Novel Energy Management System for a DC MicroGrid

Transcription

1 vel Enegy Management System fo a DC MicoGi Ashan Imantha Banaa 1, Pah Binuhewa 2, Lilantha Samaanayake 3, Janaka Ekanayake 4 Dept. of Electical Eng. Univesity of Peaeniya Peaeniya, Si Lanka 1. ashanimhb31@gmail.com; 2. pah@ee.pn.ac.lk; 3. lilantha@ee.pn.ac.lk; 4. jbe@ee.pn.ac.lk Abstact This pape pesents a esign an simulation of a ule base enegy management system fo a c MicoGi that consies a cost function to eflect the tey egaation an that elates to the actual tey paametes.the eivation of the tey cost function an the utilization of that to ensue an optimum utilization of the tey enegy stoage wee pesente. The etaile esciption of the algoithms use to implement the EMS was pesente. Simulation on PSCAD/EMTDC softwae was use to emonstate the opeation of the EMS both une gi connecte an islane moes. Futhe, the inetia suppot povie by the supe-capacito to avoi the collapseof the c link of the MicoGi was emonstate. Keywos - MicoGi; EMS; tey; supe-capacito ***** I. INTRODUCTION The avese effects to the envionment cause by buning of fossil fuel an epletion of fossil fuel tiggee to seach fo altenative electicity geneation souces. As an altenative, enewable enegy souces such as photovoltaics an win ae now emege as main steam powe geneation souces. As the enewable enegy esouce is intemittent an vaiable, they have intouce challenges in tems of maintaining voltages, line flows an stability of utility netwoks. In oe to ovecome some of these challenges MicoGis have been consiee. A MicoGi is a low-voltage powe system, smalle in capacity, consisting local geneation an local loas with ability to opeate autonomously o gi connecte moes [1]-[4]. Custome point of view, MicoGi impoves the eliability of powe wheeas fom the utility point of view, MicoGi enables to connect highe pecentage of enewables without estabilizing the existing utility netwok. In oe to facilitate the stable opeation of a MicoGi une autonomous moe, enegy stoage within the MicoGi is essential. Even though ealy MicoGis consist of ac feees, only c MicoGis an hybi MicoGis ae emeging [1]-[4]. Thee ae two main easons to attact inteest fo c MicoGis [1], [5]-[7]. Renewable enegy souces such as PV an enegy stoage pouce c voltages. In oe to integate them to ac MicoGi, a c-c-ac convesion stage is essential. Futhe, many loas such as ICT equipment, entetaining equipment, potable appliances, etc. opeates on c intenally thus equiing ac-c(-c) convesion stages when connecting to the ac MicoGi. A c MicoGi consists of numbe of micosouces (<5 kw) such as PV systems, win tubines, an fuel cells [8], [9]. These micosouces integate to the MicoGi though single-stage powe convesion stage (often c-c). The utility inteconnection shoul allow bi-iectional powe flow thus equiing a bi-iectional ac-c convete. The c MicoGi also equies enegy stoage to ovecome the tansient in the system an to negate meium o long tem eman-supply mismatches. Supecapacitos an flywheels ae use to ovecome the tansients within the MicoGi while tey stoage is use fo meium o long tem eman supply matching [1]-[14]. Hieachical contol that incopoates tetiay, seconay an pimay contol stages ae usually employe fo a c MicoGi. Pimay contol, which efes to the oop-contol, espons to the paametes set by the seconay contol such that the voltage is maintaine within the acceptable values. Seconay contol ensues that the powe shae by each souce is in accoance with the values scheule by the tetiay contol. Tetiay contol efes to the Enegy Management System (EMS) that uses a ule-base system o an optimization outine base on cost o loss optimization to scheule iffeent constituent pats of the MicoGi. Diffeent EMSs ae iscusse in the liteatue. In [15] an EMS fo an ac MicoGi is pesente. Six opeating moes wee efine base on the gi voltage an fequency. A ule base EMS was use to select the most appopiate opeating moe that scheules the utility powe exchange, enegy stoage, an enewable enegy souces. In [16] an EMS application foa c MicoGi establishe in an office builing is pesente. The powe balance is use as the ecision making vaiable an the cabon emission is optimize. In [17] an EMS base on a ule base ecision making system is implemente fo an isolate c MicoGi. An EMS with layee achitectue is pesente in [18]. The topmost laye is the human machine inteface. The next laye, the peiction laye, use metaata to peict the loa an souce pofiles. Then the enegy management laye efines the scheules an the 142

2 opeating laye sens the commans accoing to the scheule moel fo the egaation of the enegy stoage evice ue to given by the enegy management laye. The opeating laye is constant chaging an ischaging. Even though [21] evelope as a ule base system. Consieing two types of c consiee a cost function to eflect tey egaation, it is MicoGi configuations, istibute enegy esouces with epening on a numbe of unknown constants which ae not lumpe loas an istibute enegy esouces with istibute elate to the actual tey paametes. Consieing the loas, efeence [19] pesents a ule base EMS. An EMS with simplicity of the ule base system, in this pape an EMS was fuzzy contol fo a c MicoGi is pesente in [2]. Hee in evelope using a ule base system while consieing a cost oe to impove the life cycle of the tey, the fuzzy function that eflects the tey egaation an that elate to contolle manages the esie state of chage of the tey. A the actual tey paametes. Futhe a supe-capacito was complex EMS consieing a multi-objective optimization with use fo inetia suppot. foecasting of esouces is pesente in [21]. Except in [21], none of the othe EMS implementations consiee the etail MicoGi Contolle Enegy Management System AC Utility Connection CB AC (PCC) V DC(s) V * DC (s) + - Contolle of Contolle Rectifie I (s) I * (s) G V(s) + - G I(s) m q A V DC(t) CB SLR V * MPPT (s) V in(s) + - Contolle of sola pv convete I * L (s) H V(s) + - H _Sl I(s) B I L(s) HV Feee 38 V CB V DC_Link * (s) V DC(s) + - Contolle of tey Stoage convete I * Lb (s) H V_(s) + - H I_(s) I Lb(s) _ C E F LV Feee 1 & 2 48 V Supe Capacitos CB SC V DC_Ref(s) V DC(s) V * 48 (s) + - Contolle of Supe-Capacito convete + _SC - C p(s) + - H I_SC(s) D I L_SC(s) Contolle of LV Feee I * L_48 (s) H V_48(s) + - H I_48(s) DC Link _48 V 48(s) I L(s) Figue 1. Popose c MicoGi topology II. MICROGRID PLATFORM The popose MicoGi is shown in Fig. 1. It has sola photovoltaic (PV) as local geneation, connecte to the utility ac gi, a tey an a supe-capacito as enegy stoage system (ESS) elements an two feees to local loas. The utility inteface etemines the powe exchange between the MicoGi an the ac utility netwok. Thus when thee is a eficit powe in the MicoGi the contolle will use convete A to impot powe fom the ac utility netwok. Convesely when thee is excess powe, contolle of convete A will expot powe fom MicoGi to ac utility. This is one by a efeence, Rf Gi, eceive fom the EMS to the powe egulation contolle (this is not shown in Fig. 1). As Sola PV is a non-conventional enewable enegy souce, the contolle of the PV system extacts the maximum available powe at a given instance an aely euces the output fom the available maximum.occasionally PV output is she though a efeence, Rf PV, eceive fom the EMS. The tey stoage is assigne to supply steay state powe equiement as scheule by the EMS in both gi connecte an islane moes. Convete C chages the tey when thee is excess powe an ischages when thee is a powe shotage in the c MicoGi. This is one by a efeence, Rf, eceive fom the EMS. Thus supe-capacito is assigne to supply the api powe emans of the MicoGi. Due to the vaiations in loas an souces c link voltage vaies. This voltage vaiation inclues both tansient an steay state components. Howeve, when the EMS maintaining the powe balance the vaiation of the c link is mainly tansient vaiations an the supe-capacito is contolle by an oute loop that maintains the c link voltage to a efeence.as enegy can be extacte fom the supe-capacito elatively 143

3 fast, the above contol action also povies inetia suppot to The tey constant voltage, E, is given by: the c MicoGi. E VFull K RI A (2) III. A. tey moel COST FUNCTION OF THE BATTERY The tey moel escibe in efeence [22] was aopte fo this stuy. The moel is shown in Fig. 2. It is base on an feeback loop that computes the intenal tey voltage base on (1): t B I t Q E E K Ae t whee in (1) an Fig. 2, E = loa voltage (V) E (1) Q I t = tey Constant Voltage K = Polaization Voltage (V) Q = tey Capacity (Ah) t I t = Utilize tey chage (Ah) A = Exponential zone amplitue (V) B = Exponential zone chage constant (Ah-1) V = tey teminal voltage V Full V Exp V nom E + - equation (1) Voltage (V) R Figue 2. tey moel t I + V - The polaization voltage, K, is given by: V K Full V nom A e B. Qnom 1 Q Q The iffeent values of (3) can be obtaine fom the typical ischage cuve shown in Fig. 3. The Exponential zone amplitue, A, an exponential zone chage constant, B ae given by: A V Full V Exp (4) Q nom Q Exp nom (3) 3 B (5) The intenal Resistance of the tey is given by [23]: Vnom1 R (6) C. Q ate whee = Efficiency of the tey Exp C ate = ischage cuent multiplie B. Cost function Evey time the tey chages an ischages, it is being egae. The state-of-chage (SOC), state-of-health (SOH) an epth-of-ischage (DOD) of the tey ae the main factos that etemine the egaation of a tey. These paametes eflect the effects of opeating tempeatue, opeating cuent an teminal voltage of the tey. In oe to ecie whethe to take the powe fom the gi o fom the tey, a cost function that eflects the egaation of the tey was eive. This was base on efeence [24]. The cost of enegy usage of a tey is given by: F C P P in S/h (7) whee C is the cost of utilizing the tey in $/kwh P is the ischaging powe P is the losses incopoate with ischaging opeation Q exp Qnom Figue 3. Typical ischage cuve Capacity (Ah) The cost of utilizing the tey is given by: C C C (8) Chag Avail whee is the cost of chaging the tey CChag C Avail is the availability cost which is the cost of keeping 1 kwh stoage capacity available. R = Intenal Resistance I = te cuent 144

4 If enewable enegy is puely use fo chaging the Fig. 4. Inputs shown in Fig. 4 ae escibe une each tey CChagcan be consiee as zeo. Thus C Avail is the opeating moe. cost incopoate with the tey usage an is given by: Replacement Cost C Avail (9) C whee C is the total life time cycling capacity of the tey P = PPV P Stat Rea Inputs PGi, PPV, P, PSC, P GiSts, SOCBt, PiEsell, PiEbuy, Pi SOCMin, SOCMi, SOC, P_B, P_G RfGi, RfPV, Rf, RfSC, Rf GiSts == 1 P = PPV P P>= P>= The total life time cycling capacity, C, of the tey epens on the ate capacity of the tey ( C ), ate epth-of-ischage ( DOD ) an life time in tems of cycles ( L ). Fo a Li-Ion tey C is given by (1). C C DOD.9L.1) ` (1) Moe 1 Expot Pioity Moe 2 Impot Pioity Retun Moe 3 ESS Pioity Moe 4 Deman Pioity The numbe of cycles fo Li-Ion teies is given as a cuve in [25]. Fom cuve fitting (11) was obtaine to epesent L ln DOD L exp (11).685 The losses associate with the ischaging the tey (shown in (7)) is given by whee P R 2 P P V K SOC C. K t V SOCt t SOC K an R ae as efine in equations (3) an (6) V is the ate voltage of the tey IV. PROPOSED EMS SYSTEM (12) The popose EMS system is implemente as a eal time opeating algoithm. Befoe commencing the algoithm a set of vaiables ae initiate insie the EMS. Pio to selecting the most suitable opeating moe, the EMS algoithm fist check the status of the utility gi (Gi Sts ) to etemine whethe the MicoGi is in gi connecte moe (Gi Sts =1) o in islane moe (Gi Sts =). Next it checks the powe balance ( P ) between sola PV ( P PV ) an Loa ( P ) using equation (13): P P P (13) Depening on the powe balance an availability of the utility the EMS ecies fou opeating moes as shown in PV Figue 4. The block iagam of the Popose EMS A. Expot Pioity Moe The algoithm use fo this moe is shown in Fig. 5. The EMS will fist evaluate the state-of-chage of the tey ( SOC ). If SOC is less than the maximum allowable SOC level, SOC, then the excess powe is use to chage the tey. The conition SOC SOC is efee to as SOC constaint in subsequent sections. While maintaining the ate epth-of-ischage the limit can be ajuste SOC to shift the chaging pofile of the tey. Befoe scheuling the chaging powe of the tey, EMS checks the powe ating of the convete C (Fig. 1). If the excess powe is moe than the ate powe ( P _ B ) of the tey inteface convete, the EMS will scheule the tey chaging powe efeence ( Rf ) to maximum. Othewise it will scheule the tey to chage using the available powe. Once the tey is fully chage then the tey inteface convete goes into ile state. Then the EMS checks the possibility of expoting available powe to the ac utility. If the excess powe is moe than the ating of the ac utility inteface convete (A), P _ G, the EMS scheules the expot powe ( Rf Gi ) to be the maximum an initiate a PV sheing scheme in oe to keep the powe balance within the MicoGi. The amount of PV to be she was calculate using (14). B. Impot Pioity Moe Rf P P (14) PV Gi In the gi connecte moe if the total local loa is moe than PV geneation, the EMS shifts to the impot pioity moe. The contolle ectifie is scheule to impot powe fom the ac utility o tey inteface convete is scheule to ischage an supply the powe to keep the powe balance 145

5 insie the c MicoGi. Futhe in this moe tey is chage if the utility Time of Use (ToU) pice is minimum. The algoithm use fo this moe is shown in Fig. 6. In this moe the scheuling is pimaily one accoing Initially algoithm checks whethe C C ; in othe to the cost of impoting powe fom the ac utility ( C ), Utility an the cost involve in ischaging the tey ( C ). The ac utility pice, _ C Utility, is the selling pice of the enegy fom sevice povies to the MicoGi an assume as a ToU taiff. The cost of ischaging the tey was compute using (7) by multiplying F with the time step of each iteation. Set Chaging Rf = P Moe 1 Expot Pioity SOC< SOC P < P_B Retun Set powe Chaging Rf = P_B Set tey convete off Rf = P < P_G ance Powe Expots to the gi Set powe expot RfGi = P_G PV Sheing Figue 5. The Expot Pioity moe opeating block iagam Moe 2 Cost Pioity _ Utility was whethe the cost of impoting powe fom the gi is less than the ischaging the tey. If the tey enegy cost ( C ) is moe than (C ), the EMS will impot _ Utility powe fom the ac utility. To pocee futhe the EMS checks whethe the powe balance is less than the ating of the contolle ectifie (P_G ). Then EMS checks whethe the utility enegy pice is the minimum pice of ToU C ). Also it checks the SOC constaint. The esie ( Utility _ Min chaging powe of the tey is set accoing to (15) whee k is a constant use to ensue that the total impot powe is within P_G. P _ G P ; k 1 Rf k (15) c Futhe, the balance powe is impote fom the ac utility though the utility inteface convete.on the othe han if the P is moe than P_G, the algoithm examines whethe the tey has sufficient chage, i.e. SOCMin SOC, to supply the eman that cannot be supplie solely by impoting powe fom the ac utility. Then the tey convete is scheule to ischage moe accoing to (16). Howeve if te oesn t have enough chage then the eman sie management (DSM) is initiate to maintain powe balance. Rf P _ G P (16) c P < P_G CUtility = CUtility_Min SOC<SOC Set Chaging Rf = k*(p_g - P) Set Dischaging Rf = k*(p_b - P) Set Dischaging Rf = P C_ > CUtility Tun Off Rf = ance Powe Impot fom the gi GiReq == 1 Set Dischaging Rf = P_G - P imum Powe Impot fom the gi SOCMin < SOC P < P_B Set powe Dischaging Rf = P_B P < P_G Tun Off Rf = SOCMin < SOC Tun Off Rf = Convesely when the extacting enegy fom the tey C _ is cheape than utility pice, C Utility, the EMS will scheule the tey stoage to supply the eman instea of utility inteface. Howeve the c link contol is hanle by the utility inteface convete. Fistly the contolle checks whethe SOCMin SOC. If the tey has sufficient SOC, then the convete ating is checke against P. If the ating is aequate then P is supplie by ischaging the tey.howeve in an instance whee the ac utility opeato equests suppot fom the MicoGi, it is going to act as a goo citizen. So in Impot pioity moe when the tey enegy is cheape it checks whethe ac utility equest suppot (Gi Req = 1). In such situation the tey is scheule accoing to (17)in oe to incease the ate of ischage an sell electicity to the ac utility. Rf k P _ B P ; k (17) 1 Retun Deman Sie Management Figue 6. Block iagam of Impot Pioity Moe Futhe, in impot pioity moe the utility inteface convete is pimaily impoting powe fom the utility o keep in ile while contolling the c link. Howeve if ac 146

6 utility equie suppot then it expots the equie amount of inteface) ae scheule to opeate while maintaining the powe fom c MicoGi to ac utility. powe balance in islane c MicoGi. Thus the efeence C. Enegy Stoage System (ESS) Pioity Moe powe of the tey inteface convete ( Rf ) is automatically ajuste to P. ESS Pioity moe occus uing islaning (Gi Sts =) whee the MicoGi has excess powe ( P is positive). Since thee is no gi connection thee is no oppotunity to keep the powe balance within the MicoGi by expoting available excess powe. Only possibility is to use the excess powe to chage the tey. It also checks whethe the tey is ovechage. Fig.7 shows the block iagam of the ESS pioity moe. When ESS pioity moe is initiate, fist it inspects the SOC constaint of the tey. If this conition satisfie, the EMS check the excess powe against the powe ating of the tey convete. When the available powe is less than powe ating of the Convete C, the tey is set to chage using P.. D. Deman Pioity Moe The fouth opeating moe of the EMS is the eman pioity moe. This is the most citical opeating conition of the c MicoGi. The eman pioity moe is activate in islane moe when the P is negative. Thus in this moe the high pioity is given to ensue the uninteupte supply to the loas an stability of the MicoGi. The coesponing block iagam is given in Fig. 8. Moe 4 Deman Pioity Moe 3 ESS Pioity SOC > SOCMi SOCMin < SOC < SOCMi PPV > P < P_B SOC < SOC P < P_B Deman Sie Management ance Powe supplie by ischaging the tey PV Sheing Retun Shutown Figue 8. Block iagam fo Deman Pioity Moe ance Powe use to chage the tey Retun Figue 7. Block iagam of ESS Pioity Moe Othewise it chages at the maximum ating of the convete. Howeve one o both constaints in elation to SOC o convete ating fail then to ensue the powe balance PV sheing is initiate to spill the unuse excess powe. The amount of PV to be she was calculate accoing to (18). Rf P P (18) PV In the islane moe, the tey stoage contols the c link voltage. Simila to the opeation of the utility inteface convete in gi connecte moe, the tey inteface convete cannot be scheule iectly to efeence powe levels. Instea the othe convete (sola PV an loa Fist the SOC of the tey, SOC, is checke against a peefine SOC level, SOC Mi. If the constaint, SOC Mi SOC is satisfie then the powe ating of the Convete C is checke by the EMS. If equie powe eman is moe than the tey inteface convete ating then the eman sie management is state. Othewise MicoGi opeates nomally while supplying the eman by ischaging the enegy stoage togethe with available PV. When constaint given by SOCMi SOC fails then the following constaint is checke by the EMS to avoi eep ischaging of the tey: SOC SOC SOC (19) Min If the SOC of the tey is within the limits, the EMS initiates DSM potocol an shes unwante loas to incease the opeating uation of the c MicoGi. Moeove if this constaint fail, in othe wos that thee is not enough chage to elive equie powe using the tey, the EMS inquies whethe PV is available to supply at least a cetain amount of Mi 147

7 6: 7:35 9:1 1:45 12:2 13:55 15:3 17:5 18:4 2:15 21:5 23:25 1: 2:35 4:1 5:45 Powe (W) 6: 8:15 1:3 12:45 15: 17:15 19:3 21:45 : 2:15 4:3 Powe (W) Intenational Jounal on Recent an Innovation Tens in Computing an Communication ISSN: loas. Depening upon the amount of PV availability the B. PV Pofile DSM algoithm ajusts the loas of the MicoGi. The Powe geneate fom sola PV in a typical ay is Eventually if thee is neithe PV no SOC available EMS shown in Fig. 1. This cuve was geneate using fiel sen a shutown signal an MicoGi contolle initiates the measuements at the same builing fom which the loa shutown sequence to halt the opeations of the c pofile was obtaine. MicoGi. C. Utility Enegy Pice E. Deman Sie Management (DSM) As explain befoe in impot pioity moe an eman pioity moe the Deman Sie management is use to scheule available powe in the c MicoGi. Five DSM potocols wee efine an they wee activate accoing to the EMS ecisions. The amount nee to euce fom loas ae calculate in gi pioity moe using (21) an in islane moe using (22). The new powe efeence value fo loa feees is set accoing to (23). Sh P P P P (21) Sh Rf Gi P P P (22) Sh The DSM moes ae given in Table 1. TABLE I. PV PV P (23) DSM GUIDELINES DSM Desciption Moe 1 The loa feee convete will be scheule using (21) an (23). 2 The loa feee convete will be scheule using (22) an (23). 3 The total loa will be euce to 75% of the peicte. 4 The total loa will be euce to 5% of the peicte. 5 The total loa will be euce to 25% of the peicte. V. CASE STUDY Two case stuies have been conucte to investigate the pefomance of the c MicoGi with the same PV an loa pofiles. Fist case stuy was one fo a gi connecte MicoGi an the secon case stuy was one with gi failue scenaio. Using the case stuies pefomance of the c MicoGi with EMS was evaluate. A. Loa Pofile The popose c MicoGi was assume as a commecial builing. Thus the loa pofile shown in Fig. 9 was use (extacte fom a eal builing). It is woth noting that the night time loa was vey small compae to the ay time loa. ToU pice was assume as the utility selling pice. Fom 6. to 1.3 an fom 12.3 to 19., enegy pice is SLR 25/kWh; fom 1.3 to 12.3 it is SLR 3/kWh; fom 19. to 22. it is SLR 54/kWh; an fo the emaining peio it is SLR 13/kWh. D. Case Stuy 1 The fist case stuy was one fo a nomal ay opeation. In oe to match the simulations with eal wol system it was consiee that 15 min in eal system is equal to.25 sec in simulation. Thus a full ay is epesente by 24.5 sec. An initial elay of.5 sec was intouce to complete the statup pocess. The etails of the tey is given in Appenix A. Since this case stuy is pimaily a gi connecte opeation, the EMS woks on the expot pioity an impot pioity moes. The scheuling is one by consieing the utility taiff, tey ischage cost an the SOC of the tey. As explaine befoe, the supe-capacito wascontolle to maintain the tey voltage tansiently Time (h) Figue 9. Loa Pofile of the builing Time(h) Figue 1. Vaiation of sola PV Simulations wee caie out to obseve the pefomance of the MicoGi contolles an convetes. The esults ae pesente in Fig

8 Powe (W) Powe (W) Powe (W) Intenational Jounal on Recent an Innovation Tens in Computing an Communication ISSN: Fig. 11 (a) an (b) shows the vaiation of loa an PV geneation. Both followe, the pofiles pesente in Fig. 9 an 1. The vaiation of powe supplie fom contolle ectifie an tey inteface convete ae pesente in Fig.11 (c) an () espectively. As shown in Fig. 11 (c) uing.5 sec to 5 sec peio, most of the powe was impote fom the ac utility to the c MicoGi though the contolle ectifie. (a) Vaiation of sola PV output powe This peio is equal to 6: h to 1:3 h in eal time. The sola PV geneation was less than the total loa in this uation. Afte that fom 5 sec to 6.75 sec (i.e. fom 1:3 h to 12:15 h) the utility taiff incease moe than the tey enegy cost. Theefoe the tey convete was activate an supplie majoity of equie powe eman. The powe impote fom the ac utility is euce by the utility inteface convete in oe to maintain the powe balance. Howeve afte 6.75 sec (i.e. afte 12:15 h) again utility enegy pice (b) Vaiation of Loa eceases compae to tey enegy pice. Also the sola iaiance incease moe than the total loa. Hence the EMS scheules the tey to chage moe. So the MicoGi contolle switche the tey inteface convete to the chage moe an the SOC of the tey eaches to its maximum limit (not shown in Fig 11) at 9. sec (i.e. at 14.3h). Afte that the tey convete is put into ile an the utility inteface convete an the PV convete supplie the eman. At 13.5 sec (i.e. at 19. h) anothe taiff (c) Vaiation of powe supplie fom contolle ectifie incement appeas in the ac utility enegy pice. Hence the MicoGi contolle sets the contolle ectifie to expot powe since the EMS scheules the tey inteface convete to ischage the tey an suppot the utility gi uing its peak eman. Afte tey eache to its citical SOC level this opeation stoppe (15.25 sec, i.e.at 21. h) an the contolle ectifie impot powe fom the ac utility to supply the base loa. At 17 sec (i.e. at 22:15 h) the () Vaiation of powe supplie fom tey impote powe incease because EMS scheule the tey convete to chage the tey to eay fo the next ay. Fig. 11 ()shows the powe vaiation of the tey inteface convete. With efeence to the afoementione iscussion, in 5 sec to 6.75 sec (i.e. fom 1:3 h h) peio the tey convete state to supply powe by ischaging the tey. Fom 6.75 sec to 9 sec because of the euction of loa, the tey convete sets back to chaging (e) Vaiation of powe supplie fom Supe-capacito moe an chage the tey using the excess sola powe Figue 11. Vaiations of the utility taiff an output powe in case stuy 1 without expoting to the ac utility. In between sec Powe (W) Powe (W) (i.e. fom 14.3 h to 19. h), the teyconvete set into ile moe by the contolle since most of the eman was supplie fom the contolle ectifie. Fom 13.5 sec (i.e. at 19: h) onwas the tey convete scheule to be in the gi suppot moe. The ole of the supe-capacito is to supply the powe eficit an absobs excess by looking at the vaiation of the 149

9 Powe (W) Powe (W) Intenational Jounal on Recent an Innovation Tens in Computing an Communication ISSN: c link voltage. At evey instance it chages an ischages Duing the islaning pocess, the c link voltage contol by supplying equie powe iffeence. This vaiation is of the MicoGi is tansfee to the tey convete fom pesente in Fig. 11 (e). Because of this the stesses of the the contolle ectifie. Howeve the EMS signals wee contolle ectifie which contols the c link voltage is euce an the c link voltage becomes moe stable. E. Case Stuy 2 In the secon case stuy, a scenaio when gi failue occue was analyze. The gi failue conition was simulate by isconnecting the MicoGi fom the ac utility an the contolle ectifie was put into a cuent contolle moe with zeo cuent efeence. Two gi failues, one at 8.36 h an estoe at 9.12 h, an the othe at h an estoe at h, wee consiee. The same PV pofile as shown in Fig 1 was consiee in this case stuy as well. Even though the same loaing patten shown in Fig. 9 was use, uing the peio of the gi failue, the loa was euce though DSM. Fig. 12 shows the esulte powe pofiles of the c MicoGi. By compaing Fig. 9 an 1, it can be notice that, at the fist gi failue (at 3.1 sec (8.36 h)) the PV geneation is moe than the loa. Thus EMS switche to the ESS pioity moe an use the excess enegy to chage the tey. Once gi is available afte.6 s (18 min) the EMS switche back to the gi connecte moe. In the secon gi failue at 5.7 sec (i.e. at 11.12h) since the total loa is moe than the available PV geneation, EMS switche back to islane moe with the eman pioity moe. Hence when SOC eaches its mi-level, the DSM scheme is activate an euce the loa. This loa euction can be obseve by compaing Fig. 9 an Fig 12 (a). Fig 12 (b)shows the vaiation of powe supplie by the contolle ectifie. Accoing to the figue fom 3.1 sec to 3.7 sec (i.e. fom 8:36 h to 9:12 h) an fom 5.7 sec to 7.8 sec (i.e. fom 11:12 h to 13:18 h), the contolle ectifie oesnot exchange powe ue to the gi failue. At this instant whee the MicoGi lost utility powe, the supecapacito convete is activate an it supplie powe to the MicoGiuntil the tey convete was activate an state to supply powe to stabilize the c MicoGi. Futhemoe, by looking at Fig 12 (c) at 3.1 sec (i.e. at 8:36 h) an at 5.7 sec (i.e. at 11:12 h), it can be seen that the tey convete took the contol of c link stability an state to supply powe. Duing these intevals the EMS opeate in the ESS pioity moe an eman pioity moe.in eman pioity moe, the EMS use SOC as one of the ecision making vaiable. Once the SOC of the tey stoage state to euce below SOC Mi the EMS initiates the DSM algoithms. At 6.1 sec (i.e. at 11:36 h) SOC eache to SOC Mi an DSM scheule is activate by the EMS thus eucing the loa. When the gi came back at 7.8 sec (i.e. at 13:18 h), loas ae estoe an the c link contol was hane ove to the contolle ectifie. (b) Vaiation of powe supplie fom contolle ectifie (c) Vaiation of powe supplie fom tey () Vaiation of powe supplie fom Supe-capacito Powe (W) Powe (W) (a) Vaiation of Loa powe Time Time (s) (s) Figue 12. Vaiation of the utility taiff an output powe in case stuy 2 ispatche in.5 sec (at 15 min) intevals an in this case the gi failues occue at the mile of EMS ispatching intevals. Until such time the EMS sens the comman to the tey convete, the stability of the c link was maintaine by the supe-capacito convete. This inetia action can be clealy seen in Fig. 12 (). VI. CONCLUSIONS Fom case stuies it was obseve that the popose EMS was capable of hanling the powe shaing of iffeent enegy souces in elation to the eman, une gi connecte an islane moes. As can be seen fom Case stuy 1, when thee is excess powe, the EMS scheule the tey convete eithe to 15

10 utilize its enegy stoage within the MicoGi o expot it to [3] C.-M. Lai, C.-T. Pan, an M.-C. Cheng, High-Efficiency the utility. On the othe han when thee is powe shotage Moula High Step-Up Inteleave Boost Convete fo cthe EMS scheule to impot powe fom the ac utility to Micogi Applications, IEEE Tans. In. Appl., vol. 48, no. keep the powe balance in moe cost effective manne. 1, pp , 212. Case stuy 2 emonstate the opeation of the c [4] D. Chen an L. Xu, Autonomous c Voltage Contol of a c Micogi With Multiple Slack Teminals, IEEE Tans. MicoGi une all opeating moes of the EMS. The key Powe Syst., vol. 27, no. 4, pp , 212. featue to note hee is that the tansition of the contols [5] Y. Ito, Y. Ito, Y. Zhongqing, an H. Akagi, c micogi between gi connection an islaning opeations. Powe base istibution powe geneation system c micogi shaing between each convete an loas was one base istibution powe geneation system, in Powe seamlessly an MicoGi contolles hanle the powe set Electonics an Motion Contol Confeence, 24. IPEMC points accoing to the scheule ispatche by the EMS. The 24. The 4th Intenational, 24, vol. 3, pp DSM was effectively utilize to maintain the health of the Vol.3. tey base on a pe-efine SOC level. [6] Y.-K. Chen, Y.-C. Wu, C.-C. Song, an Y.-S. Chen, Design The opeation of the supe-capacito inteface convete an Implementation of Enegy Management System With helpe to minimize the c link ipples. Also uing islaning, Fuzzy Contol fo c Micogi Systems, IEEE Tans. Powe it povie the inetia suppot to the MicoGi to avoi the Electon., vol. 28, no. 4, pp , 213. collapse. [7] H. Kakigano, Y. Miua, an T. Ise, Distibution Voltage Moe impotantly the constantly monitoing the Contol fo c Micogis Using Fuzzy Contol an Gainegaation of the tey though the ischage cost function Scheuling Technique, IEEE Tans. Powe Electon., vol. is a unique contibution of this piece of wok. As the EMS 28, no. 5, pp , 213. continuously monitos the cost associate with ischaging [8] J.A.P. Lopes, C.L. Moeia, an A.G. Maueia, Defining the tey with the utility pice, this ensues an optimum contol stategies fo MicoGis islane opeation, IEEE Tansactions on Powe Systems,, vol. 21, 26, pp utilization of the tey enegy stoage. VII. APPENDIX A tey Specification [16] fom the ata sheet of the smat tey, SB 1 Paamete Data Technology Class LiFePO4 minal Voltage 36. V Rate Capacity 3.3 kwh Rate DOD 8 % SOC 9% SOC Min 1% Numbe of Cycles 15 Replacement Cost Rs.2,/= ACKNOWLEDGMENT Authos wishes to acknowlege the National Reseach Council of Si Lanka (Gant : NRC 14-15) an Sustainable Enegy Authoity of Si Lanka fo poviing financial suppot fo this wok. REFERENCES [1] J.-D. Pak an J. Canelaia, Fault Detection an Isolation in Low-Voltage c-bus Micogi System, IEEE Tans. Powe Deliv., vol. 28, no. 2, pp , 213 [2] J. M. Gueeo, J. C. Vasquez, J. Matas, L. G. e Vicuña, an M. Castilla, Hieachical Contol of Doop-Contolle ac an c Micogis #x214;a Geneal Appoach Towa Stanaization, IEEE Tans. In. Electon., vol. 58, no. 1, pp , Jan. [9] C.L. Moeia, F.O. Resene, an J.A.P. Lopes, Using Low Voltage MicoGis fo Sevice Restoation, IEEE Tansactions on Powe Systems, vol. 22, 27, pp [1] B. Koposki, R. Lassete, T. Ise, S. Moozumi, S. Papatlianassiou, an N. Hatziagyiou, Making micogis wok, IEEE Powe an Enegy Magazine, vol. 6, 28, pp [11] Y. Kojima, M. Koshio, S. Nakamua, H.A.M.H. Maejima, Y.A.F.Y. Fujioka, an T.A.G.T. Goa, A Demonstation Poject in Hachinohe: Micogi with Pivate Distibution Line, IEEE Intenational Confeence on System of Systems Engineeing, SoSE, 27, pp [12] A. Yokoyama, Oveview of Micogi R&D in Japan, Symposium on MicoGis, Univesity of Califonia, San Diego: 29. [13] T. Tsukaa, T. Tokumoto, T. Ogata, an S. Tagami, DEMONSTRATION OF MICROGRID THROUGH THE ACTIVITIES TOWARD HOLONIC ENERGY SYSTEMS, 6th Intenational Confeence on Inoo Ai Quality, Ventilation & Enegy Consevation in Builings - IAQVEC, Senai, Japan, 27: QVEC27%5CTsukaa.pf accesse on ,. [14] A. Dena, Shimizu s Micogi Reseach Activities, Symposium on Micogis, Canaa, 26: tation_6_atsushi_ena.pf access on ,. [15] N. Koaa an M. K. Misha, Gi Aaptive Powe Management Stategy fo an Integate Micogi With Hybi Enegy Stoage, IEEE Tans. In. Electon., vol. 64, no. 4, pp , Ap

11 [16] K. Shimomachi, R. Haa, H. Kita, M. itake, H. Hoshi, an K. Hiose, Development of enegy management system fo DC micogi fo office builing:-day Ahea opeation scheuling consieing weathe scenaios-, in 214 Powe Systems Computation Confeence, 214, pp [17] I. Tank an S. Mali, Renewable base DC micogi with enegy management system, in 215 IEEE Intenational Confeence on Signal Pocessing, Infomatics, Communication an Enegy Systems (SPICES), 215, pp [18] B. Wang, M. Sechilaiu, an F. Locment, Intelligent DC micogi with smat gi communications: Contol stategy consieation an esign, in 213 IEEE Powe & Enegy Society Geneal Meeting, 213, pp [19] R.K. Chauhan, B.S. Rajpuohit, F.M. Gonzalez-Longstt an S.N. Singh, Intelligent Enegy Management System fo PVtey-base Micogis in futue c homes, Intenational Jounal of Emeging Electic Powe Systems, Vol 17(3), 216, pp [2] Yu-Kai Chen, Yung-Chun Wu, Chau-Chung Song, Yu-Syun Chen, Design an implementation of Enegy Management System with fuzy conol fo c Micogi system, IEEE Tansactions on Powe Electonics, Vol 28(4), 213, pp [21] Eun-Kyu Lee, W. Shi, R. Gah an W. Kim, Design an implementation of a Micogi Enegy Management System, Sustainability. Vol 8, 216, pp [22] O. Temblay, Expeimental Valiation of a tey Dynamic Moel fo EV Applications, Wol Elect. Veh. J., vol. 3, 29. [23] O. Temblay, L.-A. Dessaint, an A.-I. Dekkiche, A geneic tey moel fo the ynamic simulation of hybi electic vehicles, in Poceeings IEEE Vehicle Powe an Populsion Confeence, VPPC 27. Sep. 27, pp [24] T. A. Nguyen an M. L. Cow, Stochastic Optimization of Renewable-Base Micogi Opeation Incopoating tey Opeating Cost, IEEE Tans. Powe Syst., vol. 31, no. 3, pp , May 216. [25] Tony Makel an Anew Simpson, Plug-in Hybi Electic Vehicle Enegy Stoage System Design, pesente at the Avance Automotive tey Confeence, timoe, Maylan, 19-May