-微電網(wǎng)運(yùn)行歷程與電力市場(chǎng)中的虛擬電廠

AReviewonOperationofMicroGridsand

VirtualPowerPlantsinthePowerMarketsElahehMashhour*S.M.,Moghaddas-Tafreshi**K.N.ToosiUniversityofTechnology,FacultyofElectricalEngineering,Tehran,IRANE-mail:mashhour@ee.kntu.ac.irAbstract-TheshareofDistributedGeneration(DG)inthepowersystemgenerationisincreasinglygrownupandfortheeconomicalandtechnicalreasons;theirintegrationisdeeplyconcentratedbytheresearchers.ThispaperreintroducestheintegrationofDistributedEnergyResources(DER),i.e.DGs,controllableloadsandenergystorages,intomicrogridandVirtualPowerPlant(VPP)andalsoreviewstheiroperationinthepowermarket.Moreover,itdiscussestheperspectiveofmarkettransactionsoffutureVPPsinactivedistributionnetworks.Keywords:VirtualPowerPlant,MicroGridI.IntroductionTheworldisgoingtouseDG,bothfossil-fuel-basedandrenewable-basedone,duetoappearanceofenvironmentalviewpointsandlimitationoffossilfuels.Atpresent,severalsupportiveregulationsinthewholeworldsuchasseparategreenmarketforelectricityproductionofrenewableresources11-3],EuropeanRESDirectivefordevelopmentofrenewableresources[4],EuropeanCHPDirectiveforenergyefficiencyimprovement[5],andsimilarsupportiveregulationsinothercountries,RenewablePortfolioStandard(RPS)inseveralcountries[6,7],Kyotoprotocolwhichhasaroleinthereductionofgreenhousegasemissions,andsoonarethefactorsthataccelerateDGgrowth.Therefore,thepenetrationofDGinthepowersystemwillbehighlyincreasedinthenewfuture.DuetotheeffectofDGontechnicalparameterofthenetworkandalsoconsideringtherapidextensionofpowermarketinthewholeworld,itisnecessarytocontemplatebothtechnicalaspectsofnetworkoperationandmarkettransactionsinDGoperation.Thesesubjectsaredescribedinfollowing.Firstofall,sincetechnicalparametersofthenetworksuchasnodevoltagesandlinecurrentsstronglydependontheDGoperation,thehighpenetrationofDGmaycreateseveralproblemsinthedistributionnetworksconcerningtostabilityandpowerquality.Furthermore,someconsumerswhoareownersofsomeDGsmayinjecttheirsurpluspowertothegridinsomehoursandcompensatetheirshortagebythegridinothertimes.Therefore,thepowerflowcurrentinthenetworkmaybealteredduringthedayinhighpenetrationofDG.ThispowerexchangebetweentheDGownerandthenetworkisrequiredtobehandled.Inthiscondition,thestandardparadigmofcentralizedcontrol,whichisusedinthecurrentelectricityinfrastructure,willnolongerbesufficientandthedistributedcontrolwillbeconsidered..微電網(wǎng)中心控制器（MGCC）。.本地控制器（LC）,微源控制器或負(fù)載控制器。DMS負(fù)責(zé)管理和控制分布區(qū)域包括幾個(gè)干線包括數(shù)個(gè)微電網(wǎng)。在DMS之間的主界面微電網(wǎng)是MGCC。它是主要負(fù)責(zé)的微電網(wǎng)運(yùn)行的優(yōu)化，或者說，它能簡(jiǎn)單地協(xié)調(diào)本地控制器，它主要責(zé)任是進(jìn)行這種優(yōu)化。下控制級(jí)別是由LC控制DERoA.微電網(wǎng)集中調(diào)節(jié)的市場(chǎng)政策在微電網(wǎng)集中控制，MGCC是負(fù)責(zé)該微電網(wǎng)價(jià)值最大化和其操作的優(yōu)化。它采用的市場(chǎng)價(jià)格電力及可能需求管理（DSM）請(qǐng)求，以確定功率，該微電網(wǎng)的量應(yīng)與分配系統(tǒng)交換，優(yōu)化當(dāng)?shù)厣a(chǎn)的能力。它可能會(huì)使用負(fù)荷預(yù)測(cè)（電氣和熱可能）和功率預(yù)測(cè)生產(chǎn)能力。優(yōu)化操作方案內(nèi)容是通過控制微源取得和在微電網(wǎng)可控負(fù)載通過發(fā)送控制信號(hào)到外地。在此框架下，在必要的情況下，非關(guān)鍵可控負(fù)載可以去掉。止匕外，有必要監(jiān)測(cè)的實(shí)際有功和無(wú)功組件。這些技術(shù)可以被認(rèn)為是等價(jià)于相互連接網(wǎng)格［23］的輔助控制。兩種市場(chǎng)政策被假定為MGCC就像一個(gè)好公民，行為像一個(gè)理想的公民行為［23,25］o在第一個(gè)政策時(shí)，MGCC旨在滿足地方生產(chǎn)所需的能源，當(dāng)它是財(cái)政有利，而不利用電源上游配電網(wǎng)。這等同于良好公民的行為。對(duì)于整個(gè)配電系統(tǒng)運(yùn)行，這樣的動(dòng)作是有利的，因?yàn)橐驗(yàn)樵谛枨蟾叻鍖?dǎo)致電價(jià)高的時(shí)候。微電網(wǎng)通過部分或完全減輕可能出現(xiàn)的用電高峰滿足其能源需求。但從用戶終端看，該MGCC最小微電網(wǎng)的運(yùn)行成本，考慮到市場(chǎng)價(jià)格，需求和DG投標(biāo)。用戶終端的微電網(wǎng)的加入降低的運(yùn)營(yíng)成本。在這種情況下MGCC收集市場(chǎng)價(jià)格波動(dòng)，負(fù)載的需求（通過預(yù)測(cè)可能短期負(fù)荷方案）和微型電網(wǎng)以最小化對(duì)整個(gè)微電網(wǎng)的能量成本為每個(gè)定義的時(shí)間間隔，例如每15分鐘間隔，受到限制，如有功功率和無(wú)功功率平衡，PQ曲線每一個(gè)的發(fā)生器單元和每個(gè)單元等［23］的網(wǎng)格技術(shù)限制。在這兩種政策中，需求方投標(biāo)和功率質(zhì)量問題，包括在優(yōu)化例程。.VPP操作在［26］VPP調(diào)度其單位僅根據(jù)最小化的服務(wù)短期可變成本提供。為了達(dá)到這個(gè)目的，VPP解決最優(yōu)化程序，其中，所述目標(biāo)函數(shù)是熱的總和，電以及CHP裝置的燃料成本增加成本/收入的電力的交換與電網(wǎng)中的每小時(shí)。約束函數(shù)是電動(dòng)的平衡以及VPP發(fā)生器和VPP負(fù)載之間的熱能之間的關(guān)系。該［26］通過提出在發(fā)展自己的［27］模型的作者VPP和DSO的協(xié)調(diào)優(yōu)化，以保持配電網(wǎng)的安全性。這是因?yàn)镈SO是負(fù)責(zé)維持分配的安全網(wǎng)。它應(yīng)處理網(wǎng)絡(luò)中的這樣一種方式，該在每個(gè)總線電壓容差避免達(dá)到高峰。事實(shí)上，如果不進(jìn)行VPP優(yōu)化DSO監(jiān)管，即VPP運(yùn)營(yíng)商最大限度地降低獨(dú)立其總的短期成本，包括VPP的生產(chǎn)成本單位和與電網(wǎng)電力交換的成本，并從而提供其加熱和電的需求，這可能導(dǎo)致違反的電壓和電流的分布范圍網(wǎng)絡(luò)。較差的解決辦法是，在DSO執(zhí)行通過作用于主調(diào)節(jié)網(wǎng)絡(luò)上的動(dòng)作變電站有載分接開關(guān)變壓器(OLTCT)和上可用的分流補(bǔ)償器。但適合的解決方案是協(xié)調(diào)VPP和DSO的優(yōu)化。在所提出的算法［27］是逐步的優(yōu)化問題，其目的是協(xié)調(diào)兩個(gè)DSO和VPP的，以實(shí)現(xiàn)所述的操作以最小的成本續(xù)流所需的監(jiān)管，一個(gè)額外的成本占銷售網(wǎng)絡(luò)的損失。這里，所述DSO將執(zhí)行一種虛擬的有功和無(wú)功的在分布式發(fā)電通過求解優(yōu)化電力調(diào)度問題，以減少其對(duì)應(yīng)于所述網(wǎng)絡(luò)的損失減少進(jìn)口有功功率和無(wú)功功率的成本高壓電網(wǎng)，由于分布式發(fā)電和需求是固定的邊界條件。為了做到這一點(diǎn)，該DSO需要系統(tǒng)狀態(tài)的完整知識(shí)(生成并要求有功功率和無(wú)功功率的任何母線)和VPP發(fā)生器的成本函數(shù)。該約束包括在每一個(gè)功率流平衡方程網(wǎng)絡(luò)為有功功率和無(wú)功功率的公交車，電壓界限和所述饋線的電流限制。但應(yīng)指出，DG的那有功和無(wú)功功率這是屬于VPP,被認(rèn)為是固定的單位在每個(gè)總線的電力平衡約束值，而他們是優(yōu)化變量VPP優(yōu)化算法。作為優(yōu)化的結(jié)果，該算法提供了一個(gè)估計(jì)的節(jié)點(diǎn)價(jià)格有功和無(wú)功電網(wǎng)通過VPP優(yōu)化算法所需的交流電源。VPP具有選擇適當(dāng)其生產(chǎn)的基礎(chǔ)上這樣的信號(hào)，在這種情況下，回流成本會(huì)最小化。從而整體優(yōu)化過程是雙方DSO和迭代應(yīng)用程序完成VPP優(yōu)化算法，其中，所述公共變量被可選地視為在一個(gè)優(yōu)化參數(shù)算法和其他固定邊界條件。該終止標(biāo)準(zhǔn)是價(jià)值的最小能量在網(wǎng)絡(luò)中的變化。在［26,27］,但VPP交換電力與電網(wǎng)在考慮到價(jià)格批發(fā)市場(chǎng)，它在市場(chǎng)上被動(dòng)的角色交易。它是由于這樣的事實(shí)，即它不出價(jià)到電力市場(chǎng)的參與者。在［15,16］,為的操作的總體框架VPP電力市場(chǎng)的建議。在這個(gè)方案中，DG單位提供他們的提議出售能源的VPP運(yùn)營(yíng)商，誰(shuí)制定了能源價(jià)格的談判市場(chǎng)或直接與客戶。確定后商業(yè)戰(zhàn)略，VPP協(xié)商的電力市場(chǎng)。談判的時(shí)期，市場(chǎng)操作后，決定了商業(yè)交易。市場(chǎng)結(jié)果應(yīng)該由系統(tǒng)操作員進(jìn)行驗(yàn)證°當(dāng)技術(shù)限制被違反，就必須以顯示臨界指向生產(chǎn)者和顧客以允許它們裁決其他生產(chǎn)商。值得注意的是，在的情況下的限制能量的供給由VPP,所述情況是由單一生產(chǎn)商不同，因?yàn)閂PPS能改變調(diào)度，或最終注入的地方的產(chǎn)生，以減少在該地方的代導(dǎo)致的技術(shù)問題。這將是一個(gè)非常重要的信貸的VPP。如果在技術(shù)上沒有問題分析，系統(tǒng)操作者將傳達(dá)給市場(chǎng)經(jīng)營(yíng)者，讓他實(shí)現(xiàn)交易。在每日市場(chǎng)上，VPP必須承擔(dān)的永久控制由每個(gè)伙伴生產(chǎn)者傳送到網(wǎng)絡(luò)中的能量，補(bǔ)償不可分派的產(chǎn)生的變化技術(shù)。在這個(gè)框架的工作，同時(shí)VPP參與電力市場(chǎng)，具有一定的市場(chǎng)里本身所有的DG單位出價(jià)吧。由于分布式發(fā)電的幾個(gè)特別是那些屬于住宅或小型商用消費(fèi)者低容量和它們的主人通常不了解情況的電力業(yè)務(wù)，這是推斷，只有一些分布式電源特性由作者考慮。止匕外，有什么市場(chǎng)被認(rèn)為是沒有解釋的市場(chǎng)特征不會(huì)被清零。作者［17］提出VPP是為了推動(dòng)分布式電源買賣的批發(fā)能源市場(chǎng)和提供某些服務(wù)，以支持傳輸系統(tǒng)管理。A.未來VPPS的市場(chǎng)前景對(duì)于DG是一種無(wú)源網(wǎng)絡(luò)改變包含負(fù)載普及率增長(zhǎng)的特性配電網(wǎng)，它是同時(shí)包含負(fù)載和發(fā)電機(jī)［28］。在這個(gè)新的環(huán)境中，角色DSO在保持安全配送系統(tǒng)是相同的傳輸系統(tǒng)的ISO的作用。在自主配電網(wǎng)中，傳統(tǒng)的DISCO功能分拆成技術(shù)和商業(yè)任務(wù)，包括提供配套設(shè)施。一些輔助設(shè)施，作為電壓控制有當(dāng)?shù)氐淖匀缓推渌恍ㄈ鐑?chǔ)備，真正的功率損耗更換等）有半自然，他們可以提供本地或全球范圍內(nèi)，以減輕壓力。在DISCO控制區(qū)域內(nèi)，DSO應(yīng)該提供一些配套設(shè)施通過生產(chǎn)者（那些有本地或半當(dāng)?shù)氐淖匀唬?。DISCO能源與分布式電源和負(fù)荷呈現(xiàn)在控制收購(gòu)市場(chǎng)方式［29］。這個(gè)市場(chǎng)是以批發(fā)市場(chǎng)，DG資源和可控負(fù)載等，DSO操縱以滿足DISCO的終端客戶的需求。兩個(gè)DG的單位被視為組，即獨(dú)立的DG單位管理還是從DISCO獨(dú)立擁有而那些依賴其由被管理或擁有DISCO。獨(dú)立DG單位發(fā)出的能量報(bào)價(jià)（價(jià)格為能量的函數(shù)），以DSO目的，經(jīng)營(yíng)成本依賴的人直接認(rèn)為是DSO輔助功能。作者［29］從發(fā)展角度提出模型單周期由一個(gè)多周期能量采集模型［30］,僅取決于分布式電源被［30］。在新的未來，當(dāng)DG在電力系統(tǒng)中的份額大約媲美傳統(tǒng)的設(shè)施，DISCO市場(chǎng)將被開發(fā)，并VPPS將參加DISCO市場(chǎng)能源和配套服務(wù)。這個(gè)問題是很好解決的［31］。因?yàn)槲磥鞻PPS可包括在寬的各種DG技術(shù)在低壓和中壓配電網(wǎng)絡(luò)，分布式發(fā)電在電力市場(chǎng)的準(zhǔn)入門檻，即分布式電源和一些分布式電源的隨機(jī)性質(zhì)的尺寸小，將通過VPP概念刪除，所有分布式電源的可能在VPPS和整合可見對(duì)市場(chǎng)的功能將被用于提供的安全性系統(tǒng)。.結(jié)論DG在電力系統(tǒng)發(fā)電的份額日益成長(zhǎng)和深入研究人員有直接關(guān)系。一般兩種不同的整合策略是存在的，包括集成微電網(wǎng)以及VPPo微電網(wǎng)概念是基于假設(shè)大量微發(fā)電機(jī)連接到配電網(wǎng)中，并且這些可以用來降低用于傳輸和高壓配電要求成本。VPP是一個(gè)概念聚集了一批DER不同的技術(shù)和不同的操作模式，連接到各點(diǎn)中的分布網(wǎng)絡(luò)的提議，交易電能或提供系統(tǒng)支持服務(wù)，微電網(wǎng)可以交換功率措施的電網(wǎng)，像良好的行為公民，就像理想的公民行為。此外，VPPS提出交易DG的批發(fā)市場(chǎng)。在今后的DSO在維持安全的積極作用配電系統(tǒng)如ISO角色傳輸系統(tǒng)和DISCO市場(chǎng)是由運(yùn)營(yíng)DSO將開發(fā)和未來VPPS將參加在DISCO市場(chǎng)對(duì)能源和配套設(shè)施將是相同的。致謝作者非常感謝Khouzestan配電公司對(duì)本次研究支持。978-1-4244-3523-4/09/S25.00c2009IEEE273978-1-4244-3523-4/09/S25.00c2009IEEE273Secondly,thepowerindustryinthewholeworldisrapidlyrestructuringandthepowersystemoperationshouldbemarket-based.However,ingeneralDGunitscannotbeviablebythemselvesonlyinthepowermarketduetotheirspecialcharacterssuchastheirsmallsizeandstochasticnatureofsomeunits(e.g.windandphotovoltaic).Tosolvetheseissues,DGunitsshouldbecombinedtogetherinoneentity,integratedentity,andalsocontrolledbyEnergyManagementSystem(EMS),whichisknownasanessentialinfrastructureofthedistributedcontrol.Therefore,amarket-baseddistributedcontrolwillberealizediftheoperatorofintegratedentityisparticipatedinthepowermarketonbehalfofitscomponents.Generallytwointegrationstrategiesareexisted,includingintegrationinamicrogridandinaVPP[8-27,31].ThispaperreintroducestheconceptsofmicrogridandVPPandalsoreviewstheiroperationinthepowermarket.Moreover,itdiscussestheperspectiveofmarkettransactionoffutureVPPsinactivedistributionnetwork.Theremainingofthepaperisorganizedasfollows.SectionIIdefinesmicrogridandVPP.SectionIIIandIVreviewtheoperationofmicrogridandinthepowermarketrespectively.Thediscussionsandconclusionsareprovidedinfinalsection.ILDefinitionofIntegratedEntitiesMicrogridThemicrogridconceptisbasedontheassumptionthatlargenumbersofmicrogeneratorsareconnectedtonetworkandthatthesecanbeusedtoreducetherequirementfortransmissionandhighvoltagedistributionassets.Accordingtotherelevantliterature,differentdefinitionsareprovidedformicrogrid.In[8],microgridisaclusterofloadsandmicrosourcesoperatingasasinglecontrollablesystemthatprovidesbothpowerandheattoitslocalarea.Microsourcesaresmall(lessthan100kW)unitswithpowerelectronicinterfaces,placedatcustomersites,lowcost,lowvoltageandhighlyreliablewithfewemissions.AccordingtothedefinitionproposedbyConsortiumforelectricalReliabilityTechnologySolutions(CCERTS_),microgridisanintegratedpowerdeliverysystemconsistingofinterconnectedloadsanddistributedenergyresourceswhich,asanintegratedsystem,canoperateinparallelwiththegridorinaninternationalislandmode[9].MicrogridisdefinedinEuropeanmicrogridsprojectasfollows:Interconnectionofsmall,modulargenerationtolowvoltagedistributionsystemsformsanewtypeofpowersystem,themicrogrid[10J.Microgridscanbeconnectedtomainpowernetwork(non-autonomousmode)orbeoperatedislanded(autonomousmode)inacoordinatedandcontrolledway[101.Intheautonomousmode,themicrogridservestheelectricalloadwithoutpowerfromtheutility;basicallythemicrogridisitsownstand-alonegrid.Inthenon-autonomousmode,themicrogridproducespowerwhileinterconnectedtotheutilitysystem[11].Maintainingofvoltagesandload-frequencycontrolinanautonomousmicrogridissocomplicatedthannon-autonomousone.Innon-autonomousmode,ifproblemswiththeDGresourcescomeup,thecustomercanstillhavepower,whilemaintenanceisperformedontheDGresources.Inthismode,thecustomerscansigncontractswiththeutilitytosellexcesspowerintotheutilitygrid.Also,iftheutilityhasapoweroutage,theDGresourcesofthecustomerwilldisconnectfromtheutilitygridandserveonlythecustomer'sconnectedload.Theautonomousmicrogridsareusedforplacesthatarefarawayfromthenetworkandthenetworkextensionisexpensive[H].Virtualpowerplant(VPP)Similartomicrogrid,VPPisacombinationofDGs,controllableloadsandenergystorages;however,itisawiderconceptthanmicrogrid.Ingeneral,VPPisaconcepttoaggregateanumberofDERofvarioustechnologieswithvariousoperatingpatternandavailabilitythatconnectedtovariouspointsindistributionnetworkforthepurposeoftradingelectricalenergyortoprovidesystemsupportservices.Accordingtotherelevantliterature,differentdefinitionsareprovidedforVPP.In[12,13],VPPisanaggregationofmanycombinedheatandpowermicrounitswhichareconnectedtolowvoltagedistributionnetwork.In[14J,VPPisdefinedasanaggregationofdifferenttypesofdistributedresourceswhichmaybedispersedindifferentpointsofmediumvoltagedistributionnetwork.In[15,16JVPPdefinesasamulti-technologyandmulti-siteheterogeneousentity.AccordingtoEuropeanfenixproject,VPPiscomposedofanumberofvarioustechnologieswithvariousoperatingpatternsandavailabilitywhichtheycanconnecttodifferentpointofdistributionnetwork[17,181.Accordingtothisdefinition,VPPisaflexiblerepresentationofaportfolioofDERthatcanbeusedtomakecontractsinwholesalemarketandtoofferservicestothesystemoperator.TwotypesofVPParedefinedinfenixproject,i.e.CommercialVPP(CVPP)andTechnicalVPP(TVPP).ACVPPhasanaggregatedprofileandoutputwhichrepresentsthecostandoperatingcharacteristicsfortheDERportfolio.TheimpactofdistributionnetworkisnotconsideredintheaggregatedCVPPprofile.TheTVPPconsistsofDERfromthesamegeographiclocation.TheTVPPincludestherealtimeinfluenceofthelocalnetworkonDERaggregatedprofileaswellasrepresentingthecostandoperatingcharacteristicsoftheportfolio[18].OperationofMicroGridsIncontrolstrategiesofmicrogrid,thereareseverallevelsofdecentralizationthatcanbepossiblyappliedrangingfromthefullydecentralizedapproachtoahieraticalcontrol[19].Accordingtothefullydecentralizedapproach,themainresponsibilityisgiventothecontrollersofthemicrogeneratorsthatcompetetomaximizetheirproductioninordertosatisfythedemandandprobablyprovidethemaximumpossibleexporttothegridtakingintoaccountmarketprices[19,20,21].Thisapproachisbasedonthemulti-agenttechnologyandprovideseffectivesolutionsforanumberofspecificoperationalproblemsincontrollingmicrogrids[19,20].Inordertoachievethefullbenefitsfromtheoperationofmicrogrids,itisimportantthattheintegrationofthemicrosourcesintolowvoltagegridsandtheirrelationwiththemediumvoltagegridwillcontributetooptimizethegeneraloperationofthesystem[22].Toachievethisgoal,thehierarchical(centralized)controlofmicrogridisproposedforwhichthreecontrollevelsaredistinguished[19,23,24]:1-DistributionManagementSystem(DMS).MicroGridCentralController(MGCC).LocalControllers(LC),whichcouldbeeithermicrosourcecontrollersorloadcontrollers.DMSisresponsibletomanageandcontrolthedistributionareacomprisingseveralfeedersincludingseveralmicrogrids.ThemaininterfacebetweentheDMSandthemicrogridistheMGCC.Itisthemainresponsiblefortheoptimizationofthemicrogridoperation,oralternatively,itsimplycoordinatesthelocalcontrollers,whichassumethemainresponsibilityforthisoptimization.ThelowercontrollevelconsistsoftheLCthatcontrolDER.A.MarketpoliciesofamicrogridwithcentralizedcontrolInamicrogridwithcentralizedcontrol,MGCCisresponsibleforthemaximizationofthemicrogridvalueandtheoptimizationofitsoperation.ItusesthemarketpricesofelectricityandprobablyDemandSideManagement(DSM)requeststodeterminetheamountofpowerthatthemicrogridshouldexchangewiththedistributionsystem,optimizingthelocalproductioncapabilities.Itmightuseloadforecasts(electricalandpossiblyheat)andforecastsofpowerproductioncapabilities.Thedefinedoptimizedoperatingscenarioisachievedbycontrollingthemicrosourcesandcontrollableloadsinthemicrogridbysendingcontrolsignalstothefield.Inthisframework,non-criticalcontrollableloadscanbeshed,whenitisnecessary.Furthermore,itisnecessarytomonitortheactualactiveandreactivepowerofthecomponents.Thesetechniquescanbeconsideredequivalenttothesecondarycontroloftheinterconnectedgrid[23]?TwomarketpoliciesareassumedforMGCCthatcontainofbehaviorlikeagoodcitizenandbehaviorlikeanidealcitizen[23,25].Inthefirstpolicy,theMGCCaimstosatisfythelocalenergydemandusingitslocalproduction,whenitisfinanciallybeneficial,withoutexportingpowertotheupstreamdistributiongrid.Thisisequivalenttothegoodcitizenbehavior.Fortheoveralldistributionsystemoperation,suchbehaviorisbeneficial,becauseatthetimeofpeakdemandleadingtohighelectricityprices,themicrogridrelievespossiblenetworkcongestionbypartlyorfullysupplyingitsenergyneeds.Fromtheend-userpointofview,theMGCCminimizestheoperationalcostofthemicrogrid,takingintoaccountmarketprices,demandsandDGbids.End-usersofthemicrogridsharethebenefitsofreducedoperationalcosts.InthiscaseMGCCcollectsthemarketpricesforpower,theloaddemands(probablyforecastedbyshorttermloadforecastingprograms)andthebidsofmicrogridstominimizetheenergycostsforthewholemicrogridforeachofdefinedinterval,e.g.eachof15minutesinterval,subjectedtotheconstraintssuchasactiveandreactivepowerbalance,P-Qcurveforeachoneofthegeneratorunitsandthegridtechnicallimitsofeachunit,etc[23].Inthesecondpolicy,themicrogridparticipatesintheenergymarketofthedistributionarea,buyingandsellingactiveandreactivepowerfrom/tothegrid,probablyviaanaggregatororsimilarenergyserviceprovider.Accordingtothispolicy,theMGCCtriestomaximizethevalueofthemicrogrid,i.e.maximizethecorrespondingrevenuesoftheaggregator,byexchangingpowerwiththegrid.Theend-usersarechargedfortheiractiveandreactivepowerconsumptionatmarketprices.Themicrogridbehavesasasinglegeneratorcapabilitytorelivethepossiblenetworkcongestion,notonlyinthemicrogriditself,butalsoviaexportingenergytonearbyfeedersofthedistributionnetworklikeanidealcitizen.Inthiscase,MGCCconsidersthemarketpriceforbuyingandsellingenergytothegrid,thepowerdemand(probablyfromshorttermloadforecasting),thebidsofmicrosourcesforactivepowerandthemaximumcapacityallowedtobeexchangedwiththegrid(withregardtosomecontractualagreementoftheaggregatororthephysicallimitsoftheinterconnectionlinetogrid).Thenitismaximizedthemicrogridvaluethatisthedifferencebetweenincomesandexpenses,subjecttorelatedconstraints.Theconstraintsareincludethepreviouspolicyconstrainsplustotheconstraintsrelatedtocapacityoftheinterconnectionandtheactivepowerpolicycontractedbytheaggregator[23].Inthebothpolicies,demandsidebidsandadequacyorpowerqualityissuescanbeincludedintheoptimizationroutines.OperationofVPPIn[26]VPPdispatchesitsunitsonlybasedontheminimizationofshorttermvariablecostsforserviceproviding.Forthispurpose,VPPsolveanoptimizationprogram,inwhichtheobjectivefunctionisthesumofheat,electricaswellasCHPplantsfuelcostsaddtocost/revenueoftheelectricpowerexchangedwiththegridineachhour.TheconstraintfunctionisthebalanceofelectricaswellasthermalenergybetweenVPPgeneratorsandVPPloads.Theauthorsof[26]developtheirmodelin[27]byproposingthecoordinatedoptimizationofVPPandDSOtomaintainthesecurityofdistributionnetwork.ThisisbecauseDSOisresponsibletomaintainthesecurityofthedistributionnetwork.Itshouldhandlethenetworkinsuchawaythatthevoltagetoleranceineachbustobemetandthecongestiontobeavoided.Infact,ifVPPoptimizationisperformedwithoutDSOregulation,i.e.VPPoperatorindependentlyminimizesitstotalshorttermcostsincludingproductioncostsofVPPunitsandthecostofpowerexchangewiththegrid,andtherebysuppliesitsheatingandelectricaldemand,thismayleadtoviolationofvoltagesandcurrentslimitsindistributionnetwork.AninferiorsolutionisthattheDSOperformstheregulatingactionsonthenetworkonlybyactingonthemainsubstationOnLoadTapChangerTransformer(OLTCT)andontheavailableshuntcompensators.ButthecoordinatedoptimizationofVPPandDSOisbetterandsuitablesolution.Theproposedalgorithmin[271isbasedonthesolutionofafurtheroptimizationproblem,whichisaimedtoharmonizetheoperationsofbothDSOandVPPinordertoachievethedesiredregulationwithminimumwheelingcosts,anextracostaccountingforthedistributionnetworklosses.Here,theDSOwouldperformasortofvirtualactiveandreactivepowerdispatchingoftheDGsbysolvinganoptimizationproblemtominimizethenetworklosseswhichcorrespondtominimizethecostofactiveandreactivepowerimportedfromtheHVgrid,sincethedistributedpowergenerationanddemandarefixedboundaryconditions.Inordertodoso,theDSOneedscompleteknowledgeofthesystemstate(generatedanddemandedactiveandreactivepoweratanybusbar)andcostfunctionsoftheVPPgenerators.Theconstraintsareincludedpowerflowbalanceequationsateachbusofthenetworkforbothactiveandreactivepower,voltagesboundariesandthecurrentlimitationsofthefeeders.ItistobenotedthatactiveandreactivepoweroftheDGunitswhicharebelongtotheVPP,areconsideredasfixedvaluesinpowerbalanceconstraintofeachbus,whiletheyareoptimizationvariablesinVPPoptimizationalgorithm.Asaresultoftheoptimization,thisalgorithmprovidesanestimationofthenodalpricesforactiveandreactivegridexchangepowerrequiredbytheVPPoptimizationalgorithm.VPPhasthechoicetoadequateitsproductiononthebasisofsuchsignals,inwhichcasethewheelingcostswouldbeminimized.ThustheoveralloptimizationprocedureisaccomplishedbytheiterativeapplicationofbothDSOandVPPoptimizationalgorithms,wherethecommonvariablesarealternativelytreatedasoptimizationparametersinonealgorithmandfixedboundaryconditionsintheother.Theterminationcriterionistheminimizationofthepricevaluesvariationofenergyinthenetwork.In[26,27],althoughVPPexchangeselectricpowerwiththegridinregardtothepricesofwholesalemarket,ithasapassiveroleinmarkettransactions.Itisduetothefactthatitdoesnotbidtothepowermarketasaparticipant.In[15,16],ageneralframeworkforoperationoftheVPPinthepowermarketisproposed.Inthisscheme,theDGunitsoffertheirproposalsforsaleofenergytotheVPPoperator,whoformulatestheenergypricetonegotiateinthemarketordirectlywithcustomers.Afterdefiningthecommercialstrategy,VPPnegotiatesinthepowermarket.Aftertheperiodofnegotiation,themarketoperatordeterminesthecommercialtransactions.Themarketresultsshouldbevalidatedbythesystemoperator.Whentechnicalconstraintsareviolated,itisnecessarytoshowthecriticalpointstotheproducersandcostumerstoallowthemtoadjudicatethesupplytoanotherproducer.ItisnoticeablethatincaseofrestrictiontothesupplyofenergybyaVPP,thesituationisdifferentfromsingleproducersbecauseVPPscanchangethescheduling,oreventually,theplaceofinjectionofthegeneration,toreducethegenerationintheplaceswherecausestechnicalproblems.ThiswillbeaveryimportantcredittotheVPP.Iftherearenoproblemsinthetechnicalanalysis,thesystemoperatorwillcommunicatethistothemarketoperatortoallowhimtorealizethetransactions.Inthemarketday,VPPmustundertakeapermanentcontroloftheenergydeliveredtothenetworkbyeachpartnerproducer,tocompensatethevariationofthegenerationofthenon-dispatchabletechnologies.Inthisframework,VPPwhileparticipateinthepowermarket,hasamarketinsideitselfandallDGunitsbidtoit.SinceseveralDGsespeciallythosebelongtoresidentialorsmallcommercialconsumershavelowcapacitiesandtheirownersarecommonlyuninformedofpowerbusiness,itisdeducedthatonlysomeDGswithspecialcharacteristicsareconsideredbytheauthors.Moreover,whatmarketisconsideredisnotexplainedandthecharacteristicofmarketarenotcleared.Theauthorsof[17]proposeVPPinordertofacilitateDGstradinginthewholesaleenergymarketandtoprovidesomeservicestosupporttransmissionsystemmanagement.A.MarkettransactionsoffutureVPPsBasedontheDGpenetrationgrowth,thenatureofthedistributionnetworkisalteredfromapassivenetworkthatitisonlycontainloadstoanactiveone,whichiscontainbothloadsandgenerators[28].Inthisnewenvironment,theroleofDSOinmaintainingthesecuredistributionsystemisthesameasISOroleintransmissionsystem.Inactivedistributionnetworks,conventionalDisCofunctionsareunbundledintotechnicalandcommercialtasks,includingtheprovisionofancillaryservices.Someancillaryservicessuchasvoltagecontrolhavelocalnatureandsomeothers(e.g.reserves,realpowerlossreplacementandetc.)havesemi-localnaturewhichtheycanprovideeitherlocallyorglobally,eventhoughitisbetterthattheyprovidelocallytoalleviatethecongestion.DSOshouldprovidesomeancillaryservices(thosehavealocalorsemi-localnature)viatheproducerswhichareinsidetheDisCocontrolarea.ADisCoenergyacquisitionmarketmodelwithDGsandcontrollableloadsispresentedin[29].ThismarketisoperatedbyDSO,whotriestomeettherequirementofDisCo9sendcustomersfromwholesalemarket,DGresourcesandcontrollableloads.TwogroupsofDGunitsareconsidered,i.e.independentDGunitswhicharemanagedorownedindependentlyfromtheDisCoanddependentoneswhicharemanagedorownedbytheDisCo.IndependentDGunitssendtheenergyoffers(priceasafunctionofenergy)toDSO,andtheoperationcostsofdependentonesaredirectlyconsideredinDSOobjectivefunction.Theproposedmodelin[29Jisdevelopedfromsingle-periodtoamulti-periodenergyacquisitionmodelbytheauthorsof[30].OnlydependentDGsareconsideredin[30].Inthenewfuture,whentheshareofDGinthepowersystemgenerationisapproximatelycomparablewiththetraditionalunits,DisComarketwillbedeveloped,andVPPswillbeparticipatedinDisComarketforbothenergyandancillaryservices.Thissubjectiswelladdressedin[31].SincefutureVPPsmaybeincludedthewidevariousDGtechnologiesinlowvoltageandmediumvoltagedistributionnetworks,theentrybarrierofDGsinthepowermarkets,i.e.smallsizeofDGsandstochasticnatureofsomeDGs,willberemovedthroughtheVPPconceptandallofDGsmaybevisibleforthemarketbyintegratinginVPPsandtheircapabilitieswillbeusedforprovidingthesecurityofthesystem.ConclusionsTheshareofDGinthepowersystemgenerationisincreasinglygrownupandintegrationofthemisdeeplyconcentratedbytheresearchers.Generallytwointegrationstrategiesareexisted,includingintegrationinamicrogridandinaVPP.Themicrogridconceptisbasedontheassumptionthatlargenumbersofmicrogeneratorsareconnectedtonetworkandthatthesecanbeusedtoreducetherequirementfortransmissionandhighvoltagedistributionassets.VPPisaconcepttoaggregateanumberofDERofvarioustechnologieswithvariousoperatingpatternandavailabilitythatconnectedtovariouspointsindistributionnetworkfortheproposeoftradingelectricalenergyortoprovidesystemsupportservicesMicrogridscanexchangepowerwiththegridundertopolicies,thebehaviourlikegoodcitizenandthebehaviourlikeidealcitizen.Moreover,VPPsareproposedfortradingDGinwholesalemarket.Inthenewfuture,theroleofDSOinmaintainingthesecureactivedistributionsystemwillbethesameasISOroleintransmissionsystemandDisComarketwhichisoperatedbyDSOwillbedevelopedandfutureVPPswillbeparticipatedintheDisComarketforbothenergyandancillaryservices.AcknowledgmentTheauthorsgratefullyacknowledgethesupportsofKhouzestanElectricPowerDistributionCompanyinthisresearchwork.ReferencesMozumder,P.,Marathe,A.,"Gainfromanintegratedmarketfortradablerenewableenergycredits,"EcologicalEconomics,Vol.49,No.3,July2004,pp.259-272.Morthorst,P.E.,"Thedevelopm