A problem encountered in AC motors that use frequency converters for speed control is that they eventually generate reactive power and need capacitor banks to compensate for this energy being dispensed to the power grid, and even then they will only solve around 90% of the problem. In the case of DC motors this does not happen, because the speed can be regulated by the insertion of a rheostat in the field circuit, to provide correct flow.
It is preferable to use a DC motor 4035 163 8 which will not generate reactive power in relation to the total rated power of the motor. This gives the equipment extra security even if it has to use higher powers in some unforeseen circumstances.
The speed control of the alternating current motors allows the speed to be obtained from the zero axis up to twice the synchronous speed, by the known rotor system with the switch, by means of the brush offsets. In an induction motor, the speed of rotation is different from the speed of synchronism. This fact is due to the existence of a speed difference between the rotor and the rotating field of the stator. This difference is called slipping.