Adaptive Single-Terminal Fault Location for DC Microgrids

TL;DR

The paper addresses fault-location in low-voltage DC microgrids under increasing power-electronic integration by introducing an online, single-terminal method that does not require inter-terminal communications. The approach estimates the current that the opposite terminal would contribute during a fault ($\hat{i}_{dc2}(t)$) and combines it with local measurements through consecutive-sample processing to solve for the fault distance via a quadratic relation, enhancing accuracy for predominantly low-resistance faults. It demonstrates that the method yields superior accuracy for $R_f$ up to about $1\Omega$ and maintains comparable performance to other single-terminal methods up to $5\Omega$, with robustness to measurement noise and parameter variations. MATLAB simulations on point-to-point and multi-terminal LVDC test systems show the method works with minimal external modification (via CLRs) and without communications, offering practical applicability for rapid fault localization and system restoration.

Abstract

Identifying faulty lines and their accurate location is key for rapidly restoring distribution systems. This will become a greater challenge as the penetration of power electronics increases, and contingencies are seen across larger areas. This paper proposes a single terminal methodology (i.e., no communication involved) that is robust to variations of key parameters (e.g., sampling frequency, system parameters, etc.) and performs particularly well for low resistance faults that constitute the majority of faults in low voltage DC systems. The proposed method uses local measurements to estimate the current caused by the other terminals affected by the contingency. This mimics the strategy followed by double terminal methods that require communications and decouples the accuracy of the methodology from the fault resistance. The algorithm takes consecutive voltage and current samples, including the estimated current of the other terminal, into the analysis. This mathematical methodology results in a better accuracy than other single-terminal approaches found in the literature. The robustness of the proposed strategy against different fault resistances and locations is demonstrated using MATLAB simulations.

Figures (7)

• Figure 1: LVDC Test System formed by (a) point-to-point, (b) multi-terminal configuration
• Figure 2: Simplified network for point-to-point configuration under (a) PTP fault, (b) P-PTG fault
• Figure 3: Simplified multi-terminal test system
• Figure 4: Variation of ratio of transient voltages, $\gamma_{1}$ vs time for different fault distances.
• Figure 5: Estimated terminal current (kA) vs time (sec) for a P-PTG fault at $t=1 \text{ s}$ at 25$\%$ and 50$\%$ with $R_{f}=1 \text{ m}\Omega$, $R_{f}=1\Omega$ and $R_{f}=5\Omega$.