Design and Control of a Cascaded H-Bridge Converter based Solid State Transformer

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1、ABSTRACTZHAO,TIEFU.DesignandControlofaCascadedH-BridgeConverterbasedSolidStateTransformer(SST).(UnderthedirectionofDr.AlexHuang.)Asaresultoftherecentdevelopmentofthesmartgridsystem,itisinevitablethatthefutureofpowergenerationanddistributionwillinvolveahighdegreeofdistributedresourcesinterc

2、onnectedtothegirdviafully-ratedpowerelectronicinterface.Theinterfaceisrequiredtoaddfunctionalities,suchasvoltageregulationandreactivepowercompensation,intelligentpowermanagementandplug-and-playfeaturesforthedistributionresources.Themotivationforthisdissertationistodesignanewsolidstatetrans

3、formertoreplacethemostcommonlyused,100-yearoldinterface---distributiontransformers.ThepurposeofthisresearchhasbeentodesignacascadedH-BridgeconverterbasedSolidStateTransformer(SST)andtoinvestigatecontrolmethodsandthehardwareimplementation.TheSST,includingAC/DCrectifier,DualActiveBridge(DAB)

4、andDC/ACinverterisdesignedtointerfacewiththesinglephase7.2kVdistributionsystem.First,theswitchingmodel,averagemodelandsmallsignalmodeloftheSSTaredeveloped.TheSSTcontrollerisdesignedbasedonthesmallsignalmodelbodeplot.TheaverageandswitchingmodelsimulationareimplementedtoverifytheproposedSSTf

5、eatures.DuetothecharacteristicsofcascadedH-bridgeconverters,thevoltageunbalancecanappearonDCbusesofdifferentH-bridges.Meanwhile,thepowerunbalancealsobecomesunavoidablefortheparallelDABmodules.Inthisdissertation,anewvoltagebalancecontrollerisproposedtobalancethecascadedH-Bridgecapacitorvolt

6、ages.TheintrinsicconstraintsofthevoltagebalancecontrolforthecascadedH-Bridgetopologyarederived.Meanwhile,anewpowerbalancecontrolmethodisproposedtobalancetheparallelDABpowerintheSST.Theproposedbalancemethodisverifiedbysimulationsandexperiments.Furthermore,anewfeed-forwardpowerripplecontroli

7、sproposedandapowersynchronizationmethodisdesignedtominimizetheDCbusvoltagerippleandtherequiredcapacitorsize.Finally,theSSTrectifierhardwareprototypeisdesignedandimplemented.TheSSTfeaturesandcontrollerareverifiedbythehardwareexperiment.Inordertoinvestigatethefe