What is the effect of EPS grounding impedance on radiated EMI?

The grounding impedance of an EPS system directly affects its radiated EMI (RE) level. Higher grounding impedance can lead to:

1. Increased common-mode noise voltage: When common-mode noise current flows through the grounding impedance, a voltage drop occurs, causing fluctuations in the potential of the equipment casing and cable shielding relative to the "ideal ground." This fluctuation drives common-mode current to radiate outwards through the cable, acting like an antenna.

2. Decreased filter effectiveness: As mentioned earlier, filters require low-impedance grounding to function effectively. Poor grounding weakens the filter's ability to suppress common-mode noise, leading to more noise current flowing into the cables and increasing radiation.

3. Reduced shielding effectiveness: The shielding effect of cable shielding and cabinets depends on low-impedance grounding. High grounding impedance prevents the induced noise current on the shielding layer from dissipating quickly, resulting in decreased shielding effectiveness and easier radiation of internal noise.

Therefore, reducing the high-frequency impedance of the grounding system is a fundamental measure for controlling radiated EMI.