Unified Impedance-Based Relaying Scheme for the Protection of Hybrid AC/DC Microgrid

Even though the implementation of hybrid AC/DC microgrid is increasing, their protection schemes face multiple challenges such as inconsistent fault current supply from DGs, difficulty in discriminating internal/ external faults and missing of universal protection scheme for both AC and DC distribution networks. In this regard, a unified fault detection and localization scheme is proposed for hybrid AC/DC microgrid. By measuring the impedance at system frequency for AC circuit and at a specific pre-inserted frequency for DC network, the suggested technique achieves proper discrimination between internal faults and external events. Several fault scenarios such as internal/external faults, single/double line faults with varying fault location and fault resistance have been investigated on both AC and DC circuits by modeling hybrid AC/DC microgrid in PSCAD/EMTDC environment. The results reveal the effectiveness of the proposed algorithm in discriminating internal faults with external events and also in estimating accurate fault location even under noisy environment. Finally, a comparative evaluation of the proposed unified AC/DC protection scheme with other individual AC/DC protection schemes shows its superiority in combining both the AC and DC schemes together into a single relay, having an improved fault detection time and an increased fault localization accuracy.