Directional Current Selectivity in a MW-Level Solid-State Switchgear for DC Fast Charging Infrastructure

Solid-state circuit breakers (SSCBs) utilize semiconductors to isolate the fast-developing direct-current (DC) faults within several microseconds. However, the ultra-fast interruption speed and the autonomous fault detection in SSCBs bring challenges to the existing practice of overcurrent coordination in a complex MW-Ievel system. The absence of mutual communication among SSCBs makes the system vulnerable to unnecessary interruptions while isolating a single-point fault. To tackle the above difficulties, an autonomous SSCB coordination strategy utilizing directional current selectivity and early fault detection and prevention technology is proposed in this paper. The strategy is demonstrated with an MW-level, multi-port solid-state switchgear containing more than five SSCBs. The application targets a DC fast charging station with both a grid-tied source and a battery-backed system on the supply side, and multiple DC extreme fast chargers (XFCs) on the load side. A total of five fault scenarios are simulated in the system analyses, of which the three most representative fault cases are tested with SSCB prototypes in lab experiments.