An electronic drive that controls motor speed and torque by varying the frequency and voltage of the power supply to the traction motor.
Full Definition
A variable frequency drive (VFD), also known as an inverter drive or VVVF drive (variable voltage variable frequency), is the primary power control device for modern AC traction elevator motors. It converts the fixed-frequency mains supply to a variable-frequency, variable-voltage output, allowing precise speed control throughout the acceleration, constant speed, and deceleration phases of each trip. VFDs enable smooth, accurate levelling, reduced mechanical stress, and significant energy savings compared to older rheostatic or two-speed control methods. Regenerative VFDs feed braking energy back to the grid. EN 81-20 requires that the drive operate safely under all fault conditions including drive failure.
