What is AC Drive?
A.C drive is also known as Variable Frequency Drive (VFD), variable speed drive (VSD) or Adjustable speed drive (ASD).
AC drive (alternating current drive) converts AC supply to DC using rectifier-based converter circuits and switches back to DC from DC using an inverter to control the speed of electric motors, especially three-phase motors.
AC Supply → Converted to DC → Again Inverted to AC → Electric Motor.
What is DC Drive?
DC drive technology is efficient, dependable, low-cost, user-friendly, and relatively simple to implement. DC drives have numerous advantages over AC drives, particularly in regenerative and high-power applications. DC drives have become popular in industrial drive applications due to their ability to provide extremely precise control.
Also read: # What is DC Drive and How does it work?
Difference between Ac and DC Drives
| Characteristics | DC Drives | AC Drives |
|---|---|---|
| Description | DC drivers convert the input AC supply to DC using a rectifier-based converter circuit to operate DC motors. | AC drive converts AC supply to DC using rectifier-based converter circuits and switches back to DC from DC using an inverter to control the speed of electric motors, especially three-phase motors. |
| Supply | Run by DC Supply | Run by AC Supply |
| Breaking Mechanism | Breaking occurs when resistance is applied at rotor. | When the supply frequency changes, it breaks and accelerates |
| Self Start | Available | Not available |
| Application | Generally used for DC motors. | Generally used for AC motors. |
| Circuit Design | The circuit design of DC drives is not complicated due to single power conversion, i.e. converts AC to DC at once. | The circuit design of AC drives is a bit more complicated because of the inverter and converter that converts AC into DC and converts DC to AC. |
| Commutation | Because of commutation, they are more heavy and costly. | There is no commutation which makes AC Drives less bulky and inexpensive |
| Speed Control | Speed control is done by armature and field control. | Speed control is done by changing the supply frequency. |
| Speed Limitation | Speed is limited | Maximum speed is possible |
| Motor Speed (RPM) | Up to 2500 RPM | Up to 10,000 RPM |
| Speed Torque | Can achieve easily | complex to adjust the speed torque curves. |
| Starting Torque | High | Low |
| Inverter | Have converter and chopper circuits and it doesn’t need an inverter. | Have both inverter and converter |
| Rectification | Rectification circuit is needed | No need of rectification circuit |
| Transformer | Transformer is needed at voltage higher than 100V. | Can connect directly to main supply (transformer) |
| Power Usage | Less power usage compared to DC | High power usage compared to AC |
| Noise | Less noisy | Very high noisy |
| Dynamic Response | Low | High |
| Maintenance | Frequent and more | Less |
| Cost | Less expensive | Vey expensive |
| Harmonics | Do not produce harmonics | Converters produce harmonics on supply and load |
| Battery Operation | Run directly through batteries | Need an extra circuit to run in batteries |
| Brushless Life | Low (about 3000 hours) | High (about 10,000 hours) |