Transient Current Correlation Based Protection for DC Distribution System

DC distribution systems play indispensable and significant roles in power systems for most loads, such as renewable sources and charging piles that are dc-supplied. A single line-to-ground fault will not cause an overcurrent due to the large grounding resistance applied in the dc side of the distribution system. However, the dc line-to-line fault results in shutting down of all the converters, which can greatly prolong the fault recovery time. It is difficult to extract fault information accurately due to the converter's time-varying impedance and strong nonlinearity during a fault. Therefore, to address the problem of line-to-line short-circuit faults, dc protections that offer quick fault detection and isolation are essential. This article proposes a current correlation based new protection algorithm (only considers line-to-line short-circuit faults) for the dc distribution system. The fault current characteristics are investigated in detail and their correlation relationship is adopted to fully distinguish internal and external faults. Simulation and experimental results show that short-circuit faults of different fault resistances can be distinguished within 0.5 ms and the performance of the proposed protection is little affected by distributed capacitance and noise.