碳化硅（silicon carbide，SiC）器件开关频率高、损耗低，采用SiC代替传统硅（Silicon，Si）模块化多电平换流器（modular multilevel converter，MMC）可实现更高频次谐波注入，从而进一步减小子模块的电压波动。通过探究SiC MMC的谐波注入边界，提出了一种多次谐波协同注入的子模块电容电压波动抑制方法。首先基于传统MMC模型探明了MMC注入谐波的频次边界；接着，建立了多次谐波协同注入的子模块电容电压波动抑制优化模型，通过2+3+4+8次谐波协同注入，进一步抑制了子模块的电压波动。结果表明所提策略相比于环流抑制和典型2次环流注入方案，其电容电压波动分别降低了71.12 %和54.17 %，为MMC的轻量化设计提供了有力支撑。

Silicon carbide （SiC） devices feature high switching frequency and low switching loss. Replacing traditional silicon （Si） modular multilevel converters （MMCs） with SiC enables higher-frequency harmonic injection, thereby further reducing submodule voltage fluctuations. By exploring the harmonic injection limits of SiC MMCs, a method for suppressing submodule capacitor voltage fluctuations through coordinated multi-harmonic injection is proposed. Firstly, the frequency boundary for harmonic injection in conventional MMCs is determined based on the traditional MMC model. Secondly, an optimization model for submodule capacitor voltage fluctuation suppression via coordinated multi-harmonic injection is established. By injecting a combination of 2nd, 3rd, 4th, and 8th harmonics, the submodule voltage fluctuations are further mitigated. The results show that the proposed strategy reduces capacitor voltage fluctuations by 71.12% and 54.17% compared with circulating current suppression and typical 2nd harmonic injection schemes, respectively, providing strong support for the lightweight design of MMCs.