How can the capacitance value of the PCSX/Y capacitor in an energy storage system balance EMC and safety regulations?

The selection of X/Y capacitor values in a PCS is crucial for balancing EMC filtering performance with safety limits. Larger X capacitor (differential mode filter) values result in better low-frequency attenuation, but inrush current and size/cost must be considered; metallized film capacitors are typically chosen. Y capacitor (common mode filter) values are directly limited by safety leakage current requirements. For example, for Class I industrial equipment, the leakage current to ground is usually required to be less than 3.5mA. The total allowable Y capacitor value under maximum operating voltage can be calculated using the formula I=2πfCV. In practice, to balance high-frequency filtering performance and safety requirements, a common approach is to use multiple small-capacity safety-compliant ceramic Y capacitors connected in parallel. For example, several 2.2nF or 4.7nF Y capacitors can be distributed across different noise injection points. This satisfies leakage current requirements while providing an effective path to ground for broadband common-mode noise.