A Unified Startup Strategy for Modular Multilevel Converters With Deadbeat Predictive Current Control

Modular multilevel converters (MMCs) are very promising and attractive in medium-/high-voltage applications. One of the main technical challenges associated with MMCs is to precharge all submodule (SM) capacitors to their nominal voltage values during a startup process. This article proposes a simple and effective startup strategy for MMCs based on a deadbeat predictive current control. This strategy can realize a fast precharge for all the SM capacitors from either ac-side or dc-side main voltages without any inrush current and, thus, guarantees a rapid and safe startup of MMCs. With the developed strategy, precharge currents from both ac-side and dc-side can be easily regulated in a closed-loop manner with an excellent dynamic performance. Moreover, conventional controller design and parameter tuning are not necessary, which greatly reduces design burdens and structural complexities of the control algorithm, and consequently facilitates its implementations. Detailed design processes and considerations of the proposed startup strategy are introduced and analyzed. The effectiveness and performance of the developed strategy are verified by sufficient experimental results.