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1、Chapter 1 Power Devices,a power device a switch Switching States:*on state(static)Von-state=0 ideally Current ratings continuous,average,RMS,peak*off state(static)Ileakage=0 ideally off-state voltage ratings-forward and reverse*commutation state(dynamic)dv/dt,di/dt=ideally dv/dt rating(an equivalent
2、 capacitor in off-state,a displacement current i=C dv/dt)di/dt rating(a hot point in the region where the first conduction occurs),pswitch,Switch Energy Losses:Wstatic=Won+Woff=on-time ion(t)von-state(t)dt+off-time ileakage(t)voff(t)dt,Won-major loss at lower-frequency operation Wswitch-significant
3、at high-frequency operation,Wswitch=turn-on i(t)v(t)dt+turn-off i(t)v(t)dt Paverage=(Wstatic+Wswitch)/T,Power Devices,A POWER SWITCHING DEVICE*permits current flow in one direction only*can withstand a forward voltage(except diodes)*can be turned on or off by a relatively small controlling current o
4、r voltage Study focuses:(Diode,SCR,GTO,BJT,MOSFET,IGBT,IPM)characteristics,rather than the physics firing requirements ratingscomparisons of the devices,Power Devices,Power Devices,Structure and symbol,Characteristics,1-1.Diode,Power Devices,reverse recovery time trr,Typical turn-off condition of a
5、diode.,Fast Recovery Diode trr,1-2.Thyristor(SCR),Power Devices,Structure and symbol,Characteristics with no gate current,Characteristics with gate current,Firing requirements a.Gate-cathode poor P-N junction within a given production batchIgmin Ig Igmax Vgmin Vg Vgmax IgVg Pgmax b.pulse firing curr
6、ent with a fast rise and a sufficient length,Power Devices,1-3.GTO(Gate Turn-off Thyristor),(a)Conventional thyristor symbol.(b)Conventional thyristor P-N-P-N structure.(c)Gate turn-off thyristor symbol.(d)Gate turn-off thyristor structure.,Power Devices,A reverse voltage with the cathode positive w
7、ill break down the anode junction at a low level.,Turn-on conditions:similar to the thyristor but the latching current higher&the gate current continuous a.turn-on high level gate current for a longer time b.after turn-on a low level of gate current to minimize the anode-cathode voltageTurn-off cond
8、itions:by applying a negative voltage across the gate-cathode a.turn-off voltage high enough but less than the breakdown b.a reverse gate current with a peak value of 1/51/3 of the anode current established in less than 1s,Power Devices,1-4.Power Transistor(GTR/BJT),Power Devices,N-P-N transistor.(a
9、)Structure.(b)Symbol.,P-N-P transistor.(a)Structure.(b)Symbol.,Power Devices,Common emitter characteristic for N-P-N transistor.,Profile of the base to the collector current base current just sufficient to maintain saturation a.at turn-on,the base current high enough to give a fast turn-on b.any cha
10、nge in the collector current matched by a change in the base current c.at turn-off,the base current reduced at a rate the collector current can follow,Power Devices,*Secondary breakdown*High switching loss,2-5.Power MOSFET,Power Devices,(a)Symbol.(b)Simplified cross-sectional structure.,Power Device
11、s,Electrical circuit.(b)Output characteristic.Power MOSFET,Power MOSFET*Very fast switchingvoltage controlled without any stored charge*Low power rating narrow induced conducting channel*High conduction losshigh constant resistance*Positive temperature coefficient for resistance simple paralleling o
12、f devices,Power Devices,1-6.IGBT(Insulated Gate Bipolar Transistor),Power Devices,(a)Simplified cross-section.(b)Equivalent electric circuit.(c)Symbol.,The collector-emitter characteristics are similar to those of the power transistor but the control features are those of the MOSFET.,Current tailing
13、,Ideally as a controlled switch the device would have:1.Controlled turn-on and off MOSFET、IGBT、BJT、GTO、SCR2.Unlimited voltage and current ratingsSCR、GTO、IGBT、BJT、MOSFET3.Instant turn-on and off times MOSFET、IGBT、BJT、GTO、SCR4.Zero conduction loss SCR、GTO、BJT、IGBT、MOSFET5.Zero gate firing power requir
14、ement MOSFET、IGBT、BJT、SCR、GTO6.Low cost SCR、GTO、BJT、IGBT、MOSFET,Power Devices,2-7.Device Comparisons,Power Devices,Research and development work is constantly being undertaken to improve the present devices and to develop new devices closer to the ideal electronic switches.MCT(MOS-controlled thyrist
15、or)is one of the new devices under development which has the anode-cathode characteristics similar to those of thyristors but the control features similar to those of the MOSFET.IPM(Intelligent Power Module)is another kind of new devices which is currently commercially available.It usually integrate
16、s a power device,say,an IGBT,plus its gate driving circuit and some protection logics such as short circuit,over current,over temperature and under voltage.,Real Loads and Sources Appendix 1-1,LOADSnot a simple resistance with few exceptions;with wires having inductance and capacitance;often contain
17、ing electrical sources,interface filters,etc.;many non-linear.,Two broad categories:quasi-steady loads&transient loads,A common feature:series inductanceexhibiting current source behavior on short time scale,Critical inductance the lowest value of load inductance for which iload0 at all times.,Appen
18、dix 1-1,Special types of wires to reduce internal self-inductance.,Appendix 1-1,Circuit model for a battery on charge.,Induction motor circuit model.,SORCES An ideal voltage source provides a defined v(t)value at any current.It displays zero impedance to current flow.An ideal current source maintain
19、s a defined i(t)value at any voltage.It displays infinite impedance to external voltage.,Ideal and real voltage sources compared,Appendix 1-1,Series inductance of a real voltage source exhibits current source behavior on short time scale.,DC source interfaces(Lext or Cext for enhancing current or vo
20、ltage behavior),Appendix 1-1,Cext,AC source interfaces series or parallel LC pair for enhancing current or voltage behavior(Lext/Cext)sLs,(L/C)sLs,Appendix 1-1,Inductors,Capacitors and Resistors Appendix 1-2,Study on your own with reference to Chapter 11 and 12 of the textbook,“Elements of Power Electronics”by Philip T.Krein.Submit a paper to me in two weeks describing your understanding.You will get a bonus up to 5 points.,
