Stability analysis of grid-connected inverter systems based on sequential impedance modelling accounting for grid strength

With the increasing number of renewable energy sources connected to the grid, the stability of grid-connected inverter systems has attracted much attention. The effect of grid strength on stability has also become a hot research topic. In order to investigate the influence of grid strength on the grid-connected inverter system, this paper firstly constructs a grid-connected inverter system containing a grid-constructing inverter and a grid-following inverter, and then adopts the harmonic linearization method to derive the sequential impedance model of the two inverters. Based on the sequential impedance model, a three-port equivalent model of the grid-connected inverter system taking into account the grid strength is established. The stability of the grid-connected inverter system is analyzed by plotting the Nyquist curve. In addition, a simulation model is established, and the Nyquist curves are compared with the simulation results to verify the correctness of the obtained conclusions, which lays the foundation for the future design of system parameters and optimization of control strategies.