-微电网运行历程与电力市场中的虚拟电厂

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..微电网中心控制器（MGCC）。.本地控制器（LC）,微源控制器或负载控制器。DMS负责管理和控制分布区域包括几个干线包括数个微电网。在DMS之间的主界面微电网是MGCC。它是主要负责的微电网运行的优化，或者说，它能简单地协调本地控制器，它主要责任是进行这种优化。下控制级别是由LC控制DERoA.微电网集中调节的市场政策在微电网集中控制，MGCC是负责该微电网价值最大化和其操作的优化。它采用的市场价格电力及可能需求管理（DSM）请求，以确定功率，该微电网的量应与分配系统交换，优化当地生产的能力。它可能会使用负荷预测（电气和热可能）和功率预测生产能力。优化操作方案内容是通过控制微源取得和在微电网可控负载通过发送控制信号到外地。在此框架下，在必要的情况下，非关键可控负载可以去掉。止匕外，有必要监测的实际有功和无功组件。这些技术可以被认为是等价于相互连接网格［23］的辅助控制。两种市场政策被假定为MGCC就像一个好公民，行为像一个理想的公民行为［23,25］o在第一个政策时，MGCC旨在满足地方生产所需的能源，当它是财政有利，而不利用电源上游配电网。这等同于良好公民的行为。对于整个配电系统运行，这样的动作是有利的，因为因为在需求高峰导致电价高的时候。微电网通过部分或完全减轻可能出现的用电高峰满足其能源需求。但从用户终端看，该MGCC最小微电网的运行成本，考虑到市场价格，需求和DG投标。用户终端的微电网的加入降低的运营成本。在这种情况下MGCC收集市场价格波动，负载的需求（通过预测可能短期负荷方案）和微型电网以最小化对整个微电网的能量成本为每个定义的时间间隔，例如每15分钟间隔，受到限制，如有功功率和无功功率平衡，PQ曲线每一个的发生器单元和每个单元等［23］的网格技术限制。在这两种政策中，需求方投标和功率质量问题，包括在优化例程。.VPP操作在［26］VPP调度其单位仅根据最小化的服务短期可变成本提供。为了达到这个目的，VPP解决最优化程序，其中，所述目标函数是热的总和，电以及CHP装置的燃料成本增加成本/收入的电力的交换与电网中的每小时。约束函数是电动的平衡以及VPP发生器和VPP负载之间的热能之间的关系。该［26］通过提出在发展自己的［27］模型的作者VPP和DSO的协调优化，以保持配电网的安全性。这是因为DSO是负责维持分配的安全网。它应处理网络中的这样一种方式，该在每个总线电压容差避免达到高峰。事实上，如果不进行VPP优化DSO监管，即VPP运营商最大限度地降低独立其总的短期成本，包括VPP的生产成本单位和与电网电力交换的成本，并从而提供其加热和电的需求，这可能导致违反的电压和电流的分布范围网络。较差的解决办法是，在DSO执行通过作用于主调节网络上的动作变电站有载分接开关变压器(OLTCT)和上可用的分流补偿器。但适合的解决方案是协调VPP和DSO的优化。在所提出的算法［27］是逐步的优化问题，其目的是协调两个DSO和VPP的，以实现所述的操作以最小的成本续流所需的监管，一个额外的成本占销售网络的损失。这里，所述DSO将执行一种虚拟的有功和无功的在分布式发电通过求解优化电力调度问题，以减少其对应于所述网络的损失减少进口有功功率和无功功率的成本高压电网，由于分布式发电和需求是固定的边界条件。为了做到这一点，该DSO需要系统状态的完整知识(生成并要求有功功率和无功功率的任何母线)和VPP发生器的成本函数。该约束包括在每一个功率流平衡方程网络为有功功率和无功功率的公交车，电压界限和所述馈线的电流限制。但应指出，DG的那有功和无功功率这是属于VPP,被认为是固定的单位在每个总线的电力平衡约束值，而他们是优化变量VPP优化算法。作为优化的结果，该算法提供了一个估计的节点价格有功和无功电网通过VPP优化算法所需的交流电源。VPP具有选择适当其生产的基础上这样的信号，在这种情况下，回流成本会最小化。从而整体优化过程是双方DSO和迭代应用程序完成VPP优化算法，其中，所述公共变量被可选地视为在一个优化参数算法和其他固定边界条件。该终止标准是价值的最小能量在网络中的变化。在［26,27］,但VPP交换电力与电网在考虑到价格批发市场，它在市场上被动的角色交易。它是由于这样的事实，即它不出价到电力市场的参与者。在［15,16］,为的操作的总体框架VPP电力市场的建议。在这个方案中，DG单位提供他们的提议出售能源的VPP运营商，谁制定了能源价格的谈判市场或直接与客户。确定后商业战略，VPP协商的电力市场。谈判的时期，市场操作后，决定了商业交易。市场结果应该由系统操作员进行验证°当技术限制被违反，就必须以显示临界指向生产者和顾客以允许它们裁决其他生产商。值得注意的是，在的情况下的限制能量的供给由VPP,所述情况是由单一生产商不同，因为VPPS能改变调度，或最终注入的地方的产生，以减少在该地方的代导致的技术问题。这将是一个非常重要的信贷的VPP。如果在技术上没有问题分析，系统操作者将传达给市场经营者，让他实现交易。在每日市场上，VPP必须承担的永久控制由每个伙伴生产者传送到网络中的能量，补偿不可分派的产生的变化技术。在这个框架的工作，同时VPP参与电力市场，具有一定的市场里本身所有的DG单位出价吧。由于分布式发电的几个特别是那些属于住宅或小型商用消费者低容量和它们的主人通常不了解情况的电力业务，这是推断，只有一些分布式电源特性由作者考虑。止匕外，有什么市场被认为是没有解释的市场特征不会被清零。作者［17］提出VPP是为了推动分布式电源买卖的批发能源市场和提供某些服务，以支持传输系统管理。A.未来VPPS的市场前景对于DG是一种无源网络改变包含负载普及率增长的特性配电网，它是同时包含负载和发电机［28］。在这个新的环境中，角色DSO在保持安全配送系统是相同的传输系统的ISO的作用。在自主配电网中，传统的DISCO功能分拆成技术和商业任务，包括提供配套设施。一些辅助设施，作为电压控制有当地的自然和其他一些（如储备，真正的功率损耗更换等）有半自然，他们可以提供本地或全球范围内，以减轻压力。在DISCO控制区域内，DSO应该提供一些配套设施通过生产者（那些有本地或半当地的自然）。DISCO能源与分布式电源和负荷呈现在控制收购市场方式［29］。这个市场是以批发市场，DG资源和可控负载等，DSO操纵以满足DISCO的终端客户的需求。两个DG的单位被视为组，即独立的DG单位管理还是从DISCO独立拥有而那些依赖其由被管理或拥有DISCO。独立DG单位发出的能量报价（价格为能量的函数），以DSO目的，经营成本依赖的人直接认为是DSO辅助功能。作者［29］从发展角度提出模型单周期由一个多周期能量采集模型［30］,仅取决于分布式电源被［30］。在新的未来，当DG在电力系统中的份额大约媲美传统的设施，DISCO市场将被开发，并VPPS将参加DISCO市场能源和配套服务。这个问题是很好解决的［31］。因为未来VPPS可包括在宽的各种DG技术在低压和中压配电网络，分布式发电在电力市场的准入门槛，即分布式电源和一些分布式电源的随机性质的尺寸小，将通过VPP概念删除，所有分布式电源的可能在VPPS和整合可见对市场的功能将被用于提供的安全性系统。.结论DG在电力系统发电的份额日益成长和深入研究人员有直接关系。一般两种不同的整合策略是存在的，包括集成微电网以及VPPo微电网概念是基于假设大量微发电机连接到配电网中，并且这些可以用来降低用于传输和高压配电要求成本。VPP是一个概念聚集了一批DER不同的技术和不同的操作模式，连接到各点中的分布网络的提议，交易电能或提供系统支持服务，微电网可以交换功率措施的电网，像良好的行为公民，就像理想的公民行为。此外，VPPS提出交易DG的批发市场。在今后的DSO在维持安全的积极作用配电系统如ISO角色传输系统和DISCO市场是由运营DSO将开发和未来VPPS将参加在DISCO市场对能源和配套设施将是相同的。致谢作者非常感谢Khouzestan配电公司对本次研究支持。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