Danfoss supplies a sine-wave filter to dampen the acousticmotor noise.The filter reduces the ramp-up time of the voltage, thepeak load voltage UPEAK and the ripple current ΔI to themotor, which means that current and voltage becomealmost sinusoidal. Consequently, the acoustic motor noiseis reduced to a minimum.The ripple current in the sine-wave filter coils also causessome noise. Solve the problem by integrating the filter in acabinet or similar.3.7.6 dU/dt FiltersDanfoss supplies dU/dt filters which are differential-mode,low-pass filters that reduce motor terminal phase-to-phasepeak voltages and reduce the rise time to a level thatlowers the stress on the insulation at the motor windings.This is especially an issue with short motor cables.Compared to sine-wave filters (see chapter 3.7.5 Sine-waveFilters), the dU/dt filters have a cut off frequency above theswitching frequency.3.7.7 Common-mode FiltersHigh-frequency common-mode cores (HF-CM cores) reduceelectromagnetic interference and eliminate bearingdamage by electrical discharge. They are special nanocrys-talline magnetic cores, which have superior filteringperformance compared to regular ferrite cores. The HF-CMcore acts like a common-mode inductor between phasesand ground.Installed around the 3 motor phases (U, V, W), thecommon mode filters reduce high-frequency common-mode currents. As a result, high-frequency electromagneticinterference from the motor cable is reduced.The number of cores required is depedent on motor cablelength and frequency converter voltage. Each kit consistsof 2 cores. Refer to Table 3.19 to determine the number ofcores required.Cable length1) Enclosure size[m] A and B C DT2/T4 T7 T2/T4 T7 T750 2 4 2 2 4100 4 4 2 4 4150 4 6 4 4 4300 4 6 4 4 6Table 3.19 Number of Cores1) Where longer cables are required, stack additional HF-CM cores.Install the HF-CM cores by passing the 3 motor phasecables (U, V, W) through each core, as shown inIllustration 3.30.PE U V W130BD839.10Illustration 3.30 HF-CM Core with Motor Phases3.7.8 Harmonic FiltersThe Danfoss AHF 005 and AHF 010 are advanced harmonicfilters, not to be compared with traditional harmonic trapfilters. The Danfoss harmonic filters have been speciallydesigned to match the Danfoss frequency converters.By connecting the Danfoss harmonic filters AHF 005 orAHF 010 in front of a Danfoss frequency converter, thetotal harmonic current distortion generated back to themains is reduced to 5% and 10%.System Integration Design GuideMG20N602 Danfoss A/S © 09/2014 All rights reserved. 713 3
