高功率电子学第5章开关技术pulsed power switching

1、High Power SwitchesJames DickensHigh Power Switches: OverviewHigh Power gaseous SwitchesState of the art forrepetitive pulsed power10 15 years agoEnvironmental issue: HgProduction and developmentstopped 10 years agoLow efficiencyNowadays: Trend: Off gaseous switches to semiconductor switches!The goa

2、l of the lecture is: Qualify you to make the right choice despite the trend!History of High Power Switch DevelopmentGlass envelope Thyratrons Langmuirs first thyratron1953: Xenon-filledThyratron fom BBC1949: Hg-filledThyratron fom BBCGerman spark gap(Telefunken)Ferranti TriggeredSpark GapEdiswan spa

3、rk gapTodayToday:B. Basic Physics of Gaseous High Power SwitchesBasic Physics of Gaseous High Power SwitchesVoltage Self-sustainedNon-self sustainedARC regimeTOWNSEND Breakdown criterionIn order to maintain a self-sustained discharge it is necessary to create for each primary electron at least one s

4、econdary electron by -process. This process can be described by the following mechanisms:gi . (ead-1) = 1Volume processes are described by the 1. Townsend-coefficient, feedback by the generalized 2. Townsend-coefficient (/+ gi)Ion avalanchePrimary electron starts at the cathodeavalancheanodePhotonsc

5、athodeelectron release by gTOWNSEND-criterion: U=(E/N)Nd = Ed with /N = f(E/N) and ( gi) = f(E/N) gas type and-pressureE-field conditiongeometryTOWNSEND Breakdown CriterionElectron avalancheThe time behaviour which characterizes the electrical breakdown of gases is described by two time lagsThe stat

6、istical time lag := time until the first seed electron appears (for a TOWNSEND discharge typically 10-5 -10-3 s)The formative time lag := time of growth of avalanches until breakdown occursIn (triggered) switches the statistical time lag minimized by a trigger method which provides artificially elec

7、tronsA,B are experimentalconstants, for each gas differentPaschen 定律Gas BreakdownWith Magnetic FieldSeveral 100 V1-10 Torr - cmpdVBVariable Definitions:VB: Breakdown Voltagep: Pressured: Gap DistanceB: Gyro Frequencyc: Collision FrequencypdVBIncreasing BPaschen Curve:Breakdown VoltageFor low pd (spa

8、ce environment): magnetic field decreases breakdown voltage for all directions of BBoundary condition for the PASCHEN -lawThe PASCHEN law is based on the TOWNSEND mechanismsVolume processes by electron impact ionization (-coefficient) and Electrode processes by secondary electron emission (-coeffici

9、ent)The PASCHEN law is not valid if there are other electron emission processes involved likeField emissionThermionic emission field enhanced thermionic emission thermionically enhanced field emissionBriefly: Importance of Electrode Mechanisms1: ionization by radiation (photons, cosmic rays)2: charg

10、e transfer by particles3: e-emission (field, secondary, photo)4: field desorption and ionization5: impact ionization of electrode surface materials6: charge multiplication in avalanches (by impact)7: evaporation of charged adsorbed particles8: dissociation of neutral particles9: conduction through i

11、nsulator and polarization10: conduction over adsorbed layers11: conduction through supportProcesses, which contribute to breakdownC. Commercially Available High Power Switches classified according to the Nature of the Switching MediumEnergy density achievable with different switching mediaHigh Power

12、 Switches: Operating RegionsCalculated Resistive Phase Fall Time Against Pressure for Many of the Known Switch DevicesPSSPressure Range ofHigh Power SwitchesPulsed Power and High Power SwitchesCapacitive/Inductive Energy Discharge CircuitsCapacitive Energy Discharge CircuitInductive Energy Discharge

13、 CircuitRoScCVoZLVpScLRLSoIoZLSwitch CharacteristicsHold-off VoltagePeak CurrentAverage CurrentCoulombs Per ShotImpedance( in system )Voltage DropDelay TimeRecovery TimeRepetition RateDuty CycleJitterPre-FireTriggering RequirementsThermal DissipationCooling RequirementsLifetimeReliabilityMaintainabi

14、lityFault ModesWeightVolumeCostEase of Installation and removalOrientationConfiguration: Coaxial, Stripline, Etc.Shielding Requirements, RF, Etc.Operating Environment e.g. Pressure ( altitude ), Temperature, Radiation (UV, Neutrons, Gammas, Etc.), Stress (Acceleration, Magnetic Pressure)OthersThe On

15、e We ForgotThe One That Does You In?Pulsed Power and High Power Switches1. Vacuum tubes: - Triggered Vacuum Gap (TVG)TVG: Triggering by plasma injectionPlasma triggeringPeak CurrentCharge TransferAction IntegralRecovery dI/dtOperating VoltageRussian TVS-4050kA9 Cb0.3 MA2-s660 A/s20 kVThomason Shorts

16、45kA10 Cb3.0 MA2-s500 A/s13 kVTVG 300450kA83 Cb28 MA2-sNo Data60 kVGE G1150 kA800 Cb95 MA2-s57 A/s84 kVGE Experiment240kA1270 Cb240 MA2-sNo DataNo DataMain application as crowbar switchPrincipally one can operate TVGs in series and in parallel!2. Gas filled Plasma Switches- low-pressure devices with

17、 cold cathode . Pseudospark Switch (pss)Low ErosionLong Lifetime100% Reversal CapabilityHigh dI/dtHigh Repetition RateHigh Current CapabilityPseudospark SwitchesFundamentals of the PseudosparkPaschen (1889): Uz=f(p d)Potential distribution:within the gap 10kV/cmwithin hollow cathode 100V/cmhollow ca

18、thode effectpendulum electronseasily triggerable from theback of the hollow cathodePaschen Curve and PseudosparkElectron Kinetics in the Pseudospark DischargeTwo e- populations existMonoenergetic beam e-Bulk e-Primary beam e- bounce within the cathode hollow several times before exiting into anode r

19、egionPrimary e- beam get both secondary beam e- and bulk e-Secondary beams escape HC and bombard anode with large energies in the anode is higher than in the cathodeInfluence of Hollow CathodeLow E/N favors ionization growth“Pendulum electrons” reflect between cathode sheaths and intensifies ionizat

20、ion (Helm 1972)Plasma-Wall interaction extremely important+ Ions accelerated into HC space charge “virtual anode”When carrier production losses, space charge leads to field distortion breakdown by formation of an ionization waveTrigger by injection of carriersNIF ApplicationRadial Design:Eliminates

21、problems associated with self-magnetic pinchGreatly reduces current density, resulting in decreasedElectrode erosion and increased lifetimeProvides a low inductance switchRepetitive Operation of Pseudospark SwitchesPRF: 100 kHz (burst mode)di/dt: 5 x 1011 A/sV 20kVI 10kARecovery Corroborated by Hart

22、mann: No re-ignition below 30 kV/s - 1 sNovel Trigger:pre-ionize with DC Glow in HCApply 2kV electrical “trigger”0.1mJ/pulse trigger energyDesign of the fundamentalpseudospark geometrysingle channelgeometryfor mediumpowermulti channelgeometry(coaxial) forhigh powerradial multichannelgeometry for hig

23、h powertwo gap geometryfor highanode voltagesDifferent Pseudospark GeometriesParameters of a common pseudospark dischargeDischarge geometry:-electrode distance: 2 5 mm-bore hole diameter: 2 5 mmPressure p: 5 80 Pa (all gaseous media)Hold-off voltage: 30 kVPeak current:1A multi kiloampsPlasma paramet

24、ers:- ionization degree: partially ionized- electron density: 1012 - 1015- electron temperature: 2 10 eV- ion temperature: 109Yes 5 ns200 ns 107no30 ns 107 107 107YesYes 10 ns 1.0 s 50 ns 100ns 10 nse-beamLife timeDependence onpressureJitterDelayno High dielectric triggerfinger tipscontact 2dielectr

25、ic probemetallic layerprobe holdercontact 1 High dielectric Probe 2000 - 2700 Contact 1: Probe holder Contact 2: Finger tips Trigger methodsHigh Dielectric Triggercontact to discfinger contactHigh dielectric samplevariation of wiringtriggerpulse(pos. or neg.)RRtriggerpulse to finger(pos. or neg.)R=0

26、R=50 R= 1kR= infHigh dielectric TriggerBasic scheme of pseudospark geometry and b.) sealed-off device with feedthroughs for trigger pulse and reservoir heaterMain switchTrigger unitSingle gap Pseudospark switch: Ub 35 kV, Ip 10 kA, f 40 kVIp 30 kAPRR 250 HzPulsed Technologies ltd.,5, Yablochkova str

27、., 390023.Ryazan, Russia,pulsetechmail.rureservoirtriggerhollow cathodehollow anodeSAES GetterPseudospark Switch: Cross-section and ReservoirTwo Gap High Voltage SwitchTrGap 1Gap 2Design with intermediateelectrodeDRTrGap 1Gap 2drift space design“Basic designs of multigap pseudospark switchesFour gap

28、s with onetrigger unitFour gaps with fourtrigger unitsPrototypes of Multi-Gap Pseudospark Switchesb. low-pressure devices with hot cathode (heated oxyd cathode). ThyratronThyratron Layout Principle of Thyratron Operation (I)Paschen law for hydrogen and deuteriumThyratron operation (II)PowerlossPb =

29、VI x prfAverage CurrentIAV = C x V x prfThyratron Dissipation Loss = V(t)I(t)dtGrid spikingAnode Heating FactorSwitching cyclePrinciple of Thyratron Operationgas depletionquenching/latchinggas heatingCritical domains of the thyratronSpace charge limited electron emissionHotcathodee-beam formation an

30、d grid-anode arcingMulti-Gap ThyratronE2V ThyratronsA range of over 300 standard productsAnode voltages from 5 kV to 155 kVPeak currents from 100 A to 40,000 ALowest operating costs with high quality devicesDedicated engineering supportMetal envelopethyratronThyratron familyThyratron application: Kl

31、ystron modulatorc. Magnetic SwitchesImportant: MagneticAssist!(2)Magnetic SwitchPulse compressionMagnetic Switchd. High-pressure devices with cold cathode- Spark GapFrom E2V UKTrigger methods:- apply an overvoltage- field distortion- surface flashover (trigatron)- e-beam initiation- laser beam initi

32、ationHold-off voltage of vacuum and high pressure gasHigh pressureregimeField Distortion TriggercathodeanodeNo!YesVoltage change of trigger electrode when pulse triggering Spark Gap (Overvolted)Triggered Spark Gap (Trigatron)ABC1-R+2+R-3+R+4-R-Priority listing of relative electrode polarity for best

33、 triggering actionElectrode B is the Reference ElectrodeElectrode ErosionFactors:di/dtIp idt I2dtElectrode Material and FabricationGas TypeGeometryPolarityTrigger MethodElectrode CoolingGas FlowRep-ratelog(ve)log( Your “Favorite” pulse Parameters (Idt, Ip, I2dt)Typical Erosion CurveErosion Region:In

34、dividual filament interaction with the electrode surface (vaporization - local)Collective filament interaction with the electrode surface (molten metal removal - bulk)Collective filament interaction with the electrode surface (vaporization - bulk)Increasing: m, , Teff Arc Velocity Mechanical Strengt

35、h Gap Spacing Electrode DiameterDecreasing: Pressure Rep-rate Resistivity123Integrated Charge Per Shot CVolume Eroded Per Shot x 10-5 cm3Erosion vs. MaterialElectrode MaterialVolume Eroded Per Shot x 10-5 cm3CuNbCCuW-2CuMoCuW-3CuC-2MoCuCrZrCuZrCuTOTAL HIGH CURRENT EROSION vs. MATERIALOscillatoryIp =

36、 240kACharge = 3.85C1.27 cmD = 1 cmAIR12060402001008016789102453Volume Eroded per Shot cm3Switch Lifetime # of ShotsPeak Current kAState of the “Art” for Stationary Arc SwitchesElectrode ErosionSources: Affinito et al., 1979; Belkin and Kiselev, 1967, 1978; Bickford et al., 1982; Bold and Barnes, 19

37、73; Burden and James, 1972a,b; Buttram and Rohwein, 1978; Carder, 1974; Donaldson, 1982, 1990; Elkins et al., 1982; Fitch and McCormick, 1959; Gordon et al., 1983; Gruber and Suess, 1969; Komelkov, 1970; Krizhanovskii et al., 1981; Limpaecher and Schneider, 1982; Mace, 1979; Milde et al., 1976; Naff

38、 et al., 1981; Reddy et al., 1985; Rohwein, 1980; Suzuki et al., 1981; Wilson, 1955. Specific value of the data can be found in Donaldson 1990.The effect of electrode erosion on switch lifetime as a function of peak current.The lowest erosion rate for a given set of conditions is plotted.The effect

39、of electrode erosion on switch lifetime as a function of the integrated charge transferred per shot.Volume Eroded per Shot cm3Switch Lifetime # of ShotsIntegrated Charge per Shot CState of the “Art” for Stationary Arc SwitchesElectrode Erosion Factors Affecting Rep-rated OperationGas flow rateGas ty

40、peGas PressureCurrentVoltageCharge transferGap spacingElectrode shapeElectrode materialGrace periodRecharge timeRep-rateHydrogen Spark GapGas Recovers static VBrEarly time recovery dominated by atomic ratesRecovery 10 ms for Air, N2, Ar, O2 and SF6HP H2High molecular speed500 kV/cm at 1000 psiRecove

41、rs in 100 usRecovery energy independentTested at energies 5J, 200J, and 12.5kJStaticOvervoltedGas DensityHermetically Sealed, Repetitive Trigatron 500 Hz PRF50 kV DC 70 J/pulseHermetically SealedGas Replenish 1 yearLength 2.5 inchParameter For High Voltage Breakdown in GasesExisting Body of Literatu

42、re Current Research Examining New Parameter SpaceRise time2 10 ns20 200 psPulse Duration100s of nsFew nsPressureFew Atm150 + AtmVoltageFew MVsFew MVsE-field1 MV/cm10s of MV/cmCommercially Available Spark GapsVoltage Range: 150 - 500 kVPeak Current: 10 - 300 kAInductance Typically 40 - 100 nHLife tim

43、e 103 - 104 shotsSpecialty Switch3 MA40 C120 kV 5 nH, 5000 shotsSpark Gap Configuration: RailgapCommercially Available Spark GapsT-150 Spark Gap Switch and TG-1292 Trigger GeneratorT-150 Spark Gap Switch and TG-1292 Trigger GeneratorST-4198Schematic Drawing of the Rimfire Switch5 MV400kADt2ns3-5 Cha

44、nnelsInsulatorLaser HoleTrigger SectionInsulating GasElectrodesContainment VesselConclusionsExcellent research has been performed in the many aspects of Switching TechnologyStill a Critical Technology AreaRecent trends are towardCompactRepetitiveShort burst/or long livedHigher current/or higher volt

45、age6. Semiconductor Switches . Power transistors . Thyristors (example: Light triggered IGBT)Thyristor NomenclatureThyristor Switching ModelFrom Thyristor Switching ModelThyristor StructureThyristor V-I CharacteristicsThyristor Turn On SpeedLimited by the geometry of the gate electrodeGate current f

46、lows initially at the gate edgeThyristor conduct under gate regionVoltage across thyristor falls (gain is reduced in the rest of the device)Conducting electron-hole plasma diffuses laterally at 104 cm/secThyristor ConstructionFrom Dave Singh “POST SILICON MEGAWATT REVIEW”Thyristor SummarySolid state

47、 device current triggeringVoltage limited to 10 kV / deviceMost efficient conduction switchOptical triggering achieved ns turn onMOS-SCR turn On and Off with voltage controlThyristor Gate Current and Reverse Recovery TimePTS5325 C771LNABB ThyristorsFrom Light-triggered thyristors for ETC-application

48、LTT samplesOptically-triggered thyristor: Structure and mechanical layoutOptically_triggered thyristor with laser diodeLaser diode seperateLaser diode integratedElectrically triggered thyristorOptically triggered thyristorOptically triggered thyristors7. Other conceptsSiC DevicesGTOsOptical trigger ThyristorsMOS type devicesDiodes Commercial and pro