-微電網運行歷程與電力市場中的虛擬電廠

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..微電網中心控制器（MGCC）。.本地控制器（LC）,微源控制器或負載控制器。DMS負責管理和控制分布區(qū)域包括幾個干線包括數(shù)個微電網。在DMS之間的主界面微電網是MGCC。它是主要負責的微電網運行的優(yōu)化，或者說，它能簡單地協(xié)調本地控制器，它主要責任是進行這種優(yōu)化。下控制級別是由LC控制DERoA.微電網集中調節(jié)的市場政策在微電網集中控制，MGCC是負責該微電網價值最大化和其操作的優(yōu)化。它采用的市場價格電力及可能需求管理（DSM）請求，以確定功率，該微電網的量應與分配系統(tǒng)交換，優(yōu)化當?shù)厣a的能力。它可能會使用負荷預測（電氣和熱可能）和功率預測生產能力。優(yōu)化操作方案內容是通過控制微源取得和在微電網可控負載通過發(fā)送控制信號到外地。在此框架下，在必要的情況下，非關鍵可控負載可以去掉。止匕外，有必要監(jiān)測的實際有功和無功組件。這些技術可以被認為是等價于相互連接網格［23］的輔助控制。兩種市場政策被假定為MGCC就像一個好公民，行為像一個理想的公民行為［23,25］o在第一個政策時，MGCC旨在滿足地方生產所需的能源，當它是財政有利，而不利用電源上游配電網。這等同于良好公民的行為。對于整個配電系統(tǒng)運行，這樣的動作是有利的，因為因為在需求高峰導致電價高的時候。微電網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最小微電網的運行成本，考慮到市場價格，需求和DG投標。用戶終端的微電網的加入降低的運營成本。在這種情況下MGCC收集市場價格波動，負載的需求（通過預測可能短期負荷方案）和微型電網以最小化對整個微電網的能量成本為每個定義的時間間隔，例如每15分鐘間隔，受到限制，如有功功率和無功功率平衡，PQ曲線每一個的發(fā)生器單元和每個單元等［23］的網格技術限制。在這兩種政策中，需求方投標和功率質量問題，包括在優(yōu)化例程。.VPP操作在［26］VPP調度其單位僅根據(jù)最小化的服務短期可變成本提供。為了達到這個目的，VPP解決最優(yōu)化程序，其中，所述目標函數(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中的每小時。約束函數(shù)是電動的平衡以及VPP發(fā)生器和VPP負載之間的熱能之間的關系。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)調優(yōu)化，以保持配電網的安全性。這是因為DSO是負責維持分配的安全網。它應處理網絡中的這樣一種方式，該在每個總線電壓容差避免達到高峰。事實上，如果不進行VPP優(yōu)化DSO監(jiān)管，即VPP運營商最大限度地降低獨立其總的短期成本，包括VPP的生產成本單位和與電網電力交換的成本，并從而提供其加熱和電的需求，這可能導致違反的電壓和電流的分布范圍網絡。較差的解決辦法是，在DSO執(zhí)行通過作用于主調節(jié)網絡上的動作變電站有載分接開關變壓器(OLTCT)和上可用的分流補償器。但適合的解決方案是協(xié)調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)調兩個DSO和VPP的，以實現(xiàn)所述的操作以最小的成本續(xù)流所需的監(jiān)管，一個額外的成本占銷售網絡的損失。這里，所述DSO將執(zhí)行一種虛擬的有功和無功的在分布式發(fā)電通過求解優(yōu)化電力調度問題，以減少其對應于所述網絡的損失減少進口有功功率和無功功率的成本高壓電網，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，該DSO需要系統(tǒng)狀態(tài)的完整知識(生成并要求有功功率和無功功率的任何母線)和VPP發(fā)生器的成本函數(shù)。該約束包括在每一個功率流平衡方程網絡為有功功率和無功功率的公交車，電壓界限和所述饋線的電流限制。但應指出，DG的那有功和無功功率這是屬于VPP,被認為是固定的單位在每個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)化的結果，該算法提供了一個估計的節(jié)點價格有功和無功電網通過VPP優(yōu)化算法所需的交流電源。VPP具有選擇適當其生產的基礎上這樣的信號，在這種情況下，回流成本會最小化。從而整體優(yōu)化過程是雙方DSO和迭代應用程序完成VPP優(yōu)化算法，其中，所述公共變量被可選地視為在一個優(yōu)化參數(shù)算法和其他固定邊界條件。該終止標準是價值的最小能量在網絡中的變化。在［26,27］,但VPP交換電力與電網在考慮到價格批發(fā)市場，它在市場上被動的角色交易。它是由于這樣的事實，即它不出價到電力市場的參與者。在［15,16］,為的操作的總體框架VPP電力市場的建議。在這個方案中，DG單位提供他們的提議出售能源的VPP運營商，誰制定了能源價格的談判市場或直接與客戶。確定后商業(yè)戰(zhàn)略，VPP協(xié)商的電力市場。談判的時期，市場操作后，決定了商業(yè)交易。市場結果應該由系統(tǒng)操作員進行驗證°當技術限制被違反，就必須以顯示臨界指向生產者和顧客以允許它們裁決其他生產商。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商不同，因為VPPS能改變調度，或最終注入的地方的產生，以減少在該地方的代導致的技術問題。這將是一個非常重要的信貸的VPP。如果在技術上沒有問題分析，系統(tǒng)操作者將傳達給市場經營者，讓他實現(xiàn)交易。在每日市場上，VPP必須承擔的永久控制由每個伙伴生產者傳送到網絡中的能量，補償不可分派的產生的變化技術。在這個框架的工作，同時VPP參與電力市場，具有一定的市場里本身所有的DG單位出價吧。由于分布式發(fā)電的幾個特別是那些屬于住宅或小型商用消費者低容量和它們的主人通常不了解情況的電力業(yè)務，這是推斷，只有一些分布式電源特性由作者考慮。止匕外，有什么市場被認為是沒有解釋的市場特征不會被清零。作者［17］提出VPP是為了推動分布式電源買賣的批發(fā)能源市場和提供某些服務，以支持傳輸系統(tǒng)管理。A.未來VPPS的市場前景對于DG是一種無源網絡改變包含負載普及率增長的特性配電網，它是同時包含負載和發(fā)電機［28］。在這個新的環(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。在自主配電網中，傳統(tǒng)的DISCO功能分拆成技術和商業(yè)任務，包括提供配套設施。一些輔助設施，作為電壓控制有當?shù)氐淖匀缓推渌恍ㄈ鐑?，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，以減輕壓力。在DISCO控制區(qū)域內，DSO應該提供一些配套設施通過生產者（那些有本地或半當?shù)氐淖匀唬?。DISCO能源與分布式電源和負荷呈現(xiàn)在控制收購市場方式［29］。這個市場是以批發(fā)市場，DG資源和可控負載等，DSO操縱以滿足DISCO的終端客戶的需求。兩個DG的單位被視為組，即獨立的DG單位管理還是從DISCO獨立擁有而那些依賴其由被管理或擁有DISCO。獨立DG單位發(fā)出的能量報價（價格為能量的函數(shù)），以DSO目的，經營成本依賴的人直接認為是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DG在電力系統(tǒng)中的份額大約媲美傳統(tǒng)的設施，DISCO市場將被開發(fā)，并VPPS將參加DISCO市場能源和配套服務。這個問題是很好解決的［31］。因為未來VPPS可包括在寬的各種DG技術在低壓和中壓配電網絡，分布式發(fā)電在電力市場的準入門檻，即分布式電源和一些分布式電源的隨機性質的尺寸小，將通過VPP概念刪除，所有分布式電源的可能在VPPS和整合可見對市場的功能將被用于提供的安全性系統(tǒng)。.結論DG在電力系統(tǒng)發(fā)電的份額日益成長和深入研究人員有直接關系。一般兩種不同的整合策略是存在的，包括集成微電網以及VPPo微電網概念是基于假設大量微發(fā)電機連接到配電網中，并且這些可以用來降低用于傳輸和高壓配電要求成本。VPP是一個概念聚集了一批DER不同的技術和不同的操作模式，連接到各點中的分布網絡的提議，交易電能或提供系統(tǒng)支持服務，微電網可以交換功率措施的電網，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。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市場是由運營DSO將開發(fā)和未來VPPS將參加在DISCO市場對能源和配套設施將是相同的。致謝作者非常感謝Khouzestan配電公司對本次研究支持。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