Stability Studies of Grid-Forming and Grid-Following Inverter Penetrated Systems With Different External Power System Models
Fujian Li, Jin Ma
Abstract
It is well known that the Grid-Following Inverter (GFLI) alone is not sufficient for a 100% renewable integrated power grid due to its limits on voltage control. Thus, there have been many research efforts to study the Grid-Forming Inverter (GFMI), which can contribute to grid-voltage forming and maintain system stability by providing electrical inertia, especially in a weak power system. However, the majority of existing studies model an External Power System (EPS) as only a voltage source with internal impedance when investigating the impacts of GFLI and GFMI on the integrated power system stability. Nonetheless, neglecting the dynamics of EPS has the potential to result in inaccurate assessments. To better compare the impacts of these two types of inverters on the power system, this study utilizes two EPS models to evaluate two inverter-penetrated systems under weak power systems. The study, based on DQ impedance analysis, illustrates that when taking into account the dynamic characteristics of EPS, the stability margin difference between two different inverter penetration systems narrows dramatically in some cases. This indicates the insufficiency of the current widely used EPS models in renewable connection studies. The simulation results also support this conclusion.