Robust Microgrid Control System for Seamless Transition Between Grid-Tied and Island Operating Modes

Critical facilities require electric power systems to stay fully energized during transitions between grid-connected and island modes. Providing this seamless transfer between island and grid modes is a complex challenge because of multiple dynamic interactions between distributed energy resources (DERs), electrical loads, and the bulk electric power system. Further complicating these transitions are the reduced kinetic energies and new dynamics associated with the black-box controls of power electronic DERs, such as photovoltaic (PV) and battery storage. The solutions to these challenges are fast, reliable, and adaptive protection and control systems commonly called microgrid control systems (MGCSs). This paper explains the design, testing, and results of an MGCS that uses subcycle (less than 16 ms) fast and deterministic control strategies to improve grid and island resiliency during the transitions from grid mode to island mode. The MGCS is known to prevent power outages (blackouts) during events such as islanding, synchronization, PV shading, islanded loss of generation, and variable loading under islanded conditions.