Comparison of Planar- and Trench-IGBT-Modules
for resonant applications
M. Helsper
F. W. Fuchs
M. Münzer
Christian-Albrechts-University of
Kiel
Faculty of Engineering
Power Electronics and Electrical
Drives
Kaiserstr. 2
24143 Kiel
Germany
Tel. +49 431 880 6105
Fax. +49 431 880 6103
mth@tf.uni-kiel.de
Christian-Albrechts-University of
Kiel
Faculty of Engineering
Power Electronics and Electrical
Drives
Kaiserstr. 2
24143 Kiel
Germany
Tel. +49 431 880 6100
Fax. +49 431 880 6103
fwf@tf.uni-kiel.de
EUPEC GmbH + Co. KG
Max Planck Str. 5
59581 Warstein
Germany
Tel. +49 2902 764 1195
Fax. +49 30 74
Mark.Muenzer@eupec.com
Abstract:
For the qualification in resonant converters in the Zero Voltage Mode at high frequencies a StandardIGBT-Module, a Fast-IGBT-Module, both with IGBT’s of the 2. generation with a planar gate
structure and a new Trench-Gate-IGBT-Module of the 3. generation are characterized and compared.
Investigations show that the Trench-IGBT-Module can be driven at high frequencies in a low loss
manner like the Fast-IGBT-Module which is optimized this mode. Indeed for the Trench-IGBT these
advantage exists at a mode at high voltages and relatively low switch off currents. At high switch off
currents and high frequencies the Fast-IGBT-module has the best performance. At lower and medium
frequencies the new Trench-IGBT works with the lowest losses.
In resonant applications like microwave, arc
welding or battery chargers IGBT-modules are
increasingly used according to their good static
and dynamic performance [1,2,]. The IGBTmodules work in these applications usually at
frequencies higher than 20 kHz. Maximum
frequencies between 100 kHz and 200 kHz are
possible [3] in soft switching topologies. In this
operation besides a good static ability especially
the switching behaviour of the IGBT-modules is
very important. To evaluate the properties of
IGBT-modules for soft switching applications the
datasheets give not enough information. Thus
numerous publications [4, 5, 6, 7] have dealt with
this topic.
This paper presents an investigation and
comparison of three IGBT-Modules from one
manufacturer in terms of their abilities for the
application in resonant inverters which work in
the Zero Voltage Mode at high frequencies.
Woff [mWs]
I. Introduction
15
10
standard
IGBT
Trench
IGBT
5
fast
IGBT
0
0
1
2
3
4
VCEsat [V]
Figure 1: Trade off between saturation voltage
VCEsat and switch-off losses Woff for the
investigated IGBTs at hard switching, cond.:
IC=75 A, VCC=600V, TJ=125°C
This is at first a planar Standard-IGBT-Module,
type BSM75GD120DN2, of the 2. generation,
optimized for hard switching applications with low
and medium switching frequencies. Second a
planar Fast-IGBT-Module of the 2. generation,
type FS75R12KS4, specialized for high
frequency applications is tested. Third a new
Trench-IGBT-Module of the 3. generation, type
FS75R12KE3, with a trench gate structure and a
field stop zone [8] is measured. This IGBT is first
of all provided for applications in hard switching
converters with lower and medium frequencies.
Figure 1 shows in which manner the necessary
trade off between saturation voltages and the
switching losses is realized for the modules at
hard switching. The general advantage of the
Trench-IGBT is clearly to be observed here. An
important question of this investigation is to find
out if the Trench-IGBT is well suited for ZVS
applications with high frequencies also without
special optimization.
II. ZVS test circuit
For the investigations a test circuit, see figure 2,
has been built which operates under application
specific conditions. It has the topology of a
voltage source series loaded resonant dc-to-ac
converter [9].
=
VCC/2
IL
=
RL
LL
S1
D1
CS/2
S2
D2 VCE
CS/2
CL
VCC/2
VGE
IC
VGE
IC
VCE
PV
Figure 3: Behaviour of an Trench IGBT Module
in the ZVS-Mode, 1µs/DIV, Ch. 2: VGE 10 V/DIV,
Ch. 3: IC, ID 40 A/DIV, Ch. A: VCE = 200 V/DIV,
Ch. C: PV 10 kW/DIV
If the upper IGBT S1 switches off the diode D2
takes over the load current for a short time. The
IGBT S2 goes in a switch on standby to this time.
At the zero crossing of the load current the IGBT
S2, switches on passively at nearly zero voltage
and takes over the load current. Before the end
of this half sinus wave the IGBT S2 is soft
switched off. In practice the switch off is
performed usually at low load currents to limit the
losses, moreover snubber capacities CS are used
to reduce the switching losses.
To guaranty the test at a defined chip
temperature the test mode is limited to only 4
periods. By means of mounting on a controlled
heat plate a control of the chip temperature TJ is
possible. All IGBT-modules are tested under the
same test conditions to ensure a good
comparability.
Figure 2: Principle test circuit
To realize the zero voltage switching mode of the
IGBT-modules the resonant circuit must be
driven at frequencies higher than the resonant
frequency of the load. Figure 3 shows the typical
behaviour of the IGBT S2 and its anti-parallel
diode D2 in this mode.
III. ZVS switch off
In the ZVS-mode the switch off of the IGBT has a
superior importance. Figure 4 shows the active
switch off of the Trench-IGBT in this mode.
8
VCES2
Standard IGBT
25°C 600V 13.6nF
6
Fast IGBT 25°C
600V 13.6nF
Woff [mWs]
VGE S2
4
ICS2
Trench IGBT 25°C
600V 13.6nF
2
0
20
WS2
In opposite to the hard switching at inductive load
the collector emitter voltage VCE starts rising at
the beginning of the collector current fall. This is
caused by the snubber capacitors CS. According
to the size of CS the rise of VCE is limited. It is
very important to remark that at soft switch off the
tail current dominates the losses. In addition the
switch off behaviour of the IGBTs depends on
different parameters especially temperature,
supply voltage and switch off current.
Woff [mWs]
6
4
2
0
0
5
10
15
20
25 30
CS [nF]
50
60
70 80
Ic off [A]
At reduced current at switch off it can be seen
that at VCC=600V the losses of the Trench-IGBT
converge to that of the Fast-IGBT.
Standard IGBT
25°C 600V 75A
FAST IGBT 25°C
600V 75A
Trench IGBT 25°C
600V 75A
Trench IGBT
125°C 600V 75A
Standard IGBT
125°C 600V 75A
Fast IGBT 125°C
600V 75A
Figure 5: Switch off losses of the IGBTs via CS at
rated current
With an increase of CS (fig. 5) it is possible to
decrease the switch off losses. But the size of
this decrease is not very high compared to hard
switching. This is caused by the high influence of
the tail current. The Fast-IGBT shows the best
performance at switch off at rated current of the
module at all measured CS-values.
4
3
Woff [mWs]
Figure 4:
Soft switch off of a Trench-IGBT
cond.: VCC=600V, CS=13.6nF, TJ = 25°C,
0.2µs/DIV Ch. 2: VGE 10 V/DIV, Ch. 3: IC 20
A/DIV, Ch. A: VCE 100 V/DIV, Ch. C: PL 10
KW/DIV, Ch. D: W 2 mWs/DIV
8
40
Figure 6: Switch off losses of the IGBTs via IC off
PVS2
10
30
Trench IGBT
125°C 600V
13.6nF
Fast IGBT 125°C
600V 13.6nF
2
1
0
200
300
400
500
600
VCC [V]
Trench IGBT 25°C
30A 13.6nF
Trench IGBT 125°C
30A 13.6nF
Standard IGBT
25°C 30A 13.6nF
Standard IGBT
125°C 30A 13.6nF
Fast IGBT 25°C
30A13.6nF
Fast IGBT 125°C
30A 13.6nF
Figure 7: Switch off losses of the IGBTs via VCC
Figure 7 shows that for the standard and the fast
IGBT’s the losses linearly increase with the
voltage VCC. The Trench-IGBT losses show for
voltages more than 400V only a small increase.
This is caused by the field stop layer in this IGBT
[8]. For high voltages and low switch off currents
the Trench-IGBT can switch off with low-loss
nearly like the Fast-IGBT specialized for this aim.
III. Passive switch on
To test the passive switch on in general a special
circuit shown in figure 8 was used. The tested
IGBT S2 is in stand by every time at VGE = 15V
and switches passive on and off. The switch S1 is
used to switch actively the load current.
VGE S2
S1
=
VCC
D1
PVS2
LL
WS2
S2
15V
ICS2
Figure 8: Test circuit for passive switch on
According the inductive load a certain di/dt will be
pressed into the switch S2. Figure 9 and 10 show
the passive switch on for the Fast-IGBT and the
Trench IGBT. The voltage drop at the finish of the
current rise is due to over voltages caused by the
stray inductance of the module.
PVS2
VGE S2
WS2
ICS2
VCES2
Figure 9: Passive switch on of a Trench-IGBT,
cond.: TJ=125°C, di/dt=50 A/µs, VGE=15V,
0.5µs/DIV, Ch. 2: VGE 10 V/DIV, Ch. 4: IC 20
A/DIV, Ch. 1: VCE 5 V/DIV, Ch. C: PV 200 W/DIV,
Ch. D: W 0.5 mWs/DIV
The Trench-IGBT shows a high but very short
voltage spike at passive switch on and additional
it reaches it’s low saturation voltage very fast.
The process of conductivity modulation which is
responsible for this behaviour is finished in this
IGBT very fast. Both IGBT’s of the second
generation show similar lower voltage spikes at
passive switch on (see fig. 10 for the fast IGBT).
VCES2
Figure 10: Passive switch on of a fast IGBT,
cond.: TC=125°C, di/dt=50 A/µs, VGE=15V,
1µs/DIV, Ch. 2: VGE 10 V/DIV, Ch. 4: IC 20 A/DIV,
Ch. 1: VCE 5 V/DIV, Ch. C: PV 200 W/DIV, Ch. D:
W 1 mWs/DIV
On the other hand they need nearly double the
time to come into saturation. Further
measurements show for all IGBT’s a rise of the
overvoltage at increasing di/dt.
Table 1: Estimation of additional losses at
passive switch on
Typ
Won dyn / mWs
TJ=25°C,
di/dt=50 A/µs
Won dyn / mWs
TJ=125°C,
di/dt=50 A/µs
Fast IGBT
0.07
0.32
Trench IGBT
0 (not to be
measured)
0.16
Standard
IGBT
0.11
0.44
Table 1 specifies the additional losses caused
trough the passive switch on for a di/dt = 50 A/µs
which corresponds to a frequency of nearly 80
kHz. At low chip temperature this losses are
negligible. At high temperatures the losses for the
IGBTs of the second generation could be
important.
IV. Calculation and comparison of total IGBTand diode losses
For an estimation of the whole losses of an IGBT
and a diode of the modules a calculation was
The evaluation was performed first for 25°C.
Here the passive switch on losses of the IGBT
are neglected (see table 1). Measured values of
the IGBT switch off energy and the switching
times are used. The conduction losses were
calculated according the static characteristics of
the IGBT’s and Diodes whereas the load current
was assumed to be sinusoidal. The diagram in
figure 11 shows the calculated loss split of the
modules at f=50 kHz under this conditions
250
P [W]
200
150
PswT
PcondT
PcondD
Ptot
inductance caused through the nearly sinusoidal
load current was noted at this calculations. The
calculations without the passive switch on were
performed in the same manner as for TJ=25°C.
P [W]
performed using the program Mathcad.
Measurements show that under the test
conditions the switching losses of the diode are
negligible in the investigated frequency range.
450
400
350
300
250
200
150
100
50
0
PswT
PcondT
PonT real
PtotT
PtotT real
21
52
94
Fast IGBT
21
52
94
21
94
f [kHz]
Standard IGBT
Trench IGBT
52
Figure 12: Loss split of the IGBTs at different
frequencies with and without a consideration of
the additional losses at passive switch on, cond.:
ILmax=75A, ICoff=30 A, VCC=600V, TJ=125°C,
CS=13.6nF
100
50
22
30
50
Fast IGBT
22
30
50
Trench IGBT
30
50
Icoff [A]
Standard IGBT
Figure 11: Loss split of the IGBT-modules at
different switch off currents, cond.: ILmax=75A,
f=50kHz, VCC=600V, TJ=25°C, CS=13.6nF
The Fast-IGBT shows the lowest switching
losses but the conduction losses are relatively
high. The Trench-IGBT has very low conduction
losses and at low switch off currents nearly the
same low switching losses like the Fast-IGBT.
This leads in this range to the lowest total losses.
Additional calculations at 100 kHz show the same
results. Simulations at 20 kHz show that at this
frequency the conduction losses dominate. The
Trench-IGBT has here the lowest losses. The
IGBTs of the Fast- and the Standard-IGBTModules have nearly the same losses.
According to the results in table 1 the influence of
the passive switch on of the IGBTs at a
temperature of TJ=125°C is considered and
compared to a calculation without the influence of
the passive switch on.
For this aim the passive switch on and the
conduction phase were measured directly in the
resonant converter for some few working points
and regarded together as PonT real. Further more
the influence of the voltage drop at the stray
Figure 12 shows that at TJ=125°C a rise of the
frequency leads for all investigated IGBTs to an
increase of the difference between the calculated
losses with and without a consideration of the
passive switch on. Measurements show that with
increasing frequencies the IGBTs ever less reach
their static working point at the conduction phase.
The Trench-IGBT shows only for very high
frequencies a remarkable influence of the
passive switch on to the total losses. For the
Fast- and the especially the Standard-IGBT the
passive switch on is remarkable for frequencies
of approx. 50 kHz and more. At relatively low
frequencies the passive switch on is negligible for
TJ=125°C also.
350
300
250
P [W]
0
PswT
PonT real
PtotT real
200
150
100
50
0
22
30
50
Fast IGBT
22
30
50
30
50
I coff [A]
Trench-IGBT Standard IGBT
Figure 13: Loss split of the IGBT-Modules at
different switch off currents, cond.: ILmax=75A,
f=52kHz, VCC=600V, TJ=125°C, CS=13.6nF
The losses of the investigated IGBTs at
TJ=125°C and f=52kHz are presented in Figure
13 for different load currents. Expectedly the
losses are higher then those at TJ=25°C for all
modules. Also at TJ=125°C the Trench-IGBT has
an advantage against the Fast-IGBT especially at
low switch off currents.
V. Conclusion
Three IGBT-Modules are tested in terms of their
properties for applications in resonant inverters
which are working in the Zero Voltage Mode up
to high frequencies. These are a planar
Standard-IGBT-Module of the 2. generation, a
planar Fast-IGBT-Module of the 2. generation
specialized for resonant applications and a new
Trench-IGBT-Module of the 3. generation. To
meet the investigation goals a test stand was
established which works in the ZVS-mode. The
conduction and especially the switch off losses of
the IGBT are the most important parts of the total
losses in this mode. The passive switch on
losses are to note especially at the Standard- and
the Fast-IGBT. For the Trench-IGBT these losses
are negligible up to high frequencies. The results
show that it is possible to drive the Trench-IGBT
without special optimization up to high
frequencies on a low loss level like the Fast-IGBT
specialized for this application. Indeed for the
Trench-IGBT these advantages exists at a mode
at high voltages and relatively low switch off
currents.
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PESC 2001
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