MMC型柔性直流输电系统三次谐波注入调制策略的可行性

Feasibility of Third Harmonic Injection Modulation Strategy for MMC-HVDC Transmission System

介绍了模块化多电平换流器的基本工作原理和三次谐波注入调制策略实现方式,理论分析了三次谐波注入调制策略对换流器接地方式的要求,该调制策略只适用于直流侧接地方式的柔性直流换流器。此外,还分析了三次谐波注入调制策略对子模块电容电压波动以及桥臂电流有效值和峰值的影响,该调制策略会在子模块电压中引入较小的三、四次谐波,大幅度减小基波幅值,从而导致其波动范围变小,有助于提高换流阀电压安全裕度;同时,还会减小桥臂电流有效值和峰值,有利于提高换流阀电流安全裕度。最后搭建了RTDS仿真模型并验证了理论分析的正确性。

The basic operation principle of modular multilevel converter（MMC）and realization of the third harmonic injection modulation strategy are introduced in this paper.The requirement of MMC grounding mode is analyzed theoretically.The modulation strategy is only suitable for the DC grounding voltage-source-converter based high-voltage direct current（VSCHVDC）converter.The effects of the modulation strategy on submodule voltage fluctuations and bridge current root mean square（RMS）and peak values are analyzed theoretically.The third and fourth harmonics will be brought into submodule voltage by modulation strategy,and the fundamental component will decrease so that the fluctuation of submodule voltage will decrease.It is favor for improving the voltage safety margin of the converter valves.The bridge current RMS and peak values will decrease,which is favor for improving the current safety margin of the converter valves.Finally,the simulation model based on RTDS is built and the validity of theoretical analyses is verified.