Tech Briefs Magazine - April 2024 - 8

Q & A
Medium Voltage for More Efficient
Power Transmission
Prasad Kandula and
a group of scientists
and engineers at Oak
Ridge National Laboratory
are developing a
modular medium voltage
system to fill the
existing gap between
high voltage transmission
and low voltage power electronics.
Tech Briefs: What are the voltage
levels considered to be " medium " ?
Why is it so important?
Kandula: The medium voltage range
is from 4 kVAC to 34 kVAC. As you try to
process more power, you would want it
to be done at higher voltages and lower
currents to reduce the copper losses.
Tech Briefs: You said in the press
release that " Power conversion
using medium-voltage power
electronics is expected to be more
efficient, in addition to packing
more power into a smaller space. "
Can you please explain that?
Kandula: For our medium voltage
power electronics, we process the power
internally at high frequencies. So, all the
passive components in the system like
inductors, transformers, and capacitors,
will be reduced in size.
Tech Briefs: Could you outline what
is in the system?
Kandula: Inside the system, we convert
the low voltage DC to high frequency
AC, in the range of 10 kHz to
20 kHz, and then use a high frequency
transformer to provide galvanic isolation.
Then on the other side, the high
frequency AC is converted to medium
voltage AC with another high frequency
transformer.
However, we are finding more and
more applications for converting the low
voltage DC to medium voltage DC, rather
than AC.
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Tech Briefs: Where it would make
most sense to use DC for the output
source?
Kandula: If you wanted to connect two
distribution systems and the line is long,
let's say 15 miles or more you would need
less copper. It would essentially increase the
amount of delivery capacity using the same
power lines. It would also reduce the number
of conversion stages and improve the
efficiency of power delivery.Microgrids are
another example. They often use sources
like solar or fuel cells, which are all DC, and
most of the heavy loads are either directly
DC or they have intermediate DC in them.
For instance, chargers or even home air
conditioners run on motor drives that use
DC at some point in the conversion. So, if
the source is DC and the load is DC, why
don't we just stick with DC all the way.
Tech Briefs: Do you use different
blocks for AC and DC outputs?
Kandula: So, first is a rectifier circuit,
which converts from DC or AC to AC or
DC. The second is the high frequency
conversion block which takes in DC, internally
converts it into high frequency
AC, puts it through the transformer and
on the other side, converts it back to DC.
The function of this block is to provide
DC to DC isolation. If you needed AC
out, there would be an additional block.
Our building blocks include protection,
which is very important.
Tech Briefs: What are your next
steps?
Kandula: Today we are in the early
stages, where we are going to develop
the blocks; then we want to put the
blocks together. After that we will bring
the system controls into the picture, put
them together, and install the system in
the field or a reasonable testing environment
to demonstrate the technology.
To read the full interview, visit www.
techbriefs.com.
Tech Briefs, April 2024
http://info.hotims.com/86254-723 http://www.techbriefs.com http://www.techbriefs.com
Tech Briefs Magazine - April 2024

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