Study Of Control Strategies Applying VSC-HVDC To Start Power Grid

Aiming at the disadvantages of applying HVDC to grid interconnection that active power and reactive power can't be controlled independently, the advantages and feasibility of applying VSC-HVDC to grid interconnection are analyzed. Direct analytic expressions between the controlling and controlled variables are derived by a two-terminal VSC-HVDC steady state model. The Simplex method and designed objective function are presented to optimize PI parameters in the VSC-HVDC system. The VSC-HVDC applying to grid interconnection has the capability of providing the control strategy features of"soft-close"and"spinning reserve"when a serious fault occurs in an interconnected ac system, and the control system is designed. The mechanisms of forming the power frequence overvoltage caused by the capacitive effect of a non-loaded long overhead lines and the switching overvoltage by closing non-loaded overhead lines in the restoration are analyzed, and the control strategy and control system based on VSC-HVDC are presented. The PSCAD/EMTDC simulation results verify the advantages applying VSC-HVDC to grid interconnection over conventional HVDC.