Transient Stability Analysis of Power-Synchronized PLL-Less Grid-Following Inverters

In the realm of modern power systems, grid-connected inverters are essential for integrating renewable energy resources. While grid-following inverters (GFLIs) currently dominate the market, grid-forming inverters (GFMIs) are pivotal for technology future power systems. Furthermore, recent research emphasizes the advantages of power-synchronized GFLIs (PSGFLIs), which combine the reliable operation of conventional GFLIs in strong grids with the stability of GFMIs in weak grids. This paper presents a comprehensive analysis of transient angle stability for a specific variant of PSGFLI, referred to as the linear parameter-varying control PSGFLI (LPV-PSGFLI). First, a nonlinear dynamic model suitable for transient stability analysis is derived. Then, the necessary and sufficient stability condition is obtained using Lyapunov's linearization stability analysis method. A method for estimating the required system variables for stability assessment is proposed, along with the static stability condition to identify the presence of an equilibrium point. Additionally, a Lyapunov energy function is proposed to determine the domain of attraction for the system's equilibrium point. The accuracy of the stability condition and the calculated domain of attraction is evaluated across multiple scenarios via simulations in MATLAB/Simulink and experimental tests performed on a scaled-down inverter experimentation platform.