一种适用于直流配电网中半桥-全桥混合型MMC的全电平逼近调制策略

为改善半桥-全桥混合型子模块数量较少的模块化多电平换洗器(modular multilevel converter, MMC)运行性能,推进其在直流配电网等中低压领域的应用,提出了一种全电平逼近调制策略(full level modulation,FLM)。所提FLM利用全桥子模块(full bridge submodule,FBSM)的全电平输出能力,控制桥臂中某一FBSM运行于“脉宽调制(pulse width modulation, PWM)模式”,将所得全电平PWM波与原阶梯波叠加以进一步逼近正弦调制波。子模块工作模式由电容电压排序结果确定,相单元中任意时刻均有两个FBSM运行于“PWM模式”,输出互补的全电平PWM波。基于Matlab/Simulink的仿真结果和物理实验结果表明,在所提FLM调制策略下,交流侧电压电流质量远高于传统最近电平逼近调制策略,运行损耗、控制复杂度及循环电流均优于传统载波移相脉冲宽度调制,满足中低压领域的调制要求。

A Full-Level Modulation Strategy for Half Bridge-Full Bridge Hybrid MMC in DC Distribution Grids

In order to improve the operating performance of half bridge - full bridge hybrid modular multi-level converter (MMC) with small quantities of submodules and promote its application in medium and low voltage fields such as DC distribution grids, a novel full-level modulation (FLM) strategy is proposed in this paper. The full-level output capability of full-bridge submodule (FBSM) is utilized in the proposed FLM, where a selected FBSM in arm operates in the “PWM mode”. The obtained full-level PWM wave is superimposed with the original step wave to further approximate the sine modulation wave. The operating mode of submodules is determined by the voltage sorting result, and at any time, there are two FBSMs in the phase unit operating in the “PWM mode”, outputting complementary full-level PWM waves. The results of simulation based on Matlab/Simulink and physical experiment reveal that the quality of voltage and current on AC side under FLM is much higher than that of the conventional nearest level modulation strategy. Compared with the carrier phase-shifted pulse width modulation, FLM performs better in terms of operating loss, control complexity and circulating current, which can satisfy the modulation requirements of medium and low voltage fields.