Variable-frequency drive

A variable-frequency drive (VFD, or adjustable-frequency drive, adjustable-speed drive, variable-speed drive, AC drive, micro drive, inverter drive, or drive) is a type of AC motor drive (system incorporating a motor) that controls speed and torque by varying the frequency of the input electricity. Depending on its topology, it controls the associated voltage or current variation.^[1]^[2]^[3]^[4]^[5]

VFDs are used in applications ranging from small appliances to large compressors.^[6] Systems using VFDs can be more efficient than hydraulic systems, such as in systems with pumps and damper control for fans.^[7]

Since the 1980s, 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 include low- and medium-voltage AC-AC and DC-AC topologies.

^ Campbell, Sylvester J. (1987). Solid-State AC Motor Controls. New York: Marcel Dekker, Inc. pp. 79–189. ISBN 978-0-8247-7728-9.
^ Jaeschke, Ralph L. (1978). Controlling Power Transmission Systems. Cleveland, OH: Penton/IPC. pp. 210–215. ISBN 978-1114762060.
^ Siskind, Charles S. (1963). Electrical Control Systems in Industry. New York: McGraw-Hill, Inc. p. 224. ISBN 978-0-07-057746-6.
^ NEMA Standards Publication (2007). Application Guide for AC Adjustable Speed Drive Systems. Rosslyn, VA USA: National Electrical Manufacturers Association. p. 4. Retrieved March 27, 2008.
^ Lockley, William; Paes, Richard (2014). What's New In Medium Voltage Drives (PDF). IEEE SAS & NCS 2014 PES/IAS Joint Chapter Technical Seminar. p. slide 91 of 132. Retrieved January 28, 2022. Adjustable Speed Drive System: An interconnected combination of equipment that provides a means of adjusting the speed of a mechanical load coupled to a motor., quote is per definition on p. 4 of NEMA Standards Publication ICS 7.2-2021.
^ "Medium Voltage Integrated Drive and Motor" (PDF). energy.gov – DoE.
^ "Energy efficiency makes a difference" (PDF). Archived from the original (PDF) on September 8, 2017. Retrieved May 1, 2017.

[Campbell-1] Campbell, Sylvester J. (1987). Solid-State AC Motor Controls. New York: Marcel Dekker, Inc. pp. 79–189. ISBN 978-0-8247-7728-9.

[Jaeschke-2] Jaeschke, Ralph L. (1978). Controlling Power Transmission Systems. Cleveland, OH: Penton/IPC. pp. 210–215. ISBN 978-1114762060.

[Siskind-3] Siskind, Charles S. (1963). Electrical Control Systems in Industry. New York: McGraw-Hill, Inc. p. 224. ISBN 978-0-07-057746-6.

[NEMA-Guide-4] NEMA Standards Publication (2007). Application Guide for AC Adjustable Speed Drive Systems. Rosslyn, VA USA: National Electrical Manufacturers Association. p. 4. Retrieved March 27, 2008.

[Lockley-2014-5] Lockley, William; Paes, Richard (2014). What's New In Medium Voltage Drives (PDF). IEEE SAS & NCS 2014 PES/IAS Joint Chapter Technical Seminar. p. slide 91 of 132. Retrieved January 28, 2022. Adjustable Speed Drive System: An interconnected combination of equipment that provides a means of adjusting the speed of a mechanical load coupled to a motor., quote is per definition on p. 4 of NEMA Standards Publication ICS 7.2-2021.

[6] "Medium Voltage Integrated Drive and Motor" (PDF). energy.gov – DoE.

[ABB-energy-7] "Energy efficiency makes a difference" (PDF). Archived from the original (PDF) on September 8, 2017. Retrieved May 1, 2017.

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