Impedance Modeling and Stability Analysis of Grid-forming Converters

Grid-forming converters can provide inertial and damping support for high-penetration renewable energy grids. However, inadequate tuning of grid parameters may lead to system instability due to variations in grid strength. In this paper, based on harmonic linearization theory, the positive and negative sequence impedance models of grid-forming converters are derived. Then the suitability of grid-forming strategies in weak grids is discussed in conjunction with the Nyquist stability criterion. Additionally, the impact of grid-forming power loop parameters on system stability is revealed, aiming to provide theoretical support for the optimization design of grid-forming converter parameters. Finally, a time-domain simulation model of the grid-forming converter is constructed to validate the theoretical research under typical system parameters.