Mechanism analysis on instability caused by multiple HVDC power drop of multiple sending HVDC systems

As the high-voltage direct current (HVDC)s with large capacity are continually being commissioned, the "strong DC and weak AC" characteristic of the power gird is furtherly being presented, the influence of the multiple sending HVDC system on the stability of the interconnected power system is becoming significant. In this paper, the HVDC power drop characteristic caused by contingencies of the sending-side system is analyzed, on the base of the three-area AC/DC equivalent model, the impact of the multiple HVDC power drop on the stability of the interconnected system under different power flow directions is analyzed, and the single HVDC blocking is taken to be compared. Finally, the results are verified by the "North China-Central China-East China" power grid case system. The results show that the instability mode of the sending-side system caused by the multiple HVDC power drop is the first/second angle instability, the severity of the impact of which on the sending-side system stability is close to that of the single HVDC blocking, and further study on the effective counter-measures is quite necessary.