Current-Derivative-Based Fault Detection in Converter-Interfaced LVDC Grids: A Different Approach

Fast and reliable fault detection is critical to ensuring stability in low-voltage DC (LVDC) grids, especially in applications where system reliability and uninterrupted operation are paramount. Conventional amplitude-based fault detection inherently introduces delays, as it requires the fault current to exceed a predefined threshold-delays that become more pronounced for faults occurring further from the source. In contrast, current derivative ($\mathrm{d} i / \mathrm{d} t$) -based detection offers a fundamental advantage: the detection threshold is surpassed at the exact moment a fault initiates, enabling significantly faster response times. This paper presents a robust and simplified method for $\mathrm{d} i / \mathrm{d} t$-based fault detection in LVDC systems. Rather than relying on grid modeling or fault current estimation, the proposed approach sets the fault detection threshold based on the natural current dynamics of the grid-connected converter. Specifically, the converter's current control loop bandwidth is used to define the maximum expected $\mathrm{d} i / \mathrm{d} t$ during normal operation. The method is further enhanced by recognizing the role of internal slew rate limiting in converters, which introduces an even greater margin between nominal and fault-induced transients-enabling discrimination even under high-impedance fault conditions. The approach is validated through both offline simulations and realtime implementation using a solid-state circuit breaker (SSCB) prototype. Results confirm that the method provides rapid, reliable detection with minimal computational complexity, making it suitable for protection systems in LVDC grids.