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Chapter4TransientsElectricalEngineeringandElectronicsII4CourseHours第1页
4.Transients4.1Introduction4.2Initialstateandsteadystate4.3First-orderRCCircuits4.4First-orderRLCircuits第2页
tENewsteadystatetransientCOldsteadystateKRE+_SwitchKisclosed4.1IntroductionNewsteadystateRUs+_Conceptionofsteadystateandtransientstate?Whent=0,uc(0)=0Whent=∞,uc(∞)=UsOldsteadystate第3页
Whythetransientresponsehappens?NotransientI?Resistivecircuitt=0ER+_IKResistorisaenergy-consumptionelement,currentisproportionaltovoltage,notransientresponsewillhappenevenifchangingsource第4页
Energycannotchangeinstantlybecauseofaccumulatingordecayingperiod.ChargingordischargingChangegraduallyElectricfieldenergyEKR+_CuCEt第5页
MagneticfieldenergyChangegraduallyKRE+_t=0iLtE/REnergycannotchangeinstantlybecauseofaccumulatingordecayingperiod.第6页
Thecausesoftransients1.Energystorageelements-inductorsandcapacitorschangegradually;2.Changingcircuit,suchasswitchingsource.第7页
TransientsThetime-varyingcurrentsandvoltagesresultingfromthesuddenapplicationofsources,usuallyduetoswitching.Bywritingcircuitequations,weobtainintegro-differentialequations.Theseequationscanbeconvertedtopuredifferentialequationsbydifferentiatingw.r.ttime.Thestudyoftransientsrequireustosolvedifferentialequations.第8页
4.2InitialstateandsteadystateAssumechangingcircuitwhent=0,thent=0–isendpointofoldsteadystate;t=0+isthestartpointoftransientstate.Fromt=0–tot=0+,iL、uCcannotchangesuddenly.t=0tt=0-t=0+Thelawofchangingcircuit(换路定则)第9页
Exa4.2Solu(1)BroforeswitchWeknowthatBythelawofcircuitchangingKnowns:beforecircuitchanging,C、Lhavenoenergy;Find:thecurrentsandvoltagesofallelements。S(a)CUR2R1t=0+-LHowtogetinitialvalue第10页
Example4.2,changingmoment,capacitanceshort,changingmoment,inductanceopeniC、uLa
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