On Stability of Islanded Low-Inertia Microgrids

As the number of distributed energy sources (DERs) increases in a microgrid (MG), the likelihood of frequency and voltage instabilities increases. In particular, the control of frequency and voltage becomes a challenge in an islanded mode due to the inherent low-inertia feature of DERs compared to a grid-tied mode where there is a grid support. This instability problem becomes worse for low or medium voltage low-inertia MGs, where the line impedance is dominantly resistive. The goal of this paper is to demonstrate the stability and power quality problems that can occur in islanded medium voltage MGs. PSCAD/EMTDC simulation results for an MG with a high share of low-inertia power generation units illustrate the importance of the frequency and voltage stability as power utilities adopting more DERs.