How to reduce EMI impact during PCS closing inrush current in energy storage systems?

At the moment of power-on and closing of the PCS, the charging of the DC bus capacitor or AC side filter capacitor generates a huge inrush current. Its high-frequency components can cause transient EMI impacts on the power grid and may trigger internal protection mechanisms. Measures to mitigate this impact include:

1. Soft-start circuit: Connect a current-limiting resistor or a negative temperature coefficient thermistor (NTC, such as the MF72 series) in series in the DC or AC input circuit. After power-on, short-circuit it via a relay or thyristor. The NTC has high resistance when cold, effectively limiting inrush current; as it heats up, its resistance decreases, reducing operating losses.

2. Slow-start control: For PCS with an active front-end, control the switching transistor to slowly increase the duty cycle, gradually building up the bus voltage and avoiding instantaneous capacitor charging.

3. Pre-charge circuit: Design a dedicated pre-charge circuit to pre-charge the bus capacitor to a certain voltage with a small current before connecting the main circuit.

4. Optimize capacitor configuration: Avoid using excessively large input capacitors. These measures smooth the power-on process, reducing instantaneous interference to the power grid and internal electrical stress.