Abstract:By means of injecting a certain amount of second harmonic current, the submodule capacitor voltage ripples of modular multilevel converter (abbr. MMC) can be suppressed to reduce the demand on the submodule capacitance, thus, the volume and cost of MMC converter valve can be reduced. Besides, under the unbalanced grid voltage the voltage ripple of the submodule capacitance increases, if adequate strategy is not adopted the overvoltage of submodule might be caused. In allusion to above-mentioned problems, a second harmonic current injection strategy suitable to hybrid MMC under imbalance grid voltage was proposed. Firstly, a mathematical model for MMC under the unbalanced grid voltage was established. Secondly, the ripple characteristic of the voltage of the submodule capacitance was analyzed to reveal the relation between the voltage of the submodule capacitance and the power fluctuation of bridge arms. Thirdly, based on the instantaneous power model of bridge arms the optimizing strategy and computing process of harmonic injection parameters was put forward. Finally, on the platform of PSCAD/EMTDC, a simulation model of hybrid MMC was constructed to verify the effectiveness of the proposed strategy. Simulation results show that the capacitor voltage ripple under several typical unbalanced grid voltages can be effectively suppressed by the proposed strategy.
标题：不平衡网压下混合模块化多电平换流器子模块电容过压抑制策略
英文标题：Overvoltage Suppression Strategy of Hybrid MMC Sub-modules Capacitor Under Unbalanced Grid Voltages
