Small Signal Modeling and Discontinuous Stable Regions of Grid-connected Inverter Based on Pade Approximation

The small signal stability of grid-connected inverter is of great importance, and the state space model is one of the most efficient modeling methods to analyze the small disturbance stability of grid-connected inverters. The proposed small signal modeling of the grid-connected inverter system takes the time delays caused by digital control into consideration, and converts the time delay factor into a rational polynomial with the pade approximation method, so as to establish the state space model of the entire system. Eigenvalue analysis method is used to compare the small disturbance stability of the grid-connected inverter system with or without considering time delays under different environments. Numerical simulation results show that in the grid-connected inverter system with time delays considered, when the strength of the power grid changes, the system has discontinuous stable regions and the small signal model of the system with time delay considered is more accurate and more sensitive to changes in the controller parameters. Finally, Matlab/Simulink simulation results verify the correctness of the proposed theoretical analysis.