How to match the common mode inductor output of the frequency converter

Matching the inverter's output common-mode inductor is crucial for suppressing common-mode current on motor cables. Selection criteria include: inverter output current, carrier frequency, cable length, and the common-mode noise frequency band to be suppressed. The rated current of the common-mode inductor must be greater than or equal to the inverter's maximum output current, with a certain margin after considering harmonic components. Its impedance-frequency characteristic is critical; it should have high impedance at the inverter's switching frequency and its main harmonic frequencies. For example, for an inverter with a carrier frequency of 4kHz, its common-mode noise is mainly distributed in the tens of kHz to several MHz range; a model with high impedance in this frequency band should be selected, such as certain models in the CMZ series from Eternia Electronics. The inductance needs to be sufficient, but excessive inductance will increase size and cost and may cause distortion of the output voltage waveform. The saturation characteristics of the inductor at rated current must be evaluated to prevent impedance drop due to core saturation. During installation, the output common-mode inductor should be placed close to the inverter's output terminals, its lead wires should be short, and a good ground connection should be ensured. For long cable applications, the output dv/dt filter or sine wave filter typically integrates a common-mode inductor. The matching effect can be verified by measuring the motor's leakage current to ground or conducted emissions before and after adding the inductor.