Table of Contents
Drives
A drive is an electrical or electronic device used to control the speed and motion of electrical machines such as motors robots etc. The device used for motor speed control is an electrical drive. They are constant and variable speed controllers widely used in industrial automation.
Types of Drives
There are mainly two basic types of electric drives as follows:
- AC Drives
- DC Drives
AC Drives
AC drives (Alternating Current Drives) convert the AC supply to the DC using converter circuits based on a rectifier. It inverts it back to the AC from a DC sing inverter to control the speed of electric motors, especially three-phase motors. AC Drive is also known as VFD (Variable Frequency Drive), VSD (Variable Speed Drive), or ASD (Adjustable Speed Drive). These are classified based on the type of AC motor being used. The most common types include
- Induction
- Synchronous
DC Drives
A DC drive (Direct Current Drive) is a DC motor speed control system that converts the input AC supply to the DC using a converter circuit based on a rectifier (Diodes and Thyristors) to control the speed of DC motors.
There are two types of DC Drives:
- Analog DC Drives
- Digital DC Drives
Comparison Between AC Drives and DC Drives
| Sr no. | Characteristics | AC Drives | DC Drives |
|---|---|---|---|
| 1. | Control | AC drives control AC output from AC input | DC drives control DC output from AC input |
| 2. | Maintenance | Less | More and Frequent |
| 3. | Self Start | Self-starting | Speed control is done by changing the supply frequency. |
| 4. | Speed Control | AC drives are spark-free and can be used in wet environments. | Speed control is done by armature and field control. |
| 5. | Spark | AC drives have both an inverter and a converter | AC drives consume less power as compared to DC drives |
| 6. | Motor speed in RPM | Up to 10k RPM | Up to 2.5k RPM |
| 7. | Speed torque | AC drives consume less power as compared to DC drives | It can be achieved easily. |
| 8. | Inverter/ Converter | The operation of AC drives is highly noisy | DC drives have converter and chopper circuits. |
| 9. | Noise | The operation of AC drives is highly noisy | AC drives consume less power as compared to DC drives |
| 10. | Power usage | No need for rectification of the circuit | DC drives consume more power as compared to AC drives |
| 11. | Starting Torque | High | Low |
| 12. | Rectification | Rectification circuit is a must | DC drives can not be used in wet areas due to generated sparks in the burses. |
| 13. | Spark | AC drives are spark-free and can be used in wet environments. | AC drives run by AC power supply i.e. Single phase and three-phase AC voltages. |
| 14. | Main supply and Voltage | The converter used in DC drives doesn’t generate harmonics. | DC drives run by DC power supply i.e. Batteries and supplies sources DC voltages. |
| 15. | Harmonics | The inverter used in AC drives produces harmonics on both sides i.e. Supply and Voltage. | Converter used in DC drives doesn’t generate harmonics. |
Frequently Asked Questions (FAQs)
Define AC drive?
An AC drive is a device that is used to control the speed of an electric motor. The speed is controlled by changing the frequency of the electrical supply to the motor.
Name the types of AC drives?
There are two types of AC drives:
1. Induction motor drives
2. Synchronous motor drivesWhat are the basic elements of an electric drive?
The basic elements of an electric drive are:
1. Electric Motor
2. Control system
3. Power supplyWhat are the advantages of AC drive over DC drive?
The various advantages of A.C drives are:
1. A.C motors require less maintenance than D.C motors
2. The cost of an a.c motor is less as compared to equivalent d.c motors.What are the disadvantages of AC drives over DC drives?
The various disadvantages of a.c drives are:
1. AC drives are more complex and expensive as compared to DC drives.
2. AC drives generate harmonic distortion in the electrical supply.
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