The Difference Between AC and DC Drives.

DC Drive:
The Dc drive converts alternating current into Direct current
By means of Full Wave Bridge Rectifier which used Silicon Controlled Rectifier(SCR).
In full Wave Bridge Rectifier we used two SCR in each of three phase supply.
Applying low voltage to the gates the SCR turns on.
Applying the voltage to the Gate at a different angle of the input phase, the output current varies, by controlling out put field current we control the speed of DC Motor. We used Encoders and tachometer as a feedback for accurate control of speed.

AC Drives:
In AC Drives we change the AC voltage to DC by Means of SCR and then again convert DC to AC again by Means of IGBT Module. When we change the DC to AC current we use a Carrier frequency of 2KHZ to 200KHZ, so o/p current changes to many times.
By changing V/F Ratio we change the AC motor Speed accurately. We use Encoders for speed Feedback.

Comparison:
Both AC and DC drive have their own advantage and disadvantage.
Main difference is that DC motor with Commutator and carbon brushes need regular maintenance.
Ac motor that is Induction Motor have no such maintenance.
DC drive used where high Starting torque needed and run with constant speed and it is very simple.

AC Drives are energy efficient and can handle massive speed changes.

To Be Continued.