Stability mechanism analysis of HVDC control system for power system restoration using HVDC

This paper study the power system restoration procedure with external power supplies through HVDC transmission channel. The simplified models of the transmission system under different control modes are established and their stability margin are analyzed by root locus diagram. In consideration of the influence of the short circuit capacity and rotating inertia of power grid at sending end on the stability of HVDC control system, selection and coordinated strategies of HVDC control modes are given during different stages of system restoration. The procedure of power system restoration with HVDC supporting include two phases, phase I is DC line connecting to weak AC system in the receiving end and phase II is load picking up with HVDC power supporting. In phase I, the adaptability of general HVDC control modes are analyzed, and the appropriate control modes are given. In phase II, the control modes transfer strategies are given under large voltage declining during the receiving end AC system is weak. In both of the two phases, detailed stability analysis are carried out for checking the key controller parameters setting. For accelerating load restoration, the amount of load that can be restored once a time for different short circuit capacity of power grid at sending end and receiving end is analyzed. Last, the effectiveness of HVDC stability mechanism analysis is validated by the simulation of Ningdong-Shandong HVDC system using PSCAD/EMTDC.