Watson A.Name - "Watt Sun said:
[snip]
You could've deleted 90% of the crap that was above.
I was very fortunate that my first *real* job was designing huge (1kW - 1MW)
AC motor controllers.
When they upgraded the air conditioning in a bldg they installed those
Danfoss variable speed controllers. Now when I go to the comm room,
next door to the A/C room, all I hear is this high pitched whine coming
from the motors and wiring. Like screeching! I dunno who did that
design, but it sure is noisy!
yeah they can (and often do) scream like stuck pigs. We always used
frequency "slushing" - pseudo-random variations of around 10% of switching
frequency turn an annoying screech into a more pleasing hiss, by spreading
the total acoustic energy over a wider band. Similar approaches are used to
pass EMC tests, because of the averaging behaviour of the test instruments.
We once made up a demo for a trade show that performed "silent night"
entirely with motor acoustic noise. I looked into direct paralleling
inverters with a single motor, to then generate chords (we are talking 1MW
drives here
as the currents add linearly, but we never did it as we had
actual work to do....I thought we should have made the motor say things like
"help Im trapped inside this motor," but one of the programmers wired an
analogue input up to the waveform generator, so we could feed an audio
signal into our 250kW "speaker" - ah the fun we had
I also built a modbus driven "clonk" generator once, with a 250kW vector
drive - I added serial comms to a very heavily loaded processor. A data
burst meant the micro ran out of time, and interrupt priorities were such
that the serial won, and the field orientation lost. Re-orientation was
accompanied by a VERY loud "clonk" from the machine, the pattern of which
depended on the data
. I had to change to a faster micro.....20MHz
80C196KC vs 16MHz, which solved my problem.
Cheers
Terry
