While advancements in technology really have made AC drives
competitive, which is "better" depends on your application.
The table below lists the advantages of both types.
| AC Drive Advantages |
DC Drive Advantages |
| Use conventional, low cost, 3-phase AC induction
motors for most applications. |
Less complicated due to single-power conversion
(AC to DC only). |
| AC motors require very little maintenance and are preferred for applications where the motor is mounted in an area
not easily reached for servicing or replacement. |
Often less expensive for most horsepower ratings. |
| AC motors are smaller, lighter, more commonly
available, and less expensive than DC motors. |
DC motors have traditionally been adjustable-speed
machines and a wide range of options have evolved for this purpose |
| AC motors work better in high-speed operation
(over 2500 rpm) since there are no brushes nor commutators. |
Cooling blowers and inlet air flanges provide
cooling air for a wide speed range at constant torque. |
| Wet, corrosive or explosive operating environments
require special motor enclosures. Special AC motor enclosure types
are more common and cost less. |
Availability of accessory-mounting flanges and kits for mounting feedback tachometers and encoders. |
| Multiple motors in a system can operate simultaneously
at a common frequency/speed. |
DC regenerative drives are available for applications
requiring continuous regeneration for overhauling loads. AC drives
with this capability would be more complex and expensive. |
| It is advantageous to use an existing constant-speed
AC motor already mounted and wired on a machine. |
If done properly, brush and commutator maintenance
is minimal. |
| Lack of commutators and brushes are important
when the application load varies greatly and light loads are encountered
for prolonged periods. DC motor commutators and brushes can wear rapidly
under this condition. |
DC motors can provide starting and accelerating
torques in excess of 400% of rated. |
| Low-cost electronic motor reversing. |
Some AC drives may be noisy which is undesirable
in some applications. |
| A back up (constant speed) is available if the
controller fails. |
|