why for a 3 phase- high speed motors (50 krpm 2-pole or 4-pole) and high current (60-100 amps) we only go for a sine wave permanent magnet motors and we don't design a square wave motor? is it some sort of limitations with the inverter choice? is it only because of the higher harmonics and losses? if it is then can't we say the inverter losses to generate a PWM signal to feed the motor with sine-wave will cancel out the disadvantages of the square-wave motors?

 

That is a very high current, high RPM motor?
I think you will find that the outrunner type of 3ph motors found in miniature in RC and the larger Fisher & Paykel motor are all PWM controlled.
Although the voltage applied is non-sinusoidal, Due to the motor inductance the resultant current does not follow the voltage waveform but creates a constant mean level with sawtooth ripple.
BLDC motors are also controlled with a square wave PWM voltage.
Max.