There is no difference between a Variable Frequency Drive, Frequency Inverter, AC Drive and Variable Speed Drive. Variable Frequency Drive (VFD) can also be called AC drive, adjustable frequency drive, variable speed drive (VSD) and variable frequency inverter (VFI). Whatever the name, VFD is a type of motor controller that drives and controls an electric motor. The VFD controls the motor speed and torque to meet the application’s requirements by varying the frequency and voltage supply.
Even though the drive controls the frequency and voltage of power supplied to the motor, we often refer to this as speed control, since the result is an adjustment of motor speed.