电工学原理及应用electricalengineering经典双语详解.pptx

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