On the contrary, when the feed-forward current action is
added, a significant reduction of the CM current frequency content
ranging between 20 and 750 kHz is achieved, thus improving
the filter performance also in terms of EMI reduction. This
result is consistent with the theoretical analysis of the active
filter with and without the CM current estimator expressed by
the comparison shown in Fig. 6. In order to give a quantitative
evaluation of such an EMI reduction, a comparison of the square
sum of the CM current harmonic amplitudes in the two considered
filter configurations referred to the CM current without any
filter is given in Table VII. In particular, the following quantity
has been evaluated in the two filter configurations: