With gradual launching of large capacity highvoltage direct current (HVDC) projects

the characteristic of “strong DC and weak AC” of the power grid is becoming increasingly conspicuous. The influence of the multiple ultrahighvoltage direct current (UHVDC) sending system on the stability of the interconnected power system is apparent. The HVDC power drop characteristic caused by contingencies of the sendingside system is analyzed and

on the basis of the threeregion AC/DC equivalent model

the impact of the multiple HVDC power drop on the stability of the interconnected system in different power flow directions is accounted for

and the single HVDC blocking is used for comparison. Finally

verification is made using the “North ChinaCentral ChinaEast China” power grid case studies. 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 of effective countermeasures is necessary. This work is supported by State Grid Corporation of China.