How do EPS differential mode filtering and common mode filtering work together?

In EPS EMI filters, differential-mode filtering and common-mode filtering have distinct functions, working together to form complete protection. Differential-mode filtering primarily targets line-to-line (LN or DC+/-) noise, where the noise current is equal in magnitude and opposite in direction on both lines. Suppressing differential-mode noise mainly relies on X capacitors and differential-mode inductors (or the leakage inductance of common-mode inductors), providing a low-impedance parallel path or a high-impedance series barrier for differential-mode noise. Common-mode filtering targets noise between the line and ground, where the noise current is equal in magnitude and in the same direction on both lines. Suppressing common-mode noise mainly relies on common-mode inductors and Y capacitors. Common-mode inductors present high impedance to common-mode current, while Y capacitors provide a legitimate high-frequency return path to ground for common-mode current, preventing it from flowing to the power grid or load. During design, it is necessary to determine the frequency bands that need to be suppressed based on the measured noise spectrum and allocate the filter component parameters accordingly.