Wireless Power Trnsfer for Running EV Powering Using Multi-Prllel Segmented Rils Ki Song, Chunbo Zhu School of Electricl Engineering nd Automtion Hrbin Institute of Technology Hrbin, Chin kisong@hit.edu.cn zhuchunbo@hit.edu.cn Kim En Koh, Tkehiro Imur, Yoichi Hori The University of Tokyo Kshiw, Jpn koh@hori.k.u-tokyo.c.jp imur@hori.k.u-tokyo.c.jp hori@k.u-tokyo.c.jp Abstrct The conventionl sttic wireless powering technology for electric vehicles (EV hs the disdvntges of non-running powering nd frequent chrging times. To solve the bove problems, novel wireless power trnsfer (WPT technology for dynmic rodwy EV powering using multiple prllel segmented rils is proposed in this pper. Firstly, currently severl dynmic powering methods re compred. Then, circuit model nd trnsfer function is estblished to nlyze the topology of this proposed, respectively. Finlly, trnsient response time of the topology is clculted by using the dominnt pole method. Both simultion nd experimentl results demonstrte tht the proposed strtegy cn chieve oven power flow nd significnt efficiency improvement compred with the trditionl structure. Keywords Wireless power trnsfer; dynmic EV powering; multi-prllel segmented rils; trnsient response time; I. INTRODUCTION To sve energy nd reduce environmentl pollution, EVs hve been widely ccepted in mny countries. However, chrging hs become bottleneck for the rpid development of EVs. Conventionl plug-in chrging sttion is limited to one EV t one time. Furthermore, high voltge is used t the chrging sttion nd sfety will be nother issue. WPT is ble to mitigte bove mentioned issues. Users only need to drive the cr to the designted spot, nd the cr will begin chrging utomticlly. This technology is known s sttic wireless powering nd is currently vilble []-[]. However, frequent chrging, hevy nd costly btteries re still required for sttic chrging. The cruising distnce is lso insufficient especilly for public trnsporttion such s bus. Bsed on ll these resons, dynmic powering which cn supply electricl energy to the moving EVs through wireless power trnsfer is reserched nd developed recently []-[9]. EVs cn therefore crry smller btteries nd even without btteries. Infinity cruising distnce cn be relized, energy supplying process to EVs is sfer nd more convenient. Currently vilble dynmic powering technology is iming t solving continuous power trnsfer issue. The hrdwre of dynmic powering system minly consists of underground energy converter & trnsmitting devices s well s EV s power receiving & converter. The importnt indexes include energy trnsfer gp, efficiency, power cpbility nd lterl mislignment distnce. Currently, reserch groups in Kore Advnced Institute of Science nd Technology (KAIST, The University of Aucklnd, Ok Ridge Ntionl Lbortory (ORNL nd The University of Tokyo re working on technicl issues tht re relted to dynmic chrging, with focus minly on system modeling, power conversion, mgnetic coupling design, mgnetic shielding technology, etc. For exmple, The University of Aucklnd used long ril to solve the energy trnsfer pth switching issue when the vehicles re moving. A -T circuit ws used to utomticlly dpt to receiver circuits, nd trnsfer efficiency ws improved significntly [9]. KAIST utilized the optimized core design in the rils to increse trnsfer efficiency nd distnce. The design hs been implemented in n ctul public trnsport system [6], [8]. In ORNL, modulr coils were rrnged long the chrging pth but trnsferred power nd efficiency were uneven during cruising due to the position of the trnsmitters nd on-bord receiver []. However, WPT will induce electromgnetic field rdition. At present, electromgnetic shielding such s instlling ferrite core or luminum plte t the bottom of vehicle is commonly used to reduce exposure towrds humn inside the vehicle. On the other hnd, humn outside the vehicles, such s pedestrins t the rodside or crossing the rod will hve high risk of exposure when long ril nd high-power dynmic powering ppliction is implemented []. Therefore, the improved dynmic powering system is required to solve the electromgnetic interference (EMI issue. In this pper, multi-prllel segmented rils bsed dynmic rodwy wireless powering method is proposed. Using single inverter nd multiple modulr trnsmitters, oven mgnetic field is formed between the trnsmitters nd receivers nd the unstble trnsfer efficiency issue is solved. Also, trnsmitters re dectivted through switching when the vehicle moves wy, therefore exposure to the surrounding humn is voided. II. SYSTEM OVERVIEW A. Scheme Comprison For running EV powering, the design of underground trnsmitters is required. According to [], [], currently there re two min types of trnsmitter designs: long ril nd This work is supported by Scientific Reserch Foundtion of the Higher Eduction Institutions (HIT. NSRIF. 8 nd Heilongjing Postdoctorl Sustenttion Fund (LBH-Z77. 978--799-66-//$. IEEE
segmented ril s shown in Fig.. This pper is bsed on mgneticlly resonnt coupling to relize the dynmic powering for EV. Anlysis in terms of trnsmitter nd receiver dimension, trnsfer efficiency, lterl mislignment nd EMC re discussed for both long ril nd segmented ril solutions. efficiency is low (< 8% due to the higher coil inner resistnce of the trnsmitter. Therefore, consecutive segmented ril method is employed to ensure the stbility of power supply nd high trnsfer efficiency. ( (b Fig.. Two min dynmic powering methods ( Long ril; (b Segment ril. Firstly, the receiver size is chosen ccording to the size of the bottom plte of the vehicle (outer size cm rectngulr coil with turns nd the verticl chrging gp is cm. Without loss of generlity, the receiver size, height nd lod in ll methods discussed below re the sme. Method I, the trnsmitter nd receiver re identicl s shown in Fig. (. Fig.. Mximum efficiency vs. lterl mislignment of different trnsmitter configurtions. The stndrd outlined by The Interntionl Commission on Non-Ionizing Rdition Protection (ICNIRP is below ma/m t khz for public exposure. Exposure bove this vlue my cuse dmge to the functionlity of nervous system []. The limit for specific bsorption rte (SAR is below W/kg nd the power density is below W/m. Exposure bove these limits will cuse heting of humn cells nd tissues s shown in Fig.. Given tht the disdvntge of high-power long trnsmitter which hs strong rdition exposure when pedestrins wit t the rodside or cross the rod, segment ril bsed dynmic powering method is proposed in this pper. Fig.. Comprison of different coupling structures using sme receiver nd different trnsmitters. ( Identicl Tx nd Rx (b Long Tx (c Hlf size Tx (d Multi-hlf size Tx. Fig. shows the mximum trnsfer efficiency plot vs. the receiver lterl displcement. For Method II in Fig. (b, the trnsmitter is with outer size cm, turns nd is lrger thn the receiver. The blue line in Fig. shows tht the efficiency is mintined t bove 9% for lrge lterl mislignment. In Method III, single smll trnsmitter (outer size cm is used nd the turn number is similrly turns. The green line in Fig. shows tht the power trnsfer is only efficient within limited lterl displcement. In Method IV, two smll trnsmitters re used consecutively to trnsfer power to the receiver. All the trnsmitters re with the sme cm, the number of turns is nd the gps between two trnsmitters re cm. From the red line in Fig., the lterl chrging coverge is significntly incresed compred to single smll trnsmitter nd the efficiency is mintined bove 8%. In Method V, much longer coil with the dimension cm nd turns is employed. From the dotted line in Fig., the Fig.. EMC of dynmic powering system for people inside/outside the EV. B. System Design Single inverter nd multiple prllel segmented rils bsed dynmic powering strtegy is used to ensure stble power nd efficiency trnsfer []. Ech segmented ril consists of trnsmitter,, high frequency switching, mgnetic sensor nd controller s shown in Fig.. Mgnetic sensor is employed to detect the position of the vehicle ccurtely by sensing the chnges of the mgnetic field strength. Switching control is performed ccording to the output of the mgnetic sensor. Dynmic wireless power trnsfer cn be used to power the AC motor of the running EV directly. When the EV is stopping, for exmple, t the trffic lights, the dynmic WPT system is used to chrge the on-bord bttery. Therefore the cruising distnce cn be extended. 978--799-66-//$. IEEE
磁磁钉 Rectifier DC-Link DC/DC converter EDLC utomticlly, but lso hs high trnsfer efficiency during loded nd low loss during unloded (only coil loss. AC-Link Grid Switching Off Rectifier Mgnetic sensor Receiver Trnsmitter Controller Switching Controller Switching Controller Switching Controller Switching Controller Inverter Off Compenstion circuit On DC-AC Converter Motor Permnent Mgnet Fig.. Digrm of multi-prllel segmented rils bsed dynmic powering system. III. ANALYTICAL MODELS A. Circuit Topology The mjor demerit of bsic SS compenstion structure is tht the input impednce of the inverter is relted to the AC equivlent lod R L. Furthermore, the voltge source v is shortcircuited in the cse of no lod so tht lrge primry side current i is introduced. To solve the problem, composed of trck inductor L nd prllel cpcitor C is employed in the trditionl primry side seril topology (seril cpcitor C nd trnsmitter L. The is used to increse the pssive power compenstion for dpting the lod chnges. Thus, it improves the stbility nd relibility of the system. On Off TABLE I. PARAMETERS OF DESIGNED RESONATORS Symbol Mening Vlue L Primry side trck inductor μh R Primry side trck resistnce. Ω C Primry side prllel cpcitor 7 nf L Primry side trnsmitter inductnce 9 μf R Primry side trnsmitter resistnce. Ω C Primry side compenstion cpcitor 8. nf L Secondry side receiver inductnce 9 μh R Secondry side receiver resistnce. Ω C Secondry side compenstion cpcitor 7.7 nf R L AC equivlent lod resistnce Ω l_tx Trnsmitter length cm l_rx Receiver length cm ω Resonnt frequency 8 khz L m Mutul inductnce of double s 8.μH Fig. 7. Mutul inductnce of two prllel s. Fig. 6. Equivlent circuit of primry side. where L m is the mutul inductnce, i is the primry side current, i is the trnsmitter current, i is the secondry side current, R is the inner resistnce of L, R is the inner resistnce of L, R is the inner resistnce of receiver L, nd R in is the primry side equivlent impednce nd described s: R in ω L R ω L ω Lm ω Lm ( R R R RL R RL Obviously, when the EV (receiver yet enters the ril, it mens tht the secondry side is equivlent to open-circuit, i.e. R L. Since R, then R in. It indictes tht the primry side current i is smll nd the inverter output power is just coil loss. When the EV is entering the ril, both R L nd L m re chnging, but R in is reltively smll nd i increses. Then, the inverter cn output high power. Thus, the plys role of utomtic impednce mtching which is not only ble to control the primry side output power ( To ensure the stbility of power & efficiency, double prllel smll trnsmitters nd big receiver is designed using the bove Method IV. All the cpcitors nd inductors re identicl in ech sub- s shown in Tble I. Here, mutul inductnce is clculted by Neumnn formul [] nd mutul inductnce between two trnsmitters is. When the circuit works t the resonnt frequency ω, the prmeters re defined s: ωl ωl ωc ωc ( ωl ωc Fig. 7 shows the totl mutul inductnce L m of the two prllel s s well s single mutul inductnce L m nd L m of ech sub-, respectively. Obviously, the totl mutul inductnce of the designed double prllel trnsmitters is equivlent with the sum of the two independent sub-s, i.e. L m L m L m. According to the equivlent circuit eqution of double prllel s, the trnsmitter current is derived s: i f is i jωcv ( The secondry side current is written s: jω ( L L ω C ( L L i i v m m m m R Rc R Rc ( 978--799-66-//$. IEEE
The lod output power is descried s: ( ω C ( L L R P i R V L m m L L ( R RL Furthermore, the primry side currents of ech sub re given s: R R R R ω L ( L L The totl current of primry side is given s: L m m m i f ωcv R RL RR R RL ω Lm ( Lm Lm is ωcv R RL ( R R R R ω ( L L L m m i ωcv R RL The primry side input power nd trnsfer efficiency is described s: in L m m in ω R RL RL( ωlm ωl L m in ( L( L ( ω( m m ( (6 (7 ( R R R R ω ( L L P i R C V (8 P η P R R R R R R L L Bsed on ( nd (9, the output power nd trnsfer efficiency re only relted with the AC equivlent lod R L if L m L m is constnt. Thus, the stble trnsfer power & efficiency is gurnteed. B. Conductnce Network Model According to the equivlent circuit model of the WPT system, the trnsfer functions of primry side voltges to secondry side currents re derived s: G I ( s bs ( s 6 V( s s s s s s s where the polynomil coefficients re given by b L m CL( L L LL ( R Rc L L R ( L L Lm R L( LL CL ( CL RRCC CL CL CCC ( LR LR( R Rc CCLL CCLm CCCL ( LL C R Rc CL RRCC CL CL CL RC RC RC CC LR LR CCC L ( L L C ( R Rc ( RC RC RC ( CL RRCC CL CL CL CCCL ( LL RC RC RC C ( R Rc CCCL ( LL ( ( ( ( CCCL( LL L m (9 ( Similrly, the primry side equivlent conductnce is vilble s: G ( s I ( s ( V ( s Rin ( s Obviously, the WPT system is liner sixth-order system. In mthemtics, this mens ( hs multi-pole tht my ffect stbility nd response time of the system. Fig. 8 shows the bode plot of the WPT forwrd chnnel. Fig. 9 shows the timedomin wveform nd frequency-domin spectrum of the secondry side current. It cn be seen tht the WPT topology cts s bndpss filter. Only the fundmentl hrmonic of the inverter rectngulr voltge is pssed nd ll the higher order hrmonics re filtered. Thus, the secondry side current wveform is lwys sinusoidl nd the conduction ngle is t the operting frequency (8 khz. Since the vlue of R is very smll, this does not dd dditionl losses nd chnge the efficiency. Mgnititude Mgnitude (bs Phse (deg Mgnititude Amplitude.... 6 8-8 -6 Bode Digrm System: G Frequency (khz: 9.6 Mgnitude (bs:.96 System: G Frequency (khz: 9. Phse (deg: 8 System: G Frequency (khz: 8 Phse (deg: -.6 Frequency (khz System: G Frequency (khz: Mgnitude (bs:.8 System: G Frequency (khz: 8. Mgnitude (bs:. System: G Frequency (khz: 6 Mgnitude (bs:. System: G Frequency (khz: Phse (deg: -8 Fig. 8. Bode plot of the WPT forwrd chnnel. x System: G Liner Simultion Results Time (seconds:.6 Amplitude:. Time (seconds Frequency (khz Single-Sided Amplitude Spectrum of i(t - -.......6.7.8.9. Frequency (khz Fig. 9. Wveform nd spectrum of secondry side current. Also, Fig. shows the bode plot of the primry side equivlent conductnce G (s. It cn be seen tht the mgnitude of third hrmonic (6 khz of the primry current is lrger thn the fundmentl hrmonic (8.9 khz, which will cuse high current hrmonic distortion. Phse (deg Mgnitude (bs 9 - -9 Bode Digrm System: G Frequency (khz: 9.6 Mgnitude (bs:. System: G Frequency (khz: 8.9 Mgnitude (bs:. System: G Frequency (khz: 8 Phse (deg: -.7 System: G Frequency (khz: 9.6 Phse (deg: -. Frequency (khz System: G Frequency (khz: Mgnitude (bs:.77 System: G Frequency (khz: 6 Mgnitude (bs:.7 System: G Frequency (khz: Phse (deg: -.6 Fig.. Bode plot of the primry side equivlent conductnce. 978--799-66-//$. IEEE
C. Trnsient Response Time It is importnt to clculte the trnsient response time of the designed WPT system when the EV is displced from the trck. This decides the effective powering rnge fter the EV reentering the trck. If the trnsient response time is enough short, it indictes tht the WPT system is ble to response quickly. The higher-order step response of the system cn be written s: K ( s z bs bs b s b Cs ( s s s s ( ( m m r i m m i n n q r n n s pj s ζω k ks ωk j k q A r A j Bks Ck s j s pj k s ζω k ks ωk q r ( [ (] sin j k m ( pt j ζ ω t k k [ ] j ω ϕ ( k dk k ct L Cs A Ae Ae t Bsed on the dominnt pole method, the step response curve is relted to closed loop poles nd zeros, nd the high order response chrcteristic is minly from poles tht re ner to imginry xis nd fr from zero. The sixth-order dominnt poles re two complex conjugte poles. Thus, the WPT response cn be pproximted by the response of second-order system. Then, the setting time Ts is derived s.8 ms (in Fig.. For dynmic segmented rils powering, the powering time Tp cn be clculted through the non-zero mutul inductnce vs. lterl displcement. For exmple, when the EV velocity is 7 km/h (i.e. cm/ms, nd Tp cn be computed s ms through Fig. 7. Since Ts << Tp, this system cn chieve rpid response for the running EV. TABLE II. RESULTS OF DYNAMIC POWERING FOR MOVING LOAD Lterl Displcement RMS of Receiver (cm Current (A Efficiency (%. 8..9 8.89 6.8 8.6 9.8 8.6.8 8.6.9 8. 8. 8..7 8.. 8. 7. 8.9.8 8.76.7 8.6 Trnsmitter Receiver ( (b Fig.. Experimentl setup trnsmitter nd receiver b mesurement results using power meter. v i f x - Step Response i s Amplitude System: pprox_g Time (seconds:.8 Amplitude:.67 i -...6.8.. Time (seconds x - Imginry Axis (seconds - x Pole-Zero Mp System: pprox_g Pole : -.8e 7.9ei Dmping:.96 Overshoot (%: 98. Frequency (khz: - -..... Rel Axis (seconds - x Fig.. Time response nd pole-zero mp of pproximted nd-order system. v i i f ( i s IV. EXPERIMENT VALIDATION To vlidte the proposed method, n experimentl setup ws constructed in the lbortory with two smll trnsmitters nd big receiver (Fig.. The coil prmeters in experiment re identicl with tht in Tble I. Fig. ( shows the wveforms of v, i nd i when R L Ω. The secondry side current nd trnsfer efficiency mesured by power meter t different lterl displcements (from cm to cm re shown in Tble II. Experimentl results demonstrte tht the system hs stble power flow nd trnsfer efficiency when the receiver is moving. (b Fig.. Experimentl operting wveforms ( Experimentl operting wveforms of primry side voltge v, two trnsmitter current i nd receiver current i when R LΩ; (b Primry side currents t cm lterl displcement. Also, the primry side current wveform t cm lterl displcement is shown in Fig. (b. It is obvious tht the hrmonic distortion exists in the ech sub-prllel primry 978--799-66-//$. IEEE
side current. Tht s becuse the cts s bndpss filter, pssing both the fundmentl nd higher order hrmonic of the squre wve of the voltge source. Theoreticl nlysis in Fig. is consistent with the experimentl results. v Fig.. Experimentl step response of primry side voltge v, trnsmitter current i nd primry side current i t no-lod condition. In order to verify the trnsient response time of the, the step response is generted by turning on the switching in the AC link. As cn be seen in Fig., significnt trnsient overshoots exist in v, i nd i t no-lod condition (i.e. EV is not entering the trck due to the underdmped. The setting time mesured by the oscilloscope is pproximtely 8 μs which hs good mtch with the theoreticl step response in Fig.. V. CONCLUSION To ensure the stble nd oven power trnsfer, this pper proposed the multi-prllel segmented rils strtegy for running EV powering. Comprison in terms of trnsmitter nd receiver dimension, trnsfer efficiency, lterl displcement nd EMC were given for both long nd segmented ril solutions. Also, the time/frequency chrcteristic of ws obtined. The trnsient response nd hrmonic distortion ws nlyzed. Experimentl results demonstrte the possibility of this method for future rodwy powering ppliction. i i REFERENCES [] S. Li, nd C. Mi, Wireless power trnsfer for electric vehicle pplictions, IEEE J. Emerging Sel. Topics Power Electron., vol., no., pp. 7, Mr.. [] G. A. Covic nd J. T. Boys, Modern trends in inductive power trnsfer for trnsporttion pplictions, IEEE J. Emerging Sel. Topics Power Electron., vol., no., pp. 8, Mr.. [] G. Ngendr, G. Covic, nd J. Boys, Determining the physicl size of inductive couplers for IPT EV systems, IEEE J. Emerging Sel. Topics Power Electron., vol., no., pp. 7 8, Sep.. [] W. X. Zhong, X. Liu, nd S. Y. Hui, A novel single-lyer winding rry nd receiver coil structure for contctless bttery chrging systems with free-positioning nd loclized chrging fetures, IEEE Trns. Ind. Electron., vol. 8, no. 9, pp. 6, Sep.. [] J. M. Miller, O. Onr, C. White, S. Cmpbell, C. Coomer, L. Seiber, R. Sepe, nd A. Steyerl, Demonstrting dynmic wireless chrging of n electric vehicle: The benefit of electrochemicl cpcitor smoothing, IEEE Trns. Power Electron. Mg., vol., no., pp.,. [6] J. Shin, S. Shin, Y. Kim, S. Ahn, S. Lee, G. Jung, S.-J. Jeon, nd D.-H. Cho, Design nd implementtion of shped mgnetic-resonnce-bsed wireless power trnsfer system for rodwy-powered moving electric vehicles, IEEE Trns. Ind. Electron., vol. 6, no., pp. 79 9, Mr.. [7] W. Y. Lee, J. Huh, S. Y. Choi, X. V. Thi, J. H. Kim, E. A. Al-Ammr, M. A. El-Kdy, nd C. T. Rim, Finite-width mgnetic mirror models of mono nd dul coils for wireless electric vehicles, IEEE Trns. Power Electron., vol. 8, no., pp. 8, Mr.. [8] J. Huh, S. W. Lee, W. Y. Lee, G. H. Cho, nd C. T. Rim, Nrrow-width inductive power trnsfer system for online electricl vehicles, IEEE Trns. Power Electron., vol. 6, no., pp. 666 679, Dec.. [9] H. Ho, G. A. Covic, nd J. T. Boys, An pproximte dynmic model of -T bsed Inductive Power Trnsfer power supplies, IEEE Trns. Power Electron., vol. 9, no., pp. -67, Oct.. [] H. H. Wu, A. Gilchrist, K. D. Sely, nd D. Bronson, A high efficiency kw inductive chrger for EVs using dul side control, IEEE Trns. Ind. Inform., vol. 8, no., pp. 8 9, Aug.,. [] F. Wen, X. Hung, J. Guo, H. Qing, Y. Xu nd Y. Wng, Study on Efficiency of Electric Vehicles mobile Chrging, Interntionl Conference on Wireless Power Trnsmission Technology nd Appliction (ICWPT, Nnjing, Chin, November -6,. [] K. Song, C. Zhu, Y. Guo, Y. Li, J. Jing nd J. Zhng, Wireless power trnsfer for running electric vehicle chrging using multi-prllel primry coils, Interntionl Conference on Wireless Power Trnsmission Technology nd Appliction (ICWPT, Nnjing, Chin, November -6,. [] T. Imur nd Y. Hori, Mximizing ir gp nd efficiency of mgnetic resonnt coupling for wireless power trnsfer using equivlent circuit nd Neumnn formul, IEEE Trns. Ind. Electron., vol. 8, no., pp. 76 7, Oct.. 978--799-66-//$. IEEE