Summary The integration of distributed energy resources (DERs) with conventional systems emerges as an intelligent solution for providing uninterrupted and secure power even at times of high load demand. Better load management with a mature fault handling mechanism makes AC a viable option which has an efficiency of 78.24%. In contrast with less power loss and slightly better efficiency of 84.6%, DC microgrid is a reliable option in a low power environment. In order to accommodate all operating conditions and load types, a hybrid system can be designed with a theoretical efficiency of more than 90%. Bidirectional power flows, low inertia, the transition between different modes of operations are the challenges for the protection of alternating current (AC) and direct current (DC) microgrid systems. Power balance fluctuation, absence of zero‐crossing currents, selection of suitable grounding, and coordination between different rating devices restrict the hybrid system to achieve the said efficiency constantly. This paper reviews in detail of existing protection along with grid‐connected algorithms for both modes of operation. Finally, the limitation, major hurdles, and future course of action for a reliable, efficient, and secure hybrid grid system are figured out.

The evolution of small-scaled distributed generators and emerging power electronic devices opens up a new arena of power generation, distribution, and consumption. Operationally, the DC microgrid has attracted significant attention as it offers considerable safety benefits, cost-effectiveness, energy efficiency, and reliability as compared to traditional AC microgrid systems. Looking at the protection aspects, the DC microgrid has some serious issues both for low-voltage and mid-voltage DC system. It needs to be focused on bidirectional power flow, non-zero crossing point, detection and mitigation of grounding faults, high value of fault current, etc., for an adequate solution. In recent times, these issues are considered by various researchers to arrive at a robust and reliable approach toward protecting the DC microgrid. But certain important areas are still out of sight for researchers. In a blend of conventional and modern approaches, there are many hindrances in developing a flexible universal protective scheme. This work focuses on the protection aspects parallel with the challenges and tried to unearth the loopholes which open up a wider area of research to develop a more robust protective architecture. An extensive review has been done systematically and chronologically keeping in mind the DC microgrid architecture, standards, protection hurdles, traditional as well as latest protective measures, and suggested some reliable improvements. In addition, the futuristic possibility to invent a novel comprehensive approach based on the best technology and techniques is presented in a more secure, reliable, and efficient protection system to combat the power system faults, keeping in view the different modes of operation and configuration of the microgrid.

In the recent power system scenario, the concept of microgrid is evolving rapidly. The architecture should be robust enough to cater the complexity of integration of distributed generation sources, demand-side management, and storage. The fast growth of embedded generation with other advanced power electronic interfaces and components along with energy storage devices change the operating pattern of the integrated power system scenario. In this context, protection is the vital aspect for qualitative uninterrupted power and making the system resilient to adverse, and faulty conditions. Many associated issues, particularly related to AC microgrid systems like the large difference in the short-circuit level between integrated and isolated mode of operation, bidirectional power flow, unsynchronized reclosing, the blindness of protection, lack of natural zero-crossing current, and false tripping are needed to be focused. In light of the above factors, it motivates us to survey the previous research works on the existing protection strategies to redesign and present the critical analysis of the predicted protection issues of microgrid protection with upcoming advanced technology and methodology. This article presents a critical review of the issues and protection schemes for the DG integrated AC microgrid extensively. Here, the merits, and demerits of each protection scheme, and visible possibilities for any advancement in protection strategies to enhance the reliability, selectivity, and security of AC microgrid is emphasized keeping in mind the different connections and configurations. In addition, this work also focuses on integrating the intelligent approaches/devices that help to elevate the current protection schemes to be smarter and efficient.

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