Fault Process Modeling and Transient Stability Analysis of Grid-Following Photovoltaic Converter Grid-Connected System

With the growing integration of renewable energy into power systems, transient stability throughout the whole fault process has become a critical issue. This process comprises three distinct stages: pre-fault, fault-on, and post-fault recovery. However, existing studies have largely overlooked the influence of active power recovery on transient stability, which leads to conservative estimates of critical fault clearing time (CCT) and potential misjudgment of stability analysis. Accordingly, this paper addresses this gap by examining a grid-following (GFL) photovoltaic (PV) converter grid-connected system. Therefore, this paper investigates the transient stability of a GFL PV converter grid-connected system during the whole fault process. Firstly, a transient stability analysis model is developed using the piecewise linearization method to represent the system behavior across the whole fault process. Secondly, based on the proposed model, the impact mechanism of the control strategy in the fault recovery stage on the transient stability of the system is revealed by using the equal area criterion (EAC). Finally, the accuracy of the theoretical analysis proposed in this paper is verified by the PSCAD/EMTDC simulation platform. The results show that a slower active power recovery rate enhances the system’s transient stability, as it creates a larger equivalent deceleration area. The critical fault clearing time calculated by the proposed model is less conservative.