Variable Frequency Drives

Variable frequency drives (VFDs) are electronic devices that enable AC induction motors to operate at different speeds by controlling the power (voltage and frequency) supplied to the motor. This allows fixed-speed AC motors – which are the most common types used in industry – to better respond to variable or partial loads. As the use of VSDs reduces or eliminates the need for other load-response approaches – such as the use of throttles – they hold a significant potential to save energy and reduce operational costs in electrical motor driven applications.

The potential energy savings derived from reducing a motor’s power to manage its speed are based on the engineering laws that govern the relationship between flow, head and consumed power in relation to the shaft speed, which state:

  • change in flow is proportional to the change in shaft speed;
  • change in head (pressure) is proportional to the square of the change in shaft speed;
  • change in power consumed is proportional to the cube of the change in shaft speed (Motor Decisions Matter, 2012).

VFD systems are offered by many suppliers and are available worldwide, however they are rather costly. Consequently, their application should be considered for applications where load fluctuations are high and frequent and where systems are operated long hours (>2000 h/year).

Variable speed drives and adjustable speed drives are concepts serve the same function as VFDs, but they may also include devices that mechanically control the motor speed. 

Development Status Products

Variable Frequency DrivesCosts & Benefits

Parent Process: Core Motor System Components
Energy Savings Potential

Reducing the motor speed from 100% to 80% with the use of VSDs can reduce energy consumption by up to 50% (Carbon Trust, 2011., p. 5)

CO2 Emission Reduction Potential

Variable Frequency DrivesSchematic

Variable Frequency Drives Videos

Variable Frequency Drives Publications

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