Quasi-Fixed-Frequency Hysteresis Current Tracking Control Strategy for Modular Multilevel Converters

Abstract

This study proposes a quasi-fixed-frequency hysteresis current tracking control strategy for modular multilevel converters (MMCs) on the basis of voltage partition principle. First, by monitoring the grid voltage and the deviation between the output and reference currents, the output voltage is determined, thus prompting the output current to quickly and efficiently track the given current. Second, the voltages of the upper/lower capacitor of the arm and the voltages between the upper and lower arms are balanced by combining these arms with virtual loop mapping and arm voltage balance control, respectively. In particular, the proposed method is designed for any level and number of sub-modules. The validity of the proposed method is verified by simulations and experimental results of a five-level MMC prototype.

Comparison of Current Control Strategies in Modular Multilevel Converter

“…All three control terms are added into a single cost function, the desired performance is achieved by minimizing cost function. In addition, hysteresis current control method is proposed to control MMC [45], [46]. It is straightforward, but more effort is made on choosing voltage levels as the number of voltage level increases.…”