The calculation method of optimized AC choppers capacity in islanded MMC-HVDC system

Abstract In order to ensure the safety of renewable energy generation integration system through islanded MMC-HVDC, the AC choppers with the same capacity as sending end converter station are equipped in current projects. However, considering the actual operation needs, it is not necessary to equip so many AC choppers. The optimal capacity of the AC choppers can be calculated according to the most serious fault. The calculated capacity can meet two requirements. One is the renewable energy generation units just start to cut off when the DC voltage reaches the overvoltage limit value. Another one is to minimize the cost and floor area of the AC choppers. It can ensure that the converter station devices is not be damaged in the condition of lowest economic cost. A three-terminal and a four-terminal renewable energy generation integration system through islanded MMC-HVDC are built in PSCAD, which verifies the correctness of the theoretical analysis.