Abstract：For the half-bridge modular multilevel converter（MMC）bridge arm in a control cycle within the

input and removal of the submodule of the respective capacitance voltage sequence before and after the relationship of the characteristics of the same，based on the last cycle of the submodule switching state and the submodule capacitance voltage sequencing，the optimize bubble sorting method was put forward to reduce the number of comparisons in the sorting process. At the same time，based on the change rule of the submodule capacitance voltage law，a new type of voltage equalization strategy was proposed，which reduced the submodule switching frequency by optimizing the selection of the cast-cut submodule. According to the sub-module capacitance voltage level，the sub-module was divided into three categories of high，medium and low voltage to carry out different castcutting processing，which could effectively reduce the non-essential sub-module additional switching action. It was verified that the optimized sequencing method and voltage equalization strategy can effectively reduce the time complexity of sequencing and the switching frequency of submodules.

      Key words：modular multilevel converter（MMC）；bubbling sort；equalization control method；switching

frequency；SMs'capacitance voltage