Input EMI filter re-design in AC motor drives with active compensation of motor CM voltage

This paper deals with the design of the input EMI filter in an AC motor drive when the compensation of common mode emissions towards the motor is performed by an active filter. Both the drive and the active filter have been analyzed through an high frequency circuit model in order to identify the main propagation loops for CM disturbance. In particular the EMI emissions towards the grid are evaluated also in comparison with those generated in a configuration without the active filter. The accuracy of the model has been assessed by experimental measurements. Results show a reduction of CM EMI towards the grid in the lower frequency range of conducted emissions when the active filter is installed. This demonstrates that EMC requirements compliance of the drive can be achieved with a reduction in the size of the input EMI filter.