DC Motor Drives

The introduction of power electronics greatly improved the performance of DC motor drives, enabling them to overcome the inherent limitations of electromechanical drives used in traction vehicles, that is, low efficiency and torque ripple during the start‐up phase. The motors deliver their nominal power in the connection that provides higher voltage to the terminals, that is, normally at the nominal voltage. In no‐load operation of the motor, that is, with no induced current flux, it is necessary to separate the armature circuit of the motor field winding and power the latter with current. The speed of the rotor can be varied by varying the power supply voltage, varying the flux by acting on the mmf field, produce an additional voltage drop by a rheostat in series with the armature circuit. Most suitable forms of magnetization characteristics of the motor can be obtained with an appropriate rating of the magnetic circuit of the inductor.