A microgrid is a concept that has been developed with the increasing penetration of distributed generators. With the increasing penetration of distributed energy resources in the microgrids, along with advanced control and communication technologies, the traditional microgrid concept is being transited towards the concept of microgrid clustering. It decomposes the distribution system into several interconnected microgrids, effectively reducing problems such as voltage rise, harmonics, poor power factor, reverse power flow and failure of the conventional protection schemes. Microgrid clusters effectively coordinate power sharing among microgrids and the main grid, improving the stability, reliability and efficiency of the distribution network at the consumption premises. Despite the evident benefits of microgrid clusters to the consumers and the electrical utility, there are challenges to overcome before adopting the microgrid cluster concept. This paper is aimed at critically reviewing the challenges in design aspects of microgrid clustering. Categorization of multi-microgrids into different architectures based on the layout of the interconnections, evaluation of reported control techniques in microgrid clustering and multi-microgrid protection aspects are presented, highlighting the possible areas of future research that would improve the operational aspects of microgrid clusters.

A ring-connected microgrid cluster can be formed by connecting geographically closed microgrids for mutual power sharing to increase the system's reliability. Real-time power balance within individual microgrids and power sharing among the microgrids of an islanded microgrid cluster would be challenging during contingencies if they are not properly sized and controlled. We propose a technique to design a ring-connected microgrid cluster that has several distributed energy resources. The amount of power flow via interconnecting cables was decided considering the size of the energy storage of the neighboring microgrids. A control system was designed to minimize the effect of severe transients in the neighboring microgrids in the network. The performance of the proposed technique was verified using a ring-connected microgrid cluster with four microgrids derived based on a real distribution system. The results illustrated that the proposed ring-connected microgrid cluster could maintain the power balance of the networked microgrid during the contingencies of neighboring microgrids, increasing the resiliency of the system compared to the radial and islanded operations.