Advantages of DC Motors

  The greatest advantage of DC motors may be speed control.Since speed is directly proportional to armature voltage and inversely proportional to the magnetic flux produced by the poles, adjusting the armature voltage and/or the field current will change the rotor speed.
Today, adjustable frequency drives can provide precise speed control for AC motors, but they do so at the expense of power quality, as the solid-state switching devices in the drives produce a rich harmonic spectrum.
The DC motor has no adverse effects on power quality.

Power supply, initial cost, and maintenance requirements are the negatives associated with DC motors
Rectificationmust be provided for any DC motors supplied from the grid. It can also cause power quality problems.
The construction of a DC motor is considerably more complicated and expensive than that of an AC motor, primarily due   to the commutator, brushes, and armature windings.
An induction motor requires no commutator or brushes,and most use cast squirrel-cage rotor bars instead of true windings —two huge simplifications.