基于MMC变流器柔性直流输电系统调制方法与损耗研究

The Research of Modulation Schemes and Loss of Converter based on MMC Flexible DC Transmission System

对MMC变流器的拓扑和工作原理进行了分析,并通过求解一个工频周期内开关器件电流的有效值和平均值,得出载波移相调制下MMC变流器损耗的计算公式;通过对换流阀损耗进行分段解析计算,得出最近电平逼近调制下MMC变流器的损耗计算公式.根据损耗与子模块个数的关系,得出2种调制方式下,损耗相等时对应的临界的子模块数.然后分析了各系统参数大小的改变对这个临界子模块数的影响,为工程上选择较优的调制方式提供参考依据.最后通过仿真验证了所得结论.

MMC （modular multi- level converter） has two typical types of modulation schemes, carrier phase-shifting sinusoidal pulse width modulation（CPS-SPWM） and nearest level modulation（NLM） .The circuit characteristic of MMC and the basic principle of work were analysed. The equation for calculating the losses of MMC based on the CPS-SPWM was obtained by working out the average current and the effective current of each switching device during one period. By separating the loss of MMC based on NLM into several parts, the formula to calculate the loss was proposed. According to the relationship between the loss and the numbers of the sub- modules, the critical count of the sub-modules at which the losses of the MMC based on the two different modulation were the same, was able to calculate. Then the influence of the system parameters upon the critical count was analysed, which provided reference for choosing the best scheme on engineering. At last , simulation was given to confirmed the conclusion proposed above.