What are the main sources of EMI on the DC side of a PCS (Power Control System) for energy storage?

There are three main sources of EMI on the DC side of the PCS. First, the switching operation of the inverter bridge, where high-frequency dv/dt and di/dt are coupled to the DC side through the parasitic inductance and capacitance of the DC bus. Second, the switching noise of the upstream DC/DC converter (if any). Third, interference from the grid or load side is conducted in reverse through the PCS to the DC port. This noise exists in both common-mode and differential-mode forms. Common-mode noise mainly forms a loop to ground through the parasitic capacitance between the power devices and the heatsink/casing; differential-mode noise exists directly between the positive and negative DC buses. Therefore, an EMI filter must be installed at the DC input port to prevent this noise from propagating to the photovoltaic modules or DC power supply, ensuring system-level EMC compliance.