VFD – Variable Frequency Drive
Variable Frequency Drives
VFD’s are typically used to control the speed and torque of an electric motor. The cost of VFD’s has dropped significantly over the years thanks to lower cost for electronics, and more advanced processing, as well as higher demand with rising energy costs.
A modern VFD is a digitally controlled high frequency switching device. A microprocessor continuously measures and adjusts the current going to the motor – many thousand times per second – which results in precise control of direction, speed and torque. Typically these VFD’s have some kind of communications port that allows other equipment to control it, and also receive data on power use and actual speed.
Benefits – Energy Saving
Many fixed-speed motor load applications that are supplied direct from AC line power can save energy when they are operated at variable-speed, by means of VFD. Such energy cost savings are especially pronounced in variable-torque centrifugal fan and pump applications, where the loads’ torque and power vary with the square and cube, respectively, of the speed. This change gives a large power reduction compared to fixed-speed operation for a relatively small reduction in speed. For example, at 63% speed a motor load consumes only 25% of its full speed power. This is in accordance with affinity laws that define the relationship between various centrifugal load variables.