Transient Synchronization Stability Analysis of Weak Grid-connected VSC under Grid Fault

The weak grid-connected VSC (WG-VSC) system based on PLL synchronization has been widely applied in power electronic system. Firstly, considering the switching dynamics of multiple control modes and interaction of multiple control links, a simplified analysis model and a stability analysis method are both proposed. The transient synchronization stability during the whole fault process is quantitatively analyzed, along with the description of equivalent synchronous dynamic process. Secondly, from the perspective of control parameters, the feasible region of active and reactive currents injection is defined and constructed. By reasonably setting the current setting values during fault ride-through, transient synchronization stability of the system after fault clear is guaranteed. Finally, based on the constructed current feasible region, the influences of system short-circuit ratio and the fault point voltage are analyzed respectively, providing a guiding basis for improving the stability control performance. The above theoretical analysis processes are all verified by detailed electromagnetic transient simulations in PSCAD/EMTDC software.