基于桥臂二倍频电流分量重构的MMC降容控制方法

A Method of Determining the Second Order Component of Arm Current to Reduce the Sub-module Capacitance for Modular Multilevel Converters

模块化多电平换流器(modular multilevel converter,MMC)已显示出很好的工程应用前景。降低MMC子模块电容电压波动对实现换流器的轻型化具有非常大的工程意义。通过对国内外降低MMC子模块电容电压波动的各种控制方法进行归纳总结,可知各种通过控制方案降容的方法的实质为在桥臂上注入谐波电压和电流。在此基础上,提出一种桥臂二倍频电流量重构的方法,并在PSCAD/EMTDC仿真环境下搭建程序进行验证,仿真结果表明所提方法可有效降低子模块电容电压纹波幅值。进一步进行了低电容容值仿真验证,其在保持子模块电容电压纹波幅值不变的情况下,可有效降低子模块电容容值30%以上。另外,进行了MMC换流阀损耗分析,结果表明低电容容值工况下的换流阀损耗不大于对照工况下换流阀损耗。

Modular Multilevel Converter (MMC) has wide prospects in engineering application. It is also of great engineering significance to reduce voltage fluctuation of sub-module (SM) capacitor in MMC to realize the lightening of MMC converter. Various control methods of sub-module capacitor for voltage fluctuation reduction are made a systematic summary and the essence of all kinds of methods for capacitor voltage fluctuation reduction is to inject the harmonic voltage and current into the arm of MMC. In addition,a method for determining the amplitude of the second order circulating current and phase angle of the arm current is proposed. And simulation program used for verification is built in the PSCAD/EMTDC. The simulation waveform shows that the ripple amplitude of sub-module capacitor voltage can be effectively reduced. Further,lowcapacitance simulation is performed. It can be concluded that when the ripple voltage amplitude of the sub-module capacitor keeps constant,the capacitance of the sub-module can effectively reduce more than 30%. And a loss analysis of MMC converter is made. The result demonstrates that the loss of MMC under lowcapacitance condition is not greater than that under contrast condition.