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1PowerElectronicConceptsPowerelectronicsisarapidlydevelopingtechnology.Componentsarettinghighercurrentandvoltageratings,thepowerlossesdecreaseandthedevicesbecomemorereliable.Thedevicesarealsoveryeasytocontrolwithamegascalepoweramplification.Thepricesarestillgoingdownpr.kVAandpowerconvertersarebecomingattractiveasameantoimprovetheperformanceofawindturbine.Thischapterwilldiscussthestandardpowerconvertertopologiesfromthesimplestconvertersforstartinguptheturbinetoadvancedpowerconvertertopologies,wherethewholepowerisflowingthroughtheconverter.Further,differentparksolutionsusingpowerelectronicsarealsodiscussed.1.1CriteriaforconceptevaluationThemostcommontopologiesareselectedanddiscussedinrespecttoadvantagesanddrawbacks.Veryadvancedpowerconverters,wheremanyextradevicesarenecessaryinordertogetaproperoperation,areomitted.1.2PowerconvertersManydifferentpowerconverterscanbeusedinwindturbineapplications.Inthecaseofusinganinductiongenerator,thepowerconverterhastoconvertfromafixedvoltageandfrequencytoavariablevoltageandfrequency.Thismaybeimplementedinmanydifferentways,asitwillbeseeninthenextsection.Othergeneratortypescandemandothercomplexprotection.However,themostusedtopologysofarisasoft-starter,whichisusedduringstartupinordertolimitthein-rushcurrentandtherebyreducethedisturbancestothegrid.1.2.1SoftstarterThesoftstarterisapowerconverter,whichhasbeenintroducedtofixedspeedwindturbinestoreducethetransientcurrentduringconnectionordisconnectionofthegeneratortothegrid.Whenthegeneratorspeedexceedsthesynchronousspeed,thesoft-starterisconnected.Usingfiringanglecontrolofthethyristorsinthesoftstarterthegeneratorissmoothlyconnectedtothegridoverapredefinednumberofgridperiods.AnexampleofconnectiondiagramforthesoftstarterwithageneratorispresentedinFigure1.Figure1.Connectiondiagramofsoftstarterwithgenerators.Thecommutatingdevicesaretwothyristorsforeachphase.Theseareconnectedinanti-parallel.Therelationshipbetweenthefiringangle(﹤)andtheresultingamplificationofthesoftstarterisnon-l
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