Fault Recovery and Transient Stability of Grid-Forming Converters Equipped with Current Saturation
When grid-forming (GFM) inverter-based resources (IBRs) experience large grid disturbances (e.g., short-circuit faults), the current limiter may be triggered and GFM IBRs enter the current saturation mode, inducing nonlinear dynamical behaviors and imposing great challenges to the post-disturbance transient angle stability. This paper presents a systematic study to reveal the fault recovery behaviors of a GFM IBR and identify the risk of instability. The impact of the angle of the magnitude-saturated current on the post-fault recovery and transient stability is also investigated. The selection of the angle of magnitude-saturated current significantly influences the post-fault behaviors while a few additional dynamical conditions that have a substantial impact are also identified. It is found that the system may follow multiple post-fault recovery trajectories depending on those conditions: 1) Convergence to the normal stable equilibrium point (SEP), 2) convergence to the saturated stable equilibrium point (SSEP), and 3) divergence (instability). To examine the models' accuracy, several cases are simulated.
PDF Abstract