Coordinated Protection and Control Scheme for Smooth Transition from Grid-Connected to Islanded Mode of Microgrids

Abstract

Microgrid (MG) architecture enables integration of different kinds of distributed energy resources (DERs) into existing electricity grid operation. The MG normally operates within the main utility grid and during grid outages is able to become isolated and sustain its local loads. The successful transfer and operation of MG in islanded mode is strongly influenced by the robust protection arrangement at the point of common coupling, which helps initiate islanding along with the associated MG control actions to counteract insecure and volatile dynamics arising after islanding. Therefore, the protection and control schemes should be coordinated with each other and also be compatible with dynamics of the DER; otherwise, the stability of the MG will be impacted during its autonomous islanded operation. In this paper, a new combined protection–control scheme is devised for a low-voltage MG through which the stability of the islanded MG is continuously ensured. Furthermore, structure of an intelligent electronic device (IED) which enables the proposed protection scheme is presented. The IED directly communicates to an intelligent central controller system for the purpose of triggering the associated control scheme. The performance of the proposed coordinated scheme is successfully validated through both numerical simulations in MATLAB/Simulink environment and experimental test bed. The obtained results show that the idea can confidently meet smooth transient from on grid to off grid and vice versa in MGs.