Note(VII)-margin-estimation-11

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1、Fall2011:ECE4510LectureNote(VII):PerformanceIndicesforEstimatingLoadMargintoVoltageInstabilityProf.Hsiao-DongChiangSchoolofElectricalandComputerEngineeringCornellUniversity,Ithaca,NY14853WhilecontinuationpowerflowmethodscangenerateP-VandQ-Vcurvesinareliablemanner,theymaybe

2、tooslowforon-lineapplications.Toovercomethisdifficulty,anumberofperformanceindicesintendedtomeasuretheseverityofthe(static)voltagestabilityproblemhavebeenproposedinliterature.TheseindicesintendtoprovidesomemeasureofhowfarthesystemisawayfromthepointatwhichthesystemJacobianb

3、ecomessingular.Amongthem,thefollow-ingindicesreceiveconsiderableattentionofdifferentdegree:•minimumsingularvalue•conditionnumberofthesystemJacobian•angulardistancebetweenthecurrentstableequilibriumpointandtheclosestunstableequilibriumpointinaEuclideansense.•energydistanceb

4、etweenthecurrentstableequilibriumpointandtheclosestunstableequilibriumpointusinganenergyfunction.Theseperformanceindicescanbeviewedasprovidingsomemeasurerelativetothedis-tancebetweenthecurrentoperatingpointandthebifurcationpoint.Theseperformanceindices,however,aredefinedin

5、thestatespaceofpowersystemmodelsinsteadofintheparameterspace.Thus,theseperformanceindicescannotdirectlyanswerquestionssuchas:“Canthesystemwith-standa100MVarincreaseonbus11?”or:“Canthesystemwithstandasimultaneousincreaseof70MWonbus2and50Mvarsonbus6?".Onebasicrequirementforu

6、sefulperformanceindicesisfortheirfunctiontoreflectthedegreeofseverityofthedirectmechanismleadingtheunderlyingsystemtowardanundesiredstage.Inthecontextofvoltageinstabilityinpowersystems,ausefulperformanceindexmusthavetheabilitytomeasuretheamountofloadincreasethatthesystemca

7、ntoleratebeforeinsta-bility(whentheunderlyingmechanismofinstabilityisduetoloadvariations),orassesswhetherthesystemcansustainacontingencywithoutinstability(whentheunderlyingmechanismofinstabilityiscausedbyacontingency)andmeasuretheseverityofthecontingency.Inordertoprovidead

8、irectrelationshipbetweenitsvalueandtheamountofloadincreasesthatthesystemcanwithstandbefor