Microgrid control strategies for seamless transition between grid-connected and islanded modes

This paper provides a review of the control schemes implemented for microgrids (MGs) or grid clusters to enable seamless transition between grid-connected (GC) and islanded (IS) modes of operation. Grid of MGs is a potential solution towards a resilient power grid with high penetration of renewable energy resources (RES). The deployed MGs must be capable of operating in both GC as well as IS mode of operation in the occurrence of anomalies or natural disasters. Such required ability of the MG will ensure uninterrupted energy services to critical loads and infrastructures. This mandates the implementation of control strategies to enable smooth transition of the MG between GC and IS modes and avoid deviations in voltage/current due to misalignment in phase and frequency during the transition process. The main purpose of this paper is to provide an overview of the challenges and existing techniques in literature to mitigate voltage and frequency (V/f) fluctuations at the MG's point of common coupling (PCC) and the power grid during the transition process; and to motivate the development of advanced control schemes in this area of MG-related researches.