VFD Carrier Frequency: Balancing Motor Noise, Drive Heat and EMI

Carrier frequency, also called switching frequency, is the rate at which a variable frequency drive switches its output transistors to build the pulse-width-modulated voltage that runs the motor. It is usually set between 2 and 16 kHz, and the value you choose quietly trades motor noise against drive heat, cable stress and electrical interference.

What the carrier frequency actually is

A VFD does not send the motor a smooth sine wave. Its IGBTs switch the DC bus on and off thousands of times per second, and the width of those pulses averages out to the sine the motor needs. The carrier frequency is how often that switching happens. A higher carrier produces a smoother current waveform; a lower carrier produces a coarser one.

What you gain by raising it

• Quieter motor. At low carrier settings the switching tone sits where the ear is most sensitive, so the motor emits a whine or hum at the carrier frequency. Raise the carrier and the tone becomes much less noticeable.
• Smoother current, less motor heating. A cleaner waveform means fewer harmonics circulating in the windings, so the motor runs slightly cooler.

What it costs you

• Drive heating. Every switching event dissipates energy in the transistors. Double the carrier and you roughly double the switching losses, which is why drives derate their output current at high carrier settings.
• Insulation and cable stress. Faster, steeper voltage edges reflect along long motor cables and can nearly double the peak voltage at the motor terminals, stressing winding insulation. See insulation resistance testing for how that damage is caught.
• Bearing currents. High-frequency switching couples capacitively to the shaft and can discharge through the bearings, pitting the races over time.
• More EMI. Faster edges radiate more, so shielding and filtering matter more. Nuisance trips from heat or noise are stops too, and unplanned downtime logs show which drives repeat. This ties into wider power quality in manufacturing.

How to choose a setting

Start from the drive's default, often around 4 kHz, and change it only for a reason. Raise the carrier when audible motor noise is a problem in an occupied space.

Lower it when the drive is derating in a hot cabinet, when motor cables are long, or when insulation and bearing life matter more than noise. With long leads, add a dV/dt or sine-wave output filter rather than simply raising the carrier.

Keeping drives healthy over time

Carrier frequency is one of several drive settings that quietly shape reliability. When a drive that has run for years starts tripping, the fault codes tell the story: see ABB VFD fault codes. Logging every trip with its fault code turns those early warnings into a scheduled fix.

Fabrico logs each drive trip as a stop on connected machines, and a work order opens from a logged stop in one tap. Read how Fabrico tracks downtime to see it.

Fabrico is software for OEE, downtime tracking and maintenance. We do not sell parts or repair services.

Frequently Asked Questions

What is a typical VFD carrier frequency?

Most general-purpose drives default to around 4 kHz. Values from 2 to 16 kHz are common, with higher settings used where audible motor noise must be minimised.

Does a higher carrier frequency save energy?

Not usually. It slightly reduces harmonic losses in the motor but increases switching losses in the drive, so the net effect on total efficiency is small and often negative at high settings.

Why does my drive derate at a high carrier frequency?

Higher switching means more heat in the transistors, so the drive must reduce its continuous output current to stay within its thermal limit.

Can carrier frequency damage motor bearings?

High-frequency switching can drive small currents through the shaft that discharge across the bearings and pit the races. Shaft grounding rings and insulated bearings are the usual defences.