Three phase dc drives

  • 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.

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