Thanks for posting this link R. Legg. It makes for a very interesting read.
Unfortunately the authors don't have a clue what they are jabbering about.
I'm sure it dazzles most readers in BS however, and probably fullfilled
their university's "research" requirements for its professors.
As with most articles, it has to be taken with a grain of salt. You
will often find that there are problems with an author's approach to a
particular application. I can only suggest that you make these
observations known to the author. There are many reasons why this
paper may have been presented at EPE'99 in it's present state that
have nothing to do with actual research performed or results and
conclusions obtained.
It may be a poorly cribbed summary of more extensive work, which, if
you do query results directly, may be offered in response.
Unfortunately, a time lapse of four years can be a serious obstruction
to such communications, as authors move on.
There are numerous very serious problems with it, but something that really
caught my eye was their choice of Schottky diodes for the circuit of figure
8. They use the MBR1045 which is a 10A rated 45V schottky diode. Then they
say a couples lines under figure 8 they have an input voltage of 60V and a
19:19 (or 1:1) turns ratio on their transformer. This means their diodes
get to see an abusive 60V or so during some parts of the cycle.
The topology is series primary resonant, with a parallel-loaded
series-resonant secondary rectifier. Depending on the ratios of Llk
(they indicate that added series inductance was introduced) to Lout.
The primary series inductor Llk may have dominated, in which case the
output voltage will have effectively clamped the voltage across the
rectifiers (Vout=24V) in spite of the presence of 'Lout'. The authors
don't have to tell you this, for their research to be valid. They
don't have know that this is what saved their devices from failing -
if this was in fact the case.
"Llk and Rlk are the sum of primary and secondary leakage inductances
and resistances and additional series resonant inductor respectively"
We also know, from their explicit statement, that magnetizing
inductance values were low - I expect that magnetizing Lm should more
truthfully have been drawn in the circuit, producing a further
effective input voltage reduction.
I wonder if
they blasted a whole bunch of those MBR1045 (and the IRF530N devices) before
they finally found a set that didn't avalanche to destruction immediately
and could block the 60V.
It is not their duty to report how many parts popped while collecting
data, if this was indeed the case.
What struck me as the biggest limitation in this presentation, was
that this device was not compared to a part wound without
superconductive media. Obviously, the windings of a normal device
would not have had a 25DegC impedance of 180Ohms or greater, as this
device did.
The real proof of the value of the material change would be to test
the superconductive and normal parts at both cryogenic and normal
temperatures. This would give a figure of merit to:
a) cryogenics alone
b)superconductive winding media alone.
At a minimum, it would have produced data that others could refer to,
when using normal conductors at normal temperatures, which must be
considered as a kind of baseline.
Perhaps this data was collected. In this event the shortcoming is in
the paper alone - not in the authors or the research. Keep them
separate in your mind, to maintain faith in humin beens and your own
sanity.
RL
