A Current-Based Submodule Selection Algorithm for a Modular Multilevel Converter with Integrated Batteries

As the demand for grid-tied energy storage systems increases, battery storage systems with a multilevel inverter topology based on modular submodules are gaining more attention due to their efficiency and decreased filter demand. These systems allow to combine different types of batteries including second-life batteries, which are likely to have different current limits. This work proposes a new submodule selection algorithm to enforce these limits within a modular multilevel converter with integrated batteries. In contrast to typical algorithms for modular multilevel converters with integrated batteries the presented algorithm considers the battery current and sets it as targeted. This allows to precisely set the operation point of each battery, which is crucial in reducing the aging of the batteries. The proposed, current-based submodule selection algorithm can be combined with any sorting and selection approach for a modular multilevel converter with integrated batteries. Its operating principle is demonstrated by experiments.