This is just some observations.
I haven’t used an inverter but I used to have a 415V phase converter, if I needed one I would have an inverter.
I used to work in the Machine tool industry and the Motors that we used on our CNC machines were much bigger HP than those on conventional machines, this is because the power advantage of a mechanical speed reduction is lost.
For example a 1HP motor with a 4 to 1 mechanical speed reduction would give 4HP at the output. (losses not considered)
With electronic speed control a 1HP motor running at ¼ speed would have an output of less than 1HP taking internal losses into consideration.
See Phil Procter’s post above regarding motor speeds and cooling.
You would need to avoid running the motor too slow, a Pulley change might have to be considered to keep the speed up and the motor cool.
Someone with a two speed motor would be able to run their motor on the low speed at double the rated speed, it is better running fast than slow.
The motors that we used on our CNC machines had an independent motor driven cooling Fan allowing the main motor to have a wider speed range.
I would be interested to hear if anyone using inverters has overheating or lack of power at low motor speeds?
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