| 主权项 |
1. A ride-through and recovery method for DC short circuit faults of a hybrid modular multilevel converter based high-voltage direct current transmission (MMC-HVDC) system, the hybrid MMC comprising multiple full-bridge sub-modules and half-bridge sub-modules, and the method comprising:
1) detecting whether a DC short circuit fault occurs, and proceeding to step (2) if yes and continuing detecting if no; 2) realizing ride-through of the DC short circuit fault by performing following steps A) and B) sequentially; 3) detecting whether a DC residual voltage increases, and proceeding to step (4) if yes and continuing detecting if no; and 4) realizing DC short circuit fault recovery by performing step A) and step B) sequentially;wherein
step A) is as follows: detecting the DC residual voltage, a three phase AC voltage, and a three phase AC current, combining with a reactive power required to be injected to a grid by the MMC during failure and an active power required to be transmitted by DC lines, and obtaining an AC voltage reference required to be output for each phase of the MMC during ride-through of the DC short circuit fault; and step B) is as follows: calculating a voltage reference uif_p of full-bridge sub-modules' equivalent voltage source and a voltage reference uih_p of half-bridge sub-modules' equivalent voltage source in an upper arm of each phase, and calculating a voltage reference uif_n of full-bridge sub-modules' equivalent voltage source and a voltage reference uih_n of half-bridge sub-modules' equivalent voltage source in a lower arm of each phase, according to the AC voltage reference eiv_ref required to be output for each phase of the MMC during ride-through of the DC short circuit fault, and obtaining a switching signal for each of the sub-modules by combining with a present voltage of each of the sub-modules; wherein the subscript i equals a, b, or c, each of which represents a phase. |
