Dc dc converter for ultracapacitor boosted electric vehicle

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Dc dc converter for ultracapacitor boosted electric vehicle

  1. 1. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN IN – INTERNATIONAL JOURNAL OF ADVANCED RESEARCH 0976 ENGINEERING AND TECHNOLOGY (IJARET) 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEMEISSN 0976 - 6480 (Print) IJARETISSN 0976 - 6499 (Online)Volume 3, Issue 2, July-December (2012), pp. 71-81© IAEME: www.iaeme.com/ijaret.html ©IAEMEJournal Impact Factor (2012): 2.7078 (Calculated by GISI)www.jifactor.com DC-DC CONVERTER FOR ULTRACAPACITOR BOOSTED ELECTRIC VEHICLE Mohamed HediChabchoub and HafedhTrabelsi Computer Embedded System (CES),SfaxIngineering School, University of Sfax, Sfax, Tunisia chabchoub_medhedi@yahoo.frandhafedh.trabelsi@yahoo.fr ABSTRACT For traction system, when there is a transient high power requirement, such as an acceleration or cold start, the battery can be boosted with UltraCapacitor UC. The UC show an extremely high power density. So the UC is capable of supplying pulse energy within a short time. While the battery can provide high power, just not as high as the UC with the same size. Given The UC and the batteryon board are rechargeable, the kinetic energy won’t be wasted but can be transferred into electric energy and recaptured by the UC or battery. That will save the energy and improve the system’s efficiency by using the phase shift modulation angle of Dual Active Bridge Isolated Bidirectional Converter. Keywords: UltraCapacitor, Dual Active Bridge Isolated Bidirectional Converter, phase shift modulation angle, EV. I- INTRODUCTION Research on transport systems is constantly developing; and it aims at solving problems of air pollution, the replacement of fossil energy resources and improving the overall performance for conventional vehicles which does not exceed 30% . However, much energy is lost during braking. Electric Cars and EVs and Hybrids Electric Cars VEHs give adequate solutions to the problems of energy loss and pollution, particularly in urban areas. The use of UCs in these vehicles reinforces the main source of energy providing power peaks of short duration during starting and acceleration.The UCs are characterized by a high power density and low Equivalent Series Resistance ESR, and they have several advantages: the ability reaches thousands of Farads per cell, they loaded and unloaded quickly with currents of several hundred amperes. At room temperature, the UCs may reach one million cycles of loading and unloading. Themost remarkable disadvantage of UCs is the low cell voltage (2.5 to 2.7V) [1] [2]. It is therefore necessary to connect in series, a large number of UCs cells so that the 71
  2. 2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEMEvoltages at its terminals reach the main source of energy. This connection requires theaddition of a circuit balancing the voltages at the terminals of the cells [3] [4]. II- DESIGN OF ELECTRIC TRACTION SYSTEMSThe electric car is an ecological growing concern for the industrialists in order to adequatelymeet the needs of road users. The electric traction system may include apart from the battery,the main energy source, a bidirectional DC-DC converter, an UC, an inverter and an electrictraction machine Fig.1. Fig.1 System ofelectric tractionIn the last decade, research on high performance of bidirectional DC-DC converters hasgained momentum. This type of converter plays a key role to establish a conversion and anefficient supply of energy in such systems [2] [5]. It plays the role of the interface circuit,connecting the latter to SCs, to achieve a two-way exchangeof power flow.To control theflow of energy, while regulating the DC bus voltage and load or unload the UCs, severaltopologies of DC-DC converters of the type insulated or not insulated have beenimplemented [2] [5] [6] [7].The not isolated topology has the advantage of being simple andlightweight. But since the voltage of a cell UC is relatively low, the series connection of cellscauses an increase in the ESR and a decrease in equivalent capacity. Bidirectional topologyof multiple inputs is used to connect multiple energy sources of different voltages. Thistopology has been used for small electric cars [2]. To overcome these drawbacks, the isolatedtopologies can transfer more energy at reduced voltage [6] [7]. A high frequency transformer(THF), is incorporated in the converter. Thus, loading and unloading of the UC can be doneat low voltage with high current. Side of the battery voltage is higher with a lowercurrent.The bidirectional converter and isolated DC-DC may be, half-bridge, has two bridges[6], or a push-pull circuit [5]. For the management of high power, double-bridgeconfiguration is most favorable. III- ARCHITECTURE OF DC-DC CONVERTERIn Fig. 2, battery, main source of energy, provided in the normal state, the power is in charge(Load). The SC, temporary stored of energy recovered during braking supports peak powersrequired by the load (traction motor) during start-up and acceleration.In the mode of loadingof the UC, the bridge, the DC bus side, operates as an inverter, operates in the secondarybridge rectifier and provides power to the UC. In the discharge mode, the secondary bridgeoperates as an inverter, while the primarybridge operates as a rectifier. 72
  3. 3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEMEFig.2 isolated bidirectional DC-DCdouble-bridge converter for the management of the UC powerIn the configuration considered:• Because the operating frequency is high, the size of the THF binding is very small the load isa synchronous machine, combined with athree-phase inverter.• L0 Includes the leakage inductance of THF reduced the secondary side and any other series inductance.We denote by:• vpAnd vs respectively the primary and secondary voltages of THF.• m=Ns/Np=Vs/Vp The transformation ratio of THF,• v2 The supply voltage of the second bridge.• vL0= vs – v2 the voltage across the inductor L0.• Tc The half-switching period, the frequency being is fc=1/2Tc• Φ The phase shift between vs=mvp voltages and v2 (this is the phase shift between the commands of the two bridges).Viewedinhandlingrelatively low voltagesearch of the twobridgesis based onMOSFETsQ1,Q2, Q3 and Q4 inthe primary side and Q5, Q6,Q7 and Q8 in the secondary side[8].Withaconstantswitching frequencyfcandduty cyclesD1=D2=0.5, the primaryvoltagevp(t)is+Vbor-Vbandthe secondary voltagev2(t)(feeding the second bridge) is+Vscor-Vsc. Sincevs(t+Tc)=-vs(t), the secondary currentis(t)in the inductorL0rebuilt duringeach halfcyclewithoppositesigns. The modeof operation is basedon the shapeof this current.Thecontrol signalsof the two bridgesare generated by aDSP, amicroprocessororaspecialized chiplikeUC3875generatesaPWM control. 1- UCcharge mode.Analytically and with electronic switches ideal, gaits, current is(t), voltage vL0(t) andcontrol signals in this mode are given in Fig.3.This mode of operation covers six segments. Down the same Fig.3, gives a summary table,over a period, the status of each electronic switch.• Between t0 and t2 the current is(t) increases linearly with the following expression: 1 i s (t ) = i s (t 0 ) + (mVb + Vsc )t (1) L0• At t=t1the current passes throughzero.• Fromt2 to t3thecurrentis(t) increased linearly witha smaller slope, 73
  4. 4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEMEFig.3: Waveformidealcharging modeUC, Fig.4:WaveformidealdischargemodeUC,control signals, vs(t) andv2(t). vL0(t) and control signals, vs(t)and v2(t).vL0(t) and is(t): is(t): a)mvb>Vsc, b) mvb=Vsc, a )mvb>Vsc, b) mvb=Vsc, c) mvb<Vsc. c) mvb<Vsc. 74
  5. 5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEME Its expression is: 1 is (t ) = is (t2 ) + (mVb − Vsc )(t − t2 ) (2) L0• Att3=Tcthe current is (t3 ) = −is (t0 ) = I s max• Fromt3 to t5thecurrentis(t) decreases linearlyaccording tothefollowing expression: 1 is (t ) = I s max + (−mVb − Vsc )(t − Tc ) (3) L0• At t=t4the current passes throughzero.• The last segment fromt5 tot6thecurrent has continued to decreaselinearlyin the words: 1 is (t ) = is (t5 ) + (−mVb + Vsc )(t − t5 ) (4) L0• Att6,end of theperiod: i s (t 6 ) = i s (t 0 ) = − I s maxDuring loadingof the UC, the waveformof the current is(t) changesevery moment.Thevoltage VSC increases, it goestoavaluelower than mVbFig.3.a, to a greater value Fig.3.c.Attwo voltagesequal, obtainthe shape of theFig.3.b. 2- UC discharge modeIt is worth noting that the same reasoning of analytical development of current expressionapplies to discharge modeof theUC. However we must to distinguish thedifferencesbetween charge and discharge modes (seeFig.4). 3- Thepower transferredThe average powertransfercan becalculated on thehalfperiodby: TcP = T1c ∫ 0 vs (t ) × is(t )dt (5)we obtain: mVbVscφ (π − φ ) P= (6) 2π 2 f c L0Depending on thephase angle Φ, the power transferredas shown inFig.5has twoextrema at±π/2.It is easy tocontrol the transfer ofpowerby modulating thephase angle Φ.For 0<Φ<π the poweris positive, itis transferred to theSC for theload.For -π<Φ<0 the poweris negative, it is transferred tothe DC busto restore theenergyrecovered.Thepower transferredis highestfor Φ=±π/2 and it is equal to: mV V Pmax = ± b sc (7) 8 f c L0Depending on the system,to managethe amount of energyto be transferred,we havethepossibility of choosing, thetransformation ratio of theTHF, thebattery voltage, thenumber of cells of UCs and the inductance L0. 75
  6. 6. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEME 2000 L0=2e-6H L0=1e-6H L0=0.5e-6H 1500 1000 500 P (W ) 0 -500 -1000 -1500 -2000 -pi -5pi/6 -4pi/6 -2pi/6 -3pi/6 -pi/6 0 pi/6 2pi/6 3pi/6 4pi/6 5pi/6 pi φ Fig.5: Power transferredas a function ofphase shift Φ Fordifferentinductances L0Furthermore we havethe opportunity to actonthe switching frequencyfcandphase angle Φ.It is necessary to note that the action of the duty ratios D1 and D2 modifies the waveformof the inductor current,which ensures a zero current switching and to make them soft. Thusthe efficiency of the converter for applications with low power will be significantlyimproved [9] [10].According toexpression(5), the phasemodulationhasthe advantage of beingsimple.Butitworks bestforhigh power.Wenote thatthedualbridgeconverterisusedfor systemsofgreat powers, but it is not suitablefor low power. IV- SIMULATION RESULTSThe model parametersused(Fig.2) are:• Forthemainvoltagesource(battery) Vb=50V• For UC, the"BCAP1500" has a capacityper cellCsc=1500F rated voltage Vsc=2.7V, withinternal resistance ESR=0.47m . Since weneed to reacha charging voltageof the order of 11V, we used fourunitsin series.The total capacity is then 375F withanESR=0.18m andofa nominal voltage of 10.8V.• Forthe THFferrite magnetic circuit; theN27for example, thetransformation ratiois m=Ns/N2=0.2: theseleakageinductances: primary L1=1.2µH and secondary L2=0.2µH, itsmagnetizing inductanceisLm=1.8mH: [17].• Forthe series inductance L0=2µH.• The switching frequencyis fc=20 KHz: with a duty cycleof 50%. [4]. 76
  7. 7. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEME 1510 Vs Vsc<mVb Vs V2 8 V2 10 Vsc>mVb 6 4 Φ>0 Φ<0 5 2 t 0 0 t -2 -5 -4 -6 -10 -8-10 -15 VL VL Vsc>mVb Is Vsc<mVb Is t t VL Vsc=mVb Is VL Vsc=mVb Is t t Vsc>mVb VL VL Vsc<mVb Is Is t t Fig.6: AllurevS,v2,vL0and isduring Fig.7: AllurevS,v2,vL0and isduring chargingtheUCfor:a)mvb>Vsc, dischargetheUCfor:a)mvb<Vsc, b) mvb=Vsc,c) mvb<Vsc b) mvb=Vsc, c) mvb>Vsc 77
  8. 8. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEMETo reducethe computation time, the margin of voltage change across the UCV scislimitedto a range starting from6 to10V. Fig.6 shows the phase angleφbetween thesecondaryvoltagevs=±mVb,and one thatfeeds the secondbridgev2=±Vsc.Fig.6givestheappearance of avoltagevL0(t)andthecurrent flowing through it(secondarycurrent)is(t).We can remark that the simulation results are similar to the analytical results(see Figs. 3, 4, 6 and 7). Normally,we should notoverload thedifferentUCcells. Avoidoperation corresponding to the Fig.6.c.T hat is tosay,Vscmust always be≤mVb,otherwiseasevere degradation ofdevice characteristics U Csappears with the riskof destroying them.In the case considered, we mustlimit theloadingof allunitsto 11Vandprovidestrict oversightof the individual state of charge ofdifferent units[3] [4].Analyticallyand at constant switching frequency, the expression(12)shows, in accordancewith theFig.8that the increaseof the maximum powertransferred(with π±/2)can be achievedbydecreasingthe value ofseries inductanceL0. InFig.9, we note that theincreaseinthispoweris accompaniedbya decrease in thecorrespondingphase shiftΦ. 200 L0=1e-6H 200 L=2e-6 f=10KHz 180 L0=2e-6H L=2e-6 f=50KHz 180 160 160 140 140 120 120 P (W) 100 P(W) 100 80 80 60 60 40 40 20 1.413rd 1.965rd 1.256rd 2.9rd 20 1.256rd 1.413rd 0 2.82rd 0 1.9rd 0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3 φ φ Fig.8: power transferredto theSCas a Fig.9: power transferredto theSCas a function ofphase shift function ofphase shift fordifferentinductance forvariousdifferentswitching frequencies.Similarly, the decrease of the switching frequency, you can increase thepowerbutit isalways withacorrespondingdecrease in thephase shiftΦFig.9.In practice, thephase shift Φgivesa maximumtransferofpoweralwaysinferiortoπ±/2 basedonthetransfer direction. The choiceof this angledepends on theloadingorunloadingneedsslow or fast.Modeofloading, the phase shiftwhich allows the fastestloadingin the interval[70° 90°], otherwise the voltage gainand the energy storedinthis modewill be reduced.Indischarge mode,the phase shiftsΦ<60°, cause thefastestunloadingUCFig.11. 78
  9. 9. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEME 8 11 φ=0.4∗π φ=0.2∗π φ=0.45∗π φ=0.5∗π 0.2π 0.4π 0.45π 0.5π 0.95π 10 7 9 6 8 5 7 V s c (V )V s c (V ) 4 6 5 3 4 2 3 1 2 0 1 2 3 4 5 6 7 8 9 10 0.5 1 1.5 2 2.5 3 t 5 t x 10 6 x 10 Fig.10: voltage, fordifferentphase Fig.11: voltage, fordifferentphase shiftsduring loadingof theUC. shiftsduring the unloadingof theUC. (c) (a) Φ=0.2π VL Is VL Φ=0.3π Vsc=7V Is Vsc=4V t t Fig.12: Alluresof vL0and isduring loadingtothe UCfor different values (b) ofphase shiftΦto keepa triangular VL shapeallowingcurrentsoft switching Φ=0.25π Is Vsc=6V t Fig.13: Improvement ofefficiency of the converterby modulating thephase shiftΦ 79
  10. 10. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEMEWith the modulation phase angle Φcan make in soft switching Fig.12 (zero current), wellthe switching losses are reduced and the efficiencyincreases Fig.13 V- CONCLUSIONWith the aim to design an electric ecological vehicle, a study of a traction system involvingUCs is conducted. This paper carries out the simulation to verify the normal operation ofthe converters and the effectiveness of control method thanks to phase shift angle.Simulation results confirm those calculated analytically. The consolidation of the batteryby the UC by providing peak power is even more interesting by acting on the phase shiftbetween Φ orders of the two bridges sometimes associated with an action on the cyclicalorder of the two bridges.Indeed the appropriate choice of the phase angle Φ minimizes switching losses and henceimproved performance of exchange between the battery and the SC is provided.REFERENCES1. Z. Pfof, P. Vaculík, 2010, "Ultracapacitors Utilization for Automotive Applications» ActaPolytechnica Vol.50 No.12. L. Zhihao, O. Omer, K. Alireza, 2009 "Design and Control of a Multiple Input DC/DC Converter for Battery/Ultracapacitor Based Electric Vehicle Power System" IEEE, Power Electronics Applied Power Electronics Conference and Exposition,APEC.34th-p.591–596.3. A. Vivek Ravi, V. John2010, "Ultracapacitor Based Ride Through System for Control Power Supplies in High Power Converters" 16th National Power Systems Conference,4. V.V. Haerri, D. Martinovic 2007 "Supercapacitor Module SAM for Hybrid Busses: an Advanced Energy Storage Specification based on Experiences with the TOHYCO- Rider Bus Project" I.E.S, IECON Taipei 33rd Annual Conference of the IEEE p268– 273.5. T. Mishima, E. Hiraki, M. Nakaoka 2010 "A High Frequency-Link Bidirectional DC- DC Converter for Super Capacitor-Based automotive Auxiliary Electric Power Systems" Journal of Power Electronics, Vol.10, No.1,6. B. Hua, C.M. Chunting,G.Sonya 2008, "The Short-Time-Scale Transient Processes in High-Voltage and High-Power Isolated Bidirectional DC–DC Converters”IEEE,Vol.23,No.6,7. G.C. Lopez, A. J. Forsyth, 2011 "High-Power Dual-Interleaved ZVS Boost Converter with Interphase Transformer for Electric Vehicles" International Journal of Computer and Electrical Engineering, Vol.3, No.1,8. Z. Haihua and A. M. Khambadkone 2009 "Hybrid Modulation for Dual-Active-Bridge Bidirectional Converter With Extended Power Range for Ultracapacitor Application," IEEE Transactions on Industry Applications, vol. 45, pp. 1434-1442.9. Y. Wang, S. W. H. de Haan, and J. A. Ferreira 2009 "Optimal Operating Ranges Of Three Modulation Methods in Dual Active Bridge Converters," in IEEE 6th 80
  11. 11. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEME International Power Electronics and Motion Control Conference (IPEMC 09), China, pp. 1397-1401.10. H. Yan Lu, J. Guo Zhu, S. Y. Ron Hui, 2003"Experimental Determination of Stray Capacitances in High Frequency Transformers " IEEE Transactions on power electronics, VOL. 18, NO. 5, p-1105-1112.11. H. Xiao, S. Xie, 2008"A ZVS Bidirectional DC–DC Converter With Phase-Shift Plus PWM Control Scheme" IEEE, T.P.E., VOL.23,NO.2, March, p 813-823. 81

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