Research On Simulation Of Voltage Sourced Converter Based Direct Current Transmission (VSC-HVDC)

During the early state of power network restoration, because of the relatively small capacity of power system, adding large power load at one time will impact the power system severely and affect its frequency stability. For fear of this, the restoration speed has to be slowed down. During the process of the transmission line and transformer restoration, overvoltage cannot be ignored. Above all are the critical issues that remain to be solved during the process of black start. In addition to find ways in the power system, VSC-HVDC(Voltage Sourced Converter based HVDC), which is rapidly developing in these years, provides another feasible option for power system black start.Based on a comprehensive research and contrastive analysis on the aspect of multilevel VSC-HVDC state-of-the-art, performance principles and its control strategies, diode-clamped VSC is selected and finished test simulation in PSCAD/EMTDC, results proved topology and control stategy are valid. Based on a deep learning of the principle and control mode of AGC(Automatic Generation Control), a test simulation on AGC has been finished in PSCAD/EMTDC and proved the validity of it. A customized governor which can proceed secondary frequency modulation is modeled in PSCAD/EMTDC, and several test simulations for the governor have been finished and proved it can modulate the output of generator effectilvely. Based on the work above, a restoration strategy which VSC-HVDC assisted by AGC has been proposed, and the role of VSC-HVDC during the whole restoration has been investigated. At last, the whole model compresses Diode-clamped three level VSC-HVDC connected to the improved five-node power system has been established and simulated in PSCAD/EMTDC, which added excitation system and customized governor to the generator has been broken down, waiting for restoring by the Diode-clamped three level VSC-HVDC. The simulation results show that the restoration strategy can coordinate the output power of two generators in the five-node system and induce power of VSC-HVDC successfully. Moreover, it can increase the restoration scale of the system load significantly, which at the same time controlling the power network remain stable can increase the power system restoration speed.