An MMC Submodular Capacitor Voltage Balancing Scheme Based on Improved Bucket Sorting

Submodular capacitor voltage balancing problem is becoming increasingly prominent with the rapid development of high voltage and large capacity modular multilevel converter (MMC). The traditional submodular capacitor voltage balancing strategy based on bubble sorting has high time complexity, quantities of comparisons, and consumes a lot of computing resources. A new submodular capacitor voltage balancing method based on improved bucket sorting is proposed in this paper. The scheme utilizes bucket sorting to divide capacitor voltage into different buckets, and then sort the elements in only one bucket by improved quick sorting which sets the Mth data as the reference value and just sorts on one side of benchmark. The strategy can accurately find sub-modules with the smallest or largest capacitor voltage, while time complexity of the algorithm is O(n). Finally, a 227 level one-terminal MMC is used to verify the effectiveness of proposed method.