Small signal security region of droop coefficients in autonomous microgrids

This paper studies the small signal stability of microgrids in autonomous operation with droop control. A special power flow algorithm is employed to calculate the equilibrium point (EP) of a microgrid. The dynamic model of the microgrid is linearized at different EPs which are influenced by different droop coefficients. The system eigenvalues are compared with those obtained by other methods, in which the microgrid model is linearized at a fixed EP. Comparison results show that neglecting the impact of EP change will lead to either optimistic or conservative conclusions. The small signal security region (SSSR) formed by active power and reactive power droop coefficients is further sketched based on the bifurcation theory. Simulation using PSCAD/EMTDC verifies the accuracy of the SSSR. This research gives a way to quantitatively estimate the microgrid small-signal stability in high-dimensional parameter space, and the results can effectively guide the operation of autonomous microgrids.