How to control differential mode interference at the DC input of an EPS power supply?

The differential-mode interference at the DC input of the EPS mainly originates from the switching frequency harmonic current of the downstream inverter. The key to control this is the use of a differential-mode filter. An X capacitor is connected in parallel between the positive and negative DC input buses to provide a low-impedance path for high-frequency differential-mode current. The selection of the X capacitor value requires a trade-off between high-frequency attenuation and system power-on inrush current. Furthermore, the impedance of the differential-mode path can be increased by utilizing the leakage inductance of the input common-mode inductor or by adding an additional differential-mode inductor in series. In terms of layout, the loop distance from the DC bus capacitor to the inverter bridge should be minimized to reduce loop parasitic inductance, thereby reducing the ringing amplitude of the differential-mode voltage. For high-frequency noise, low-ESL thin-film X capacitors can be used for absorption, ensuring the filter remains effective at high frequencies.