How to match the common mode inductor for industrial servo output?

Improper matching of the common-mode inductor in the servo output can lead to decreased filtering performance or even resonance. Correct matching requires consideration of motor cable parameters and interference spectrum. The matching steps at Yinte Electronics are as follows:

First, use an impedance analyzer to measure the common-mode impedance characteristics of the motor cable.

Then, select a CMZ or CML series common-mode inductor whose resonant frequency (determined by the inductance and parasitic capacitance) should avoid the main harmonics of the switching frequency. Typically, an inductance value of 51μH-200μH (e.g., CML4532A-510T) is chosen.

Next, calculate the possible LC resonant point formed by the inductor and cable parasitic capacitance, ensuring it is not in a sensitive frequency band (such as the encoder operating frequency).

Finally, verify through actual testing: after installing the inductor at the output, the common-mode voltage between the motor terminals and ground should be reduced by more than 60% without causing overvoltage breakdown risk.

A well-matched common-mode inductor can reduce radiated interference at the motor terminals by 10-15dB. It is also important to note that the inductor saturation current should be greater than 1.2 times the peak current of the motor.