An AC drive, also referred to as variable frequency drive (VFD), is a device used in various industrial equipment that’s used to control the speed of an electric motor.
AC drives are installed to enhance process control, reduce energy usage, and decrease mechanical stress on motor control applications.
In today’s article, we take a look at the mechanics of AC drives and the different types available.
How do AC drives work?
An AC drive controls the speed of an electric motor by changing the frequency of the electrical supply. In an AC motor, the connection between the three-phase voltage and the national electric grid creates a rotating magnetic field which is followed by the motor’s rotor.
The speed of the motor is controlled by the AC drive which converts the frequency of the network up to 300 Hz and above, meaning it is controlled in proportion to the frequency.
There are different components in an AC drive that makes this possible:
- Rectifier unit: Supplies the electrical network and can be unidirectional or bidirectional.
- DC circuit: Stores the electrical energy ready for use by the inverter.
- Inverter unit: Supplies energy from the rectifier to the motor and uses modulation techniques to create the required three-phase AC voltage output. Frequency can be adjusted depending on the process.
Types of AC drives
AC drives can be categorised based on the type of AC motor that is being used. There are three common types of AC motor: Induction, synchronous, sensorless vector, and servo drives.
Induction
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In this type of motor, the current is induced into the rotor windings without the requirement of a physical connection to the stator windings. This type of AC motor is adaptable to various environments and can provide considerable power and good speed control. Note that with these motors, there is typically a loss of exact speed tracking. There is often slip when this type of motor is used. |
Synchronous
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Synchronous motors function at a constant speed up to full load and are often used in applications that require an exact speed that must be maintained. In this type of motor, the rotor speed is equal to the speed of the stator’s rotating magnetic field and there is no slip. |
Sensorless vector drives
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This type of motor employs independent control of voltage and frequency and low-speed torque output, nearing that of DC motors. They offer good speed control and are sensorless, indicating that there is no feedback sensor involved such as an encoder or resolver. |
Servo motors
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Servo motors are permanent magnetic synchronous motors that offer low torque-inertia rations for high acceleration. They often utilise brushless commutation and hall effect sensors to provide feedback. |
Selecting the right AC motor drive
When it comes to examining the features of an AC motor drive, there are some important factors to consider.
First of all, look at the regeneration capabilities as the drive can act as both a motor and a generator in some conditions.
Secondly, be sure to check the programmability and configuration to ensure the AC drive aligns with your needs.
Additionally, check whether or not it offers an auto-restart feature as this will automatically resolve current overload and other common errors that can occur when using an AC drive.
Discover a range of AC drives with Preferred Spares
As one of the leading industrial automation equipment and spare parts suppliers in the Middle East, Preferred Spares offers a range of AC drives for various industrial applications. Whether you’re looking for an AC drive, variable speed drives, or an AC motor, you can find it all at Preferred Spares.
Delivering only the highest quality, most robust products, Preferred Spares supplies a range of AC drives and motors from the world’s leading manufacturers. Promising expedient delivery across the region and high quality service, you can trust Preferred Spares for all your industrial automation needs.
To find out more or to explore the range of AC motors and spare parts available, visit the Preferred Spares website today.
