US 12,431,782 B2
Modular multilevel converter and control method thereof
Peng Xiao, Shanghai (CN); and Yi Zhang, Shanghai (CN)
Assigned to Delta Electronics (Shanghai) Co., Ltd., Shanghai (CN)
Filed by Delta Electronics (Shanghai) Co., Ltd., Shanghai (CN)
Filed on Oct. 18, 2023, as Appl. No. 18/381,592.
Claims priority of application No. 202211393764.2 (CN), filed on Nov. 8, 2022.
Prior Publication US 2024/0154513 A1, May 9, 2024
Int. Cl. H02M 7/217 (2006.01); H02M 1/00 (2006.01); H02M 1/32 (2007.01)
CPC H02M 1/0003 (2021.05) [H02M 1/32 (2013.01); H02M 7/2173 (2013.01)] 10 Claims
OG exemplary drawing
 
1. A control method for a modular multilevel converter, the modular multilevel converter comprising a bridge arm and a controller, the bridge arm comprising n upper bridge arm submodules and n lower bridge arm submodules, the modular multilevel converter being electrically connected with a voltage bus, a midpoint of the voltage bus being electrically connected with a power grid, the modular multilevel converter receiving an AC input voltage from the power grid, the AC input voltage having a positive peak value and a negative peak value relative to the midpoint of the voltage bus, the controller being coupled with the n upper bridge arm submodules and n lower bridge arm submodules, the control method comprising steps of:
when the AC input voltage from the power grid is lower than a drop threshold value and the modular multilevel converter is in a drop state, the controller determining the number of working units in the n upper bridge arm submodules and the n lower bridge arm submodules based on the instantaneous value of the AC input voltage;
controlling y upper bridge arm submodules of the n upper bridge arm submodules and (n−y) lower bridge arm submodules of the n lower bridge arm submodules to be in an on-state, so that (n−y) of the n upper bridge arm submodules are idle upper bridge arm submodules and y of the n lower bridge arm submodules are idle lower bridge arm submodules; and
in one or more times, controlling x idle upper bridge arm submodules of the (n−y) idle upper bridge arm submodules and x idle lower bridge arm submodules of the y idle lower bridge arm submodules to be in the on-state,
wherein when the instantaneous value of the AC input voltage is the positive peak value, at most m upper bridge arm submodules of the n upper bridge arm submodules are in the on-state, and at least (n−m) upper bridge arm submodules of the n upper bridge arm submodules are idle, wherein when the instantaneous value of the AC input voltage is the negative peak value, at most m lower bridge arm submodules of the n lower bridge arm submodules are in the on-state, and at least (n−m) lower bridge arm submodules of the n lower bridge arm submodules are idle, wherein x≤(n−m).