WOPCOM Blog: Water: Machine Motor Drive Control – Understanding the jargon!, by Ken Cupitt

When we buy a new machine we seldom ask about the drive of the electrical motors or the technology of the electrical control system but technology has improved the performance, plus reduced the energy costs in use, and helped to avoid the cause of future machine failures. We may be told our beautiful new machine has a micro processor control and because of this is more efficient but how is this possible?

Almost all of the electrical motors used on equipment in our industry use AC Motors and in the last thirty years these are now being controlled by a device referred to as an AC Drive, or a VFD. A variable-frequency drive (VFD), other names being adjustable-frequency drive (AFD), variable-voltage/variable frequency (VVVF) drive, variable speed drive (VSD), micro drive or inverter drive, as well as AC Drive and these are all types of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage. AC Drives are used in our industry in many applications ranging from small equipment to large complex systems. It is thought that about 25% of the world’s electrical energy is consumed by electric motors in industrial applications, which can be made more efficient when using these VFDs in drive load service, and these have been developed over the last four decades, with power electronics technology reducing both cost and size. With this has come improved performance through advances in semi-conductor switching devices, control techniques, control hardware and software.

All electrical motors consume electricity so need a corresponding amount of energy to provide the torque or speed needed. If the torque or speed is too high or low, mechanical controls, such as the VFD, are used to control the output. A motor’s speed should match exactly what is required by the process; otherwise the result is inefficiency with a lot of wasted energy. Not being able to control motors can mean a lot of energy gets wasted which isn’t good for any business and a way to control these motors, which not only saves energy, but improves productivity and reduces maintenance costs, is to use an inverter.

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