Does impedance mismatch in the differential-mode filter of the BMS control board reduce the interference suppression effect?

Impedance mismatch in differential-mode filters significantly reduces their interference suppression effectiveness. Filter design should follow the impedance mismatch principle, meaning the filter's input and output impedances should be as opposite as possible to the source and load impedances. For BMS power ports, differential-mode noise sources are typically low-impedance switching power supplies. Therefore, an ideal differential-mode filter should present high impedance at the noise frequency, for example, using a differential-mode inductor. If a filter with capacitive input impedance is incorrectly used, noise current will easily flow into the power grid through the capacitor due to impedance mismatch, resulting in poor filtering performance. During design, the noise source impedance must be estimated, and an appropriate L-type, π-type, or T-type filter topology should be selected to achieve optimal insertion loss.