A Variable Frequency Drive (VFD), also known as a VVVF (Variable Voltage Variable Frequency) inverter or AC drive, is an electronic power control device that regulates the speed of the traction machine motor by varying the frequency and voltage of the electrical supply. VFDs enable smooth, stepless acceleration and deceleration of the elevator car, precise floor levelling, reduced starting current, significant energy savings, and regenerative energy return to the grid during downward travel with load. VFDs are standard in all modern traction elevator installations.