Optimal settings of multiple inverter-based distributed generation for restoring coordination of DOCRs in mesh distribution networks

Integrating the inverter-based distributed generation (IBDGs) into distribution systems has a great impact on coordinating directional overcurrent relays (DOCRs). The IBDGs shifts the fault current level leading to relay time grading errors and incorrect order of operations. For mitigating this problem, this paper proposes a method building on the versatility of IBDGs controls. The proper settings of IBDGs current magnitude and angle restore the fault current level and the corresponding DOCRs operating times. The settings of IBDGs are formulated as a non-linear optimization problem to maintain the operating times of individual DOCRs within a narrow band after IBDGs integration. Also, the settings of IBDGs are optimized in the presence of dispersed synchronous generators (DSGs). The optimal sizing and siting for IBDGs are determined according to DSGs position. The interior-point algorithm is employed to find the optimal IBDGs settings. Applications are carried out on two meshed networks: the 33 kV 30-node distribution system and the 15-bus test system. The proposed settings are insensitive to fault locations. For IBDGs outages, less than 2% of the relay pairs are sensitive to these outages. The proposed approach introduces a zero-cost strategy for mitigating the IBDGs impact and preserving the protection coordination without re-setting DOCRs.