapingcontrol technique used to implement a high power factor power supply,”in Proc. Conf. IEEE Telecommun. Energy Conf. (INTELEC’02), 2002,pp. 361–365.

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Luiz Carlos Gomes de Freitas (S’03–M’06) re-ceived the B.S., M.S., and Ph.D. degrees in electricalengineering from the Federal University of Uber-landia (UFU), Uberlandia (MG), Brazil, in 2001,2003, and 2006, respectively.

He is currently with the Industry Division,Centro Federal de Ensino Tecnológico de GoiásUNED-Jataí, where he has been working to establishresearch and education activities in industry appli-cation of power electronics converters. His researchinterests include high-frequency power conversion,

active power-factor correction techniques, multipulse rectifiers, and cleanpower applications.

Marcelo G. Simões (S’89–M’95–SM’98) receivedthe B.Sc. and M.Sc. degrees in electrical engineeringfrom the University of São Paulo, São Paulo, Brazil,in 1985 and 1990, respectively, the Ph.D. degree fromThe University of Tennessee, Nashville, in 1995, andthe D.Sc. degree from the University of São Paulo,São Paulo, Brazil, in 1998.

He joined the faculty of the Colorado School ofMines, Golden, in 2000 and has been working toestablish research and education activities in thedevelopment of intelligent control for high power

electronics applications in renewable and distributed energy systems.Dr. Simões received the NSF Faculty Early Career Development (CAREER)

in 2002. He is serving as IEEE Power Electronics Society IntersocietyChairman, Associate Editor for Energy Conversion and Editor for Intelli-gent Systems of the IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC

SYSTEMS, and Associate-Editor for Power Electronics in Drives of the IEEETRANSACTIONS ON POWER ELECTRONICS. He served as the Program Chair forPESC’05, Power Electronics Specialists Conference, and the Conference Chairfor PEEW’05, Power Electronics Education Workshop, both held in Brazil.He has been actively involved in the Steering and Organization Committee ofthe IEEE/DOE/DOD 2005 International Future Energy Challenge.

Carlos Alberto Canesin (S’87–M’97) receivedthe B.S. degree from São Paulo State University,Ilha Solteira (SP), Brazil, in 1984 and the M.S. andPh.D. degrees from the Federal University of SantaCatarina, Florianópolis (SC), Brazil, in 1990 and1996, respectively, all in electrical engineering.

He started the Power Electronics Laboratory LEPat the UNESP-São Paulo State University-FEIS,where he is currently an Associate Professor. Hisinterests include soft-switching techniques, dc todc converters, switching-mode power supplies,

solar/photovoltaic energy applications, electronic fluorescent ballasts, andactive power-factor correction techniques.

Luiz Carlos de Freitas (S’85–M’92) received theM.Sc and Ph.D. degrees from the Federal Universityof Santa Catarina, Florianópolis (SC), Brazil, in 1985and 1992, respectively.

He has authored a variety of papers in the areas ofsoft-switching, dc–dc, dc–ac, ac–dc converters, elec-tronic fluorescent lamps, and multipulse rectifiersfor clean power systems. Currently, he is with theFederal University of Uberlandia (UFU), Uberlandia(MG), Brazil, where he is a member of the PowerElectronics Research Group.


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