You might want to consider that a induction motor that is driven acts
as a induction generator. Jim Pentagrid has posted some very accurate
information about induction generators. To summarize, they are very
load sensitive if they are used as a stand alone generator. But if
they are connected to the power grid, they work very well.

So you can make a motor generator using a single phase motor driving a
three phase motor which has one phase connected to the same single
phase that drives the single phase motor. Nota Bene In order to
actually be driving the three phase motor, you have to drive it faster
than the rpm that it would run at when running on single phase as a
idler. The way to do this is with a belt drive. One pulley should be
a variable pulley. So one can measure the current drawn by the single
phase motor and adjust the pulley so the single phase motor draws its
nameplate current or somewhat less.

This is the way to make a phase converter for driving something as a
surface grinder that is sensitive to variations in torque.

I made one like this some twenty years ago to run a centerless sander.
Worked slick. The single phase motor worked as a pony motor to start
the three phase motor and then drove the three phase motor to produce a
better three phase than most rotary three phase converters.

Dan

Robert Swinney wrote:
What Grant said . . . a single phase motor driving a generator would, in
fact, be a motor/generator -- but -- the 3 phase generator portion of the
combination would have to be an alternator; a machine with a stationery set
of coils (stator) and a revolving magnetic field set of coils, or vice
versa. The field would either have to be excited by direct current (DC) or
be made up of permanent magnets. Large steam driven turbo-alternators are
an example. Those are synchronous machines, whereby the speed of rotation
determines the output frequency; their magnetic fields are generally excited
by DC generators of 110 volts, sometimes 220, and their may be other DC
voltages for excitation.

Contrast this to a rotary phase converter. The type RPC we are familiar
with is basically 2 three-phase motors running on single-phase current with
their 3rd legs tied together. The motors are not operated in parallel.
They may run with or without capacitor augmentation which aids in supplying
phased current to the 3rd leg of each motor. In a manner of speaking each
motor is a sort of rotating transformer which is responsible for energizing
the 3rd leg or "manufactured phase". The idler motor, viewed as a source
( not a strictly accurate analogy) has to be larger than the load motor in
order to keep the 3rd leg "generated" voltage from sagging down.
Capacitance from the single-phase line to the 3rd leg(s) lowers impedance in
those paths and may be thought of as forming a very broadly tuned series
resonance circuit. Current flow in a RPC is quite complex and does not
readily yield itself to mathematical modeling..

Bob Swinney