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Hitachi Europe Ltd.
Current rail inverters are mainly designed
for a high voltage of 1500V from over-
head wires and therefore downsizing of
high voltage power modules is impor-
tant. Hitachi has developed a compact
3.3kV/1200A hybrid module for rail car
inverters having a high voltage resist-
ance of 3.3kV using SiC. The hybrid mod-
ule developed combines 3.3kV SiC-SBDs
(Schottky barrier diode) and Si-IGBTs. To
achieve a compact size module, Hitachi
optimized both the SiC-SBD structure and
the Si-IGBT device characteristics taking
full advantage of device, circuit and loss
simulations, and succeeded in reducing
the module size to approximately two-
thirds that of current Si modules.
In 2009, Hitachi developed 3kV-class
SiC-SBDs which employ a JBS (Junction
Barrier Schottky) structure that combines
Schottky junctions with pn junctions,
and mounted these in a power mod-
ule, which led to the development of this
compact SiC hybrid module for railcar
inverters. Features of the technology
developed are as below:
SiC-SBD
To achieve a compact power module, it
is necessary to pass a large current across
the SiC-SBD which has a limited sur-
face area. By employing the JBS struc-
ture which combines Schottky junctions
and p-n junctions, both conduction loss
and leakage current can be reduced.
This effect was further enhanced by ap-
plying device simulation to optimize the
JBS structure successfully resulting in in-
creased current per SiC-SBD surface unit
area. Further, as the internal electric field
of SiC is approximately 10 times that of
Si, the optimal device edge structure was
designed using device simulation to de-
crease the electric field around the device
edge and assure the reliability required
for rail cars.
Si-IGBT
Si-IGBT device with trench gate structure
was developed, whose cell size was one
third of previous generation device, lead-
ing to 20% loss reduction. The device
characteristics were optimized by apply-
ing circuit and loss simulation in rail ap-
plication circuits.
The compact 3.3kV/1200A hybrid mod-
ule with the size two-thirds that of con-
ventional Si module and maximum op-
erating temperature of 150°C, was
fabricated combining the Si-IGBT and
the SiC-SBD technologies.
Hitachi also developed SiC hybrid inverter
for rail cars that is compatible with
1,500V DC overhead power supply using
the compact hybrid module and light-
weight oil-free capacitors.
Size and weight of 40% smaller and
lighter than current mainstream inverters,
and 35% reduced power loss are suc-
cessfully achieved.
