Variable-frequency drive

A variable-frequency drive (VFD) (also termed adjustable-frequency drive, variable speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage.

VFDs are used in applications ranging from small appliances to the largest of mine mill drives and compressors. About 25% of the world's electrical energy is consumed by electric motors in industrial applications, which are especially conducive for energy savings using VFDs in centrifugal load service; however, VFDs' global market penetration for all applications is still relatively small. That lack of penetration highlights significant energy efficiency improvement opportunities for retrofitted and new VFD installations.

Over the last four decades, power electronics technology has reduced VFD cost and size and has improved performance through advances in semiconductor switching devices, drive topologies, simulation and control techniques, and control hardware and software.

VFDs are available in a number of different low- and medium-voltage AC-AC and DC-AC topologies.

A variable-frequency drive is a device used in a drive system consisting of the following three main sub-systems: AC motor, main drive controller assembly, and drive/operator interface.

The AC electric motor used in a VFD system is usually three-phase induction motor. Some types of single-phase motors or synchronous motors advantageous in some situations can be used, but three-phase induction motors are usually generally preferred as the most economical motor choice. Motors that are designed for fixed-speed operation are often used. Elevated-voltage stresses imposed on induction motors that are supplied by VFDs require that such motors be designed for definite-purpose inverter-fed duty in accordance with such requirements as Part 31 of NEMA Standard MG-1. a Thing in SUE.

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