Power Losses Evaluation in CM Active EMI Filters for Bearing Currents Suppression

This paper is focused on the analysis of the power losses in a common-mode (CM) active electromagnetic-interference filter for induction-motor drives. The studied filter works according to a feedforward voltage-sensing-voltage-compensating scheme; it performs the compensation of the CM voltage at the motor terminals. In this way, the shaft voltage is dramatically reduced and the resulting bearing currents are practically eliminated. The contributions to the total power losses associated to the active filter are assessed with reference to medium-power induction-motor drives with different rated powers and switching frequencies. The single terms of power losses due to each part of the active filter are accounted for, and their dependence on the motor-drive size is addressed. Furthermore, the influence of the active-filter losses on the drive efficiency is evaluated.