Analytical Stability Criterion and Parameter Tuning of Limited Grid-forming Photovoltaic with DC Voltage Protection

Grid-forming (GFM) control is a key technique for power systems with high penetration of converter-interfaced generation. However, its application to photovoltaic (PV) systems faces challenges related to DC voltage transient stability. This paper investigates a common countermeasure involving a PI-based DC voltage controller for GFM-PV systems, revealing that their small-signal stability is sensitive to parameter tuning. The study develops a generalized DC voltage-dominated 2nd-order GFM model and successfully conducts complex torque analysis, showing that this approach can be effectively extended to other dynamics governed by DC voltage-dominated GFM systems. Subsequently, the paper establishes a stability criterion for GFM-PV systems and proposes a parameter tuning method for DC voltage controllers that incorporates damping margin considerations. The performance of the tuned single-machine-infinite-bus GFM-PV system is validated on the RT-LAB real-time simulation platform under scenarios involving solar irradiance fluctuations and grid frequency disturbances. The proposed method proves effective in ensuring the stability of the GFM-PV system, with robust theoretical support.