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What is the difference between a Variable Frequency Drive’s (VFD) fundamental frequency and the VFD’s carrier (switching) frequency?

A VFD’s fundamental frequency is the frequency of the output current, typically >0 to 400HZ for most VFD’s. This frequency determines the speed of the motor and is simulated by the drive’s higher carrier frequency output.

The VFD’s Carrier (Switching) frequency is the frequency of the PWM (Pulse Width Modulation) pulses, i.e. the frequency at which the VFD’s output transistors; usually IGBTs (Insulated Gate Bipolar Transistors), are switching. This typically ranges from 2 to 20 kHz. This high frequency PWM current output simulates a lower frequency sine wave and provides the drive’s variable fundamental frequency output.