Functionality Enhancement of 3rd-Generation Direct Liquid Cooling
Power Modules for Automotive Applications Equipped with RC-IGBT
SATO, Kenichiro * ENOMOTO, Kazuo * NAGAUNE, Fumio * ABSTRACT
Fuji Electric has developed a 3rd-generation direct liquid cooling power module for automotive applications such
as hybrid and electric vehicles. Power modules for automotive applications are required to be compact and exhibit
low power loss. We have improved heat dissipation performance of the module by using an aluminum water jacket
that combines the liquid cooling fins with cover as well as refrigerant inlet and outlet ports with a flange structure. In
addition, employing a reverse conducting IGBT (RC-IGBT) that integrates an insulated gate bipolar transistor (IGBT)
with free wheeling diode (FWD) enables the power module with the same active area to reduce power loss by 20%.
As a result, the power module has achieved a lower loss and a smaller size.
1. Introduction
To reduce CO2 emissions and conserve the earth’s
resources, countries of the world are accelerating their
efforts and automakers are actively working on the development of hybrid electric vehicles (HEVs) and electric vehicles (EVs). HEVs and EVs use inverters for
driving electric motors, and one of the key components
that play an important role is an insulated gate bipolar
transistor (IGBT) module. IGBT modules are required
to be compact and exhibit low power loss so that the
electric power of batteries can be efficiently used.
In order to meet these requirements, Fuji Electric has offered IGBT modules that employ a direct
liquid cooling system as products, and continued with
their development(1). We have recently developed a
3rd-generation direct liquid cooling power module for
automotive applications (3rd-generation module for
automotive applications). It has had the performance
and functionality further enhanced from those of conventional direct liquid cooling power modules for automotive applications.
This paper describes the functionality enhancement for the 3rd-generation direct liquid cooling power
module for automotive applications integrating a reverse-conducting IGBT (RC-IGBT(2)).
2. Features
Figure 1 shows the external appearance of the developed 3rd-generation module for automotive applications. This product has achieved higher heat dissipation performance than that of conventional products
by optimizing the refrigerant flow channel design. An
aluminum water jacket combined with a cover and
*Electronic Devices Business Group, Fuji Electric Co., Ltd.
256
Flange
Flanged refrigerant
inlet/outlet port
(a) Front side
(b) Back side
Fig.1 3rd-generation module for automotive applications
flanged refrigerant inlet and outlet ports have been
employed and all the user needs to do is ensure that
the refrigerant is run through the flanged inlet and
outlet ports at the specified flow rate.
Table 1 shows the major product specifications of
the 3rd-generation module for automotive applications,
and Fig. 2 shows an equivalent circuit diagram of the
Table 1 Major
‌
specifications of 3rd-generation module for
automotive applications
Item
Rating / Characteristic
Collector-emitter voltage
750 V
Rated current
800 A
Maximum operating temperature
175 °C
Dimensions
Withstand voltage
W162 × D116 × H24 (mm)
2,500 V (AC RMS value)
IGBT saturation voltage
1.45 V (25 °C, 800 A)
FWD forward voltage
1.50 V (25 °C, 800 A)
IGBT / FWD thermal resistance
Mass
0.14 °C / W (10 L / min, LLC)
560 g
loss caused by high-speed switching and to reduce the
surge voltage in current interruption(3).
IGBT gate terminal
IGBT emitter terminal
Temperature detection diode anode terminal
Temperature detection diode cathode terminal
Current detection terminal
Terminal for collector voltage detection
P2
P3
31 (P)
7 (A1)
17 (A3)
27 (A5)
8 (K1)
18 (K3)
28 (K5)
6 (S1)
16 (S3)
26 (S5)
10 (G1)
20 (G3)
30 (G5)
9 (E1)
19 (E3)
29 (E5)
U
V
W
4 (A2)
14 (A4)
24 (A6)
5 (K2)
15 (K4)
25 (K6)
3 (S2)
13 (S4)
23 (S6)
1 (G2)
11 (G4)
21 (G6)
2 (E2)
12 (E4)
22 (E6)
N1
N2
N3
Fig.2 Equivalent
‌
circuit of 3rd-generation module for automotive applications
module. The main features of the product are as follows:
(1) Miniaturization of power module
The 7th-generation chip technology has been applied to the IGBT in order to reduce power loss. Furthermore, an RC-IGBT integrating an IGBT and freewheeling diode (FWD) in one chip has been employed
to reduce the power module size by 15%. In addition,
the RC-IGBT has been equipped with a function of
detecting the current running through the IGBT and
junction temperature. This allows a good chip performance to be realized with the small size maintained
and the protection operation can be ensured against
short-circuiting and overheating.
With the 3rd-generation module for automotive
applications, as shown in Fig. 2, the IGBT of each arm
is provided with anode and cathode terminals of the
diode for temperature detection and a terminal for current detection. Each arm also has gate and emitter
terminals required for driving. The diode for temperature detection is integrated in the RC-IGBT.
(2) Cooler structure with high heat dissipation performance
Improved heat dissipation performance and a
lower profile have been realized by using a cooler
structure combining liquid cooling fins and a cover. A
flanged structure is employed for the refrigerant inlet
and outlet ports and watertightness with the inverter
housing is ensured by using an O-ring.
(3) Reduction of inductance of main terminal wiring
We have reduced the Inductance by providing independent input terminals for the respective phases
connected to the smoothing capacitor and minimizing
the length of the wiring so as to reduce the switching
3.1 RC-IGBT design technology
Figure 3 shows a schematic structure of the RCIGBT. The structure employs a field stop (FS) IGBT
and has the IGBT and FWD regions alternately laid
out in stripes in one chip. Integration in one chip
makes it possible to reduce the region called a guard
ring for ensuring withstand voltage around the chip. This makes the chip area smaller than a conventional
product composed of 2 chips. The heat generated during IGBT operation is dissipated from the FWD regions as well and vice versa. This provides the effect
of reducing thermal resistance during the respective
IGBT and FWD operations. Furthermore, the latest
wafer thinning technology, trench structure and channel density optimization have achieved lower power
loss and chip miniaturization, contributing to miniaturization of power modules. The ratio between the
IGBT and FWD regions has been optimized by taking
into account inverter power running*1 operation and
regenerative*2 operation. In addition, by integrating
the IGBT and FWD, turn-off loss can be reduced with
the RC-IGBT by also using the FWD regions as the
carrier emission path during turn-off operation of the
IGBT.
With this development, we have employed an RCIGBT, optimized the allocation of the IGBT and FWD
regions and utilized the latest-generation chip technology. In this way, the electrical characteristics as an
IGBT module can also be improved, and this has led to
a reduction of power loss. With the same active area, a
power loss reduction of 20% has been achieved(4).
3.2 RC-IGBT protective technology
As one generation of IGBT technology makes way
for another and saturation voltage and switching loss
IGBT region
n+ n+
FWD region
IGBT region
FWD region
n+
Gate pad
n+ n+
Field stop layer
p+
Fig.3 Schematic structure of RC-IGBT
*1: ‌Power running: Transmission of the motive power of a
motor for acceleration
*2: ‌Regeneration: Returning of the electric power generated
by a motor in deceleration to the battery
Functionality Enhancement of 3rd-Generation Direct Liquid Cooling Power Modules for Automotive Applications Equipped with RC-IGBT
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issue: Power Semiconductors Contributing in Energy Management
P1
3. Elemental Technologies for Functionality
Enhancement
Chip thickness
G:
E:
A:
K:
S:
P:
are reduced, short-circuit protection takes on importance. That is, a short-circuit current increases as saturation voltage decreases. This makes it necessary to
interrupt the current in a short time without exceeding
the maximum short-circuit energy capability and to
suppress any increase of the surge voltage. If a short
circuit occurs in the RC-IGBT, for quick and reliable
interruption, the 3rd-generation module for automotive applications uses short-circuit protection with a
current detection system (see Fig. 4). In this system,
part of the short-circuit current is split to the current
detection terminal and the voltage for current detection VSC generated on the resistor connected is used for
starting short-circuit protection operation. The value
of the current for starting short-circuit protection is
determined by setting the resistance values for resistors RSE1 and RSE2 connected in series. Fuji Electric
provides drive boards for module evaluation that are
equipped with a short-circuit protection circuit based
on a current detection system. Here we present the
functions of drive boards for evaluation use and describe the concept of short-circuit protection.
(1) Drive board for evaluation use
Figure 5 shows the external appearance of the
drive board for evaluation use mounted on the 3rd-generation module for automotive applications. The drive
Collector
Gate
VSE
Sense
RSE1
Emitter
VSC
RSE2
Fig.4 Short-circuit
‌
protection based on current detection system
board for evaluation use is equipped with IGBT drive
circuits for 6 arms and the gate drive voltage is + 15/ -0
V (on-state voltage / off-state voltage). To suppress the
short-circuit current just as a short circuit is detected,
a function is provided to clamp the gate drive voltage. In addition to the short-circuit protection function, the
drive board is provided with a function to monitor the
direct current voltage input to the power module. This
is done by using the terminals for collector voltage detection of the power module shown in Fig. 2.
Figure 6 shows an example of short-circuit protection waveforms of the 3rd-generation module for automotive applications obtained by using the drive board
for evaluation use. The following describes the flow
of operation of short-circuit protection for these waveforms.
(a) A short circuit occurs and VSC (see Fig. 4) rises
(see Fig. 6 ①).
(b) When VSC has exceeded the threshold voltage
judged as a short-circuit current, the gate-emitter voltage is gate-clamped to 12 V so as to suppress the short-circuit current (see Fig. 6 ②).
(c) As the short-circuit state continues, the gateclamped state also continues (see Fig. 6 ③).
(d) When the gate-clamped state has continued for
a certain period, the state is judged as an abnormality with a short circuit. Then, soft interruption operation is performed in which the gateemitter voltage is gradually reduced (see Fig. 6
④).
(e) The soft interruption operation is finished at a
gate-emitter voltage sufficiently lower than the
gate threshold voltage of the IGBT and the gateemitter voltage is turned off in the normal interruption state (see Fig. 6 ⑤).
(2) Points in short-circuit protection design
What is required is to provide short-circuit protection by reliably detecting short circuit operation without element breakdown. The following lists the points
in short-circuit protection design.
VCE: 100 V/div, IC: 1,000 A/div, VGE: 5 V/div
VSC: 2 V/div, t : 2 µs/div
②
③
④
Gate − emitter voltage: VGE
⑤
Collector − emitter voltage: VCE
①
Voltage for current
detection: VSC
Collector current: IC
Fig.5 Drive
‌
board for evaluation use mounted on 3rd-generation module for automotive applications
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Fig.6 Short-circuit protection operation waveforms
FUJI ELECTRIC REVIEW vol.62 no.4 2016
VCE: 100 V/div, IC: 200 A/div, VGE : 5 V/div
VSC: 2 V/div, t : 400 ns/div
Gate − emitter voltage: VGE
Collector current: IC
i
ii
iii
Voltage for current
detection: VSC
Collector − emitter voltage: VCE
Fig.7 Turn-on operation waveforms
Short circuit operation
-50
Short circuit detection voltage
Turn-on operation
0
50
100
Chip temperature Tj (°C)
150
200
Fig.8 C
hip temperature dependence of voltage for current
detection
should be detected in this period. However, to prevent any misdetection, VSC must be set lower than
the short circuit detection voltage in normal switching.
(c) Period iii
In this period, the turn-on current and gateemitter voltage shift to the specified set values and
VSC is low.
Figure 8 shows VSC at turn-on, indicating values in
period ii, which must be lower than the short circuit
detection voltage in the entire current and temperature ranges applied. In addition, the gate clamp period
in short-circuit protection operation must be set in consideration of period i in normal switching as described
above.
3.3 Technologies applied to high heat-dissipating cooler
The 3rd-generation module for automotive applications adopts an aluminum water jacket combined
with a cover and flanged refrigerant inlet and outlet
ports. By integrating the heat sink and water jacket
and devising an effective fin shape, heat dissipation
performance has been improved by 30% from conventional products(4),(5). The 3rd-generation module for automotive applications is characterized by the adoption
of a flange structure for the refrigerant inlet and outlet
ports. This section describes how sealing performance
of the flange structure is ensured by using an O-ring.
The direct liquid cooling power module is mounted
on the equipment housing by a flange via a sealing
material. A seal for preventing refrigerant leakage is
required even when the operating temperature or refrigerant pressure changes. Figure 9 shows an example
of use of an O-ring for the 3rd-generation module for
automotive applications. In reality, deformation and
vibration may be generated in the entire equipment
depending on the use environment and current applying conditions. Therefore, it is necessary to maintain a
state in which the O-ring is always in contact with the
flange and housing in use environment with an appropriate crush width.
Functionality Enhancement of 3rd-Generation Direct Liquid Cooling Power Modules for Automotive Applications Equipped with RC-IGBT
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issue: Power Semiconductors Contributing in Energy Management
Voltage for current detection VSC (a.u.)
(a) Short circuit detection voltage
Determine the voltage value at which a shortcircuit current is detected.
(b) VSC maximum voltage
The maximum voltage shall be at or lower than
the withstand voltage of the drive IC.
(c) Gate clamp voltage
Determine the limit value for a short-circuit current.
(d) Gate clamp hold time and soft interruption operation time
Determine the respective periods for ensuring
that the short circuit energy is kept at or below the
breakdown level.
In normal IGBT switching operation, VSC must
be lower than the short circuit detection voltage and
within the range of the maximum applicable current. In the unlikely event of misdetection of a short circuit
in normal operation, IGBT switching loss may be increased or malfunction of the equipment may occur. In setting the short circuit detection voltage for shortcircuit protection described above, behavior of VSC in
normal operation must also be considered.
(3) Example of evaluation results
Figure 7 shows operation waveforms including behavior of VSC at turn-on, and Fig. 8 the chip temperature dependence of VSC in a short-circuit state and at
turn-on.
The following describes the behavior of VSC in periods i to iii in Fig. 7.
(a) Period i
The collector current increases, and the inclination of the current causes a transient rise of VSC. This period is within the range of normal operation
and must be specified not to detect short circuits.
(b) Period ii
In this period, the collector current has reached
a certain level but the gate-emitter voltage is held at
the IGBT threshold voltage level for a certain time
and high VSC occurs in this period. Short circuits
O-ring diameter: > 2.4 mm
P15 (JIS standard shape)
Material: NBR (nitrile rubber)
Hardness: 70
Cooler
Groove depth: O-ring diameter
× 0.7 to 0.8
Refrigerant jacket
Fig.9 Example of seal using O-ring
O-ring
(a) Main unit
(b) Mounted
Fig.10 Adapter for flange connection
Fuji Electric offers an adapter to connect with a
flange to run a refrigerant for user evaluation use. Figure 10 shows the external appearance of the adapter
for flange connection.
4. Postscript
ment for the 3rd-generation direct liquid cooling power
module for automotive applications integrating an RCIGBT. RC-IGBT is an elemental technology for realizing functionality enhancement of power modules,
and it has protection technology and the technologies
applied to coolers for realizing direct cooling. They
support users with inverter equipment design. In the
future, we intend to move forward with further technology innovations and provide a wider selection of
easier-to-use high-functionality products.
References
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(2) Yoshida, S. et al. RC-IGBT for Automotive Applications. FUJI ELECTRIC REVIEW. 2015, vol.61, no.4,
p.263-266.
(3) Adachi, S. et al. “Automotive power module technologies for high speed switching”. Proceedings of PCIM
Europe 2016, May 10-12, Nuremberg, P.1956-1962.
(4) Arai, H. et al. 3rd-Generation Direct Liquid Cooling Power Module for Automotive Applications. FUJI
ELECTRIC REVIEW. 2015, vol.61, no.4, p.252-257.
(5) Gohara, H. et al. Packaging Technology of 3rd-Generation Power Module for Automotive Applications. FUJI
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This paper has described functionality enhance-
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