Effect of Averaging Voltage Regulation Control on Steady-State Analysis of Modular Multilevel Converters

The modular multilevel converter (MMC) is a popular research topic in power electronics and is a promising topology for high-power applications. Many steady-state analysis models have been investigated for MMCs. The circular interaction among the electrical quantities in an MMC has been established and improved models have been proposed, with consideration of the second-order circulating current controller and line harmonic currents in the analysis. So far, no steady-state analysis models have addressed the effect of averaging voltage regulation control, which influences switching function of MMC upper and lower arms, and finally, the accuracy of steady-state analysis. In this article, we discuss the validity of existing models with and without averaging control. After extensive simulations, it is found that the accuracy is affected, showing the weakness of existing models and verifying the effect of averaging voltage regulation control on steady-state analysis of MMCs. Then, to solve this problem, an improved analysis model is proposed. In this model, averaging control is considered at the beginning of circular-interaction-based analysis. The new model presents a higher accuracy compared with the existing ones.