Model-Predictive Control for Modular Multilevel Converters Operating at Wide Frequency Range with a Novel Cost Function

Modular multilevel converters (MMCs) have been a promising topology in medium-voltage motor drive applications over the past few decades. The main challenge that hinders the widespread use of the MMC in medium-voltage motor drives is the large voltage fluctuation under low-speed conditions. In this article, we propose a model-predictive control (MPC) for the MMC operating in a wide frequency range. Unlike conventional MPC methods, a novel cost function has been designed to realize the output current control and the voltage balancing control for both low- and high-frequency operations. Compared with the high-frequency circulating current injection method, the proposed method can easily achieve a tradeoff between the modulation range and the amplitude of injected common-mode voltage under different operating conditions. In addition, due to the exclusion of the switching process between low- and high-frequency operations, the control structure of this method is more straightforward. Finally, the experimental results verify the effectiveness and superiority of the proposed method.