《电力电子技术》课程教学课件（PPT讲稿）Topic 07 Snubber Circuits Overview • Diodes/SCR/MOSFET/IGBT Snubber • Turn-on and turn-off snubber • Driver Circuits for Power Switches

Topic 7Main contentsSnubber Circuits OverviewDiodes/SCR/MOSFET/IGBT SnubberTurn-on and turn-off snubberDriver Circuits for Power Switches

Main contents • Snubber Circuits Overview • Diodes/SCR/MOSFET/IGBT Snubber • Turn-on and turn-off snubber • Driver Circuits for Power Switches Topic 7

27-1Induction1 The issues which the switch faced in applications（电力电子器件应用时面临的问题）(1) switching lossVaIf, (te(on) + te(off))2→Switchingloss oc fs,wewant f↑ So L, C sizel, butVdetlosses limit us.fe)Figure 2-6 Ceneric-switch switching characteristics (linearized): (a) simplified clampedinductive-switching circuit, (b) switch waveforms, (c) instantaneous switch power loss

3 27-1 Induction 2 s Vd Io fs (tc(on) + tc(off ) ) P = ⑴ switching loss →Switching loss  fs , we want fs↑ So L, C size↓, but losses limit us. 1 The issues which the switch faced in applications (电力电子器件应用时面临的问题)

(2)Overshoots（电压过冲）odi.+dtVdLVswoVsWL1，L2，L3=strayinductance（杂散电感L。=L1+L2+L3

⑵ Overshoots (电压过冲) Io Vd L1 L2 L3 Sw vsw + - i c Vd L dic dt  vSW L1 , L2 , L3= stray inductance (杂散电感) Lσ=L1+L2+L3

(3) Safe operating area (SOA)Some devices have limitations on simultaneous voltage+ current applied instantaneously (IGBT, MOSET, etc.)SWTurn-offilocusDevice can operate at Iand can operate at Vin:SOAbut not at same timeswVinVswsw5

5 ⑶ Safe operating area (SOA) Some devices have limitations on simultaneous voltage + current applied instantaneously (IGBT, MOSET, etc.) Device can operate at IL and can operate at Vin, but not at same time isw iL SOA Turn-off locus vsw Vin vsw isw

(4) di/dt or dv/dt limitsAlso, some devices have di/dt or dvldt limits (espthyristortype devices).(5) EMIHigh di/dt, dvldt lead to EMl, affects control circuits.(dvldt→ capacitive coupling, di/dt→ inductivecoupling)

⑷ di/dt or dv/dt limits Also, some devices have di/dt or dv/dt limits (esp. thyristor type devices). ⑸ EMI High di/dt, dv/dt lead to EMI, affects control circuits. (dv/dt→ capacitive coupling, di/dt→ inductive coupling)

2 The ways which the switchbeing overstressed inapplications（电力电子器件承受的过度冲击的方式/类型）Five possibilities foroverstresses:Overvoltage and high dvldt at turn-off.Overcurrent and high di/dt at turn-on,Excessivepowerdissipation

2 The ways which the switch being overstressed in applications (电力电子器件承受的过度冲击的方式/类型) Five possibilities for overstresses： Overvoltage and high dv/dt at turn-off, Overcurrent and high di/dt at turn-on, Excessive power dissipation

>Snubber circuit can be added to the basic converterto reduce the stresses to safe levelsixThe di/dt is limited by adding a series inductor LsCThe dvldt is limited bsyconnecting a capacitor C

➢Snubber circuit can be added to the basic converter to reduce the stresses to safe levels. i Ls The di/dt is limited by adding a series inductor Ls C The dv/dt is limited bsy connecting a capacitor Cs

3 Snubber'sFunction☆:Protectsemiconductordevices by:>Shaping the switching trajectory of the device as itturns on/off and lows the device dissipation（改变器件开通/关断轨迹来降低器件的开关损耗）>Limiting device yoltaaes during turn-off transients>Limiting the rate-of-rise (dvldt) of voltages across thesemiconductor device at device turn-off(限制器件关断期间承受的电压和承受的dvldt)

3 Snubber’s Function ☆ : Protect semiconductor devices by: ➢Shaping the switching trajectory of the device as it turns on/off and lows the device dissipation. (改变器件开通/关断轨迹来降低器件的开关损耗) ➢Limiting device voltages during turn-off transients ➢Limiting the rate-of-rise (dv/dt) of voltages across the semiconductor device at device turn-off. (限制器件关断期间承受的电压和承受的dv/dt)

3 Snubber'sFunction☆:Protectsemiconductordevices by:>Limiting device currents during turn-on transients>Limiting the rate-of-rise (di/dt) of currents through thesemiconductordevice atdeviceturn-on（限制器件开通期间承受的电流和承受的di/dt）

3 Snubber’s Function ☆ : Protect semiconductor devices by: ➢Limiting device currents during turn-on transients ➢Limiting the rate-of-rise (di/dt) of currents through the semiconductor device at device turn-on (限制器件开通期间承受的电流和承受的di/dt)

4TypesofSnubber Circuits☆(1)Unpolarized R-C snubbers(无极性RC缓冲电路Used to protect diodes and thyristors by limiting themaximum voltage and dvldt at reverse recoveryOT11本+RSA6Dr4CsBCSwsnubberO1A

11 4 Types of Snubber Circuits ☆ (1) Unpolarized R-C snubbers (无极性RC缓冲电路) Used to protect diodes and thyristors by limiting the maximum voltage and dv/dt at reverse recovery - + Df Rs Cs L Vd Io Sw snubber 1 3 5 4 6 2 - + - - Rs A B id C P vcn + van vbn + L L L Cs