How should the auxiliary power supply filter of the PCS in an energy storage system be designed?

The auxiliary power supplies inside the PCS, such as flyback and LLC switching power supplies, are themselves significant sources of EMI noise, making their filtering design crucial. A π-type filter, including a common-mode inductor (CMC series surface-mount common-mode inductors can be used for low-power applications) and X/Y capacitors, is required at the input to prevent switching noise from backflowing to the DC bus and interfering with the main power circuit. An LC filter is needed at the output to suppress high-frequency switching ripple, ensuring a clean voltage for the control board and driver ICs.

Key design considerations:

1. High-frequency path design: Y capacitors should be placed as close as possible to the primary and secondary windings of the transformer to provide the shortest possible path for switching noise.

2. Isolation and safety: Safety isolation is required between the primary and secondary windings of the auxiliary power supply; the Y capacitors used for bridging must be safety-certified isolation capacitors.

3. Layout isolation: Input and output filters should be placed close to the power module ports, and traces before and after the filters should be separated to avoid noise recoupling.