Transient Synchronization Stability Control for LVRT With Power Angle Estimation

Power synchronization control (PSC) is an effective control method for a voltage-source converter (VSC) connected with a weak grid, where the short-circuit ratio is close to 1. The grid voltage sag will induce the synchronization instability of PSC-VSC and then trigger the catastrophic cascading failure in the power system. This letter presents the transient power angle nature of PSC under the grid disturbance by phase portrait, and the critical condition of transient synchronization instability for PSC is derived. The virtual orthogonal power (VOP) is elaborated and the power angle estimation method is presented by VOP. Then, a mode adaptive transient synchronization stability control scheme is proposed for the low-voltage ride through with the power angle estimation scheme. By using the proposed transient synchronization stability control scheme, the PSC-VSC can maintain synchronization with the grid during the fault of grid voltage sag. The control method theoretical analysis is verified by the experimental tests.