How can an unreasonable PCS return path in an energy storage system cause EMI?

Improper return path design is the root cause of many EMI problems in PCS. High-frequency currents follow the path of least impedance for return. If poorly designed, this forces switching noise currents to flow through the common ground, signal ground plane, or chassis structure, leading to severe EMI. Specifically, this manifests as:

1. Increased common-mode EMI: Noise current flows into the chassis through parasitic capacitance, forming a common-mode radiating antenna.

2. Disruption to sensitive circuits: The power return path overlaps with the signal return path, allowing noise to couple directly into the control circuit.

3. Ground bounce noise: Rapidly changing return current generates a voltage drop across the inductance of the grounding conductor, disrupting logic levels.

A proper design requires: providing a wide copper foil return path close to the direction of high-frequency power current; using a complete ground plane to reduce impedance; connecting the noisy power ground to the clean signal ground at a single point; and ensuring that the grounding terminal of the filter capacitor is directly connected to the noise reference point.