VFD Selection Guide: Match Load Characteristics

VFD selection is a critical step in industrial drive system design. Improper selection may lead to unstable operation or energy waste. This article provides a practical selection methodology.\n\n1. Identify Load Type\n- Constant torque loads (conveyors, mixers): Require rated torque at low speed; vector control recommended\n- Variable torque loads (fans, pumps): Torque proportional to speed squared; V/F control sufficient\n- Constant power loads (winders, machine spindles): Wide speed range needed; closed-loop vector recommended\n\n2. Determine Speed Range\n- Speed ratio within 1:10: V/F control is economical\n- Speed ratio 1:10-1:100: Open-loop vector control\n- Speed ratio exceeding 1:100 or zero-speed full torque: Closed-loop vector + encoder feedback\n\n3. Control Precision Requirements\n- Speed accuracy within ±0.5%: V/F control sufficient\n- Speed accuracy ±0.1%: Vector control required\n- Position control needs: Servo system recommended instead of VFD\n\n4. Capacity Selection Principles\n- Fan/pump loads: VFD capacity = motor capacity × 1.1\n-\n- Constant torque loads: VFD capacity = motor capacity × 1.2-1.5\n- Frequent start-stop or shock loads: Select one size larger