How does a Variable Frequency Drive (VFD) control motor speed?

A VFD converts fixed-frequency AC to variable-frequency AC to control motor speed. Three stages: rectifier (converts AC to DC), DC link (capacitor for filtering), and inverter (converts DC to variable-frequency AC using PWM). Motor speed is proportional to frequency (N = 120f/P). V/f ratio is kept constant to maintain flux and torque capability. Modern VFDs include advanced control algorithms (vector control, direct torque control) for high-performance applications like robotics and machine tools.