- Large dc motor are always three phase converters for their speed control.
- A three phase controlled converters feed power to the armature circuit for containing speeds below base speed.
- Another three phase controlled converter is inserted in the field circuit for getting speeds above base speed.
- The output frequency of three phase converter is higher than those single phase converter.
- Therefore, for reducing the armature current ripple, the inductor in a three phase dc drive is of lower value than that in a single phase dc drive.
- As the armature current is mostly continuous, the motor performance in 3 phase dc drives is superior to those in single phase dc drive.
The three phase dc drive, as in single phase dc drive, may be subdivided an under :