Estimating the Critical Clearing Time of Grid Forming Inverter via Lyapunov's Energy Functions

With the increase in distributed generation capacity connected to the power grid, the power grid exhibits weak grid characteristics. Traditional grid-following inverters may have stability issues under weak grid conditions. Therefore, the concept of grid-forming inverters has been emphasized again, as they exhibit better small-signal stability performance under weak grid conditions. However, as these inverters estimate the operation of traditional rotational synchronous generators, they also face transient stability issues such as power angle stability, and the current limiter will bring more complexity to this issue. Therefore, this paper focuses on the transient stability of grid-forming inverters and adopts Lyapunov's Energy Functions from nonlinear system stability analysis to investigate the transient behavior of grid-forming inverters when grid voltage dips, considering the current limiter. Meanwhile, the stability boundary will be drawn and the critical clearing time will be given. The accuracy of this method will be verified through a single-stage inverter experimental platform.