The 3-phase motor pictured above is for commercial use, but in your home, AC motors
are used as well. A vacuum cleaner uses an AC motor to clean the carpet; a blender uses
an AC motor to process food; and the clothes dryer uses an AC motor to dry clothes. In
each of these examples, how is the AC motor controlled?
When controlling motors in the home we control them by applying AC power, and
removing it, usually through a switch. Obviously when power, 120 or 240 VAC, is applied to
the motor it runs. With no power, the motor stops.
With the use of a Variable Frequency Drive (VFD) not only can the AC motor be
started and stopped as in the home, but more sophisticated controls are accomplished. A
VFD can send a modulating signal to the motor, which allows a variety of speeds to be
delivered not just an ON/OFF signal. This variety of speeds can be used to match the motor
to a particular task. There are a number of functions that the VFD accomplishes with
commercial 3-phase AC motors, which are covered in the pages that follow.
Motors in the home are almost always single-phase motors which require additional
electric parts to rotate the magnetic field. Because of these extra parts, single-phase motorsdo NOT operate correctly with a VFD.