Comprehensive modeling of grid-connected inverters in weak grid systems

Introduction. The stability of grid-connected inverters is critical for the integration of renewable energy into modern power systems. However, this stability is significantly challenged under weak grid conditions, characterized by high impedance and low short-circuit ratios. Problem. Under such conditions, complex dynamic interactions arise between the inverter control systems, the grid, and the phase-locked loop, which is essential for synchronization. These interactions can degrade phase tracking and even lead to system instability. Such complexities render traditional models inadequate for accurately evaluating system behavior or guiding robust control design. The goal of this work is to develop and validate a compact, linearized state-space model of a grid-connected inverter under weak grid conditions, enabling stability analysis and supporting the design of robust control strategies. Methodology. Using small-signal modeling, a state-space representation of the inverter system is derived, incorporating control dynamics, grid impedance, and the power converter. The model’s accuracy is validated through detailed nonlinear simulations, ensuring strong consistency between both mod