An adjustable speed drive (ASD), also referred to as a variable speed drive (VSD) or variable frequency drive (VFD), is an electronic device that controls the speed and torque of an AC motor by varying the frequency and voltage of the electrical power supplied to it. This enables precise motor control, improved process performance, and potential energy savings in a wide range of industrial applications.

An ASD converts incoming AC power to DC through rectification, then inverts it back to a controlled three-phase AC output at variable frequency and voltage. This output allows the connected motor to operate at the desired speed. Adjustable speed drives are commonly applied in pumps, fans, compressors, conveyors, and other variable-torque systems.