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AC drives explained

AC motors are used in a whole range of applications, from residential to industrial. But in order to do their jobs properly, these motors need to be driven, using what’s known as an AC drive.

What are AC drives?

An AC drive is a device that converts a fixed AC signal, like the one that comes out of your wall, into one that can be adjusted either via a potentiometer, or using a digital signal.

How do they work?

To do this work, a little bit of conversion has to first take place. First, the fixed AC signal is converted to DC using a device called a rectifier. Then it’s converted back into an AC signal of the voltage and frequency that the motor in question is designed to understand and cope with. Keeping the signal within the bounds of what’s acceptable is the main function of the drive, and matching the capability of the drive and the motor will play a considerable role in determining performance.

Most AC motors requires a three-phase AC voltage input. The speed at which the motor turns is a function of the frequency of the incoming signal.

What components make up an AC drive?

Within an AC drive you’ll find three discrete components. There’s the motor, which is sometimes a separate component, but which is often bundled into the drive device itself as an all-in-one solution. There’s the controller, which is what determines the speed at which the motor turns. Then there’s the operator section, which provides an interface via which a user can influence the controller.

Where might you find an AC drive?

AC drives are used wherever the speed of a motor needs to be precisely controlled. They’re usually employed in conjunction with sensors, which are arranged in such a way that the speed of the motor is adjusted constantly to maintain a desired result. For example, you might have a refrigeration unit which dials the speed up or down in order to keep things at the desired temperature.

You might also find an AC drive in a conveyor belt in a mining operation. They tend to be more efficient to run than many of the alternatives, and so they’re increasingly being installed wherever it’s practicable.

Benefits of AC drives

AC drives tend to be more energy-efficient than many of the older technologies that they’re replacing. This is so in part because of their ability to respond to fine adjustments. By tweaking flow rates on the fly, a more efficient system can be created. Moreover, the process as a whole can be easily changed whenever required. AC drives also tend to demand reduced current upon start-up, which minimises the stress placed on an entire system when it is coming to life.

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Alice Instone-Brewer

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