Chapter 1 Power Electronic Devices (Part I)

Power ElectronicsChapter 1Power Electronic Devices(Part I)

Power ElectronicsOutline1.1 An introductory overview of power electronic devices1.2 Uncontrolled device — power diode1.3 Half-controlled device — thyristor1.4 Typical fully-controlled devices1.5 Other new power electronic devices1.6 Drive circuit for power electronic devices1.7 Protection of power electronic devices1.8 Series and parallel connections of power electronicdevices2

Power Electronics1.1 An introductory overview of powerelectronic devicesThe concept and featuresConfiguration of systems using power electronic devicesClassificationsMajor topics3

Power ElectronicsThe concept of power electronic devicesPower electronic devices:are the electronic devices that can be directly used in the powerprocessing circuits to convert or control electric power.In broad senseVacuum devices: Mercury arcrectifier thyratron, etc. . seldomin use todaypower electronic devicesSemiconductor devices:major power electronic devicesVery often: Power electronic devices Power semiconductor devicesMajor material used in power semiconductor devices—— Silicon4

Power ElectronicsFeatures of power electronic devicesThe electric power that power electronic devicedeals with is usually much larger than that theinformation electronic device does.Usually working in switching states to reduce powerlossesOn-stateVoltage across the device is 0v 0p vi 0Off-stateCurrent through the device is 0i 0p vi 05

Power ElectronicsFeatures of power electronic devicesNeed to be controlled by information electronic circuits.Very often, drive circuits are necessary to interfacebetween information circuits and power circuits.Dissipated power loss usually larger than informationelectronic devices — special packaging and heat sinkare necessary.6

Power ElectronicsPower losses on power semiconductordevicesvtitpO n -s ta te( c o n d u c t io n s t a t e )tu r n in g o ffO ff-s ta te( b lo c k in g s t a t e )t u r n in g-o ntTotal power loss on conduction loss turn-off loss off-state loss turn-on losspower semiconductor(on-state loss)Switching loss7

Power electronicsystem:Electric isolation:optical, magneticControl circuit (in a broad sense)Control circuitPower ElectronicsConfiguration of systems using powerelectronic devicesdetectioncircuitdrivecircuitPower circuit(power stage,main circuit)Protection circuit is also very often used in power electronicsystem especially for the expensive power semiconductors.8

Power ElectronicsTerminals of a power electronic deviceA power electronicdevice usually hasa third terminal ——control terminalto control thestates of the device.CA power electronic devicemust have at least twoterminals to allow powercircuit current flow through.GDriveCircuitEControl signal from drive circuit must be connected between thecontrol terminal and a fixed power circuit terminal (thereforecalled common terminal ).9

Power ElectronicsA classification of power electronic devicesUncontrolled device: diode(Uncontrollable device)has only two terminals and can not be controlled by control signal.The on and off states of the device are determined by the powercircuit.Half-controlled device: thyristor(Half-controllable device)is turned-on by a control signal and turned-off by the power circuitFully-controlled device: Power MOSFET, IGBT,GTO, IGCT(Fully-controllable device)The on and off states of the device are controlled by control signals.10

Power ElectronicsOther classificationsCurrent-driven (current-controlled) devicespower electronic devicesVoltage-driven (voltage-controlled) devices(Field-controlled devices)Pulse-triggered devicespower electronic devicesLevel-sensitive (level-triggered) devicesUnipolar devices (Majority carrier devices)power electronic devicesBipolar devices (Minority carrier devices)Composite devices11

Power ElectronicsMajor topics for each deviceAppearance, structure, and symbolPhysics of operationStatic characteristicsCharacteristicsSwitching characteristicsSpecificationSpecial issuesDevices of the same family12

Power ElectronicsPassive components in power electroniccircuitTransformer, inductor, capacitor and resistor:these are passive components in a power electroniccircuit since they can not be controlled by control signal andtheir characteristics are usually constant and linear.The requirements for these passive components by powerelectronic circuits could be very different from those byordinary circuits.13

Power Electronics1.2 Uncontrolled device Power athode14

Power ElectronicsPN junctionDirection ofinner electric field- 。- 。。- · · · - 。- 。。- - 。- 。。- · · · · · · - 。- 。。- - 。- 。。- p regionSpace chargeregion(depletion region,potential barrierregion) · · ·· · · n regionSemiconductor (Column IV element, Si)Electrons and holes.Pure semiconductor (intrinsic semiconductor)Doping, p-type semiconductor. N-type semiconductorPN junctionEquilibrium of diffusion and drift15

V- Power ElectronicsPN junction with voltage applied in theforward direction- - p-n - WWo16

Power ElectronicsPN junction with voltage applied in the reversedirectionEffective directionof electronic field- - -p V - n -- WoW17

Power ElectronicsConstruction of a practical power diodeAnodei p V-19Na 10 cm10 μm-3n - epiNd 10 cmn substrateNd 10 cm14-3Breakdownvoltage dependent19-3250μmCathodeFeatures different from low-power (information electronic) diodes– Larger size– Vertically oriented structure– n- drift region (p-i-n diode)– Conductivity modulation18

Power ElectronicsForward-biased power diode19

Power ElectronicsReverse-biased power diodeBreakdown– Avalanche breakdown– Thermal breakdown20

Power ElectronicsJunction capacitorThe positive and negative charge in the depletion region isvariable with the changing of external voltage.—–Junction capacitor CJ .Potential barrier capacitor CBJunction capacitor CJDiffusion capacitor CDJunction capacitor influences the switching characteristics ofpower diode.21

Power ElectronicsStatic characteristics of power diodeIIFO UTOUFUThe I-V characteristic of power diode22

Power ElectronicsSwitching (dynamic) characteristics of powerdiodeTurn-off transientIFdiFdttrrtdUFt F t0tft1t2URtdiRdtIRPURPReverse-recovery process:Reverse-recovery time, reverse-recovery charge,reverse-recovery peak current.23

Power ElectronicsSwitching (dynamic) characteristics of powerdiodeTurn-on transientuiUFP2V0iFuFtfrtForward recovery process:forward-recovery time24

Power ElectronicsSpecifications of power diodeAverage rectified forward current IF(AV)Forward voltage UFPeak repetitive reverse voltage URRMMaximum junction temperature TJMReverse-recovery time trr25

Power ElectronicsTypes of power diodesGeneral purpose diode (rectifier diode):standard recoveryFast recovery diodeReverse recovery time and charge specified. trr is usuallyless than 1μs, for many less than 100 ns —— ultra-fastrecovery diode.Schottky diode (Schottky barrier diode-SBD)– A majority carrier device– Essentially no recovered charge, and lower forward voltage.– Restricted to low voltage (less than 200V)26

Power ElectronicsExamples of commercial power diodes27

Power ElectronicsHistory and applications of power diodeApplied in industries starting 1950sStill in-use today. Usually working with controlleddevices as necessary componentsIn many circumstances fast recovery diodes orschottky diodes have to be used instead of generalpurpose diodes.28

Power Electronics1.3 Half-controlled device—ThyristorHistoryAnother name: SCR—silicon controlled rectifierThyristor Opened the power electronics era––––1956, invention, Bell Laboratories1957, development of the 1st product, GE1958, 1st commercialized product, GEThyristor replaced vacuum devices in almost every powerprocessing area.Still in use in high power situation. Thyristor till has thehighest power-handling capability.29

Power ElectronicsAppearance and symbol of thyristorAppearanceSymbolCathodeKGateAnodeGA30

Power ElectronicsStructure and equivalent circuit of thyristor Structure Equivalent circuit31

Power ElectronicsPhysics of thyristor operationEquivalent circuit: A pnptransistor and an npn transistorinterconnected togetherPositive feedbackTriggerCan not be turned off by controlsignalHalf-controllable32

Power ElectronicsQuantitative description of thyristor operationIc1 α1 IA ICBO1（1-1）Ic2 α2 IK ICBO2（1-2）IK IA IG（1-3）IA Ic1 Ic2（1-4）α2IG ICBO1 ICBO2IA 1 (α1 α2 )（1-5）When IG 0, α1 α2 is small.When IG 0, α1 α2 will approach 1, IA will be very large.33

Power ElectronicsOther methods to trigger thyristor onHigh voltage across anode and cathode—avalanche breakdownHigh rising rate of anode voltagte — du/dt too highHigh junction temperatureLight activation34

Power ElectronicsStatic characteristics of thyristorIAforwardconductingincreasing IGIU RSM U RRMreverseblockingavalanchebreakdownI G2IG 0I G1HOforwardblockingU DRMU boU DSMU AkBlocking when reversebiased, no matter if thereis gate current appliedConducting only whenforward biased and thereis triggering currentapplied to the gateOnce triggered on, will belatched on conductingeven when the gatecurrent is no longerappliedTurning off: decreasingcurrent to be near zerowith the effect of externalpower circuitGate I-V characteristics35

Power ElectronicsSwitching characteristics of thyristoriA100%90%10%0 tduAKTurn-on transient–––trDelay time tdRise time trTurn-on time tgttTurn-off transientIRMtOtrr– Reverse recoverytime trr– Forward recoverytime tgr– Turn-off time tqURRM tgr36

Power ElectronicsSpecifications of thyristorPeak repetitive forward blocking voltage UDRMPeak repetitive reverse blocking voltage URRMPeak on-state voltage UTMAverage on-state current IT(AV)Holding current IHLatching up current ILPeak forward surge current ITSMdu/dtdi/dt37

Power ElectronicsThe family of thyristorsFast switching thyristor—FSTTriode AC switch—TRIAC(Bi-directional triode thyristor)IIG 0T1OGUT2Reverse-conducting thyristor—RCTKLight-triggered (activited) thyristor—LTTAKGGGAKA38

Power Electronics1.4 Typical fully-controlled devices1.4.1 Gate-turn-off thyristor —GTO1.4.2 Giant transistor —GTR1.4.3 Power metal-oxide-semiconductor field effecttransistor — Power MOSFET1.4.4 Insulated-gate bipolar transistor —IGBTFeatures– IC fabrication technology, fully-controllable, high frequencyApplications– Begin to be used in large amount in 1980s– GTR is obsolete and GTO is also seldom used today.– IGBT and power MOSFET are the two major powersemiconductor devices nowadays.39

Power Electronics1.4.1 Gate-turn-off Kb)Major difference from conventional thyristor:The gate and cathode structures are highly interdigitated, withvarious types of geometric forms being used to layout thegates and cathodes.40

Power ElectronicsPhysics of GTO operationThe basic operation of GTO is thesame as that of the conventionalthyristor.AIAPNPV1G IGSEGIc2Ic1NPNRV2IKKEAThe principal differences lie in themodifications in the structure toachieve gate turn-off capability.– Large α2– α1 α2 is just a little larger thanthe critical value 1.– Short distance from gate tocathode makes it possible todrive current out of gate.41

Power ElectronicsCharacteristics of GTOStatic characteristic– Identical to conventional thyristor in the forward direction– Rather low reverse breakdown voltage (20-30V)Switching 4ttt5t6t42

Power ElectronicsSpecifications of GTOMost GTO specifications have the same meaningsas those of conventional thyristor.Specifications different from thyristor’s––––Maximum controllable anode current IATOCurrent turn-off gain βoffTurn-on time tonTurn-off time toff43

Power Electronics1.4.2 Giant Transistor—GTRGTR is actually the bipolar junction transistor that can handlehigh voltage and large current.So GTR is also called power BJT, or just BJT.Basic structureSymbolcbe44

Power ElectronicsStructures of GTR different from itsinformation-processing counterpartMultiple-emitter structureDarlington configuration45