AiVibeVariable Frequency Drive (VFD)
A variable frequency drive is a power electronic device that controls the speed and torque of an AC motor by converting the fixed-frequency mains supply into an output of adjustable frequency and voltage.
Most low-voltage VFDs rectify the incoming AC supply to a DC link and then use an inverter of IGBT switches with pulse-width modulation to synthesise a variable-frequency, variable-voltage output. Because the synchronous speed of an induction motor is proportional to supply frequency, changing the frequency changes the speed. Control modes range from simple voltage-to-frequency (V/f) control to sensorless vector and closed-loop vector control, which regulate torque more precisely.
VFDs are used on pumps, fans, compressors, conveyors, mixers, extruders and hoists. On centrifugal pumps and fans, reducing speed instead of throttling flow can save substantial energy, because the power drawn falls steeply as speed decreases. Drives also provide soft starting, controlled stopping and motor protection, and they connect to PLCs through hardwired signals or networks such as PROFINET, EtherNet/IP and Modbus.
Drives introduce harmonics into the supply and fast voltage edges at the motor, so installations may need line reactors, filters, shielded motor cables and attention to bearing currents and motor insulation. IEC 61800 is the series covering adjustable speed electrical power drive systems, with safety functions such as Safe Torque Off defined in IEC 61800-5-2. Parameter changes and installation must follow the drive manufacturer's documentation and be carried out by qualified personnel.
Key points
- Rectifier, DC link and PWM inverter produce variable frequency and voltage
- Induction motor speed follows the output frequency
- Control modes include V/f, sensorless vector and closed-loop vector
- Speed control of pumps and fans can save substantial energy
- IEC 61800 covers adjustable speed drives; IEC 61800-5-2 covers safety functions
Where AiVibe comes in
AiVibe designs and manufactures the AiAmbA AI Factory, whose edge devices and AI agents let people talk to PLC, CNC and robot controllers in plain language. Agents only propose changes, a trained operator confirms each one, and the AI Factory never replaces a machine's control or safety systems.
Related terms
- Safe Torque Off (STO)PLC & Industrial Control
- Servo Drive and Servo MotorPLC & Industrial Control
- PID ControllerPLC & Industrial Control
- Motion ControlPLC & Industrial Control
- ModbusPLC & Industrial Control
- PROFINETPLC & Industrial Control