Grid Forming Inverter Power Control Stability Analysis

Stable system operation is being actively attempted by introducing grid-forming inverters (GFMs) which mimic synchronous generators (SGs). Although the introduction of GFMs intended to replace traditional grid-following inverters (GFLs) provides system inertia and contributes significantly to fault current, it paradoxically exhibits unstable output characteristics under high short circuit ratio (SCR) conditions. In this paper, a mathematical plant model of the basic GFM structure is implemented along with the model integrating grid-connected GFM and the SCR of the system for maintaining the grid dynamics. For this end, a single input single output (SISO) model of an GFM with active power control (APC) is proposed for analyzing the stability in small grid events, and the system frequency response model considering the dynamic performance of SG and GFM APC was also configured for simulating large grid events. The performance of the proposed APC for step response and frequency response characteristics is compared with an existing APC method, such as droop and virtual synchronous machine (VSM). Simulation results using MATLAB and PSS/e verify the performance of the proposed method and stable operation can be expected by actively composing the controller during the SCR that continuously changes in both small and large grid events.