DESIGNOFBIDIRECTIONALZETACONVERTER.pdf

The 7th International Conference on Power ElectronicsOctober 22-26, 2007 / EXCO, Daegu, Korea

Design of Bidirectional PWM Sepic/Zeta DC-DC Converter

TUC1·3

In-Dong Kim,Pukyong Nat. Univ.Dept of Elec. Eng.

Busan, Korea,[email protected]

Young-Ho Lee, Byoung-Ho MinPukyong National University

Dept of Electrical Eng.Busan, Korea,

Eui-Cheol NhoPukyong Nat. Univ.Dept of Elec. Eng.

Busan, Korea,[email protected]

Jin-Woo AhnKyungsung Univ.

Dept of Elec Eng.Busan, Korea,

[email protected]

Abstract- Bidirectional DC-DC converters allow transfer ofpower between two de sources, in either direction. Due totheir ability to reverse the direction of flow of power, theyare being increasingly used in many applications such asbattery chmgerldischmgers, de unintemJptibie power supplies,electrical vehicle motor drives, aerospace power systems,telecom power supplies, etc. This paper proposes a newbidirectional Sepic/Zeta converter. It has low switching lossand low conduction loss due to auxiliary communicatedcircuit and synchronous rectifier operation, respectively.Because of positive and buck/boost-like DC voltage transferfunction (M=D/I-D), the proposed converter is desirable foruse in distributed power system. The proposed converter alsohas both transfonner-Iess version and traosfonner one. Thepaper also suggest some design guide line for the proposedconverter.

I. INTRODUCTION

Bidirectional dc-dc converters allow power flowbetween two dc sources in either direction. They canreverse the direction of current flow, and thereby powerflow while maintaining the voltage polarity of bothsource ends unchanged. In some necessary case,high-frequency transformer for galvanic isolation can beincorporated inside them. Due to such good features,bidirectional dc-dc converters are being increasinglyused in applications such as battery charger anddischarger, fuel cell applications, dc uninterruptiblepower supply, aerospace power systems and motordrives.

Bidirectional dc-dc converters for use in batterycharger and discharger are not only to control thebattery charging and discharging current, but also toregulate the output voltage of discharger to apredetermined value when again using the stored energyin the battery. In that case, if unidirectional dc-dcconverter is adopted instead of bidirectional converter,

two separate unidirectional converters should beprovided for either direction.

But the use of bidirectional half-bridge dc-dcconverters in[I-2] for low power application and fuelcell applications, or bidirectional buck/boost convertersin [4] for aerospace power systems can simplify thesystem structure, thus resulting in reduction of systemvolume, weight and cost. Especially in case of dc UPSsuggested in [3], the bidirectional buck/boost convertermay improve system efficiency as well.

In addition, the use of bidirectional dc-dc converterin the dc link of brushless dc motor drive dedicated toEVs allows the control of both motoring andregenerative braking operations [5]. It can contribute tosignificant improvement of the motor drive performance.For motoring operation, the bidirectional buck-boostconverter in [5] is used to adjust the inverter inputvoltage and motor speed to reduce the ripple of motorcurrent. For regenerative braking, the bidirectionalconverter is to control power flow reversal so that asignificant amount of the vehicle kinetic energy can berecovered to battery or additional ultra-capacitor tank,thereby resulting in good system efficiency.

As examined above, bidirectional dc-dc convertersmake system simplification, efficiency improvement andperformance upgrade a lot possible. The bidirectionaldc-dc converters presented so far are as follows;

(1) Bidirectional buck/boost DC-DC converter [4],(2) Bidirectional quasi-resonant DC-DC converter [6],(3) Bidirectional buck-boost DC-DC converter [5],(4) Bidirectional Cuk DC-DC converter [7, 11],(5) Bidirectional flyback DC-DC converter [8],(6) Bidirectional half bridge DC-DC converter [1-2],(7) Bidirectional full-bridge DC-DC converter [9]

Vi

<Sa>r----i1 Sal I 11 --.J 11 1

:s:l :1 .1

Fig. 1 Proposed bidirectional ZVS PWM Sepic/Zeta DC-DC converter

978-1-4244-1872-5/08/$25.00 © 2008 IEEE 614

The 7th International Conference on Power ElectronicsOctober 22-26, 2007 I EXCO, Daegu, Korea

Sa Sa0 0

Sl Sl0 0

S2 S20 0

iLl 0

0 iLl

iL2 00 iL2

Vs1 Vs10 0

Vs2 Vs20 0

is1 iD10 0

iD2 is20 0

iLr iLr0 0

'M

'M M56

(a) Forward operation(Sepic) (b) Backward operation(Zeta)Fig. 2 Operating waveforms of the proposed converter

These bidirectional converters have their own featuresand applications. But so far, bidirectional Sepic/Zetadc-de converter has not fully been researched whichcould be regarded as a kind of combination of basicSepic and Zeta converter. So, this paper proposes thenew bidirectional Sepic/Zeta dc-de converter. Theproposed converter does not only have the capability ofbilateral power flow, but also low switching loss andconduction loss due to zero voltage switching andsynchronous rectifier operation. Furthermore, thanks topositive and buck/boost-like DC voltage transferfunction (M=D/I-D), the proposed converter is desirablefor use in distributed power system. The proposedconverter also has both transformer-less version andtransformer one.

II. PROPOSED BIDIRECTIONAL ZVS PWMSEPIC/ZETA DC-DC CONVERTER

The power stage circuit diagram of the proposedconverter is shown in Fig. 1. The circuit can bedivided into two parts, that is, hard-switchedbidirectional Sepic/Zeta dc-de converter and auxiliaryresonant commutated pole circuit. The hard-switchedbidirectional Sepic/Zeta dc-de converter is also a newbidirectional dc-de converter as a skeleton of theproposed converter. It operates like a conventional

hard-switched Sepic converter for forward power flow,and like a Zeta converter for backward power flow.The main switches SI and S2 switch on and off withanti-parallel connected diodes D1 and D2, respectively,carrying out synchronous rectifier operation. Theinductor current through L1 and L2 are positive forforward power flow and vice versa.

The auxiliary resonant commutated pole circuit:ARCPC) is composed of a small MOSFET St, andresonant inductor Lr. The ARCPC circuit provides thehard-switched bidirectional Sepic/Zeta dc-de converterwith ZVS operation, and is rated for a small powerwhen compared to the output power. The ZVSoperation for both the main MOSFET devices anddiodes results in improved circuit efficiency.Furthermore since the ZVS switching occur during ashort time when compared to the switching period, itdoes not have significant influence on the overalloutput characteristics of basic AC/DC converter such asPWM control and linear input and output conversioncharacteristics.

The forward operation of proposed converter issimilar to the operation of Sepic converter and thuscan be named Sepic mode operation here. Its operatingwaveforms are shown in Fig. 2(a). The backwardoperation of proposed converter is similar to theoperation of Zeta converter. It is also named as Zeta

615


mode operation. Its operating waveforms are shown inFig. 2(b).

When looking into the forward(Sepic mode) andbackward(Zeta) operation of the proposed converter inmore detail~ its operation can be divided into 8operation modes for one switching period~ respectively ~

as shown in Fig. 2(a) and (b).

III. DESIGN OF PROPOSED BIDIRECTIONAL ZVSPWM SEPIC/ZETA DC-DC CONVERTER

In order to verify the effectiveness of the proposedconverters and suggest the design guideline in realapplications~ the prototype converter is properlydesigned with rated power 1.0[kw]~ controlled outputvoltage 1OO[V]~ input voltage range of 40--60[V]~ andswitching frequency 40[kHz] above acoustic noisefrequency.

The proposed converter has the auxiliary resonantcommutated pole circuit(ARCPC) composed of a smallMOSFET St~ and resonant inductor Lr. But theauxiliary circuit has little effect on the overall PWMoperation characteristics of hard switching PWMSepic/Zeta converter. So~ in steady-state~ the averagevalues of inductor currents iLl and iL2 are equal tozero~ resulting in the following equation (1)

Vi == ~1 (1)

The voltage across the inductor L2 during on-statetime Ton and off-state time Toff of switch Sl is Vi andVo~ respectively. Since the flux increment of inductorL2 during on-state time is equal to its flux decrementduring off-state time~ the following equation can beobtained.

d Vi == Vo (1 - d) (2)Thus~ the voltage conversion ration ~/Vi of

proposed bidirectional ZVS Sepic/Zeta converter can beexpressed as

is

(7)

(8)

(13)

By using the above derived equation (8)~ the maximumvalue of the average inductor current through L 2 isIL2.avg == 15 [A]. When considering the ripple factor of20% in the inductor current through L1 and L2 ~ themaximum current value I;;.max of switches ~ and ~is given as

I;;.max == 1.2 X (IL1.avg + IL2.avg) == 48 [A]. (11)

On the other hand~ the switch voltage V:1 across ~

~1 == Vi + ~ == 160 [V]. (12)

Thus~ MOSFETs IXFN130N30 with rated current130[A] and rated voltage 300[V] are selected forexperimental prototype by considering design margin of100%.

The current waveform through L1 at the dutycycle d of 2/3 is shown as Fig. 3 and the peak-to-peakvalue L1 ILl of current ripple through L1 is given as(13).

~ == (ILl + I L2 ) (1 - d )

From equations (6) and (7)~

I-dI L2 == -d-IL1 == la·

Since the input voltage ranges from 40[V] to 60[V]and the output voltage is to be controlled to 1OO[V]~

the variation range of duty cycle d in practicalconverter control is as follows;

O.63<d<O.71. (9)

In this condition~ the average current value IL1.avg

through the inductor Ll has maximum value atd == 0.63 ~ being expressed as

T - 1000 [W] - 25 [A] (10)1L1.avg - 40 [V] - .

to the output side~ and thus the following equation canbe obtained.

(3)Vo dVi I-d

Thus~

where the duty cycle d of switch 81 can be definedas d = ToniT where Ton and T is the on-state timeand switching period of switch Sl ~ respectively.

In addition~ as the steady-state power balance issatisfied~

When limiting the peak-to-peak current value L1IL1within 25% of the rated current~

Fig. 3 Inductor current iLl at d =2/3

--TI

I TX2I3[usec) r---+1 TX1/3[usec)14 . .. -I II I I ~ t

(4)

(5)

By combining equations (3) and (5)~ we can get the

following equation (6).

ILl _ _ d_ (6)Ia-l-d

On the other hand~ when ~ is in on-state~ theinductor current ILl and I L2 flow together through ~

616


(19)

To ensure ZVS operation of switches SI and S2, theauxiliary circuit parameters c;. and 4. of ARCPC areselected as 23.5 [nF] and 10 [uH], respectively,according to conventional design rules.

Upon turning on the auxiliary switch Sal the auxiliaryinductor current i Ir increases linearly with the risingslope of (18).

diu = ~ =.!QQl!1 = 10 [A/JLsec] (18)dt Lr 10 (JLH]

When i m = 40 [A], the time interval Llt1 of mode 1 is

given as (19).

On the other hand, the resonant period 1;. of auxiliaryresonant parameters c;. and Lr is given as (20).

11',. = iT = 211" ;r;a (20)

Thus, the time interval Llt2 of mode 2 can be

calculated as (21).

L1t2 = 1;./4 = 0.76 [Jlsec] . (21)

In addition, the rising increment L1ilit of the auxiliaryinductor current i Lr during mode 2 is equal to (22).

L1. =~+~= 160[V] = 7.75 [A]. (22)ZLr {T; ./ 10lpRj

Vq V23.5 [nF]

At the beginning point t3 of mode 3, the auxiliaryinductor current i Ir is equal to i Lr (t3 ) = 45 [A] • It takesLlt3 as (23) until the auxiliary inductor current iu isreduced to zero.

L1t3

= iI:" (t3 ) = i b' (t3 )

dzLrldt ~/Lr

= 60 [~J:ltLH] = 3.75 [p.sec] (23)

The switching timing diagrams of main switches SI,S2. and auxiliary switches Sal, Sa2 are shown as Fig. 6to ensure ZVS operation of main switches and ZCSoperation of auxiliary switches. The crossing point ofreference PWM signal and triangular carrier is thecriterion point to tum on and off the main andauxiliary switches. As shown Fig. 6, at the up slope ofthe triangular carrier, the auxiliary switch Sal is turnedon Lltbebefore the crossing point, thus increasing thestored energy in the auxiliary inductor. The storedinductor energy enables ZVS tum-off operation ofswitch S2. After the resonant operation, it also enablesZVS tum-on operation of switch SI. Finally, after thestored energy is discharged to zero, the auxiliary switchSal is turned off Lltaf after the crossing point. At thedown slope of the triangular carrier, the main andauxiliary switch Sa2 are turned on and off in the sameway as the up slope. In the prototype, Lltbeand Llta/are

properly selected as 2[usec] and 4[usec] considering thetime intervals Llt1 , Llt2 , Llt3 of mode 1, 2, and 3.

(17)

-----------------~) t

Fig. 5 Current waveform Is2 of MOSFET S2 andvoltage waveform Vo of capacitor C2

~IL1 = 50 [V] x 25 [JLsec] x 1. = 25 [A] x 0.25 (14)L1 3

Thus, by solving (14) and considering design margin,the designed circuit parameter of inductor ~ is selectedas 133[uH] with saturation current of 25[A]. Inaddition, the circuit parameter of ~ is also selectedequal to that of ~ , but with the different saturationcurrent of 15[A].

When neglecting the circuit influence of ARCPC, thevoltage and current waveform of Ct is shown as Fig.4 .and the peak-to-peak voltage value L1 V::l ofcapacitor C1 can be given as (15).

L1 V.I = ~ h2 X Ton (15)

_.....J!....-__!.- ..:..-__....:.... ... t.

To limit the peak-to-peak voltage value L1 V::l within25% of the input voltage, C1 should be selected aspolypropylene capacitor of 40 [uF], 12 [Arms].

Fig. 5 shows the current waveform ~2 throughswitch S2 and the voltage waveform Va across outputcapacitor C2. The peak-to-peak voltage value Ll Va ofoutput capacitor C2 is derived as (16).

L1 Va = ;;2 (Is2 - I,,)(T- Ton) (16)

To limit the peak-to-peak value Ll Va within 1% ofpredetermined output voltage, the output capacitorshould be selected as C2 = 400 [J.tF] •The ripple current of output capacitor C2 can becalculated as (17)

1 fT.2 [A]I = - ~ C2dt = 17C2.riPIie T 0

Thus, the output capacitor c; should be designed as400 [uF], 17 [Arms].

Fig. 4 Current waveform iCI and voltage waveform VCI

of capacitor CI

=-040lAl- - - - - DJ-

1.2

~~~ ~10[A]. t.

I.- -,- -.I I I II I I II

VO I

617


Fig. 6 Switching timing of switches Sal, Sa2 for ZVSSwitching

operation. As shown in Fig. 11, 12, the proposedconverter also operates very well in Zeta mode(backward power flow). Fig. 13 shows the measuredefficiency of the proposed converter in both Sepic andZeta. It shows that the proposed converter has goodefficiency.

V,

Fig. 7 Control block diagram of the proposed converter

Fig. 9 Current waveforms iLl, iL2 of inductors Ll andL2 in Sepic mode operation

Otlu~/rliv

O.lusldiv

V~l

·:50.0·V/div

50.0 V/div·

.50.0 ..Vldiv

lOAO A/rliv

(c) ~ ~ ___

(b)~--_......-...-----,.

(a)

Fig. 8 (a) Voltage VSl and current iSl waveforms ofswitch Sl in Sepic mode operation, (b) during turn-oninterval, (c)during turn-off interval.

Vo"

In order to verify the operation of the proposedbidirectional ZVS PWM Sepic/Zeta dc-dc converters,the prototype converter was properly implemented withrated power 1.0[kw], output voltage 100[V] and inputvoltage 40--60[V]. The detailed converter ratings andcircuit parameters are shown in table II. The prototypeconverter is controlled through PWM operation withcarrier frequency 40[kHz]. Fig. 7 shows the overallcontrol block diagram of proposed converter. Thecontrol block diagram consists of two feedback loop,that is, inner current loop and outer voltage loop. Theouter voltage loop is to regulate the output voltage Vo

and generate the current command for the inner currentloop. The inner current loop is to control the inductorcurrent and generate the reference voltage of PWMgenerator which supply the PWM gate signal to eachMOSFET switch.

Fig. 8(a) shows the measured voltage VSl and currentiSl waveforms of switch Sl in Sepic mode operation.Fig. 8(b) and (c) shows their zoomed up waveformsduring turn-on interval and turn-off interval,respectively. They prove that the proposed converterachieves good ZVS switching by using ARCPC circuit.Fig. 9 shows the measured current waveforms iLl, iL2of inductors Ll and L2 in Sepic mode operation. Itshows that the proposed converter is very wellcontrolled through PWM method. Fig. 10 shows themeasured current iLr of auxiliary resonant inductor Lrand gate voltage VGS(SaI) of auxiliary switch Sal inSepic mode operation. As shown in Fig. 10, theresonant inductor current increases from zero afterturning on the auxiliary switch Sal, and then it returnsto zero before turning off it. It proves that theauxiliary switch also get good ZCS switching operation.

Fig. 11 shows the measured voltage VSl of switchSl and current inl waveform of diode Dl in Zeta modeoperation. Fig. 12 shows the measured voltage VS2 andcurrent iSl waveform of switch S2 in Zeta mode

IV. EXPERIMENTAL RESULTS

618


Fig. 11 Voltage VSl of switch Sl and current IDI

waveform of diode Dl in Zeta mode operation

Fig. 10 Current iLr of auxiliary resonant inductor Lrand gate voltages VGS(Sal) of auxiliary switches Sal inSepic mode operation

Power rating 1.0 [kW] CI 40[uF]

VI 48[V] CZ 470[uF]

VZ 100[V] Cr 23.5[nF]

Ll, L2

133[uH]Lr 10[uF]

25[A}, 15{A]

fs 40[kHz] MOSFET IXYS IXFN130N30

TABLE 1 EXPERIMENTAL COMPONENT PARAMETERS

buck/boost-like DC voltage transfer function(M=D/I-D), the proposed converter is desirable for usein distributed power system, battery charger/dischargers, dc uninterruptible power supplies. Thepaper also suggest some design guide line for theproposed converter.

ACKNOWLEDGMENT

This work has been supported by KESRI(R2005-B-I09), which is funded by MOCIE (Ministryof commerce, industry and energy).

REFERENCES

::0::

................ - .

..~5us1div .

... [ [ :1::··50..0· ·V/div::

··:ysi:····

-- .. . .

~ ~ .. -lIZ· j ..

·5~O~l·AI~iv··

V. CONCLUSION

[1] M. Jain, M. Daniele, and P. K. Jain, "A Bidirectional DC-DCConverter Topology for Low Power Application", IEEE Trans.Power Electronics, vol. 15, no. 4, pp. 595-606, July 2000.

[2] F. Z. Peng, H. Li, GJ. Su, and lS. Lawler, "A New ZVSBidirectional DC-DC Converter for Fuel Cell and BatteryApplication", IEEE Trans. Power Electronics, vol. 19, no. 1, pp.54-65, Jan 2004.

[3] K.-W. Ma, and Y. S. Lee, "A Novel Uninterruptible dc-dcConverter for UPS Applications", IEEE Trans. IndustryApplications vol. IA-28, no. 4, pp. 808-815, July/Aug. 1992.

[4] D. M. Sable, F. C. Lee, and B. H. Cho, "AZero-Voltage-Switching Bidirectional Battery Charger / Dischargerfor the NASA EOS Satellite", IEEE APEC Rec., 1992, pp.614-621.

[5] F. Caricchi, F. Crescimbini, and A. Di Napoli, "20kWWater-Cooled Prototype of a Buck-Boost Bidirectional DC-DCConverter Topology for Electrical Vehicle Motor Drives", IEEEAPEC Rec., 1995, pp. 887-892.

[6] B. Ray, "Single-Cycle Resonant Bidirectional DCIDC PowerConversion", IEEE APEC Rec., 1993, pp. 44-50.

[7] J. Majo, L. Martinez, A. Poveda, L. Vicuna, F. Guinjoan, A.Sanchez, M. Valentin, and J. Marpinard, "Large-Signal FeedbackControl of a Bidirectional Coupled-Inductor Cuk Converter,"IEEETrans. Industrial Electronics vol. 39, no. 5, pp. 429-436, Oct.1992.

[8] G. Chen, Y.-S. Lee, S. Y. R. Hui, D. Xu and Y. Wang,"Actively Clamped Bidirectional Flyback Converter", IEEE Trans.Industrial Electronics vol. 47, no. 4, pp. 770-779, Aug. 2000.

[9] L. Zhu, "A Novel Soft-Commutating Isolated Boost Full-BridgeZVS-PWM DC-DC Converter for Bidirectional High PowerApplications," IEEE Trans. Power Electronics, vol. 21, no. 2, pp.422-429, March 2006.

[10] G. Spiazzi and L. Rossetto, "High-Quality Rectifier Based onCoupled-Inductor Sepic Topology", IEEE PESC Rec., 1998, pp.336-341.

[11] D. S. L. Simonetti, l Sebastian, and l Uceda, "TheDiscontinuous Conduction Mode Sepic and Cuk Power FactorPreregulators: Analysis and Design," IEEE Trans. IndustrialElectronics, vol. 44, no. 5, pp. 630-637, Oct. 1997.

[12] J. J. Jozwick and M. K. Kazimierczuk, "Dual Sepic PWMSwitching-Mode DC/DC Power Converter", IEEE Trans. onIndustrial Electronics, vol. 36, no. 1, pp.64-70, Feb. 1989.

[13] R. W. De Doncker and l P. Lyons, "The Auxiliary ResonantCommutated Pole Converter", IEEE lAS Rec., 1990, pp.1228-1235.

1000700500300

Output Power [W]

I~SEPIC ~ZETA I

.Vs2···

100

.......... : : .

. .::>::182:.

75

70

95

90~G 85s::Q)

'u 80SU.J

Fig. 13 The measured efficiency of the proposedconverter

Fig. 12 Voltage VS2 and current iSl waveform ofswitch S2 in Zeta mode operation

This paper proposes a new bidirectional ZVS PWMSepic/Zeta dc-dc converter. The proposed converter doesnot only have the capability of bilateral power flow,but also low switching loss and conduction loss due tozero voltage switching and synchronous rectifieroperation. Furthermore, thanks to positive and

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DESIGNOFBIDIRECTIONALZETACONVERTER.pdf

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