Design Study Of Connect To The Grid Base On Modular Multilevel Voltage-sourced Converter Of High Voltage Direct Current

The grid peak shaving and scheduling problem for connet to the grid by Traditional AC Transmission or LCC HVDC are not very good solved, when application of connet to the grid of the two transmission methods was compared with VSC HVDC, the advantages is incomparable. The AC side needs a large number of filter device s and it is hard to apply larger power and higher voltage grade in VSC HVDC base on the voltage source two levels or three levels converter topology. The design concept for VSC HVDC based on modular multilevel voltage-sourced converter introducts Modular. The number of output level can be adjusted according to the number of series of sub modules. More ideal of output waveform, saving the large power filtering device cost, larger power and higher voltage grade,decrease the switching frequency of sub modules, dropping further the loss compare to the two levels and three levels are more suitable for MMC VSC HVDC applications.This paper based on the research of the working principle of SM analyzes the topology of MMC converter and introduces the switch state variables and control MMC formula. The equivalent circuit of MMC circuit model is combined with the characteristics of the equivalent circuit of MMC. Through the research on the parameters of the main devices of MMC converter switch, capacitor, reactor parameters, proposes the modular multilevel converter based on the topology, meanwhile device level control strategy of MMC is proposed.Connect to the grid is the difficulty and key points of the new energy applications. Connecting mode is very important to the grid stability and reliability for new energy connected to the grid in VSC HVDC, especially for connecting mode of MMC VSC HVDC. Overvoltage and insulation coordination and equipment selection in the converter station are discussed. System level and converter station level control strategy of MMC is proposed. Combined with the calculation method of parameters to the main circuit equipment are mentioned in this article, the calculation programs of the steady state, a simulation project analysis. The validation is based on the relevant applications of Nanao island MMC VSC HVDC.Finally, the conclution to the application of connect to the grid based on MMC VSC HVDC is feasibility, and points out some deficiencies and research direction.