Zone-Based Directional Current Protection for DC Microgrids with Constant Power Loads

DC microgrids have garnered significant attention due to their growing potential for various applications, but their fault protection issues still face severe challenges. Since DC fault currents reach their peak values within milliseconds, traditional AC protection methods are difficult to meet the needs of rapid response, and the negative impedance of constant power loads can easily lead to protection malfunctions when the system voltage drops. This paper first analyzes the negative impedance of constant power loads and transient response characteristics of DC microgrids during faults; secondly, a zone-based directional current protection is proposed. Through the dual criterion design of power change rate and current change rate, the short-circuit fault and load disturbance are accurately distinguished, which solves the malfunction of traditional overcurrent protection in constant power load scenarios, and the feasibility and selectivity of the proposed protection strategy are verified through simulation.