## 1 Introduction  
Topics related to DCMGs have achieved popularity in recent years, due to the advantages that these present compared to their counterparts, the so-called alternating current microgrids (ACMGs). Some of the advantages of DCMGs include higher efficiency, greater expandability, greater stability, easier control, greater reliability, greater compatibility with renewable energy sources, and fewer conversion steps [1, 2, 3]. However, implementation of DCMGs involves new technical challenges to reach their full potential; among them, the implementation of a suitable protection of the system [4, 5]. Moreover, it has been highlighted that there are currently no standards or guidelines for DCMG implementation [6, 7, 8, 9, 10, 11]. DCMGs are projected as the stage for modern distribution systems due to the proliferation of distributed generation (DG) [12, 13]. DCMGs can be defined as a group of loads and DC sources that function as a single controllable system, providing energy to its local and clearly defined area [2, 13]. DCMGs are composed of sources that are driven by power electronics devices. These devices, under certain operative conditions, may handle currents between two and three times the nominal current for at least tens of microseconds [14, 15], while conventional AC sources can sustain a fault current greater than 20 times their nominal current for hundreds of milliseconds [16]; in consequence, the protective devices used for ACMGs do not fulfill the minimal requirements for DCMGs. The proliferation of DCMGs is an important step in making the future power system load-adaptive, an important requirement for DG. Nonetheless, conventional MCBs for DC protection struggle to extinguish the arc generated when interrupting the fault current, and they also feature relatively slow tripping times, which represents a potential risk for sources and loads [5; 7]. The design criteria for electrical fault-protection circuit breakers in DCMGs must consider the following characteristics: low power loss, reliability, speed, continuity, economy, and simplicity [1; 8; 17]. Regarding microgrid protection, three aspects are addressed: protective circuit-breaker circuits, protection system design, grounding and ground fault isolation [7]. Regarding microgrid fault protection circuits, the most common protections are fuses, MCBs, SSCBs, and HCBs [7]. Circuit breakers' evolution for DCMGs has basically consisted of fuses, MCBs, SSCBs, and HCBs. Fuses are divided into two types: fast-acting fuses and time-delay fuses. Fast-acting fuses are used to protect the output of converters and are widely used in stationary battery protection [18; 19]. Time-delay fuses are used for high-frequency current peaks that occur when energizing certain loads or when starting motors. The selection of a fuse for an ACMG requires a response time between 10-100 ms to correctly operate and interrupt the fault; however, DCMGs require a maximum of 0.5 ms [18]. Although the fuse is an inexpensive protection device with very simple construction characteristics, it has the disadvantage of having to be replaced after each fault, and does not have the possibility of discriminating between a transient or a permanent fault. MCBs are devices that use mechanical parts to interrupt the flow of current in the event of a fault. The current interruption process is always accompanied by an electric arc at the moment of interruption. To mitigate the impact of the arc, passive and active current circuits have been proposed, in which a resonant LC series circuit is used for creating a zero-crossing that extinguishes the arc [20]. The main advantages of mechanical switches consist of having low losses and low investment costs; however, the fault clearance time is between 30 and 100 ms, which is too high for DCMG requirements. SSCBs constitute an alternative to MCBs, since they do not have mechanical moving parts to operate. Additionally, the operation of SSCBs is performed by semiconductor devices.