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motors and squarish waves

D

David Lesher

Jan 1, 1970
0
Take an induction motor. Feed it crappy AC, maybe
spiky, maybe square-wavish.

Will it care? One side says the inductance will
limit the higher frequency current. Another PoV
is the inter-winding capacitance will increase the
current, and thus the I^R losses.

What saith the s.e.d wisdom?
 
J

James Arthur

Jan 1, 1970
0
David said:
Take an induction motor. Feed it crappy AC, maybe
spiky, maybe square-wavish.

Will it care? One side says the inductance will
limit the higher frequency current. Another PoV
is the inter-winding capacitance will increase the
current, and thus the I^R losses.

What saith the s.e.d wisdom?

Stepper motors don't much care. Chopped drives commonly feed
steppers ~20-80 volt rectangular waveforms.

With typical 20KHz chopping you get a few uS feedthru pulse
from the inter-winding capacitances, and hysteresis loss in
the iron--lossy if you switch the flux too often--but all-in-
all very workable.

Cheers,
James Arthur
 
T

Tim Williams

Jan 1, 1970
0
No, that's the myth. Deep down, they're all PWMed. ;-)

Tim
 
R

Rich Grise

Jan 1, 1970
0
Take an induction motor. Feed it crappy AC, maybe
spiky, maybe square-wavish.

Will it care? One side says the inductance will
limit the higher frequency current. Another PoV
is the inter-winding capacitance will increase the
current, and thus the I^R losses.

What saith the s.e.d wisdom?

I've done PWM (rectangular waves) with a PMDC motor, and it
worked like a champ. I didn't bother to look at the waveform,
because the purpose of the device was a motor that maintained
torque down to 0 RPM, which it did, so I shipped it. :)

Cheers!
Rich
 
R

Rich Grise

Jan 1, 1970
0
It seems that no one here has got real data about AC induction motors.

Are there any good books on the design of AC induction motors and their
controls ?
Oopps! Missed the "induction" part.

Then again, one time I was working with a "Modified Sine" inverter, which
produced a string of positive and negative pulses, PWM'd to average out
to 120 RMS. They did it the lazy man's way - two output transformers
with their secondaries in series; they just drove them with two
overlapping square waves.

It ran a bench grinder OK, but weighed almost 100 pounds and cost a
fortune.

Cheers!
Rich
 
D

David Lesher

Jan 1, 1970
0
It seems that no one here has got real data about AC induction motors.
Are there any good books on the design of AC induction motors and their
controls ?

I took two quarters worth of the topic many years ago. It was a senior
level course; maybe EE 412.

It, of course, only touched the highlights.
 
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