In the case of winding rotor induction motors it is permissible to achieve any speed, from zero to close to the synchronizing speed, depending on the variation of a simple resistance attached to the rotor winding, and that it will not generate a heating of it, considering that resistance losses occur independently of the motor. In DC motors, the speed can be adjusted as required by inserting a rheostat device into the field circuit so that adjustments can be made to the flow.
Another method of regulating the speed of the alternating current motors, which ensures that the speed of the shaft is from zero to twice the synchronous speed, is made by the rotor system with a switch, by means of the brush off. Browning 2B5V80
Another possibility of change of speed in the induction motors can be achieved through the frequency inverter, which will ensure the control of the AC motor can modify the frequency, as well as also realize the change of the output voltage to be respected the characteristic of the motor voltage and frequency.