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Islanded hybrid AC/DC microgrids lack support for a large grid, and the negative incremental impedance of constant power loads (CPLs) aggravates the poor anti-disturbance capability of the system. When a single-phase ground fault (SPGF) occurs, the amount of fault impulse power that islanded AC/DC hybrid microgrids can stably withstand and when the protection equipment can work are both unknown. In this paper, the method of symmetrical components is utilized, and high-signal stability criteria for islanded hybrid AC/DC microgrids when a SPGF occurs are derived based on the mixed potential theory. The proposed criteria place quantitative constraints on the power of the PV unit, DC/AC converter current inner-loop proportional parameters, inductors, and inductor equivalent resistance, as well as energy storage unit power, CPL power, capacitors, DC bus voltage, line equivalent resistance, line equivalent inductance, equivalent inductance in the faulty branch, equivalent resistance in the faulty branch, positive-sequence equivalent impulse power of the SPGF, and zero-sequence equivalent impulse power. Furthermore, the maximum impulse power of a SPGF that islanded hybrid AC/DC microgrids could stably withstand is also presented, providing guidelines for protection equipment to decide when to work. In addition, the allowable maximum CPL power that islanded hybrid AC/DC microgrids could steadily support as a SPGF occurs is deduced, and the power is usually adopted to determine the states of an energy storage unit and load shedding in advance. Simulation and experimental validations prove the correctness of the derived high-signal stability criteria.
Liu et al. (Tue,) studied this question.