With winding rotor induction motors it is acceptable to obtain any speed from zero to approximately the synchronism speed, by modifying a simple resistance attached to the winding of the rotor, and which does not imply heating thereof, since losses in are external to the motor. Another possibility of speed change in the induction motors v belts is made by the frequency inverter, which allows the control of the alternating current motor by varying the frequency, but also realizes the variation of the output voltage so that the V / F characteristic is respected ( Voltage / Frequency) of the motor.

The coiled rotor induction motor can be used as a frequency conversion device when its rotor is activated at a given speed and the electromotive force is withdrawn through the collector rings, even in DC motors, the speed may be sufficient by the insertion of a rheostat in the field circuit, to provide flow adjustments. A method of regulating the speed of the alternating current motors, which allows to obtain in the axis a speed that can go from zero to twice the synchronous speed, is by the known system of the rotor with switch, by means of offsets of the brushes.