Variable Frequency Drives
VFDs control induction motor speed by changing frequency and voltage together.
A VFD rectifies the mains to a DC bus, then uses an IGBT inverter with PWM to create a variable-frequency, variable-voltage output.
V/f control keeps flux constant: = constant (e.g. 415 V / 50 Hz = 8.3 V/Hz). Vector control (FOC) controls torque and flux independently for servo-like performance.
Energy savings on centrifugal loads follow the affinity laws: flow ∝ speed, pressure ∝ speed², power ∝ speed³ — running a fan at 80 % speed needs only about 51 % power.
VFDs create harmonics and fast voltage edges; use proper cables, filters and earthing.
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