How does the presence of high penetration of inverter-based resources in a microgrid impact the system's short-circuit current levels compared to a traditional grid?

High penetration of inverter-based resources in a microgrid significantly reduces short-circuit current levels compared to a traditional grid. In a traditional grid, rotating synchronous generators are the primary source of fault current. Synchronous generators have inherent inertia and can supply fault current several times their rated current for a short period, typically 4 to 10 times the full load current. This high fault current is essential for fast and reliable operation of protective devices like circuit breakers and fuses. Inverter-based resources, such as solar photovoltaic (PV) systems and battery energy storage systems (BESS), are interfaced with the grid through power electronic inverters. These inverters have current limiting capabilities to protect their semiconductor devices from overcurrent. The maximum fault current contribution from an inverter is typically limited to 1.1 to 2 times its rated current. This is significantly lower than the fault current provided by synchronous generators. The lower fault current levels in microgrids with high inverter penetration pose a challenge for traditional protection schemes. Overcurrent relays, which rely on detecting high fault currents to trip circuit breakers, may not operate correctly or quickly enough to protect the microgrid components. This can lead to delayed fault clearing, increased equipment damage, and potential system instability. Advanced protection techniques, such as adaptive protection schemes that adjust relay settings based on the microgrid's operating conditions, are necessary to address this issue. For example, impedance-based protection and differential protection can be used to detect faults with lower fault current contributions from inverter-based sources.