Power Electroni cs Chapter 1 Power Electronic Devices (Part I) Power E l e ct r o n i cs 2 Outline 1.1 An introductory overview of power electronic devices 1.2 Uncontrolled device — power diode 1.3 Half-controlled device — thyristor 1.4 Typical fully-controlled devices 1.5 Other new power electronic devices 1.6 Drive circuit for power electronic devices 1.7 Protection of power electronic devices 1.8 Series and parallel connections of power electronic devices Power E l e ct r o n i cs 3 1.1 An introductory overview of power electronic devices The concept and features Configuration of systems using power electronic devices Classifications Major topics Power E l e ct r o n i cs 4 The concept of power electronic devices Power electronic devices: In broad sense Very often: Major material used in power semiconductor devices —— Silicon are the electronic devices that can be directly used in the power processing circuits to convert or control electric power. power electronic devices Vacuum devices: Mercury arc rectifier thyratron, etc. . seldom in use today Semiconductor devices: major power electronic devices Power electronic devices = Power semiconductor devices Power E l e ct r o n i cs 5 Features of power electronic devices The electronic power that power electronic device deals with is usually much larger than that the information electronic device does. Usually working in switching states to reduce power losses p=vi=0 On-state Voltage across the device is 0 v=0 p=vi=0Off-state Current through the device is 0 i=0 Power E l e ct r o n i cs 6 Features of power electronic devices Need to be controlled by information electronic circuits. Very often, drive circuits are necessary to interface between information circuits and power circuits. Dissipated power loss usually larger than information electronic devices — special packaging and heat sink are necessary. Power E l e ct r o n i cs 7 Power losses on power semiconductor devices O n-state (conduction state turning- off Off-state (blocking state) turning -on U U U W J Q = conduction loss + turn-off loss + off-state loss + turn-on loss Total power loss on power semiconductor (on-state loss) Switching loss Power E l e ct r o n i cs 8 Configuration of systems using power electronic devices Control circuit detection circuit drive circuit Power circuit (power stage, main circuit) Control circuit (in a broad sense) Electric isolation: optical, magnetic Power electronic system: Protection circuit is also very often used in power electronic system especially for the expensive power semiconductors. Power E l e ct r o n i cs 9 Terminals of a power electronic device $ & ( A power electronic device must have at least two terminals to allow power circuit current flow through. A power electronic device usually has a third terminal —— control terminal to control the states of the device. Control signal from drive circuit must be connected between the ` control terminal and a fixed power circuit terminal (therefore called common terminal ). Drive Circuit Power E l e ct r o n i cs 10 A classification of power electronic devices Uncontrolled device: diode (Uncontrollable device) Fully-controlled device: Power MOSFET, IGBT,GTO, IGCT (Fully-controllable device) Half-controlled device: thyristor (Half-controllable 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 power circuit. is turned-on by a control signal and turned-off by the power circuit The on and off states of the device are controlled by control signals. Power E l e ct r o n i cs 11 Other classifications power electronic devices Pulse-triggered devices Level-sensitive (level-triggered) devices power electronic devices power electronic devices Current-driven (current-controlled) devices Voltage-driven (voltage-controlled) devices (Field-controlled devices) Unipolar devices (Majority carrier devices) Composite devices Bipolar devices (Minority carrier devices) Power E l e ct r o n i cs 12 Major topics for each device Appearance, structure, and symbol Physics of operation Characteristics Specification Special issues Devices of the same family Static characteristics Switching characteristics Power E l e ct r o n i cs 13 Passive components in power electronic circuit Transformer, inductor, capacitor and resistor: these are passive components in a power electronic circuit since they can not be controlled by control signal and their characteristics are usually constant and linear. The requirements for these passive components by power electronic circuits could be very different from those by ordinary circuits. Power E l e ct r o n i cs 14 1.2 Uncontrolled device Power diode Appearance Structure Symbol Cathode Cathode KA Anode Anode Power E l e ct r o n i cs 15 PN junction  b  b  b  b  b  b  b  b  b  b  b  b  b  b  b + · + · + · + · + · + · + · + · + · + · + · + · + · + · + · +  +  +  +  +  p region n region Direction of inner electric field Space charge region (depletion region, potential barrier region) Semiconductor (Column IV element, Si) Electrons and holes. Pure semiconductor (intrinsic semiconductor) Doping, p-type semiconductor. N-type semiconductor PN junction Equilibrium of diffusion and drift Power E l e ct r o n i cs 16 PN junction with voltage applied in the forward direction V      O Q Wo W  Power E l e ct r o n i cs 17 PN junction with voltage applied in the reverse direction  V         O Q Wo W Effective direction of electronic field Power E l e ct r o n i cs 18 Construction of a practical power diode Features different from low-power (information electronic) diodes – Larger size – Vertically oriented structure – n drift region (p-i-n diode) – Conductivity modulation 2500 m Breakdown voltage dependent 10 0 m p Nd =10 cm n substrate -319 Na =10 cm -319+ n epi Nd =10 cm -314 + - i Anode Cathode  V - Power E l e ct r o n i cs 19 Forward-biased power diode Power E l e ct r o n i cs 20 Reverse-biased power diode Breakdown – Avalanche breakdown – Thermal breakdown Power E l e ct r o n i cs 21 Junction capacitor The positive and negative charge in the depletion region is variable with the changing of external voltage. —–Junction capacitor CJ . Junction capacitor CJ Junction capacitor influences the switching characteristics of power diode. Diffusion capacitor CD Potential barrier capacitor CB Power E l e ct r o n i cs 22 Static characteristics of power diode I O I F U TO U F U The I-V characteristic of power diode Power E l e ct r o n i cs 23 Switching (dynamic) characteristics of power diode Turn-off transient I F U F t F t 0 t rr t d t f t 1 t 2 t U R U RP I RP di F dt di R dt Reverse-recovery process: Reverse-recovery time, reverse-recovery charge, reverse-recovery peak current. Power E l e ct r o n i cs 24 Switching (dynamic) characteristics of power diode Turn-on transient U FP u i i F u F t fr t0 2V Forward recovery process: forward-recovery time Power E l e ct r o n i cs 25 Specifications of power diode Average rectified forward current IT(AV) Forward voltage UF Peak repetitive reverse voltage URRM Maximum junction temperature TJM Reverse-recovery time trr Power E l e ct r o n i cs 26 General purpose diode (rectifier diode): Fast recovery diode Schottky diode (Schottky barrier diode-SBD) standard recovery Reverse recovery time and charge specified. trr is usually less than 10 s, for many less than 100 ns —— ultra-fast recovery diode. – A majority carrier device – Essentially no recovered charge, and lower forward voltage. – Restricted to low voltage (less than 200V) Types of power diodes Power E l e ct r o n i cs 27 Examples of commercial power diodes Power E l e ct r o n i cs 28 History and applications of power diode Applied in industries starting 1950s Still in-use today. Usually working with controlled devices as necessary components In many circumstances fast recovery diodes or schottky diodes have to be used instead of general purpose diodes. Power E l e ct r o n i cs 29 1.3 Half-controlled device—Thyristor History Another name: SCR—silicon controlled rectifier Thyristor Opened the power electronics era – 1956, invention, Bell Laboratories – 1957, development of the 1st product, GE – 1958, 1st commercialized product, GE – Thyristor replaced vacuum devices in almost every power processing area. Still in use in high power situation. Thyristor till has the highest power-handling capability. Power E l e ct r o n i cs 30 Appearance and symbol of thyristor Appearance Symbol Cathode Anode Gate K G A Power E l e ct r o n i cs 31 Structure and equivalent circuit of thyristor ? Structure ? Equivalent circuit Power E l e ct r o n i cs 32 Physics of thyristor operation Equivalent circuit: A pnp transistor and an npn transistor interconnected together Positive feedback Trigger Can not be turned off by control signal Half-controllable Power E l e ct r o n i cs 33 Quantitative description of thyristor operation I c1 =α 1 I A + I CBO1   1-1 I c2 =α 2 I K + I CBO2   1-2 I K =I A +I G   1-3 I A =I c 1 +I c 2   1-4 )(1 21 CBO2CBO1G2 A αα α +? ++ = III I   1-5 When I G =0, α 1 +α 2 is small. When I G >0, α 1 +α 2 will approach 1, I A will be very large. Power E l e ct r o n i cs 34 Other methods to trigger thyristor on High voltage across anode and cathode— avalanche breakdown High rising rate of anode voltagte — du/dt too high High junction temperature Light activation Power E l e ct r o n i cs 35 Static characteristics of thyristor Blocking when reverse biased, no matter if there is gate current applied Conducting only when forward biased and there is triggering current applied to the gate Once triggered on, will be latched on conducting even when the gate current is no longer applied Turning off: decreasing current to be near zero with the effect of external power circuit Gate I-V characteristics O U Ak I A I H I G2 I G1 I G  0 U bo U DSM U DRM U RRM U RSM forward conducting avalanche breakdown reverse blocking increasing I G forward blocking Power E l e ct r o n i cs 36 Switching characteristics of thyristor Turn-on transient – Delay time t d – Rise time t r – Turn-on time t gt Turn-off transient – Reverse recovery time t rr – Forward recovery time t gr – Turn-off time t q    u AK t t O 0 t d t r t rr t gr U RRM I RM i A Power E l e ct r o n i cs 37 Specifications of thyristor Peak repetitive forward blocking voltage U DRM Peak repetitive reverse blocking voltage U RRM Peak on-state voltage U TM Average on-state current I T(AV) Holding current I H Latching up current I L Peak forward surge current I TSM du/dt di/dt Power E l e ct r o n i cs 38 The family of thyristors Fast switching thyristor—FST Triode AC switch—TRIAC (Bi-directional triode thyristor) Reverse-conducting thyristor Light-triggered (activited) thyristor —RCT —LTT I O U I G 0 K G A A G K ( , " G T 1 T 2 Power E l e ct r o n i cs 39 1.4 Typical fully-controlled devices 1.4.1 Gate-turn-off thyristor —GTO 1.4.2 Giant transistor —GTR 1.4.3 Power metal-oxide-semiconductor field effect transistor — Power MOSFET 1.4.4 Insulated-gate bipolar transistor —IGBT Features – IC fabrication technology, fully-controllable, high frequency Applications – 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 power semiconductor devices nowadays. Power E l e ct r o n i cs 40 A G K GG K N 1 P 1 N 2 N 2 P 2 b)a) 1.4.1 Gate-turn-off thyristor—GTO Structure Symbol G K A Major difference from conventional thyristor: The gate and cathode structures are highly interdigitated, with various types of geometric forms being used to layout the gates and cathodes. Power E l e ct r o n i cs 41 Physics of GTO operation The basic operation of GTO is the same as that of the conventional thyristor. The principal differences lie in the modifications in the structure to achieve gate turn-off capability. – Large a 2 – a 1 +a 2 is just a little larger than the critical value 1. – Short distance from gate to cathode makes it possible to drive current out of gate. R NPN PNP A G S K E G I G E A I K I c2 I c1 I A V 1 V 2 Power E l e ct r o n i cs 42 Characteristics of GTO Static characteristic – Identical to conventional thyristor in the forward direction – Rather low breakdown voltage (20-30V) Switching characteristic O t 0 t i G i A I A 90%I A 10%I A t t t f t s t d t r t 0 t 1 t 2 t 3 t 4 t 5 t 6 Power E l e ct r o n i cs 43 Specifications of GTO Most GTO specifications have the same meanings as those of conventional thyristor. Specifications different from thyristor’s – Maximum controllable anode current I ATO – Current turn-off gain b off – Turn-on time t on – Turn-off time t off Power E l e ct r o n i cs 44 1.4.2 Giant Transistor—GTR GTR is actually the bipolar junction transistor that can handle high voltage and large current. So GTR is also called power BJT, or just BJT. Basic structure Symbol b e c Power E l e ct r o n i cs 45 Structures of GTR different from its information-processing counterpart Multiple-emitter structure Darlington configuration Power E l e ct r o n i cs 46 Physics of GTR operation Same as information BJT device holes electrons E b E c i b i c =βi b i e =(1+β )i b Power E l e ct r o n i cs 47 Static characteristics of GTR cut-off region Amplifying (active) region O I i b3 i b2 i b1 i b1 <i b2 <i b3 U ce S a t u r a t i o n r e g i o n Power E l e ct r o n i cs 48 Switching characteristics of GTR Turn-on transient – Turn-on delay time t d – Rise time t r – Turn-on time t on Turn-off transient – Storage time t s – Falling time t f – Turn-off time t off i b I b 1 I b 2 I cs i c 0 0 90%I b1 10%I b1 90%I cs 10%I cs t 0 t 1 t 2 t 3 t 4 t 5 t t t off t s t f t on t r t d Power E l e ct r o n i cs 49 Second breakdown of GTR Power E l e ct r o n i cs 50 Safe operating area (SOA) of GTR SOA O I c I cM P SB P cM U ce U ceM Power E l e ct r o n i cs 51 1.4.3 Power metal-oxide-semiconductor field ` effect transistor—Power MOSFET Basic structure Symbol G S D P channel A classification Field Effect Transistor (FET) Metal-onside-semiconductor FET (MOSFET) Power MOSFET Junction FET (JFET) Static induction transistor (SIT) n channel p channel G S D N channel Power E l e ct r o n i cs 52 Structures of power MOSFET Also vertical structure—VMOS – WMOS, VDMOS Multiple parallel cells – Polygon-shaped cells A structure of hexagon cells Power E l e ct r o n i cs 53 Physics of MOSFET operation Off-state p-n - junction is reverse-biased off-state voltage appears across n - region Power E l e ct r o n i cs 54 Physics of MOSFET operation p-n - junction is slightly reverse biased positive gate voltage induces conducting channel drain current flows through n - region and conducting channel on resistance = total resistances of n - region, conducting channel,source and drain contacts, etc. On-state Power E l e ct r o n i cs 55 Static characteristics of power MOSFET Power E l e ct r o n i cs 56 Switching characteristics of power MOSFET R s R G R F R L i D u GS u p i D +U E i D O O O u p t t t u GS u GSP u T t d(on) t r t d(off) t f Turn-on transient – Turn-on delay time t d(on) – Rise time t r Turn-off transient – Turn-off delay time t d(off) – Falling time t f Power E l e ct r o n i cs 57 Specifications of power MOSFET Drain-source breakdown voltage U DS Continuous drain current I D Peak pulsed drain current I DM On (On-state) resistance R DS(on) Inter-terminal capacitances – Short circuit input capacitance C iss = C GS + C GD – Reverse transfer capacitance C rss = C GD – Short circuit output capacitance C oss = C DS + C GD SOA of power MOSFET – No second breakdown Power E l e ct r o n i cs 58 Examples of commercial power MOSFET Power E l e ct r o n i cs 59 Features and applications of power MOSFET Voltage-driven device, simple drive circuit Majority-carrier device, fast switching speed, high operating frequency (could be hundreds of kHz) Majority-carrier device, better thermal stability On-resistance increases rapidly with rated blocking voltage – Usually used at voltages less than 500V and power less than 10kW – 1000V devices are available, but are useful only at low power levels(100W) Part number is selected on the basis of on- resistance rather than current rating Power E l e ct r o n i cs 60 The body diode of power MOSFET The body diode Equivalent circuit Power E l e ct r o n i cs 61 1.4.4 Insulated-gate bipolar transistor —IGBT Combination of MOSFET and GTR GTR: low conduction losses (especially at larger blocking voltages), longer switching times, current-driven MOSFET: faster switching speed, easy to drive (voltage-driven), larger conduction losses (especially for higher blocking voltages) IGBT Features ? On-state losses are much smaller than those of a power MOSFET, and are comparable with those of a GTR ? Easy to drive —similar to power MOSFET ? Faster than GTR, but slower than power MOSFET Application ? The device of choice in 500-1700V applications, at power levels of several kW to several MW Power E l e ct r o n i cs 62 Structure and operation principle of IGBT Basic structure Also multiple cell structure Basic structure similar to power MOSFET, except extra p region On-state: minority carriers are injected into drift region, leading to conductivity modulation compared with power MOSFET: slower switching times, lower on-resistance, useful at higher voltages (up to 1700V) E G C N + N  a) P N + N + P N + N + P + Emitter Gate Collector Injecting layer Buffer layer Drift region J 3 J 2 J 1 Power E l e ct r o n i cs 63 Equivalent circuit and circuit symbol of IGBT Equivalent circuit Circuit symbol G E C +  + +  I D R N I C V J1 I D R on Drift region resistance G C & Power E l e ct r o n i cs 64 Static characteristics of IGBT O Active region Cut-off (forward blocking) region Saturation region (On region) Reverse blocking region I C U RM U FM U CE U GE(th) U GE Power E l e ct r o n i cs 65 Switching characteristics of IGBT IGBT turn-on is similar to power MOSFET turn-on The major difference between IGBT turn-off and power MOSFET turn-off: – There is current tailing in the IGBT turn-off due to the stored charge in the drift region. t t t     U CE I C 0 O 0 U GE U GEM I CM U CEM t fv1 t fv2 t off t on t fi1 t fi2 t d(off) t f t d(on) t r U CE(on) U GEM U GEM I CM I CM current tail Power E l e ct r o n i cs 66 Parasitic thyristor and latch-up in IGBT Location of equivalent devices Complete IGBT equivalent circuit Main current path pnp transistor and the parasitic npn transistor compose a parasitic thyristor inside IGBT. High emitter current tends to latch the parasitic thyristor on. Modern IGBTs are essentially latch-up proof Power E l e ct r o n i cs 67 Specifications of IGBT Collector-emitter breakdown voltage U CES Continuous collector current I C Peak pulsed collector current I CM Maximum power dissipation P CM Other issues: SOA of IGBT – The IGBT has a rectangular SOA with similar shape to the power MOSFET. Usually fabricated with an anti-parallel fast diode Power E l e ct r o n i cs 68 Examples of commercial IGBT Power E l e ct r o n i cs 69 1.5 Other new power electronic devices Static induction transistor —SIT Static induction thyristor —SITH MOS controlled thyristor — MCT Integrated gate-commutated thyristor —IGCT Power integrated circuit and power module Power E l e ct r o n i cs 70 Static induction transistor—SIT Another name: power junction field effect transistor— power JFET Features – Major-carrier device – Fast switching, comparable to power MOSFET – Higher power-handling capability than power MOSFET – Higher conduction losses than power MOSFET – Normally-on device, not convenient (could be made normally-off, but with even higher on-state losses) Power E l e ct r o n i cs 71 Static induction thyristor—SITH other names – Field controlled thyristor—FCT – Field controlled diode Features – Minority-carrier device, a JFET structure with an additional injecting layer – Power-handling capability similar to GTO – Faster switching speeds than GTO – Normally-on device, not convenient (could be made normally-off, but with even higher on-state losses) Power E l e ct r o n i cs 72 MOS controlled thyristor—MCT Essentially a GTO with integrated MOS-driven gates controlling both turn-on and turn-off that potentially will significantly simply the design of circuits using GTO. The difficulty is how to design a MCT that can be turned on and turned off equally well. Once believed as the most promising device, but still not commercialized in a large scale. The future remains uncertain. Power E l e ct r o n i cs 73 Integrated gate-commutated thyristor — IGCT The newest member of the power semiconductor family, introduced in 1997 by ABB Actually the close integration of GTO and the gate drive circuit with multiple MOSFETs in parallel providing the gate currents Short name: GCT Conduction drop, gate driver loss, and switching speed are superior to GTO Competing with IGBT and other new devices to replace GTO Power E l e ct r o n i cs 74 Power integrated circuit and power module Two major challenges – Electrical isolation of high-voltage components from voltage components – Thermal management—power devices usually at higher temperatures than low-voltage devices Integration of power electrons devices Integrated power electronics Module(IPEM): power devices, drive circuit, protection circuit, control circuit High voltage integrated circuit (HVIC) Monolithic integration: power integrated circuit Smart power integrated circuit(Smart power IC, SPIC, Smart switch) Ordinary power module:just power devices packaged together Packaging integration: power module Intelligent power module (IPM): power devices, drive circuit, protection circuit Power E l e ct r o n i cs 75 Review of device classifications Current-driven (current-controlled) devices: thyristor, GTO, GTR power electronic devices Voltage-driven (voltage-controlled) devices (Field-controlled devices):power MOSFET, IGBT, SIT, SITH, MCT, IGCT Pulse-triggered devices: thyristor, GTO power electronic devices Level-sensitive (Level-triggered) devices: GTR,power MOSFET, IGBT, SIT, SITH, MCT, IGCT Uni-polar devices (Minority carrier devices): SBD, power MOSFET, SIT power electronic devices Composite devices: IGBT, SITH, MCT Bipolar devices (Majority carrier devices): ordinary power diode, thyristor, GTO, GTR, IGCT, IGBT, SITH, MCT Power E l e ct r o n i cs 76 Comparison of the major types of devices Power-handling capability Power E l e ct r o n i cs 77 Comparison of the major types of devices Maximum allowed current density as a function of the switching frequency