Influence Of Different Control Modes Of Flexible HVDC On Power Grid Operation After Asynchronous Interconnection In A Power Grid

Multi-terminal DC transmission system based on VSC(VSC-MTDC)has more attention and wide application in the field of energy,and is a new generation of HVDC technology.Due to the development and application of smart grid technology in the recent years,VS-HVDC transmission technology has gained more attention both at home and abroad.By analyzing the operation of a Multi-terminal DC transmission under asynchronous control in a network with different control modes,the paper draws the conclusion that different conditions affect the system.First of all,the paper compares and analyzes the connection modes between VSC-HVDC and VSC-MTDC,and VSC-MTDC in parallel and VSC-MTDC in series are also compared in operating characteristics.Furthermore,three kinds of converters including two-level converter,three-level diode-clamped converter and MMC(Modular Multilevel Converter)are emphatically compared.And the VSC-MTDC based on MMC is determined as the focus of the paper.Then the paper analyzes the control strategy of VSC-MTDC system,which includes the coordination strategy of VSC-MTDC,stability control and AVC,the coordination strategy of converter station and station,and valve-level control strategy.The design principle of protection part in the VSC-MTDC system is based on the principle of physical or logical objects for the function of configuration,different objects exchange of information between functions as little as possible,then the impact between each other can be minimized.And the paper proposes concrete control measures to the system from many aspects.Finally,the paper compares the stability of the AC system,the transient voltage operation of the power grid and the stability of the system under asynchronous network with different control modes of VSC-MTDC system under different control modes.From the aspects of voltage stability,transient voltage sensitivity and the risk of switch refused to move and other aspects of the specific analysis,and draw different control modes for the operation of the power grid.