An ultra-fast directional protection scheme for DC microgrids based on high-order synchrosqueezing transform

Abstract

Protection of Direct Current (DC) microgrids is a challenging task because of large currents within a few milliseconds after the occurrence of a DC fault, which causes serious damage to converters. The present study introduces a protection algorithm based on Traveling Waves (TWs) to detect and locate faults. The proposed method implements the High-order Synchrosqueezing Transform (HOSST) to capture TWs using local measurements. Unlike conventional methods, HOSST can analyze signals in both time and frequency domains by creating a concentrated energy in the time–frequency representation. By extracting impulse features, HOSST detects TWs with high accuracy even in a noisy environment for different types of DC faults with various fault resistances. The proposed method can identify external and internal faults by determining the polarity of TWs, which makes the relays operate properly within their protection zone and prevents mal-operation. To demonstrate the efficiency of the proposed method, it is applied to a DC microgrid. The results show the high accuracy of the presented approach in the fault location with a slight error with selectivity, reliability, sensitivity, and high speed, which is independent of the voltage level and configuration. In addition, the certainty of the proposed method is higher than the previous studies due to the simultaneous use of current and voltage.