Control of Islanded Microgrid with Grid Forming and Following Inverters

Abstract

This paper presents the different topologies of interfacing inverters in Microgrid islanded mode. Grid forming inverters (GFM) have attained high importance in Microgrid islanded mode. When the Microgrid is in grid mode, the inverter control should be in constant current mode (P- active power, Q- reactive power mode), as the frequency and voltage are being controlled by the grid. But when the Microgrid is islanded either due to a fault on the grid or some maintenance job on the grid, the Microgrid control is to be in droop control mode, i.e., active power vs. voltage and reactive power vs. frequency, to maintain the voltage and frequency at Point of Common Coupling (PCC). The Microgrid forming inverters are suitable for synchronizing inverters to the Microgrid in islanded mode and grid following inverters (GFL), for synchronizing the inverters to the grid during resynchronizing mode. The grid-forming inverters are suitable for maintaining stability and reliability in the Microgrid for load sharing during load variations and for regulation of voltage and frequency in the islanded Microgrid. In this paper, it is proved that the coordination between GFM and GFL is possible to achieve accurate power sharing, frequency/voltage regulation, and reduce circulating vars in Microgrid. The effectiveness of the co-ordination of GFM and GFL is verified under various disturbances.