Nonlinear analysis and estimation of the domain of attraction for a droop controlled microgrid system

Abstract

Droop control is commonly used for controlling the power flow in microgrids dominated by inverters as it is simple and does not require any communication interface among inverters. Dynamic droop gains are incorporated along with conventional droop gains to improve the dynamic performance of the system without affecting the stability and regulation. The small signal model, which is linearized around an operating point is not sufficient to analyze the response of the droop-controlled system when large disturbances occur. The droop gains play a significant role in rejecting such large disturbances and this has not been investigated adequately. In this correspondence, a nonlinear model is developed for a dynamic droop controlled microgrid system where the emphasis is laid on the effects of dynamic droop gains on disturbance rejection. To achieve this, a Lyapunov based stability analysis is performed to estimate the domain of attraction for the dynamic controlled microgrid system by using Takagi-Sugeno method. In addition, a comparison with conventional droop-controlled method is also performed to illustrate the relative efficacy of the two droop gain methods in rejecting large disturbances.