Optimal Enhancement Control of Static Voltage Stability Margin for AC/DC Power System With Renewables Considering Control Mode Switching of DC Converter Stations

In an AC/DC power system with high penetration of renewable energy stations (RESs), the injected bus power has high random fluctuation, which brings great challenges to ensuring the sufficient static voltage stability margin (SVSM) of the system. In this paper, considering the impact of uncertain RES output and DC converter stations' control mode switching with the load growth, an optimal SVSM enhancement control model for AC/DC power system is proposed. In the model, the SVSM of the system under uncertain RES power is enhanced by regulating the power output and terminal voltage of generators and the parameters of multiple control modes of DC converter stations. By proposing a triangular convex hull relaxation method and using the uncertainty-aware model (UaM) method and the Karush-Kuhn-Tucker condition of inner-layer optimization model, the proposed bi-layer optimal SVSM enhancement control model is transformed into a single-layer nonlinear programming model, which can be directly solved by the CONOPT solver with high efficiency. Case study on the modified 39-bus AC/DC power system demonstrates that the obtained SVSM enhancement control scheme can accurately consider the influence of DC converter stations' control mode switching with the load growth, identify the influence of uncertain injected bus power on the system SVSM, and enhance the SVSM to satisfy the required secure operation level.