一种增加辅助子模块的MMC改进混合调制控制策略

Improved Hybrid Modulation Strategy for MMC with Auxiliary Sub-modules

传统的最近电平逼近调制NLM(nearest level modulation)具有控制简单,开关频率低的显著优势,但在输出电平数较少时,采用NLM调制的模块化多电平换流器MMC(modular multilevel converter)输出波形谐波畸变率较大。在传统三相六桥臂MMC拓扑的各桥臂中增加1个全桥结构的辅助子模块,控制该辅助子模块的电容电压为半桥子模块的一半。针对该MMC拓扑,提出了一种改进的混合调制策略,该混合调制策略可以实现半桥和辅助子模块的平衡控制。在降低MMC交流侧输出电流的谐波畸变率同时,还可以降低全桥子模块的开关频率和系统损耗。在Matlab/Simulink中搭建了详细的仿真模型,仿真结果验证了所提MMC拓扑和改进混合调制策略的有效性。

The traditional nearest level modulation(NLM)has advantages of simple control and low switching frequency.However,when the number of output levels is small,the harmonic distortion rate of output waveform from a modular multilevel converter(MMC)under the NLM modulation will be large.In this paper,a full-bridge auxiliary sub-module is added to each arm of the traditional three-phase six-leg MMC topology,and the capacitance voltage of the auxiliary sub-module is half of that of the half-bridge sub-module.Aimed at this MMC topology,an improved hybrid modulation strategy is proposed,which can realize the balance control of half-bridge and auxiliary sub-module,reduce the harmonic distortion rate of MMC AC-side output current,and reduce the switching frequency and system loss of the full-bridge sub-module.A detailed simulation model is built in MATLAB/Simulink,and simulation results verify the effectiveness of the proposed MMC topology and the improved hybrid modulation strategy.