一种基于MMC子模块电压估算的改进调制方法

为了解决传统的模块化多电平换流器(MMC)调制会产生谐波环流的问题,提出了一种基于MMC子模块电容电压估计的改进调制方法,即先利用桥臂能量来估算该桥臂子模块平均电容电压,然后将估算的电压作为参考值,利用最近电平逼近法进行调制,根据推导的公式分析了产生电容电压波动的原因,为进一步抑制二倍频环流,设计了环流抑制器,并搭建了三相仿真模型。仿真结果表明,所提改进调制方法可显著抑制谐波环流,与环流抑制器协同运行可进一步抑制环流波动。

Improved Modulation Method Based on Estimation of Sub-Module Voltages in Modular Multilevel Converter

Focusing on solving the issue of traditional modulation producing harmonic circulating currents in multilevel converter module (MMC), this paper proposed an improved modulation method based on the estimation of sub-module (SM) capacitor voltages in MMC. The average capacitor voltages of each SM was estimated by using the energy of the arm. And then the nearest level modulation (NLM) method was used to modulate according to the estimated voltages. The cause of the fluctuation of capacitor voltage was analyzed on the basis of the derived formula. Aiming at further suppression of the double-frequency circulating currents, a circulating current suppressor was designed. The three-phase simulation model was built. The results show that the improved modulation method can significantly suppress the harmonic circulating currents. The coordinated operation of the improved modulation method and the circulating current suppressor can further suppress the circulating current.