Shift Magazine - July 2021 - 21

to stop and plug something in. It's really a
game changer in that sense. "
But what does a dynamic wireless power-transfer
system even look like?
" That is an excellent question, " says
Afridi. " And that is essentially the question
still being debated. It is being debated
in the sense that there are many possible
solutions. They can be higher power
and short distance, or they can be lower
power and longer distance. " They might
also use either magnetic or electrical
fields, he says.
For a century, academics at places such
as Stanford University and Oak Ridge
National Laboratory and industry researchers
at companies such as Qualcomm and
WiTricity Corp. have been trying to crack
the tech problems and high cost of wirelessly
charging an EV using guided magnetic
fields.
Those challenges include the use of
ferrite, a fragile and expensive material;
concerns
about
exposing
passengers
to electromagnetic fields; and the risk of
the charging pad accidentally heating up
nearby metal objects.
Afridi, however, believes a more practical
and affordable system might use electrical
fields instead. Recent cost-reduction
and technical breakthroughs in power
electronics, near-field coupler designs and
semiconductor materials such as exotic
gallium nitride could make it easier to pull
off. Afridi's promising work with electrical
fields at Cornell has hit its targets
and attracted funding from the Advanced
Research Projects Agency - Energy and
the National Science Foundation.
Today, automakers such as Renault and
BMW are starting to roll out stationary
commercial EV charging stations that are
wireless; charging a battery to 80 percent
takes 30 to 40 minutes.
But Afridi says that charging moving
vehicles is more complicated and involves
vastly higher and faster power transfers.
He estimates commercial electrical-field
EV charging might be 10 or even 15 years
away. But he feels that now is the time for
discussion and development as the U.S.
government plans massive infrastructure
Cornell's wireless
charging tech uses
higher frequencies than
magnetic-field systems
to transfer more power.
investments, world EV markets surge and
auto companies announce multibillion-dollar
EV investment plans.
With dynamic wireless power transfer,
either capacitive or inductive, the vehicle's
receiving unit quickly moves past
the sending unit embedded in the road.
A vehicle might be on a half-mile-long
charging grid for 30 seconds or less. So,
both types require sophisticated power
electronics, such as a high-frequency
inverter and rectifier.
So far, only experimental roadways for
wireless magnetic-field power
transfer
Afridi: What a dynamic
wireless power-transfer
system would look like is
" still being debated. "
have been built. And these prototypes
have consistently proved to be complicated,
fragile and expensive.
Estimates by different experts and companies
range from $600,000 to $2.5 million
a kilometer, depending on individual
configurations and requirements.
" It may be possible that the magnetic
field system's economics will not work
out, " Afridi says. " The capacitive system is
a lot cheaper in principle. If nobody deploys
the magnetic-field system in the next three
to five years, we may just skip the magnetic-field
systems all together and go directly
to the electric-field system. " n
july 2021 * shift 21
Shift Magazine - July 2021

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