Transient stability enhancement control strategy for droop-controlled voltage source converter

Abstract

The droop-controlled voltage source converter (VSC) can support the voltage at the point of common coupling (PCC) and realize frequency adjustment by simulating the swing equation of the synchronous generator (SG) and has a higher stability margin in the extremely weak grid. Under large-signal disturbances such as short-circuit faults in the power grid, the active power output of the VSC decreases, and the continuous increase of the power angle causes the VSC to have a power angle instability similar to that of the SG. In addition, in order to ensure the safety of the equipment, the VSC control system contains a current-limiting strategy, which will cause a large change in the transient external characteristics of the VSC under large-signal disturbances. This paper firstly studies the transient synchronization mechanism between VSC and the power grid under grid faults and expounds on the reasons for the transient instability of VSC with the current limiting strategy. Based on the above analysis, a transient enhancement strategy is proposed to reduce the imbalance of active power and reduce the risk of VSC transient instability. It is worth mentioning that the proposed transient control strategy will not affect the steady-state output characteristics of the VSC. Finally, simulation and experiment verify the effectiveness of the proposed control strategy.