The way in which the inverter performs the frequency variation is called Pulse Width Modulation (PWM), the morally used acronym. We have seen that in practice it is a square wave organized by several variable pulses, but that, in general, competes for a sinusoid.
The current pulses are more like a sinusoid, and two transistors emitting pulses that will add up to half a current cycle. When the electromagnetic circuit of the motor reaches the PWM supply, it normally operates as if it were obtaining a normal sinusoidal supply.
In this way, the insulation suffers greatly from the pulsating variation of the voltage, at a frequency much greater than that of the sinusoid itself. To obtain the frequency and voltage variation, the frequency inverter does not amplify rigorously sinusoidal waves for both.
The power signal at the output of the frequency inverter is primarily a simulation of a sinusoid, not a real sinusoid, and for this we modify the values of the peculiarities of the similar circuit of the motor and the laws of electromagnetism in order to “deceive” the motor.