A state space model of paralleled inverters based on droop control in grid-connected microgrid

Droop control and some improved droop control methods are adopted to control microgrid inverters not only in island mode, but also in grid-connected mode. This paper presents a state space model of three phase paralleled inverters in grid-connected microgrid based on droop control to facilitate the control design and stability analysis. This model is established in rotation framework based on modern control theory and can be very easily used in microgrid composed by any arbitrary number of parallel-connected inverters. A universal state matrix for any number of inverters is derived in this paper in very compact and clear form. The stability analysis and design of the system is simplified by using the root locus. Simulation results are shown to prove the validity of the proposed state model.