How to select an input EMI filter for a frequency converter

Selecting an input EMI filter for a frequency converter requires consideration of rated current, voltage, the noise frequency band to be attenuated, and installation conditions. First, determine the filter's rated current, which must be greater than the converter's maximum input current with a margin of approximately 1.2-1.5 times. The rated voltage must match the mains voltage. A key parameter is insertion loss; based on conducted emission test results with the converter unfiltered, select a model with sufficient insertion loss in the out-of-range frequency band. For frequency converters, both low-frequency differential-mode noise and common-mode noise across the entire frequency band need suppression; therefore, a filter with good differential-mode and common-mode rejection performance must be selected.

The CMZ series of frequency converter-specific filters from Eintrasys typically include large common-mode inductors and X/Y capacitors. When selecting a filter, it's also necessary to consider whether the leakage current meets safety regulations, especially in medical or special applications. During installation, the filter should be placed as close as possible to the converter's power input, and its metal casing must have a low-impedance connection to the converter chassis. Input and output cables should be routed separately to avoid coupling. For high-power frequency converters, an external filter cabinet may be required. Providing the inverter's switching frequency and preliminary test data to the filter supplier helps obtain more accurate selection recommendations.