Small-Disturbance Stability Improvement of Weak Grid-Connected Photovoltaic Power Plant Based on Grid-Forming Controlled Converters Partial Substitution

At present, the majority of photovoltaic power stations predominantly utilize grid-following control strategies for their converters. This reliance poses challenges in maintaining safe and stable system operations within weak grid environments. In photovoltaic installations where all converters are configured with grid-following control, converting a subset of these to grid-forming control can significantly enhance operational capabilities under weak grid conditions. However, the specific mechanisms through which grid-forming controlled converters improve small-signal stability remain inadequately understood, and there is an urgent need to investigate how to determine the optimal configuration ratio of grid-forming controlled converters within photovoltaic power stations. In this paper, we establish harmonic linearization impedance models for both grid-following and grid-forming controlled converters. We compare the variations in system impedance models and small-signal stability with and without the inclusion of grid-forming controlled converters. Our analysis reveals that employing grid-forming control is effectively equivalent to reducing overall grid impedance; this reduction enhances the strength of the electrical network and subsequently improves system stability. Furthermore, based on our impedance model alongside an impedance-based stability criterion, we propose a method for configuring proportions between grid-following and grid-forming controlled converters. Finally, we validate the accuracy of our analytical findings through simulation results.