Battery & Electrification Technology - May/June 2024 - 6

Power Electronics
Burak Ozpineci, Section Head of the Vehicle
and Mobility Systems Research Section at Oak
Ridge National Laboratory. (Image: ORNL)
A chief power-electronics component, the motor inverter, is integrated with the traction motor
and gearbox in Schaeffler's " 3-in-1 " e-axle. (Image: Schaeffler)
SiC is Today's State-of-the-Art
Vishnu Medisetty, Director of Power
Electronics for Bosch in North America,
confirms that SiC devices are the mainstay
of the company's power-electronics
portfolio. Bosch began with SiC around
2001, he said in an interview with SAE
Media, and the trajectory continues
strongly upward.
" We are already on our second generation
[of SiC], " Medisetty acknowledged.
" We are working toward our third generation
and there are generational improvements
in the efficiency of the devices.
So the device efficiency improves
- but also, there's a huge cost driver behind
EV applications. What we look at is
trying to reduce the cost of the power-electronic
device, be it a charger converter
or be it an inverter that is driving
the motor. We try to reduce the size of the
die, the chip, extract more current out of
it, need less cooling for it. "
While Tesla hasn't specified just how it
will reduce SiC devices in future power6
trains,
the industry also is working on
replacing SiC semiconductors with gallium
nitride once it can solve at least one
challenge: The current moves vertically
in SiC devices but laterally along the
plane in GaN devices.
" There are no gallium-nitride vertical
devices available, " Ozpineci said. " The
challenge with them is they're usually
low-voltage, low-current right now. In a
low-power onboard charger, or if you're
looking at other DC/DC converters -
again, low-voltage, low power - you can
use GaN, which will beat SiC at the power
level. But the vertical GaN devices, which
actually will have better properties than
SiC, are not ready yet - and they might
not be ready for another 10 years. "
Bosch's Medisetty agreed, saying that
for now, gallium-nitride doesn't have the
performance needed by the transportation
sector. " [GaN devices] are quite a bit
lower-voltage, not readily suitable for automotive
electromobility applications, but
there are other gallium nitride approaches
which are more similar to silicon-carbide
devices, " he said. " These have higher voltages,
are more robust and more suited for
electromobility applications.
" Bosch is working extensively on gallium
nitride that is more suitable for electromobility
applications, " he added. " We
see a potential for it, but it's still further
out and there is lot more ground to be
covered on silicon-carbide optimization.
There're generations before we get there. "
Sandia National Laboratories started a
development project in 2019 for better
next-generation vertical GaN devices for
high-power-density electric drivetrains.
Testing both GaN JBS diodes and GaN
MOSFET devices, the teams have so far
discovered that the main problem is the
low maturity of the two devices. Engineers
have reached current limitations for both
the MOSFET devices (where the problem
lies with the current output) and the JBS
diodes (where the limitation is in the reverse
leakage due to the etch-and-regrowth
process).
Sandia said in a summer 2023 presentation
that it will conduct further tests
once either a multi-amp device can be
Battery & Electrification Technology, May/June 2024

Battery & Electrification Technology - May/June 2024

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