Coordinated Charging Optimization Strategy of Electric Vehicles

Transcription

1 1225 A publcaton of VOL. 51, 216 CHEMICAL EGIEERIG RASACIOS Guest Edtors: chun Wang, Hongyang Zhang, Le an Copyrght 216, AIDIC Servz S.r.l., ISB ; ISS he Italan Assocaton of Chemcal Engneerng Onlne at DOI: 1.333/CE Coordnated Chargng Optmzaton Strategy of Electrc Vehcles Xngpng Lu* a,d, Xangyun Luo b, Wedong L c, Shjun L d, Haomng Yu a a College of Electrcal & Informaton Engneerng; Hunan Insttute of Engneerng; Hunan Provncal Key Laboratory of Wnd Generator and Its Control, Xangtan 41111, Chna b Hunan Mass Meda Vocatonal echncal college, Changsha 411, Chna c Powerchna Zhongnan Engneerng Co. Ltd., Changsha 4114, Chna d Hunan provnce Cooperatve Innovaton Center for Wnd Power Equpment and Energy Converson, Xangtan 41111, Chna B12918@hnu.edu.cn he large-scale uncoordnated chargng threatens the safety operaton of power grd. In the paper, two coordnated chargng modes were proposed: automatc on-off chargng mode and the smoothly adjustng chargng mode. he 2 coordnated chargng modes were establshed based on exstng power dstrbuton networks n resdental areas and the constrant condtons of the dstrbuton transformer and crcut capacty n order to transmt maxmum electrc power to electrc vehcles. he establshed mode formulas were solved wth stochastc smulaton and modfed partcle swarm algorthm. akng the chargng staton n one resdental area n Shenzhen as an example, we performed the smulaton of vehcle chargng accordng to the uncoordnated chargng mode and the 2 coordnated chargng modes. We compared the voltage dstrbuton n the three modes respectvely. Based on the computaton of the proft amount and the volatlty, we proposed the concept of cost savng so as to compensate for the expense of nvolved users. he smulaton results showed that the two coordnated modes could rase user satsfacton and promote the smooth operaton of power grd. Chargng management system can choose one operaton mode as requred. 1. Introducton In Chna, electrc vehcles nclude prvate cars, buses, taxs and offcal cars, most of the parked cars n the resdental areas are prvate cars. In the coordnated chargng optmzaton mode of electrc vehcles, buses, taxes, or offcal cars were not consdered. Prvate cars are often used n the day for work or entertanment and parked n resdental areas for a short tme n the day and a longer tme n the nght. Prvate cars allow a slow chargng speed. herefore, t s necessary to optmze the coordnated chargng mode accordng to the nght chargng requrements (Roterng and Ilc, 211). 2. Analyss of chargng modes 2.1 Automatc on-off chargng mode In the automatc on-off chargng mode, one or several electrc cars automatcally start or termnate the chargng process at any tme accordng to the procedure. When the s approachng the rated capacty of the dstrbuton transformer, the chargng management system wll automatcally stop the chargng process of one or several electrc cars; when the common contnues to fall, the management system wll automatcally connect one or several electrc cars nto the grd network for chargng (Cao et.al., 212). 2.2 Smoothly adjustng chargng mode In the smoothly adjustng chargng mode, at any tme, the chargng power of the off-board charger s adjusted contnuously and automatcally. he rated chargng power of the battery charger s generally 4 kw, but the chargng power wll contnuously vary between and 4 kw to charge the electrc vehcles n the smoothly adjustng chargng mode (an et.al., 213). Please cte ths artcle as: Lu X.P., Luo X.Y., L W.D., L S.J., Yu H.M., 216, Coordnated chargng optmzaton strategy of electrc vehcles, Chemcal Engneerng ransactons, 51, DOI:1.333/CE165125

2 Coordnated chargng optmzaton mode 3.1 Coordnated chargng model n the automatc on-off chargng mode Accordng to the hstorcal average n the power dstrbuton network n the resdental area, the normal curve of a certan day can be predcted wth the 96-pont daly curve forecastng method wth the nterval of 15 mn (Clement et.al., 21). If the number of the alternatng chargng ponts n the resdental area s, accordng to the slow chargng method, the battery charger charges the lthum battery under a constant power. he model ams to realze the maxmum transmsson energy to electrc vehcles: max P x ( t) t t1 1 EV Where P EV s the rated chargng power of an electrc vehcle; n the perod t, when the th chargng pont s dsconnected wth the electrc car or the chargng s completed, x (t)=, when the th chargng pont s connected wth the electrc car and the chargng s not completed, x (t)=1 ; t s the length of the chargng perod Constrant condtons Constrants of the voltage range of the resdental area he of connected electrc cars wll cause the voltage reducton of the dstrbuton network node, whch s determned by the access pont of electrc cars and the chargng power. (Sortomme et.al., 211). he rated voltage range of the chargng pont s: V V V mn max Where V s the voltage of the th chargng pont; V max and V mn are the maxmum and mnmum voltage of the power dstrbuton network, respectvely Constrants of the transformer capacty In the perod t, the sum of the average of the resdental area and the chargng rated should not bgger than the rated output power of the transformer: (1) (2) PEV x ( t) P( t) S cos 1 (3) Where P(t) s the average of the resdental area; S s the rated capacty of the transformer; cos s the rated power factor of the transformer and generally set as.95; s the rate of the transformer and t s determned by the type and the model of the transformer and assumed to be between 3% and 65% Constrants of the chargng power o avod the large fluctuatons caused by the sudden access or removal of electrc cars, the varaton of the chargng power n the chargng staton should be restrcted n sequental chargng perods(peter et al., 212). P x ( t) P x ( t 1) P EV EV 1 1 (4) Where P s the chargng power range between the current chargng perod and the former chargng perod and defned as 2 kw n ths paper Constrants of the chargng capacty t1 P x ( t) t (1 SOC ) EV, (5) Where SOC, s the ntal state of the th electrc car; I s the battery capacty of the th electrc car Constrants of charge state contnuty PEV x () t t SOC, t SOC, t 1 (6)

3 where SOC,t s the charge state of the th electrc car n the end of the chargng perod t; SOC,t-1 s the charge state of the th electrc car n the end of the chargng perod (t-1) Constrants of chargng protecton he management system wll montor the EMS of the electrc car n the chargng state n the perod t to avod the overcharge phenomenon. P t (1 SOC ) EV, t Constrants of the crcut heat he heat of the network element refers to the rato of the apparent power of the element to ts rated power. he heat consdered n ths paper refers to the heat of the connectng crcut between transformers: L L MC MC max L MC means the heat of the crcut; L MCmax means the maxmum heat. 3.2 Coordnated chargng model n the smoothly adjustng chargng mode In order to realze the more balanced dstrbuton of the chargng power of electrc vehcles we mproved the objectve functon mentoned above by ntroducng SOC factor(h et al., 212; Su et al., 213). In the smoothly adjustng chargng mode, supposng that the chargng power can be contnuously adjusted, the maxmum chargng energy transmtted to electrc vehcles s: 1227 (7) (8) max (1 SOC ) P ( t) x ( t) t t1 1, t EV where P MC(t) s the chargng power of the electrc vehcle n the th chargng pont Constrant condtons are respectvely expressed below he chargng power of the electrc vehcles should not surpass the rated output chargng power P ( t) P EV EV (9) (1) Accordng to the current battery technology, n order to avod the wde fluctuaton of the chargng power, the constrant of the chargng power varaton range s: P ( t 1) p P ( t) P ( t 1) p EV EV EV where p s the maxmum varaton range of the chargng power of the electrc vehcles and the access/removal shftng of the chargng of electrc vehcle. It s generally defned as.5 KW. Constrants of the voltage range of the resdental area are smlar wth Eq. (2). In the perod t, the sum of the average of the resdental area and the chargng should not surpass the rated output power of the transformer: (11) PEV ( t) x ( ) ( ) cos t P t S 1 (12) Constrants of chargng capacty: t1 P ( t) x ( t) t (1 SOC ) EV, (13) Constrants of charge state contnuty PEV ( t) x ( ) t t SOC, t SOC, t 1 (14) Because the objectve functon has ntroduced the SOC factor, the overcharge phenomenon wll not come out when chargng the hgh SOC battery wth a low chargng power. hus, the overcharge condton should be neglected. he computng method of the constrants of the crcut heat s the same to Eq. (8)

4 Coordnated chargng control algorthm Combned wth the stochastc smulaton, the modfed partcle swarm optmzaton (PSO) method was adopted to solve maxmum electrc energy transmtted to electrc cars n the paper(zhan. et al., 212). akng the advantage of randomness and perodcty to generate the ntal partcle, the search dversty of the algorthm can be strengthened. hrough the ntroducton of the algorthm stagnaton mutaton mechansm, the probablty to realze global optmzaton nstead of local optmzaton wll be ncreased, thus avodng the premature convergence of the algorthm(yang et al., 213). In addton, the dynamc nerta factor W s ntroduced to balance global search ablty and local search ablty of the algorthm n the teraton process: ww t max w w ' max mn max where w max and w mn are the maxmum and mnmum dynamc nerta factors, respectvely. Generally, w max=.9, w mn =.9; w mn =.4; t and max are respectvely the present teratons and the maxmum teratons. In ths paper, only the chargng perod of 14 h from 16: to 6: n the next day was consdered. 4. Smulaton 4.1 Power dstrbuton network n resdental areas akng a resdental area n Shenzhen as an example, the model parameters are provded as follows: 2 dstrbuton transformers wth the capacty of 63 kva, the no- voltage rato of 1/.4 kv, 2.8-km long three-phase lne, 1.2km long sngle cable, and 5 domestc households. he voltage fluctuaton range of the low-voltage dstrbuton network s -1%~+1% (22 V/38 V). It s assumed that there are 6 chargng ponts and 1 electrc cars n the resdental area. Accordng to the normal dstrbuton, we dstrbuted the chargng ponts nto Dstrcts A and B n an unequal way. When all the chargng ponts are connected to the electrc cars, other electrc cars wat for chargng. he battery capacty of an electrc car s 2 kwh. In addton, the car should be fully charged before 6: n the next mornng. 4.2 Comparson of the 3 modes Uncoordnated chargng mode of electrc vehcles In the uncoordnated chargng mode, the stochastc smulaton of the arrval tme and SOC of each car was performed through the Monte-Carlo method to start the chargng process. In the uncoordnated chargng process, when a car s connected to the chargng pont, t wll be charged at the rated power untl the full chargng process s completed. In the calculatng calculaton of the average, the curve s prone to be gathered n the peak tme, as shown n Fgure 1. In the evenng, electrc car users wll start to charge cars as soon as they arrve at the resdental area. If the number of chargng ponts s not enough, partal electrc cars wll wat for chargng. If one transformer s n an overhaul, the other transformer works alone. In the perod (21: 45-22: 3), the transformer wll be serously overcharged and the crcut wll be overheated. he overheat phenomenon s not permtted. 8 7 (15) /kw User Chargng total 16:17:18:19:2:21:22:23::1: 2: 3: 4: 5: 6: tme Fgure 1: Load curves of the uncoordnated chargng mode Automatc on-off chargng mode Consderng the travel habts of users n the resdental area, n ths paper we only studed the chargng tme n the nght from 16: to 6: n the next day. In the automatc on-off chargng mode, the management system wll automatcally control the swtches of the battery charger to realze the safety operaton of the grd power accordng to the chargng requrements.

5 As shown n Fgure 2, the swtches of the car wll be shut down at the peak tme and reconnected at the low- tme, thus realzng the purpose of mnmzng the chargng cost and the gap between peak and valley tme by peak shftng Load/kW otal User On-off chargng mode automatcally he chargng mode of smooth adjustment 2 1 Chargng 16: 17: 18: 19: 2: 21: 22: 23: : 1: 2: 3: 4: 5: 6: me Fgure 2: Load curves of the coordnated chargng mode Smoothly adjustng chargng mode In ths mode, the chargng power of electrc cars can be adjusted contnuously. We have collected the data every 15 mn. he 12th car starts to charge at 19: 3 and ts chargng power s rsng. However, at the peak tme, the power decreases to. hen, the car s reconnected at 23: and the power rses to the hghest power (3.5 kw) untl : 3. he full chargng process s completed at 2: Results and analyss able 1: Parameter settngs of energy prces Chargng perods OU prce (Yuan/kWh) unform power prcng (Yuan/kWh) 16: -17: : -21: : -:.687 : -6: able 2: Smulaton results of coordnated and uncoordnated chargng modes Chargng modes Uncoordnated chargng mode Automatc on-off chargng mode Smoothly adjustng chargng mode 5% automatc on-off chargng mode 5% smoothly adjustng chargng mode Proft amount Load volatlty otal maxmum he end tme of chargng he end charged state : 1% : 1% : 1% : 1% : 1% Power grd sells the electrcty n the form of OU electrc prce, and the battery charger management sectors develop the unform power prcng system. he parameter settngs of energy prces are provded n able 1. Accordng to the smulatng calculaton wth Monte-Carlo method, total chargng electrc energy of all the electrc cars s 1442 kwh. he smulatng results of the coordnated chargng mode and un-coordnated chargng mode are provded n able 2.

6 123 Accordng to the results n able 2, the coordnated chargng mode can ncrease the proft amount of the chargng statons n the resdental area. However, the chargng statons n the resdental area are not amed at makng proft. After deductng the captal cost of the statons, the rest are assumed as the savng cost, whch wll be pad to the users so as to rase the customer response coeffcent. he cost n the two modes mentoned n ths paper s lower. herefore, they wll attract more users of electrc vehcles to partcpate n the coordnated chargng mode. For the electrc power sector, the coordnated chargng mode s helpful to reduce the volatlty of curve; for the electrc car users, the coordnated chargng mode s helpful to obtan addtonal compensaton and reduce the chargng cost. After the electrc vehcles are wdely used, the chargng staton wth the coordnated chargng mode wll be a mutually benefcal strategy. 6. Results and analyss akng a resdental area n Shenzhen as an example, we compared the two coordnated chargng modes wth the uncoordnated chargng mode and found that coordnated chargng modes could be drectly adopted n the orgnal power dstrbuton network wthout the upgrade or transformaton of the power grd nfrastructures, thus reducng the project cost. he smoothly adjustng chargng mode has a hgher proft potental and the smoother curve. he automatc on-off chargng mode s smple and relable. he two modes can both realze the mnmum chargng cost and the smallest gap between peak and valley tme by peak shftng. If the mode s promoted n a large scale, ts economc proft wll be consderable. Reference Cao Y., ang S., L C., 212, An optmzed EV chargng model consderng OU prce and SOC curve, IEEE rans. on Smart Grd, 3(1): Clement.K., Haesen E., Dresen J., 21, he mpact of chargng plug-n hybrd electrc vehcles on a resdental dstrbuton grd, IEEE rans. on Power Systems, 25(1): Hu Z.C., Song Y.H., Xu Z.W., 212, Impacts and utlzaton of electrc vehcles ntegraton nto power systems, Proceedngs of the CSEE, 32(4): 1-8. Peter R., Daman F., Andrew K., 212, Optmal chargng of electrc vehcles n low-voltage dstrbuton systems, IEEE rans. on Power Systems, 27(1): Roterng., Ilc M., 211, Optmal charge control of plug-n hybrd electrc vehcles n deregulated electrcty markers, IEEE rans. on Power Systems, 26(3): Sortomme E., Hnd M.M., Macpherson S.D.J., 211, Coordnated chargng of plug-n hybrd electrc vehcles to mnmze dstrbuton system losses, IEEE rans. on Smart Grd, 2(1): Do: 1.119/SG Sun X M., Wang W., Su S., 213, Coordnated chargng strategy for electrc vehcles based on tme-of-use prce, Automaton of electrc power systems, 37(1): an W.Q., He J.H., Jang J.C., 213, Electrc vehcle chargng spatal allocaton optmzaton algorthm, ransactons of Chna Electrotechncal Socety, 28(3): Yang B., Wang L.F., Lao C.L., 213, Research on power-chargng demand of large-scale electrc vehcles and ts mpactng factors, ransactons of Chna Electrotechncal Socety, 28(2): Zhan K.Q., Song Y.H., Hu Z.H., 212, Coordnaton of electrc vehcle chargng to mnmze actve power losses, Proceedngs of the CSEE, 212, 32(31):