Multi-Sample Differential Protection Scheme in DC Microgrids

This article proposes a novel solution to the issue of protection instability caused by time synchronization error in high-speed differential protection schemes for dc microgrids. DC microgrids provide a more efficient platform to integrate fast-growing renewable energy sources, energy storage systems, and electronic loads. However, the integration of distributed generators (DGs) may result in variable fault current magnitude and direction during fault conditions, potentially causing miscoordination of conventional time graded overcurrent relays. One identified solution to this issue utilizes high-speed differential protection schemes to maintain effective selectivity in DG-dominated dc microgrids. However, as dc short-circuit fault currents are highly transient, microseconds of synchronization error in the measured line currents may cause protection stability issues, whereby maloperation of relays may occur as a result of faults external to the protected zone. This article investigates the impact of time synchronization errors for high-speed differential protection in dc distribution systems. It then proposes a multisample differential (MSD) scheme that performs multiple differential comparisons over a sampling window to ensure the stability of high-speed differential protection schemes for external faults while maintaining the sensitivity to internal faults.