模块化多电平换流器型直流输电电平数选择研究

Selecting number of voltage levels for modular multilevel converter based HVDC

为分析模块化多电平换流器型直流输电拓扑的输出电压电平数选取原则,在采用基波频率调制方式的基础上,分析了影响换流器输出电压电平数的三个关键因素,即控制器触发频率、子模块个数和电压调制比。推导了影响电平数的两个控制器触发频率临界值,并得出了换流器输出电压总谐波畸变率与上述三个影响因素的关系曲线,为选择MMC-HVDC系统的电平数提供了理论依据。通过PSCAD/EMTDC搭建了MMC-HVDC仿真模型,仿真结果验证了该模型的合理性及上述电平数选择原则的正确性。

This paper discusses the operation principle of selecting the number of voltage levels for modular multilevel converter based HVDC（MMC-HVDC）.The fundamental frequency modulation for MMC is developed.The three factors influencing the number of output voltage levels are analyzed,including the firing frequency of the controller,the number of submodules and the voltage modulation index.Two cut-off frequencies,which significantly influence the number of output voltage levels and THDs,a re calculated to select a proper firing frequency.The relationship curve of the three factors with the AC system harmonic level is analyzed,which provides a theoretical evidence in MMC-HVDC preliminary design stage.The model of MMC-HVDC is realized by PSCAD/EMTDC,and the simulation results demonstrate that the model is reasonable and the analysis above is correct.