Impedance-based Voltage Stability Assessment for Grid-forming Typed VSG Inverters Connected via Distributed Transmission Lines

Distributed power supplies with grid stabilization functions are actively connected to the power system. Recently, many studies have been conducted on control topologies that enhance the grid stabilization effect through virtual inertia characteristics in order to achieve both transient stability of the power supply and steady-state stability of the entire system. However, these previous studies have focused on active power supply/demand and frequency stability, and few detailed studies have been conducted on reactive power transfer and voltage maintenance functions of distributed power supplies. Therefore, in this paper, first the power supplies consisting of a synchronous generator (SG) and a group of grid-forming inverters (GFMs) controlled by a virtual synchronous generator (VSG) are connected via a transmission line consisting of frequency-dependent distributed circuit to clarify the effect of inverter voltage regulation according to the SG's effective power output limit. Furthermore, the destabilizing grid operating conditions estimated from the above results were proved by impedance-based analysis, and the possibility of avoiding them by tuning the VSG control parameters was presented.