Full definition
Power electronics device controlling AC motor speed by converting fixed-frequency mains power (50/60 Hz) to variable frequency and voltage output. Operating principle: rectifier (AC→DC) → DC bus → inverter (DC→variable AC via PWM). Enables precise speed control from near-zero to above base speed, soft starting (eliminating mechanical stress and inrush current, typically limiting to 1.5x FLA vs 6-8x DOL), energy savings of 20-50% on variable-torque loads (fans, pumps per affinity laws), and dynamic braking. Key specifications: power rating (kW/HP), voltage (230V/460V/600V), overload capacity (110-150% for 60s), carrier frequency (2-16 kHz), communication protocols (Modbus, Profinet, EtherNet/IP). Brands: ABB ACS series, Siemens SINAMICS, Allen-Bradley PowerFlex, Yaskawa GA700, Danfoss VLT, WEG CFW. Per IEC 61800. Adding a VFD to an existing belt drive may require an inverter-duty motor or output reactor.