An Integrated Battery Charger for EVs Based on an Asymmetrical Six-Phase Machine

Transcription

1 9 th Annual Con. o the IEEE Industral Electroncs Socety Venna, Austra, - November An Integrated Battery Charger or EVs Based on an Asymmetrcal Sx-Phase Machne I. Subotc, E. Lev, M. Jones D. Graovac Lverpool John Moores Unversty, Lverpool L AF, U.K. Inneon, D-79 Neubberg, Germany.subotc@.ljmu.ac.uk, e.lev@ljmu.ac.uk, m.jones@ljmu.ac.uk dusan.graovac@nneon.com AbstractThe paper consders a novel battery charger topology or electrcal vehcles (EVs) that utlses an asymmetrcal sx-phase propulson machne. A sx-phase nverter and the machne are ully ntegrated nto the chargng process. The proposed ntegrated battery charger has the advantages o unty power actor operaton and zero average torque producton n the machne durng the chargng mode. The operatng prncples are based on the addtonal degrees o reedom that exst n multphase machnes and t s shown that asymmetrcal sx-phase machnes can be convenently utlsed to acheve chargng through the machne s stator wndng whle developng zero electromagnetc torque. Detaled theoretcal analyss s reported or the asymmetrcal sx-phase chargng system. A mathematcal model o the sx-phase voltage source recter (VSR) s gven, control n the chargng mode s dscussed, and the theoretcal consderatons are valdated by smulatons. I. INTRODUCTION Non-ntegrated chargers are at present standard n automotve ndustry. However, the exstng propulson mode related power electroncs components are ntegrated nto the chargng process, benets could be remarkable. Cost, whch s very hgh [], could be sgncantly reduced. Next, by avodng nstallaton o addtonal elements space could be saved and the weght decreased. An ntegrated charger was developed or the rst tme n 9 [], and many varous ntegrated solutons have been reported snce []. The majorty o EVs at present use a machne o ether nducton or permanent magnet synchronous type or propulson []. Currently, there are only ve ntegrated onboard solutons [-9] that allow ast (three-phase) chargng ncorporatng these types o machnes. In [], durng the chargng mode, motor three-phase stator wndngs are n an open-end wndng conguraton, wth one end connected to the nverter, whle the other three wndng termnals at the other sde are connected to a three-phase grd. Development o the rotatng eld occurs durng the chargng mode, so the motor must be mechancally locked durng the chargng process, whch s a severe drawback. In [], n order to provde a galvanc solaton, an nducton machne s used lke a transormer n the battery chargng mode. However, ths soluton ncreases the cost o the drve system snce t requres a wound rotor, so that the solaton advantage s completely overshadowed. Another solated soluton s presented n [7]. It avods the addtonal cost o a wound rotor by havng a stator wth two sets o three-phase wndngs, whch are shted spatally by degrees (splt-phase or asymmetrcal sx-phase conguraton). In the tracton mode each par o phases o the two three-phase wndngs that has spatal sht o degrees s connected n seres to consttute a sngle three-phase wndng set. For the chargng mode the system requres reconguraton. The rst set o three-phase wndngs s connected to the nverter on one sde, and nto the star on the other sde, whle the second set s connected nto delta on one sde, and to the grd at the other sde. In contrast to the prevous two, ths soluton has an explotaton potental. A completely derent charger topology s proposed n []. The soluton uses md-ponts o each o the three wndngs o a three-phase machne to connect them to a three-phase ac grd durng chargng (three-phase machne wth accessble md-ponts s n essence an equvalent o a symmetrcal sxphase machne). Compared to the three prevous conguratons, ths one has some dstnct advantages: there s no torque producton n the machne durng chargng mode; moreover, no hardware reconguraton between propulson and chargng mode o operaton s requred. A conguraton wth the same advantages as n [] but based on a nne-phase machne s suggested n [9]. Termnals o a three-phase grd are drectly connected to three solated neutral ponts o a nne-phase machne, and, by smultaneous control o nverter legs attached to the same machne s threephase wndng set, torque-ree operaton s ensured. Ths bre survey o the state-o-the-art shows that only the solutons based on, n essence, multphase machnes have the advantage o no average torque producton durng the chargng operaton. Multphase drves (n > ) are manly amed at hgh power/ hgh current applcatons. Ther two man advantages over three-phase systems are reduced current (power) ratng o the semconductor swtches and excellent ault-tolerant operaton eatures []. Multphase machnes are charactersed wth exstence o addtonal degrees o reedom wth regard to the control. Ths brngs n an added advantage over ther threephase counterparts n applcatons related to the ntegrated chargng o EVs, snce these addtonal degrees o reedom can be used or battery chargng wthout any average torque producton, as shown urther n ths paper, whch or the rst tme consders asymmetrcal sx-phase supply as a ast chargng opton or EVs. Developed novel sx-phase ntegrated chargng soluton s charactersed wth a unty power actor operaton, whle the machne s kept naturally at standstll durng the chargng process. The nverter and the machne are ully ntegrated nto the chargng process. The conguraton employs phase transposton rules [] n order to ensure that the motor does not develop average torque durng chargng; hence the machne naturally remans at standstll and ts stator wndng Pre-prnt. Fnal verson o ths paper appears n IEEE Xplore Dgtal Lbrary (

2 9 th Annual Con. o the IEEE Industral Electroncs Socety Venna, Austra, - November grd (o-board) tranormer wth two secondary sets a g phase transposton a g hardware recong. sx-phase machne a v a dc c L v ag c g b g S v v cg c bg C g b g BAT v eg ag cg b g a b g c g g a S S b c a b v b v a v b c g c g S c v c Fg.. Topology o the asymmetrcal sx-phase ntegrated battery chargng system. leakage nductances are utlsed or lterng durng the chargng process. The paper s organzed as ollows. In Secton II theoretcal analyss s provded or the asymmetrcal sx-phase chargng system. A mathematcal model o a sx-phase VSR s presented n Secton III. In Secton IV the control algorthm or the proposed conguraton s gven. In Secton V theoretcal results are valdated by smulatons or both chargng and vehcle-to-grd (VG) mode. The conclusons are summarsed n Secton VI. II. OPERATING PRINCIPLES OF AN ASYMMETRICAL SIX-PHASE CHARGING SYSTEM An asymmetrcal sx-phase machne can be used n ntegrated conguratons that allow sngle-phase chargng, []. However, sngle-phase systems allow only slow chargng. In ths Secton ths machne type s consdered or the ast multphase battery chargng. For chargng purposes two neutral ponts o the machne are opened and the phases are connected to the snusodal asymmetrcal sx-phase source whch s obtaned rom a three-phase transormer wth a dual secondary wndng. By connectng the two secondary wndngs n star and delta, respectvely, requred supply phase sht between two threephase wndngs o degrees s acheved (the voltage levels are made the same by proper selecton o the turn numbers or the secondares). However, nstead o connectng the motor phases a to c drectly to a to c phases o the supply, the prncple o phase transposton [] s appled to nsure operaton wth the zero average torque. The resultng connecton dagram or the chargng mode s as shown n Fg.. It can be seen that machne phases a and c are connected to grd phases a g and c g. Yet, machne phases b, c, a and b are now connected to grd phases c g, b g, b g and a g respectvely, all accordng to the phase transposton rules []. Parameters R and L n Fg. n essence represent stator leakage mpedance o the sx-phase machne. The decouplng (Clarke s) transormaton matrx or asymmetrcal sx-phase machnes s well-known and s avalable n, or example, []. For theoretcal consderatons, t s advantageous to combne pars o rows n D space vectors, whch can be ormulated as ( stands or any varable that s beng transormed, e.g. current, voltage, etc.): xy a a a a b b a a c c a a where a exp j cos j sn a a a b a b a a and /. The grd currents can be gven as a g c g b g I cos( t ) ; I cos( t / ); I cos( t / ); b g a g c g 9 c 9 c I cos( t / ) I cos( t / ) I cos( t 9 / ) The relatonshp between machne and grd phase currents s, accordng to Fg., gven wth a a g b c g c b g () a b g b a g c c g By substtuton o () and () nto (), the ollowng two space vectors are obtaned: () xy I exp( jt ) () Clearly, the lux/torque producng plane () s not excted and the grd currents low through the xy plane, so that the machne stays at standstll. Zero-sequence components are both equal to zero. III. MODELING OF SIX-PHASE VOLTAGE SOURCE RECTIFIERS Three-phase VSR model and ts control can be regarded as well-known []. Ths however s not the case wth multphase VSRs. Mathematcal model o a multphase VSR wth an even number o phases n a synchronously rotatng reerence rame can be gven wth g... d g g dq v L g dq R dt L n n g dq [ ] ( ) ( ) I [ ] nn s dq nn... g dq () () () Pre-prnt. Fnal verson o ths paper appears n IEEE Xplore Dgtal Lbrary (

3 9 th Annual Con. o the IEEE Industral Electroncs Socety Venna, Austra, - November [v g ] [ g ] [v g ] θ g, v g PLL _ θ g v g dg qg dg * qg * x g* y g* Current controller _ [ g ] dq _ [v]* x PWM [t g v x g* _ on] [ (dq)g ] y g v y g* abc.. _ Voltage controller v d * v q * θ g V dc * Fg.. Controller structure or the chargng process. dg qg dg * qg * ω g L Fg.. Decouplng network. Current controller x x d T C [ s ( dq) ] [ g ( dq) ] L (7) dt where [v g(dq) ] s the grd phase voltage matrx, [ g(dq) ] the grd phase current matrx, and [s (dq) ] the matrx o swtchng states, all n the rotatng reerence rame. v g _ v d * v q * IV. CONTROL OF ASYMMETRICAL SIX-PHASE VOLTAGE SOURCE RECTIFIERS In the chargng mode the conguraton s operated accordng to the grd voltage orented control (VOC) algorthm, usng the control scheme presented n Fg.. Measurements o the grd voltages, grd currents, and dc-bus voltage are requred or the closed-loop control. The common manner o obtanng the grd voltage poston s a phase-locked loop (PLL). When ths normaton s obtaned t s used to transorm phase currents nto the rotatng reerence rame that s grd voltage orented. I the grd current has only the d-component the chargng s wth a unty power actor. Thus, the current controller ams to keep the other current components at zero, whle chargng the battery by the d-component. As can be seen rom Fg., multphase recters, n contrast to the three-phase systems, requre more than two current controllers. The d-component s drectly proportonal to the battery chargng current, thus ts value s obtaned by a voltage controller whch s presented n Fg.. From () t can be seen that there are couplng terms between the d- and q-components. Thus current control requres a decouplng network, whch s or smplcty omtted n Fg. and s shown separately n Fg.. PWM used s o the carrer-based type, wth the zerosequence njecton. However, due to the presence o two solated (by vrtue o the transormer exstence) sets o three phase systems (a -b -c and a -b -c ), zero-sequence current rom one set cannot low nto the other, so that t s possble to nject standard three-phase system s zero-sequence components to these sets. Ths ncreases modulaton ndex n the lnear PWM mode to the same value as n the three-phase systems. In the propulson mode the drve s operated accordng to the eld orented control (FOC), whch s a well-known control method or multphase motor drves []. V. SIMULATION RESULTS To very theoretcal prncples o Secton II and the controller structure o Secton IV, smulaton o the asymmetrcal sx-phase system s perormed n Matlab/ Smulnk envronment. Asymmetrcal sx-phase grd s assumed to be already avalable. It has V voltage rms value, Hz requency, and s assumed to be perectly snusodal. Converter s workng at khz, and dead-tme eect s neglected. Dc-bus capactance s.mf. Battery s represented as a smple resstor o value R L =.Ω n seres wth an deal voltage source E. The Hz asymmetrcal sxphase nducton machne has the ollowng parameters: R s =.Ω, R r = Ω, L γs =.mh, L γr = mh, L m = 9mH, three pole pars, J =.kgm. Both chargng and vehcle-to-grd (VG) operatng modes are examned. Chargng mode o operaton s consdered rst. A. Chargng Mode o the Asymmetrcal Sx-Phase System Chargng mode s smulated wth a value o the deal voltage o a battery o E=97V. However, t s common or EVs to have a dc-dc converter between the battery and the converter so that the dc-bus voltage can be adjustable to varous values. Thus the value o E=97V s not a necessty Pre-prnt. Fnal verson o ths paper appears n IEEE Xplore Dgtal Lbrary (

4 Grd current component xg Grd current component yg Grd current component dg Grd current component qg Dc bus voltage (V) Battery chargng current L Harmonc rms (p.u.) Torque (Nm) Speed (rpm) Grd voltage v a g (V) Grd current a g Harmonc rms (p.u.) Converter phase voltage (V) Machne current component x Machne current component y Machne current component Machne current component 9 th Annual Con. o the IEEE Industral Electroncs Socety Venna, Austra, - November a dc-dc converter s employed (n the next subsecton a derent value s consdered). The reerence value or the dcbus voltage s set to V. In Fg. a grd phase voltage v ag and grd current ag are depcted. It can be seen that the current s n essence n phase wth the voltage, ndcatng a unty power actor operaton. Relatvely hgh rpple n the current s caused by the small leakage nductance o an exstng machne. Fg. b shows that the grd current spectrum contans only small values o low order harmoncs. Fg. c llustrates grd-sde current d- and q- axs components. It can be seen that durng the chargng process the q-axs current component s kept at zero value, whle the d-axs current component s kept at a constant value, whch s governed by the dc-bus voltage controller. However, sx-phase grd currents have addtonal xy components, and they are controlled to zero. Ths manner o operaton allows chargng wth unty power actor, as can be seen rom Fg. c, snce the control s grd voltage orented v a g a g FFT o waveorm (THD=.9) Harmonc requency (Hz) dg xg c) Fg.. Chargng mode: ( Grd phase voltage and current, ( grd current spectrum, (c) grd current components. qg yg x Fg.. Machne current componets: ( α and β, ( x and y x - FFT o waveorm (THD=.977). y Waveorm Harmonc requency (Hz) Fg.. Converter phase voltage and ts spectrum Torque Speed Fg. 7. ( Machne torque and speed, ( dc-bus voltage and chargng current. Machne phase current s the same as the grd phase current presented n Fg. a, but ts current components are derent than the grd current components, and they are presented n Fg.. In Fg. a t s shown that current components n the rst plane (αβ) are controlled to zero, thus there wll be no exctaton n the rst plane, and hence no torque producton. In Fg. b current components n the second (xy) plane are presented, and t s obvous that ths plane s responsble or L - Pre-prnt. Fnal verson o ths paper appears n IEEE Xplore Dgtal Lbrary (

5 Machne current component x Machne current component y Machne current component Machne current component Grd current component xg Grd current component yg Grd current component dg Grd current component qg Harmonc rms (p.u.) Grd voltage v a g (V) Grd current a g 9 th Annual Con. o the IEEE Industral Electroncs Socety Venna, Austra, - November power transer rom the grd to the battery, whch s n accordance wth the theoretcal results rom () and (). Converter phase voltage and ts spectrum are presented n Fg.. Snce the dead tme s neglected, low order harmoncs are practcally non-exstent. Machne s torque and speed are shown n Fg. 7a. The torque average value s zero, thus the speed s kept at zero. Fg. 7b presents the dc-bus voltage and chargng current. The voltage s controlled at V wthout a steady state error, and the chargng current ollows the shape o the voltage as the battery contans only a resstor and an deal voltage source n the model. B. VG Mode o the Asymmetrcal Sx-Phase System In ths subsecton conguraton s capablty o returnng the energy back to the grd s demonstrated. Snce a bdrectonal dc-dc converter s not ncluded n the smulaton model, the battery s now represented wth an deal voltage source o E = V and a resstor o R L =.Ω. Man test condtons are summarzed n Table I. Although ths presents a derent mode o operaton the control s not altered, and the only derence s that now the reerence or the dc-bus voltage has to be lower than the battery voltage, thus ts reerence s set to V. The hgher dc-bus voltage s requred due to the act that the converter phase voltage has to have the rst harmonc hgher than the grd phase voltage due to a voltage drop on the machne wndngs, whch can have hgh values prmarly due to hgh stator resstance R s o the machne (whch s n ths partcular case.ω). Needless to say, or hgher chargng currents ths voltage drop would ncrease lnearly. Fg. a presents the grd voltage and current. The current s n counter-phase wth the voltage, whch means that the energy s njected nto the grd at the unty power actor. I compared to Fg. or chargng mode o operaton, t can be seen that the grd current ampltude s slghtly lower or VG operaton. Ths occurs regardless o the act that the same voltage derence exsts between the deal voltage source o the battery and the dc-bus voltage, only n the opposte drecton. The reason or ths s that n the chargng mode the grd has to produce the power that wll charge the battery, as well as the power that wll be transerred to heat. In contrast to ths, n VG mode the power transerred back to the grd s what s let rom the battery dschargng power ater the power losses on the lter (.e. machne). Thus, consderng the xed [v g ], grd current ampltude naturally reduces. Fg. b shows the grd current spectrum, whch has very small values o low order harmoncs. Its THD s a bt hgher than or the chargng mode (Fg. because o the same rpple ampltude, whch s determned by machne parameters and has a hgher relatve value (.e. THD) or smaller unda- TABLE I. TEST CONDITIONS Chargng VG E (V) 97 (V) L - dq v a g a g FFT o waveorm (THD=.9) Harmonc requency (Hz) dg xg c) Fg.. VG mode: ( Grd phase voltage and current, ( grd current spectrum, (c) grd current components x y Fg. 9. Machne current componets: ( α and β, ( x and y. qg yg Pre-prnt. Fnal verson o ths paper appears n IEEE Xplore Dgtal Lbrary (

6 Harmonc rms (p.u.) Dc bus voltage (V) Battery chargng current L Converter phase voltage (V) Torque (Nm) Speed (rpm) 9 th Annual Con. o the IEEE Industral Electroncs Socety Venna, Austra, - November - Waveorm x - FFT o waveorm (THD=.7). Harmonc requency (Hz) Fg.. Convereter phase voltage and spectrum. mentals (as explaned n the prevous paragraph, grd currents are smaller or VG mode). Ths current at the same tme presents the machne s phase current. Grd current components are depcted n Fg. c. As n the chargng mode, the q-, x-, and y-component are kept at zero, and the d- component has a non-zero value. However, t now has a derent sgn. Fg. 9 shows machne s current components. The exctaton s agan transerred rom the torque producng (αβ) plane to the non-torque producng (xy) plane. The xy components have a derent sgn compared to Fg. b. Converter phase voltage and spectrum or VG operaton are gven n Fg.. The spectrum shows only neglgbly small values o low order harmoncs. Fg. a demonstrates that the torque has zero average value, and that the speed s kept at zero, so that the rotor does not have to be locked n ths mode o operaton ether. Dc-bus voltage s controlled at V wthout a steady state error, as can be seen n Fg. b. The battery current has exactly the same value as n the chargng mode, however t now lows n the opposte drecton. VI. CONCLUSION The paper consders an ntegrated soluton or EV battery chargng usng an asymmetrcal sx-phase machne. It thus proposes a new ntegrated on-board chargng conguraton that ncorporates nverter and propulson machne nto the chargng process. The man characterstcs o the soluton are that operaton wth zero average torque naturally results durng the chargng due to the speccs o the connecton used, and that the chargng operaton requres openng o the machne s neutral ponts (hardware reconguraton) and operaton durng chargng and VG modes n open-end wndng conguraton. Theoretcal consderatons are supported wth smulaton vercaton. ACKNOWLEDGEMENT The authors would lke to acknowledge the Engneerng and Physcal Scences Research Councl (EPSRC) or supportng the Vehcle Electrcal Systems Integraton (VESI) project (EP/I/).. -. Torque Speed Fg.. ( Machne torque and speed, ( dc-bus voltage and chargng current. REFERENCES [] Tesla Roadster speccatons, 9. [] J.M. Slcker, Pulse wdth modulaton nverter wth battery charger, US Patent,9,7, 9. [] S. Haghbn, S. Lundmark, M. Alakula, and O. Carlson, Grd-connected ntegrated battery chargers n vehcle applcatons: revew and new soluton, IEEE Trans. on Industral Electroncs, vol., no., pp. 9-7,. [] J. de Santago, H. Bernho, B. Ekergård, S. Erksson, S. Ferhatovc, R. Waters, and M. Lejon, Electrcal motor drvelnes n commercal allelectrc vehcles: A revew, IEEE Trans. on Vehcular Technology, vol., no., pp. 7-,. [] S. Knoshta, Electrc system o electrc vehcle, US Patent No.,9,, 997. [] F. Lacressonnere and B. Cassoret, Converter used as a battery charger and a motor speed controller n an ndustral truck, Proc. Eur. Con. on Power Electr. and Applcatons EPE, Dresden, Germany, CD-ROM,. [7] S. Haghbn, S. Lundmark, M. Alakula, and O. Carlson, An solated hgh-power ntegrated charger n electred-vehcle applcatons, IEEE Trans. on Vehcular Technology, vol., no. 9, pp. -,. [] L. De Sousa, B. Slvestre, and B. Bouchez, A combned multphase electrc drve and ast battery charger or electrc vehcles, Proc. IEEE Vehcle Power and Propulson Conerence VPPC, Llle, France, CD- ROM,. [9] I. Subotc, E. Lev, M. Jones, and D. Graovac. On-board ntegrated battery chargers or electrc vehcles usng nne-phase machnes, IEEE Int. Electrc Machnes and Drves Con. IEMDC, Chcago, IL, pp. 9-,. [] E. Lev, R. Bojo, F. Proumo, H.A. Tolyat, and S. Wllamson, Multphase nducton motor drves - a technology status revew, IET Electrc Power Applcatons, vol., no., pp. 9-, 7. [] E. Lev, M. Jones, S.N. Vukosavc, and H.A. Tolyat, A novel concept o a multphase, multmotor vector controlled drve system suppled rom a sngle voltage source nverter, IEEE Trans. on Power Electroncs, vol. 9, no., pp. -,. [] S. Haghbn, T. Thrnger, and O. Carlson, An ntegrated splt-phase dual-nverter permanent magnet motor drve and battery charger or grd-connected electrc or hybrd vehcles, Int. Con. on Electrcal Machnes ICEM, Marselle, France, pp. 9-97,. [] M. Jasnsk and M.P. Kazmerkowsk, Fundamentals o ac-dc-ac converters control and applcatons, n The Industral Electroncs Handbook Power Electroncs and Motor Drves (Chapter ), edted by B.M. Wllamowsk and J.D. Irwn, CRC Press,. [] E. Lev, FOC: Feld orented control, n The Industral Electroncs Handbook Power Electroncs and Motor Drves (Chapter ), edted by B.M. Wllamowsk and J.D. Irwn, CRC Press,. L Pre-prnt. Fnal verson o ths paper appears n IEEE Xplore Dgtal Lbrary (