The active filter drive technology previewed by Danfoss last year, has now entered production as, what the company claims in the first mass-produced low-harmonic drive. The technology is designed to eliminate harmonic disturbances on the mains supply by injecting currents that restore high-quality sinewave patterns.

Unlike other low-harmonic technologies whose performance depends on the stability of the grid and the load, and can affect the controlled motor, the Danfoss drives are claimed to regulate network and load conditions without affecting the motor. In particular, they will not increase stresses in the windings or shorten bearing lifetimes.

The drives operate in a similar way to noise-cancelling headphones. They measure current distortions and inject opposite currents of up several hundred amps opposite to cancel out the distortion.

The modular VLT Low Harmonic Drives, being produced in US, cover power ratings from 160–710kW. Some 80-90% of their components are standard drive components, reducing costs, improving reliability and making them easier to service, according to Danfoss.