Inverter duty motor speed limitation ?

Answer 1

Your question isn't clear.

I suspect that what you mean is "how low can I go before I can't do what I want to with the motor".

Depending on the inverter manufacturer, a typical limit is around 7 hertz. This is because reducing the frequency much lower will cause feedback issues and overheating (due to harmonics) in the drive. Also possible is the cycling frequency of the thyristors.

Most applications will prefer low-end frequencies in excess of 12 hertz - to avoid possible tuning/torsional amplification with the structure to which the motor is mounted. No sense trying to run right on a structural resonance point!

Pracitacally speaking, there's also an upper limit on frequency as well, usually imposed by the motor design. Often, this is approximately at 2.2 times line frequency (133 hertz for 60 hertz systems, 110 hertz for 50 hertz systems).

Answer 2

to control the motor speeed change the duty cycle of the applied voltage ,, this is called PWM ,,,, as on time increases the speed increases and vice versa,, for low freq. operations u may may use a heavy capacitor which can reduce transients