How to design power line carrier coupling EMC in a concentrator?

The EMC design of a concentrator power line carrier coupling circuit must balance efficient coupling and noise suppression. Coupling methods typically employ capacitive coupling or transformer coupling. Transformer coupling is more common, and its design considerations include: an electrostatic shielding layer (a layer of copper foil) between the primary and secondary windings of the transformer, with a lead wire connected to the chassis ground to suppress common-mode interference. The transformer core should be made of high-permeability ferrite to ensure high impedance in the carrier frequency band (e.g., 270kHz). A common-mode inductor CML3225A-510T should be connected in series on the primary side of the transformer to suppress grid common-mode noise. The coupling capacitor (e.g., 0.1μF/250VAC) must be a CBB safety capacitor. On the PCB layout, the coupling circuit should be kept away from the switching power supply and digital circuits and surrounded by a grounded guard trace. All components should be placed close to the coupling terminals. This design provides approximately 30dB of common-mode rejection ratio (CMRR) and withstands surge impacts as specified in IEC 61000-4-5.