Non-pilot DC Fault Protection Using ROCOC in MVDC System

This paper proposes a non-pilot dc fault detection algorithm based on the rate of change of current (ROCOC) for a full-bridge (FB) modular multilevel converter (MMC) medium voltage dc (MVDC) distribution system. The fault current is analytically derived using an RLC equivalent model of the MMC, and the threshold is determined from the analytical equation. The algorithm detects a fault when the ROCOC exceeds the threshold and persists for five consecutive samples, without requiring communication infrastructure. Its performance was validated through MATLAB/Simulink under various fault scenarios, including variations in DC reactor size, fault resistance, and fault location. In all cases, faults were detected within 1.2 ms prior to the peak fault current.