How to coordinate the input and output filters of a motion controller MC?

The input and output filters of a motion controller (MC) must work together to achieve system-level EMC performance. Input filtering, located at the power or signal input, primarily protects against external interference and internal noise. Its design focuses on high insertion loss and safety requirements, such as using filters with common-mode inductors. Output filtering, located at the drive or signal output, primarily suppresses noise generated by the controller itself, such as high-order harmonics in PWM outputs. Its design must consider load characteristics and signal integrity, such as using LC filtering.

When working together, the impedances of the two filters should be mismatched; that is, the input filter presents a high output impedance, and the output filter presents a low input impedance, to enhance overall attenuation. Note that the large capacitor in the output filter may affect the stability of the input filter; simulation analysis should be used. System-level conducted emission testing should be conducted to observe the noise spectrum of the input and output ports when operating individually and simultaneously, and the filtering parameters should be optimized. For multi-axis systems, the output filters for each axis should be designed independently to avoid mutual interference.