Start-up control of a HVDC grid based on MMC with integrating large-scale wind farms

With the rapid development of voltage source converter (VSC) based high voltage direct current (HVDC) transmission technology, the HVDC grid will be an effective solution for large-scale renewable energy generations integration. The modular multilevel converter (MMC) is one the most promising topology for HVDC and DC grid presently. The precharge of the MMCs and start-up of DC grid are essential problems. This paper studies the sequential start-up control of the VSC-HVDC grid with wind farms integration. After the discussion of control system, the precharge principle of the MMC is analyzed. A coordinated start-up control scheme of a DC grid with integrating large-scale wind farms is presented as well as sequential start-up control methods under typical operation modes with HVDC breakers are also investigated. Cases studied are carried on a four-terminal HVDC grid model in PSCAD/EMTDC to verify the proposed schemes.