Research On VSG Control Strategy Of Back-to-back VSC-HVDC And Short Circuit Characteristic Simulation Of VSC-HVDC

In order to restrain the closing current of 220kV power grid and improve the reliability of the power supply,this paper presents double back-to-back VSC-HVDC device,Using back-to-back VSC-HVDC sets up AC/DC hybrid power grid,and research on the control strategy of VSC-HVDC.DC voltage droop control and virtual synchronous generator are used respectively on VSC-HVDC.Understand the control principle of VSC-HVDC and SPWM modulation mode.Establish mathematical model and analyze the fluctuation of active power,DC voltage,current and frequency with different control strategies when three-phase to earth short circuit and load fluctuation occurs.By simulation results of PSCAD/EMTDC,the superiority of virtual synchronous generator control strategy is verified.The results show that the virtual synchronous generator control strategy can be used to provide the inertia of the system and improve the stability of the system.Gezhouba-nanqiao DC transmission capacity upgrading project will go on and VSC-HVDC technology will be used in Nanqiao converter station.The paper builds VSC-HVDC converter and control system model of receiving end combined with the project.Research on the contribution of VSC-HVDC converter to short circuit current in near area grid combined with the mechanism analysis and model simulation.When direct short circuit?short circuit via 0.lohm transition resistance or short circuit via 0.1ohm transition reactance occurs in VSC-HVDC access point,comparison VSC-HVDC provides short circuit pot with short circuit current phase and total short circuit current.The results show that VSC-HVDC can only feed 1.1?1.2 times the rated current to the AC system.When direct short circuit or short circuit via 0.1ohm transition reactance occurs,if the fault point is located in the converter bus,the current phase of VSC-HVDC feeds AC system is basically the same as before the fault;When short circuit via 0.1ohm transition resistance occurs,The current phase of VSC-HVDC feeds AC system lags 90 degrees before the fault and VSC-HVDC increases the short-circuit current if the fault point is located in the converter bus.