A Voltage Drop-Based Unified Protection Technique for Islanded Hybrid Microgrid

While hybrid microgrids (HMGs) offer several advantages, protection schemes for HMGs face several challenges, such as the inconsistent and low fault current contributions of the inverter-dominated distributed generations as well as the lack of a unified protection technique for both AC and DC sub-grids. To address these challenges, this paper develops a unified differential protection technique (UDPT) for islanded HMGs. The proposed UDPT utilizes the line parameters and the current measurements at both line terminals to calculate the voltage drop (VD) along the line. The VD is calculated twice by considering two fault locations (close end and far end). Under normal operation and external fault scenarios, the VD values calculated for the two locations have the same direction, but on the contrary, have opposite directions under internal faults. Consequently, a unified fault detection index (UFDI) is proposed to discriminate between internal faults and other scenarios. The effectiveness of the proposed UDPT is evaluated through PSCAD/EMTDC simulation on the modified IEEE 33-bus islanded HMG, involving load switching, generator switching, capacitor switching, topology changes, external faults, and internal faults. The proposed UDPT shows remarkable performance compared with previous schemes in the literature, even with inaccuracies in measurements and line parameters as well as high-resistance faults.