# Cybersecurity of Microgrid: State-of-the-Art Review and Possible Directions of Future Research
## 1 Introduction  
Various definitions of the microgrid and designs of its functional classification have been provided in the literature. In general, a microgrid is defined as a small-scale electrical distribution system that links numerous customers to numerous sources of generation and storage, and uses power electronic devices as a medium [1]. The concept of the microgrid dates back to 1882 in proposals by [PERSON], whose company built the first 50 direct current (DC) power plants [2]. A microgrid comprises elements such as energy storage, loads, and generation systems [3]. The generation system in a microgrid receives its sources from renewable energy and conventional energy sources (hybrid system). Other elements such as storage play an essential role in supplying electrical energy to the end users because the microgrid's reliability is improved through storage. Storage is also employed to overcome the problem of excess power generated from wind turbines and photovoltaic (PV) systems. Microgrids can be divided into two operational systems: isolated and grid connected. An isolated microgrid can produce energy supply in a reliable condition in a small area, and can be used as a valuable testbed for suitable control function development. The use of grid-connected microgrids, on the other hand, is more widespread in supporting distribution networks that incorporate renewable energy sources (RES) and distributed generation (DG) units [4]. A microgrid system is a promising solution for handling power supply to loads with reliable power consumption. Some of the parameters to be considered in elements of the microgrid, such as the architecture of the communication system, protocols, and tools, are stability, reliability, and optimal operation [5]. Ensuring reliable communication among microgrids is not an easy task. Factors influencing the reliability of microgrid communication include the interface for communication among components, control requirements, resilience of the microgrid, its topology, geographical extension, and mode of operation, protection schemes for it, the technology of inverter-based distributed energy resources (DER), and reliability requirements [6]. Microgrid electrical systems were initially proposed to address energy supply issues in rural areas. Supplying energy to villages is costly and technically challenging because they are far from centralized electrical grid. The microgrid is an essential aspect in large-scale applications of the smart grid. It is a necessary part of a smart grid the main objective of which is to provide a reliable and safe means of electricity distribution by using intelligent and automated technologies.To maintain the reliability requirement, microgrid integrates various information and communication technologies in its legacy physical system. While the integration of operational (physical) technology and information technology provides more advancement and sophistication to the microgrid in terms of its operation, control, performance, connectivity and delivery, it opens up microgrid to a wider surface for cyber threats. As a result, the microgrid has security vulnerabilities i.e., the interconnectivity to the cyber system in microgrid brings more challenges to maintain resiliency as hackers might exploit vulnerabilities that lie in the physical system that has been long used without any patching or update for increasing protection being implemented. Some of the challenges or cyber threats to microgrid include false data injection [7], denial of service attack [8] and signal spoofing attack [9]. To the best of our knowledge, research on microgrid cybersecurity is inadequate. Vulnerabilities in microgrid and cyber-threats to them must be studied and understood thoroughly through a comprehensive and systematic literature review. This is the motivation of this paper.