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An Integrated High Quality Rectifier withSliding-Mode Control

E. Rodriguez F. Chan N. Vazquez" J. Beristain J. Arau

CENIDETInterior Internado Palmira, Cuemavaca,Mor., MEXICO sln Apdo. 5-164, CP 62050Tel: +52 (73) 12-23-14, Fax: +52 (73) 18-77-41Email: [email protected]

Abstract. This paper describes an integrated boost-fullbridge rectEfier power factor corrector driven by asliding-mode control. Due to the sliding-mode control,fast regulation of the output voltage is achieved. Inaddition, with this scheme, the major power goesthrough a single stage to the output, while both unitypower factor and fa st dynamic response is obtained,and the eficiency as well as the power density can behigher than in a conventional two cascade stagescheme. A prototype circuit has been built to verijj thisapproach. The control strategy and experimentalresults will be presented.

I. INTRODUCTIONThe reduction of input current harmonics and highpower factor operation is an important requirement forpower supplies due to the arising of new standardsinternational. The traditional power supply scheme byrectifying the ac line voltage and filtering it with abulky capacitor draws pulsating current from the ACline with higher rms current rich in harmonic content.The commonly used approach in AC D C conversion tomeet high power quality requirements is the two-stageapproach. The first stage, usually a switching rectifierwhich has been used in order to improve the powerlevels [ l] or a Boost converter in which its input isshaped to a sinusoidal wave by controlling the inputcurrent, is used to provide an intermediate dc busvoltage. The second stage is the traditional DC/DCconverter, which regulates the output voltage withhigher bandwidth of the feedback control loop andfurthermore presents galvanic isolation for safetyconsiderations.This two-stage approach has two controllers to shapethe input current and tightly regulate the output voltageindependently. However, it suffers from severaldisadvantages. First, adding an extra power stage thecomponent count and consequently the cost is

*Institute Tecnolbgico de CelayaDepartamento de Sistemas e InformaticaAV.Tecnologico y A. Garcia Cubas s/nA.P. 57 Celaya, Gto., MEX ICO, C.P. 38010Tel: +52 (461) 1 75 7.5, Fax: +52 (461) 1 79 79

incremented, and second the power is processed twicewhich may decrease the efficiency.So far, some efforts have been reported in order tosimplify the two-stage PFC approach. Basically, theiraim is to incorporate the two stages into one byallowing them to share the active switch (es). Someexamp les are the Dither IPFC [2], the BIFRE D and theBIBRED [3]. However, these circuits are often used inlow power applications due to the high current stressesin the power switch. For relatively high powerapplications, the designers usually employ parallelswitches or parallel module techniques to solve thermalproblems and to improve: the efficiency, some of theseschemes are reported in b4 - 61.This paper proposes a new single-phase PFC topologyin order to increase the power leve l with high efficiencywithout the necessity of utilizing parallel moduletechniques and without a complex control circuit. Inaddition, this schem e onky uses four switches to providethe PFC and fast dynamic: response.

11. PROPOSEDONVERTERThe proposed converter is shown in Fig. I . Thisscheme consists of an Integrated-Boost-Rectifier (IBR)and a Full-bridge converter sharing power switches.The IBR is used as power factor corrector and the full-bridge converter is used as DC/DC regulator. The IBRreceived the same signals control that the full-bridgeconverter, it is possible due to the IBR operates indiscontinuous conductioin mode (DCM), which a highpower factor is obtained.The control method used to controller the full-bridgeconverter is sliding-mo de control, this con troller allowsto obtain a fast regulation of the output voltage and toreduce th e outp ut filter siize. This con verter operates incontinuous conduction mode (CC M).

0-7803-4489-8/98/$10.001998 IEEE 1649

Authorized licensed use limited to: Mepco Schlenk Engineering College. Downloaded on August 04,2010 at 09:44:55 UTC from IEEE Xplore. Restrictions apply.


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T T I

Vin

LB D1

I D3D5 i +VI

SLIDING-MODE1 CONTROL 1 1The IBR is connected directly to the main utility line,which can be operated in the positive and the negativesemicycle symmetrically. The full-bridge converter isconnected in series with it, but it no is necessary thatthe energy be processed twice. Due to the fact that thefull-bridge converter operates at twice the switchingfrequency with respect the IBR, it is possible to obtainthe input power directly the AC line through LBinductor. The energy stored in L B s transferred directlyto the load by the full-bridge converter. This schemeallows to obtain a high efficiency, due to only between20% to 30 % of the input power is processed by the full-bridge converter directly.

~Figure 1. Circuit of the proposed converterTO O - l:Considering the positive sem icycle, when Q1and Q4 areturned on, the LB inductor stores energy proportionallyto V,,,; D3 and D6 are on and D 1, D2, D4, and D5 , areoff. At the same time, the stores energy in TItransformer by the C1 capacitor voltage is transferredfrom the primary winding to the secondary winding andto the output filter through the diode Do,. Fig. 2a an dFig 3.TO l - 2:

This scheme presents high current stresses in the Q1 andQz power switches due to the IBR operates in DCM, inaddition to both converters share this power switches.The DCM IBR reduce the complexity of the controlstage, but this produces that the efficiency to bereduced however there is two ways to achieve anincreasing in the efficiency. The first one operates theIBR in the boundary between DCM and CCM, and thesecond one, uses IGBTs only in Q 1 and Q 2 powerswitches to reduce the condu ction losses, but due to theswitching frequency is necessary to employ a soft-switched IGBT technique as in [ 7 ] .The use of IGBTsis very attractive for high power application due to thelower conduction losses. Both ways can beimplemented very easily to further improvement in theperformance of this Converter.This topology eliminates the drawbacks of the otherschemes as [4-51, which uses two transformers toachieve a high power factor and fast regulation of theoutput voltage at high power applications.

\

Circuit DescriptionThe proposed converter presents three operation stagesfor each semicycle, which are shown inFig 2.

When Q1 and Q4 are tumed off, the major part of thestored energy in L B is transferred to the bulk C1capacitor through the diode D1, whereas the diodes D2,D3, D4 and Ds are turned off, Fig. 2 e . The other part ofthe stored energy is delivered when Q2 and 43 areturned on, this shown in Fig. 3.TO 2 - 3:When Q2 and Q3 are turned on, T I transformer storesenergy proportionally to the C I capacitor voltage and tothe stored energy by LB inductor through the D3 and D6diodes. It is shown in Fig. 2c and Fig. 3. The storesenergy in T I ransformer is transferred fiom the primarywinding to the secondary winding and to the outputfilter through the diode Do, whereas D,, D,, D,, andD5, re off. In this operation stage the major inputpower is transferred toward the load directly only bythe full-bridge converter.Three operation stages also occur in the negativesemicycle. In this case the input peak current isnegative. The circuit operation during this negativesemicycle is symmetrical to the positive half sem icycle.It is shown in Fig. 2b, 24 an d 2J

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Positive half of the line voltage

- _ _ _ _ _U !

Negative half of the line voltage-L

06

Sliding-Mode 1 j I :I Control Ia) . Q1 and 44 turned on

-Ib). Q1 and 4 4 turned on

Vi"

VO+,ontrolI I -c). 4 2 and Q3 turned on d) . Q2 and 4 3 turned on-- 4 1Sliding-mode I

e). Q l , Q 2 , 4 3 and 4 4 turned off 0.Q 1, Q2 ,Q3 and 4 4 urned offFigure 2. Circuit operation at the positive and negative harfo f the line voltage

111.CONTROLTRATEGYTon TonSystem modeling.The proposed converter can be modeled as a dc/dcbuck converter since the input stage operates in DCM.After the transformer the converter has functionally thesame operation form that the cdcd buck converter,therefore the full bridge clonverter is modeled as a dc/dcbuck converter. Taken account this consideration, thesimplified circuit of the proposed converter is the oneshown in Fig 4.

1 I I r I )

The equations for each position of the sw itch are:D 3\ t F o r u = 1

IO t l t2 t3Figure 3. Energy transferred when Q2 and Q3 urn onat the positive semicycle.

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The control law proposed is:U = Ue q + U N

where: ueg = Equivalent controluN = - sgnoFigure. 4. Simpl$ed circuit of the converter

This control law is compo sed by two terms, the fxst isonly valid on the sliding surface (ueq ) and the otherassures the existence of a sliding mode.For u = -1

ii) Existence of a sliding mode.x2= W0Xl (4 ) Existence of a sliding mode implies that thefollowing condition is fulfilled [8]:where

Vin dIo Iof i d t fib=-- - ,d=JX-+rlf- - resolving for ir :

AX+Bue , +C-Xr 1+ S B u N (10)The system equations in matrix form are:Therefore

X = AX+ Bu +C ( 6 ) In order to guarantee the existence conditions of asliding mode the following inequality must be fulfilled:Sliding controller design.

SB)O (12)Sliding mode control offers advantages such as:stability, robustness, good dynamic response and simpleimplementation. However, the control theory involvedis more complex than the traditional control theory.Many papers have been presented a variety of slidingmode control design steps 18-13]. They could besummarized as follows:

or

Therefore s , must be positive since b is alwayspositive.i) Propose the sliding surface.ii) Verify the existence of a sliding mode.iii) Analyze the stability in the sliding surface. It is important to note that thereferences are constants.X, = 0 due to the

i) The sliding surface. iii) Stability analysis in the sliding surface.The sliding surface proposed is a lineal combination ofthe state variables and the reference variables, that is: A tool developed to describe the movement in thesliding surface is the equivalent control [13] . Theequivalent control is applied when CT = 0, hence Ci = 0.These conditions imply that the system is in the slidingsurface.U = S X - S X , = S e x (7)where:

Equivalent control ( ueq ) is obtained from 6- 0 ,therefore:= State variables,X, = Reference variables1652



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ue q = - [SB]- ' [SAX+SC-SX,] (14)The ecluivalent contro l is substitute d in the mod el of thesystem and the following system is ob tained:x = D ( A x i - C )where:

D = [ I- B(SB)-'S] D =

The system is reduced to:x = Ex

where:

E =s2SI

- -Uo 0WO 0

As can be observed in E the resulting equations areindependents of a x2, and that is because of the systemis restricted to the sliding surface (order reduction). In(16) there are only one independent variable ( x1 ) du eto the order reduction.

To gu arantee the stability is necessary therefore that s2must be positive since the sl is positive in order toassure the existence condition of the sliding mode.Fig.5 shows the basic scheme to this controller.'

U FrecuencylimiterFigure 5. Block diagram of sliding-mode control.

Iv. EXPERIIMENTAL RESUL TSIn order to verify the circuit operation, large signalsimulations of the proposed converter have been builtwith the following characteristics:

V i n = 9 0 - 1 3 0 V r m s Po=400 WVo= 48 Vd cs = 10 0 KHz.Fig. 6 shows the simu lated waveforms of the proposedconverter. Fig. 7 shows the filtered line current of theproposed converter at full load. As can be seen, thewaveform is very clo se to the waveform in Fig. 6.Fig. 8 shows the transient response of the line current(bottom trace) of the sarne circuit to step change in theload current from 20% to 50% and back. The top traceshows the response of the output voltage for this circuitto the same conditions of step change in the loadcurrent. The response is very fast because it isdeterminated solely by the full-bridge converter.Fig. 9 shows the efficiency measurement for differentvalues of line voltage. This graphic was obtainedwithout the use IGBT's in the Q1 and 4 2 powerswitches. If better switches are used, IGBT's, theresults will be further improved.

8.33m 2 5 k 33.331TimFig.6. Simulated waveforms to input voltage and inputcurrent at 250 Watts; Vin = 90 Vrms.

VdtS h P S150 T lo

O i

-100 t

t 6t 4

Fig.7. Filtered line current o th e 250 W IBR-full-bridge experimental circuit.

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REFERENCES3

1

1

~~42 4-Po @75-200WI______-::

Fig.8. Transient response of the line current (bottomtrace) and of the output voltage (top trace).

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76

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1OOw 150w 2OOw 250w 300w 350w 400wOutput PowerFig.9 EfJiciency measuremen t of the IBR-full bridge.V. CONCLUSIONS

In this paper, a new single-phase power factorcorrection scheme, with fast regulation of the outputvoltage using the sliding-mode control is proposed.Compared with the conventional two-cascade scheme,it provides high efficiency. An experimental prototypehas been built and tested to verify its functioning. Thisscheme is essentially suitable for building high power,high efficiency, high density off-line power converterswith PFC requirements.The soft-switched IGBT technique can be implementedhere very easily to further improve the performance ofthe proposed topology.

[ l ] P. N. Enjeti and R. Martinez, A HighPerformance Single Phase AC to DC RectlJierwith Input Power Factor Correction, IEEE[2] Takahashi, R. Igarashi, A Switching PowerSupply of 99% Power Factor by the DitherRectzJier, INTELEC91, pp. 714-719.[3] M. Madigan, R. Erickson and E. Ismail,Integrated High QualiQ Recti~er-Regulators,[4] Y Jiang, F. C. Lee, G. Hua and W. Tang, ANovelSingle-phase Power Factor Correction Scheme[5] Y Jiang and F. C. Lee, Single-Stage Single-phaseParallel Power Factor Correction Scheme,[6] E. Rodriguez, F. Canales, J. Arau, A NovelIsolated High Quality Rectfienvith Fast DynamicResponse, PESC97,pp.550-555[7] Y. M. Jiang, G. C. Hua, E. Yang and F. C. Lee,lSoft-Switching of IGBT with the Help ofMosfets,VPEC Seminar 1992.[8] R. A. DeCarlo, S. Zak, G. P. M atthews, VariableStructure Control of Nonlinear MultivariableSystems: A Tutorial, Proceedings of the IEEE,vol. 76 No . 3, March 1988, pp. 212 - 232.[9] H. Sira-Ramirez, M. llic, A Geometric Approachto the Feedback C ontrol of Switch Mode dc-to-dcPower Supplies, Transactions on circuits andsystems, vol. 35 No. 10, Oct. 1988, pp. 1291 -1298.[IOIL. Rossetto, G. Spiazzi, P. Tenti, B. Fabiano, C.Licitra, Fast-Response High-Quality Rectifier

with Sliding-Mode Control, APEC93, pp. 175-181.[111 P. Ma ttave lli, L. Rossetto, G. Spiazzi, Generalpurpose sliding m ode controller fo r dc/dcconverter applications, PESC93, pp. 609 - 615.[12] J. Y. Hung, W. Gao, J. C. Hung, VariableStructure Con trol: A Survey, IEEE Transactions onIndustrial Electronics, vol. 40, No. I , Feb. 1993, pp.2 - 18 .[131 V.1 Utkin, Sliding Mo des An d Th eir Application InVariable Structure Systems, MIR Publishers,Moscow, 1974.

APEC93, pp. 190-195.

APEC90, pp. 1043-1051.

APEC93, pp.287-292.

PESC94, pp.1145-1151.

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58.an integrated high quality rectifier with

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