industrial//industrial automation//VFD

A **Variable Frequency Drive** controls the speed and torque of an AC motor by changing the frequency and voltage it feeds. In a machine the chain is sensors, then the PLC, then the VFD, then the motor: the PLC decides what should happen, the drive solves the electrical control of the motor.

A Variable Frequency Drive controls the speed and torque of an AC motor by changing the frequency and voltage it feeds. In a machine the chain is sensors, then the PLC, then the VFD, then the motor: the PLC decides what should happen, the drive solves the electrical control of the motor.

A PLC output rarely powers a motor directly. It commands the drive with a setpoint (speed, torque, start, stop), over a fieldbus or industrial Ethernet such as PROFINET, and the drive closes its own fast current and speed loops inside.

Drives are sold by the big automation vendors (ABB, Siemens, Rockwell, Schneider) and are one of the components a system integrator has to make talk to a PLC of another brand.

Beyond speed, a modern drive is a data source: current, torque, temperature, energy, fault codes, all readable as tags for condition monitoring (telemetry).