Influence of Power-Frequency Droop on Grid Forming Inverter Current Damping in Mixed Source Islanded Microgrids

Deployment of renewable energy and energy storage systems in islanded microgrids convey benefits including reduced emissions and avoided fuel costs by shifting load from fossil fuel based generation such as diesel generators to these predominantly inverter based resources (IBR). A widely used control strategy for automatic load sharing of IBR’s and synchronous generators is the power-frequency (P-F) droop control often used in grid forming (GFM) IBR control schemes. However, paralleling these devices can result in poor transient load sharing leading to overcurrent tripping of the IBR and potentially collapse of the microgrid. This paper provides an in-depth analysis of the influence of the P-F droop parameter selection on the damping of the output current of a GFM inverter operating in parallel to a synchronous generator in an islanded microgrid. The results illustrate that the dominant oscillatory modes of the inverter output currents are also observed in the generator rotor speed and reveal that the P-F droop parameter can play a role in improving the GFM IBR current damping, which reduces the likelihood of overcurrent tripping of GFM IBR’s following substantial load acceptances.