An Optimal Control Algorithm of Capacitor Voltage Balancing for Modular Multilevel Converter

Voltage-balancing is the prerequisite of Modular multilevel Converter (MMC) in normal Operation. In this paper, a sub-module capacitor voltage equalization algorithm is proposed. Compared with traditional sub-module voltage sorting algorithm, this scheme ensures the balance of sub-module capacitor voltage and has a strong dynamic regulation ability. Also, it avoids the problem of complex tuning of multiple controller parameters in the traditional control algorithm. In addition, the algorithm not only improves the utilization ratio of DC voltage, reduces the switching loss and output harmonic, but also greatly reduces the computation and the resource occupation of the digital controller only by requires a simple operation of addition, subtraction and shift when the sector judgement and vector action time are calculated. Consequently, a three-phase three-level low-power MMC experimental platform is built. The experimental results show that the proposed algorithm has good dynamic and steady-state performance for MMC system.