AC Drives vs. DC Drives: Which is Better?

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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.  

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