Adaptive Balancing Strategy for Cell Capacitor Voltage in a Modular Multilevel Converter

Abstract

Due to the modular structure and voltage scalable features, the Modular Multilevel Converter (MMC) has become an alternative converter for high and medium voltage-based transmission systems. Apart from this, MMC has edible features in controlling the real and reactive power for a high-voltage transmission system compared to the conventional converter. However, some of the technical challenges such as control complexity when subjected to more voltage levels, capacitor voltage balancing issues, increase in capacitor voltage ripples, DC fault handling, and circulating current affect the performance of MMC in various applications. In this paper, an adaptive balancing strategy is proposed for capacitor voltage balancing of each cell connected in the MMC. This approach balances the floating capacitor in a simplified manner and henceforth reduces the capacitor voltage ripples to the permissible limit. In addition, the circulating current present in the MMC circuit will be suppressed in comparison to the conventional method. The proposed strategy is investigated under various operating conditions to analyze the effective performance compared to the traditional technique. A comparative study of the proposed approach is presented with various parameters of MMC performed using MATLAB Simulink software.