Difference between AC Drives and DC Drives
The AC drives operate with AC signal or voltage, for instance, 1-phase or 3-phase AC voltages whereas DC drives operate with DC signal or voltage, for instance, DC supplies, and Batteries.
Generally, a DC drive changes an Alternating Current (AC) into Direct Current (DC) using a converter (Rectifier) to operate a DC motor while the AC drive changes the input AC current to DC using converter (Rectifier) and then changes this DC to AC, using an inverter, to operate the motor.
The key differences between AC and DC Drive are discussed in this article on the basis of real-world factors such as supply source, maintenance, uses, breaking mechanism, power & control circuitry, size & weight, commutation process, speed control & limit, harmonic distortion, speed regulation, starting torque, response to dynamics, noise, power consumption, brushes life, and application.The following table explains the key Differences between AC Drives and DC Drives
| Characteristics | AC Drives | DC Drives |
|---|
| Supply | Run by AC supply | Run by DC supply |
| Maintenance | Requires less maintenance. | Requires comparatively more and frequent maintenance. |
| Use/ Application | Are generally used for AC motors. | Are used for DC motors normally |
Rectifier
| There is no need of rectifier circuit | Rectifying circuit is necessary |
| Speed Control | Sped control is achieved by changing the frequency | Speed control is achieved by armature and field control |
| Cost | In AC Drives, motors are less expensive especially squirrel cage motors. | In DC Drives, motors are significantly expensive. |
| Speed limit | There is no upper limit for speed. | Speed is limited because of commutation process |
| speed | Can reach up to 10000 RPM | Can reach up to 2500 RPM |
| Starting torque | Do not produce high starting torque | Produces high starting torque |
| Battery use | Cannot be run directly by batteries without using extra circuitry | Can be run directly through batteries without adding an extra components |
| Noise | Operation is noisy which is highly unfavorable in certain applications | They are not noisy as compared to AC Drives |
| Power consumption | Consume less power | Consume more power |
| Circuit complexity | More complex as it involves inverter (DC → AC) and converter (AC → DC) | Less complex because of single power conversion process from AC to DC |
| Brushes life | Very high (~10000h) | Low (~3000h) |
Conclusion
Although the DC drives are quite renowned for offering high starting torque, bearing simplified circuitry and are effective with constant speed applications, they are believed to have a lot of problems because of commutation process and brushes in the DC Motors which require periodic and extensive maintenance. On the other side, AC drives are quite energy efficient and can manage abrupt speed changes very well. They frequently have numerous programmable parameters for protections
