改进的最近电平调制策略在模块化多电平变换器中的应用

Modified Nearest Level Modulation for Modular Multilevel Converter

为了提高模块化多电平变换器(modular multilevel converter,MMC)在子模块数量较少时使用最近电平调制(nearest level modulation,NLM)的输出电压质量,以及上下桥臂电压的平衡,提出了一种改进的最近电平调制方法。与传统最近电平调制方法相比,改进的调制方法的优势在于能够将输出电压电平数从N+1增加到2 N+1,在不改变子模块电容平均电压的情况下,降低了输出电压的总谐波失真,并且减小了子模块电容电压的波动以及上下桥臂电压均值的差异。最后通过Matlab/Simulink仿真验证了控制策略的有效性。

In order to enhance the quality of output voltage of a modular multilevel converter (MMC) with the low amount of submodules,as well as the balance of the upper and lower arms voltage when using nearest-level modulation (NLM),an improved NLM method is adopted.Compared with conventional NLM method,the advantage of proposed method is that it can increase the level number of output voltage from N+1 to 2 N+1,reduce the total harmonic distortion (THD) without changing the average voltage of submodules' capacitor and reduce the fluctuation of submodules' capacitor voltage as well as the difference between the upper and lower arms average voltage.Simulation results verified the validity of the proposed method.