Improvement of small signal stability margin and transient response in inverter-dominated microgrids

Inverter-based distributed generators (DGs) based on renewable sources are widely used in microgrids. Most of these sources operate in droop control mode for effective load sharing. Higher droop is desired in these systems to improve dynamic power sharing, however, such systems suffer from stability issues. Stability margin of a system having different combinations of inverter and synchronous generator-based sources is compared in this work. A microgrid is modeled here with three DGs on a modified IEEE 13-bus system using state space approach. The study showed that lack of stability of inverters restricts the use of higher droop gains, resulting in poor power-sharing dynamics. A modified droop control is proposed to improve transient response and stability margin in such cases. The results are validated with time domain simulations using Simulink/MATLAB.