电力电子技术英文版 Chapter09

Chapter 9

Practical Application Issues

of Power Semiconductor Devices

Measures to protect power semiconductor devices from overvoltage
Power Electronics
T S U C F D RC1 RC2 RV RC3
SDC
LB M
RC4
RCD
Lightening arrestor RC or RCD snubbers (will be discussed later) Zener diode, Metal Oxide Varistor (MOV), Break Over Diode (BOD)
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Measures to protect power semiconductor devices from overcurrent
Power Electronics
Fuse Circuit breaker Protection with current feedback control in the control circuit Protection with overcurrent detection in the gate drive circuit—the fastest measure
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Functions and classifications of snubbers
Power Electronics
Functions
Limiting voltages applied to devices during turn-off transients Limiting device currents during turn-on transients Limiting device current rising rate (di/dt) at device turn-on Limiting the rate of rise (du/dt) of voltages across devices during device turn-off Shaping the switching trajectory of the device
Classifications
According to different switching transients
– – Turn-off snubber (sometimes just called snubber) Turn-on snubber
According to the treatment of energy
– Power dissipating snubber – Lossless snubber 13

Operation principle of typical snubbers
Power Electronics
Circuit configuration
uCE iC
without turn-off snubber without turn-on snubber iC uCE
Ri VDi Li
Turn-on snubber
O
with turn-off snubber
t
with turn-on snubber
Turn-off snubber
iC
V
VDs
Rs
A
B without turn-off snubber
Cs
L VD
O
D
with turn-off snubber C uCE
Switching trajectory
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Other turn-off snubbers
Power Electronics
L
Rs
L Turn-off snubber Ed Cs VDs Rs Load Turn-off snubber
Ed
Cs Load
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Power Electronics
9.3 Series and parallel connections of power semiconductor devices
Object To increase the capability to deal with voltage or current Issues and solutions Series connection
– Issue: even voltage sharing – Solutions:
• Selection of devices that are closer to each other in the characteristics characteristics • Voltage sharing circuit
Parallel connection
– Issue: even current sharing – Solutions:
• Selection of devices that are closer to each other in the characteristics characteristics • Current sharing circuit and symmetrical circuit layout
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Series Connection of thyristors
Power Electronics
I
VT1 VT2 VT1 RP R C R C
IR O UT1 UT2 U VT2 RP
a)
b)
Voltage sharing circuit
– Steady-state voltage sharing circuit – Dynamic voltage sharing circuit
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