How should the surge protection level of the PCS in an energy storage system be designed?

Surge protection for PCS (e.g., IEC 61000-4-5) requires a graded (multi-level) protection design to discharge and clamp energy step by step. A typical three-level protection system is as follows:

1. Level 1 (Coarse Protection): Gas discharge tubes (GDTs) or varistors (MOVs, such as 14D and 20D series) are used at the very front end of the system (e.g., AC grid input, DC photovoltaic input) to discharge most of the lightning strike energy.

2. Level 2 (Intermediate Protection): Varistors with slightly lower current carrying capacity (e.g., 7D series) or TVS diodes (e.g., SMCJ and 5KP series) are used after the power filter inside the cabinet or before the DC/DC module to further clamp residual voltage.

3. Level 3 (Fine Protection): TVS diodes (e.g., SMBJ and P6KE series) or semiconductor discharge tubes (TSS) are used at the front end of sensitive circuits (e.g., control board power supply, communication interfaces) to clamp the voltage to the IC's safe range. Inductors or resistors are typically used to decouple the levels to achieve coordinated energy discharge.