Fast Sorting Method for Balancing Capacitor Voltages in Modular Multilevel Converters

The modular multilevel converter (MMC) is attracting more and more interest in high-power and high-voltage applications. Highly redundant, each arm of the converter is made of a large number of identical submodules with inner storage capability allowing to reach very high voltage without dc-link capacitor. The control of such a converter represents a challenge when it comes to the implementation of an MMC with a large number of submodules, namely in distributing the control tasks and handling the communicated values in-between controllers and submodules. This paper presents the details of an innovative submodule selection method for the submodule capacitor's voltage balancing within one arm of an MMC. “The Tortoise and the Hare” sorting method shows very fast response, high reliability, and its implementation suits a large number of implemented submodules as for high-voltage dc applications. The proposed submodule capacitor's balancing method is validated on a three-phase 10-kVA prototype with five submodules per arm.