Patent ID: 9627956
Date: 2017-04-18
CPC Classifications: H02M

Claim:
1. A method of riding through and recovering from a short circuit fault of a DC side of a high-voltage direct current transmission (HVDC) system, the HVDC system comprising a grid, multiple DC lines, and a hybrid modular multilevel converter (hybrid MMC); the hybrid MMC comprising multiple phases; each phase comprising an upper arm and a lower arm; each of the upper arm and the lower arm comprising a full-bridge sub-module and a half-bridge sub-module; the method comprising: 1) detecting whether the short circuit fault of the DC side of the HVDC system occurs by using the hybrid MMC, and proceeding to 2) if yes and continuing detecting if no; 2) sequentially performing step A) and step B) by using the hybrid MMC to ride through the short circuit fault of the DC side; 3) detecting whether a residual voltage of the DC side increases by using the hybrid MMC, and proceeding to 4) if yes and continuing detecting if no; and 4) sequentially performing step A) and step B) by using the hybrid MMC to recover from the short circuit fault of the DC side; wherein: step A) comprises: detecting the residual voltage of the DC side, a three phase AC voltage of the HVDC system, and a three phase AC current of the HVDC system; setting a reactive power required to be injected to the grid by the hybrid MMC during failure of the HVDC system and an active power required to be transmitted by the DC lines; and obtaining an AC voltage reference e step B) comprises: calculating a first voltage reference u