Abstract
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.
Highlights
In recent years, direct current (DC) microgrids have been used widely as a realistic scheme with the majority of DC loads and sources such as storage devices, fuel cells, and photovoltaic (PV) units [1] and [2]
The case studied DC Microgrid is suggested for implementing in Rø mø island in Denmark consists of PV, fuel cell (FC), battery, and offshore wind turbine (WT), and several loads, and this system is connected to the grid by an alternating current (AC)/DC converter
The protection scheme of the island is consist of component fuses, recloser switch, and overcurrent based relays for lines
Summary
DC microgrids have been used widely as a realistic scheme with the majority of DC loads and sources such as storage devices, fuel cells, and photovoltaic (PV) units [1] and [2]. DC microgrids reduce the number of converters compared to the alternating current (AC) systems, and it reduces the power losses [3]. In DC microgrids, one of the main challenges is the lack of effective protection strategy and standard [4]. Protecting the DC Microgrid against fault is difficult due to the variation of topology, lack of zero-crossing point, and presence of the power converters [5]. In DC microgrids, the components are protected by using fuses and recloser switches [6].
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