A Fuse Saving Scheme for DC Microgrids With High Penetration of Renewable Energy Resources

The high penetration of renewable energy resources (RERs) increases the fault current level of direct current (DC) microgrids and causes bidirectional flow for fault current. Therefore, it may cause a miscoordination between fuses or other protection devices. The traditional coordination methods are based on shifting the operation curve of protection devices below the characteristic curve of the fuses during temporary faults to save fuses. However, in case of low variations of the system topology and low impedance faults, these methods can be used to save fuses. Also, in the case of high penetration of RERs, due to the variations of the short circuit level, the traditional methods are not effective. On the other hand, due to the lack of standards and proper protection methods in the DC microgrids, presenting a recloser switch - fuse coordination scheme for DC microgrids is essential. To address these issues, this paper proposes a fuse saving method by finding the appropriate setting of fuses and the recloser switch, which is effective for DC microgrids with various types and penetration levels of RERs. The proposed protection method is localized, and without communication links, it is applicable for both digital and conventional protection devices installed in the DC microgrids. The proposed scheme formulates the fuse-recloser switch coordination challenge as a curve-fitting problem and solves this problem to obtain the settings of the digital recloser switch and fuse. The proposed strategy provides a robust setting for fuse and digital recloser switch by considering different topologies of the DC microgrids. The proposed method is applied to a DC microgrid in different scenarios. The effectiveness and robustness of the proposed method are illustrated by digital time-domain simulation studies in the MATLAB/Simulink software environment and comparisons with previously-reported protection strategies.