Application and Characteristics of High Voltage IGBT Modules
M.Hierholzer, eupec GmbH & Co KG, Warstein, Germany
A.Porst, Th.Laska, H.Brunner, Siemens AG, München, Germany
New IGBT modules with blocking voltage of 3300V and current capability up to 1200A became
available recently. To keep the typical IGBT advantages like low forward losses, snubberless
operation and short circuit capability, an optimized high voltage cell design has to be realized.
This design reduces the forward losses (VCEsat) to values comparable to 1600V devices. The
short circuit capability is achieved by reducing the short circuit current (ISC) by about 50%
compared to 1200V/1600V IGBT´s.
On the other hand, the new high voltage IGBT shows a different input characteristic due to
changed input and reverse transfer capacitance. This has to be taken into account when
designing a gate driver. With a RC gate drive dI/dt and dV/dt can be adjusted independent
from each other in a way that switching losses are minimized without leaving the IGBT´s and
Diode´s save operation area.
which is twice the value for 1600V devices. To
get the same short circuit power dissipation for
both devices, the current limited by the 3.3kV
IGBT has to be reduced. This is realized by an
optimized high voltage cell design which
reduces the short circuit current ISC to approx.
5 times of rated current.
Short Circuit Ruggedness
The short circuit capability of IGBTs is one of
the most important features of these devices.
During a short circuit, the current through the
device is limited to a value of 8-10 times
higher than the rated current of the IGBT. The
power dissipation in the device during a short
circuit is enormous compared to normal
operation. A current of approx. 12kA and a
voltage of 2kV make 24MW losses !!
Reduction of short-circuit current (ISC) is
necessary to reduce the power dissipation for
high voltage devices. For 3300V IGBTs the
typical DC link voltage is about 1500V-2000V,
section
determined by
Dynamic Transfer Characteristic
The IGBT cell design has considerable
influence to the input- and reverse-transfer
capacitance, and therefore important effect on
the dynamic transfer characteristic of the
device.
condition
influenced by
influence at
1
VGE < VGEth
Ciss = const.
CGE
tdon
2
VGEth < VGE < VGEM
Ciss= const.
CGE
dIC / dt
3
VGE = VGEM
VGE = const.
CGC
dUCE/dt
4
VGE > VGEM
Ciss = const.
CGE // CGC
dVCEsat / dt
Tab.1 IGBT Turn-On Sections
This means that the turn-on behaviour of
3.3kV IGBTs is very different from
1200V/1600V devices under the same drive
conditions.
capacitance CGEI determines this phase. While
IC and VCE show no change, there is only an
influence on the turn-on delay time tdon in
section 1.
When the threshold voltage is reached
(beginning of section 2), the IGBT is able to
take over current. IC rises with an dIC/dt which
depends on the change of gate-emitter voltage
(transfer characteristic) and the transconductance gfs of the device:
IGBT Turn-On Behaviour
The IGBT turn-on process can be divided into
four sections in time like seen in table 1 and
fig.1. Section 1 is determined by a gateemitter voltage smaller than the threshold
voltage of the IGBT. The time constant of gate
resistor RG and the internal gate emitter
dIC/dt = gfs(IC) * dVGE/dt
1
The dVGE/dt itself is determined by the gate
resistor and the gate-emitter capacitance. (CGC
which is in parallel to CGEI can be neglected for
high VCE).
Section 3 begins with reaching the maximum
collector-current ICmax (IRM of the FWD + load
current IL). The diode turns-off by taking over
blocking voltage (VR) and the IGBT voltage
210
180
VGE
180
160
IC
150
140
120
120
100
90
80
60
60
40
VCE
30
20
0
section:
1
2
Fig.3: IGBT Turn-On waveforms
0
3
4
VCE begins to fall. With falling VCE, the voltagedependent miller-capacitance CGC increases by a
factor 100 approx.. The whole gate current is used
to discharge the increasing miller-capacitance while
the gate-emitter voltage remains at a constant value
(miller-plateau). Section 3 is influenced by the time
constant of the gate resistor and the millercapacitance.
This time constant is responsible for the dVCE/dt of
the device and has large influence at the IGBT´s
turn-on losses.
145
-dI/dt=10kA/µs !
180
116
Eon: 2mJ/div
87
120
58
IC: 600A/div
29
VCE: 500V/div
t: 2µs/div
0
0
dIC/dt and dVCE/dt Control
Driving an IGBT with an increased millercapacitance
and
a
reduced
gate-emitter
capacitance, using a standard „R“-gate driver, leads
to increased dI/dt and reduced dV/dt. The increased
dI/dt causes high stress during reverse recovery of
the FWD (free wheeling diode) and possibly high
negative dI/dt due to diode recovery. This leads to
overvoltage caused by stray-inductance in the
power circuit (fig.2a). The low dV/dt generates high
switching losses. The conflict is to adjust dIC/dt and
dVCE/dt independent from each other because only
the value of RG can be changed.
A certain value of RG is recommanded to adjust the
dIC/dt to stay within the safe operating area of the
FWD (fig.2b).
60
Fig.2a: FZ1200R33KF1
High dI/dt due to Low Gate Resistor (10kA/µs)
300
147,5
250
118
Eon: 2mJ/div
88,5
IC: 600A/div
200
150
59
VCE: 500V/div
29,5
t: 2µs/div
0
100
50
0
Fig.2b: FZ1200R33KF1
dI/dt Control (5kA/µs) by RG result in low dV/dt
2
150
On the other side, this value leads to very low
dVCE/dt and therefore increases the turn-on losses to
unacceptable values (fig.2b).The solution is an
„RC“-gate drive where an additional capacitor CGE is
connected between the IGBT´s gate and (auxillary)
emitter. This capacitor has influence in section 2
where the gate emitter voltage increases and the
dIC/dt is generated.
In section 3, where the dVCE/dt takes place, this
additional capacitor has no influence because there
is no change in dVGE/dt. The gate resistor is now
adjusted in a way that the dV/dt at the FWD does
not exceed critical values but turn-on losses are
reduced due to high values of dVCE/dt. With this
calculated RG, the external CGE is adjusted to set the
dIC/dt.
Fig.3a,b, c show the result of the „RC“-gate drive.
The dIC/dt of all measurements is set to 5kA/µs
approx.. The dVCE/dt is increased from fig.3a to
fig.3c using different RC combinations.
120
192
IC: 400A/div
144
90
100
60
VCE: 500V/div
t: 2µs/div
0
The turn-on losses can be reduced by more than
50% using this drive concept.
IGBT Drive Conditions
High voltage IGBTs and Diodes show a limitation in
turn-off speed. The IGBT is limited in its maximum
dVCE/dt at turn-off, while the FWD has a limitation in
dIF/dt.
The IGBT´s gate drive conditions can be adjusted
for both limits. The FWD turn-off is controlled by the
IGBT turn-on drive conditions. The turn-off drive
conditions make sure, that the IGBT operates in ist
SOA. For independent control of turn-on dV/dt, dI/dt
and turn-off dV/dt, three passive components are
necessary. Fig.4 shows a standard +15V/-15V gate
driver where the IGBT/FWD slopes are adjusted via
a turn-on gate resistor Ron (dVon/dt), a turn-off gate
resistor Roff (dVoff/dt) and a gate-emitter capacitor
CGE(dIon/dt).
96
VCE: 500V/div
48
t: 2µs/div
0
0
Fig.3c: dV/dt control due to RC-Driver
(RG:1.0Ω, CGE:330nF, dIC/dt:5kA/µs, Eon:2.8J)
90
30
50
30
120
60
150
IC: 400A/div
150
FZ1200R33KF1
200
FZ1200R33KF1
0
Fig.3a: dV/dt control due to standard R-Driver
(RG:8.2Ω, CGE:0, dIC/dt:5kA/µs, Eon:6.4J)
+15V
150
IGBT
200
Gatedriver
FZ1200R33KF1
Ron
120
IC: 400A/div
150
90
CGE
Roff
100
60
GND
VCE: 500V/div
30
-15V
50
t: 2µs/div
0
0
Fig.4 RC-Driver: Ron, Roff and CGE adjust dV/dt,
dI/dt
Fig.3b: dV/dt control due to RC-Driver
(RG:3.3Ω, CGE:100nF, dIC/dt:5kA/µs, Eon:4.1J)
3
This capacitor has only neglectible influence to the
IGBT turn-off dI/dt like seen in fig.5.
Conclusions
With respect to the save operation area of high
voltage IGBT´s and high voltage FWD´s an RC-gate
drive with three passive components (Ron, Roff,
CGE) can be adjusted to control the voltage and
current slopes for turn-off.
The different input- and transfer-characteristic as a
result of the ratio between gate-emitter and gatecollector capacitance can be compensated using
this drive concept.
10
9
IGBT Turn-Off
8
7
dIC/dt:
(kA/µs)
6
5
IGBT Turn-On
4
3
0
100
200
300
400
CGE (nF)
Fig.5 Influence of CGE on dIC/dt for FZ1200R33KF1
Acknowledgments
The authors gratefully acknowledge R.Zoulek for his
support during his diploma, M.Bruckmann for the
technical
discussions,
measurements
and
suggestions and Prof.Dr.E.Wolfgang.
4