双半桥子模块MMC的降频降复杂度运行策略

Frequency and Complexity Reduction Operation Strategy of MMC with Double Half Bridge Submodule

为了改善模块化多电平换流器(modular multilevel converter,MMC)中电容电压均衡难度大和换流站运行损耗高的问题,本文针对双半桥子模块(double half bridge submodule,D-HBSM)设计了一种降频降复杂度运行策略。首先介绍了D-HBSM的串联、并联、旁路工作模式,根据桥臂输出电平数目推导了处于三种工作模式的子模块数。接着,基于子模块轮换思想,分别设计了适用于高压与中低压直流系统的D-HBSM工作模式确定方法。此外,对比了不同电压等级直流系统中D-HBSM与HBSM的运行损耗,体现了D-HBSM的降频效果。最后,基于MATLAB/Simulink的仿真结果表明,所提降频降复杂度运行策略的能够有效改善换流器运行特性。与传统HBSM相比,在相同的电容电压一致性的前提下,D-HBSM的子模块电容利用率提高至70%,高压直流系统中开关频率降低50%,计算负担减小75%。

In order to reduce the difficulty of capacitor voltage equalization and operating loss in modular multilevel converter(MMC),a novel frequency and complexity reduction strategy based on double half bridge submodule(D-HBSM)was proposed in this paper.First,the bypass,series and parallel working modes of D-HBSM were introduced and the number of D-HBSM in three working modes was deduced based on the number of output levels of bridge arm.Then,based on the submodule rotation idea,the methods for determining the working mode of D-HBSM for high-voltage and medium-low-voltage systems were designed.In addition,the operating losses of D-HBSM and HBSM in DC systems of different voltage levels were compared,which reflects the frequency reduction effect of D-HBSM.Finally,the simulation results based on MATLAB/Simulink show that the proposed operating strategy of frequency and complexity reduction can effectively improve the operating characteristics of the converter.Compared with the traditional HBSM,under the premise of the same capacitor voltage consistency,the capacitance utilization rate of D-HBSM is increased to 70%,in high-voltage DC system,the switching frequency and the calculation burden are respectively reduced by 50%and 75%.