Capacitor voltage balance control strategy based on MMC-MTDC

Abstract

The MMC is composed of a large number of sub-modules. The operating conditions of each sub-module are different, which will inevitably affect the capacitor voltage of each sub-module, resulting in the difference of the capacitor voltage of each sub-module. The problem of uneven voltage of the sub-module capacitor voltage of the MMC system is unavoidable, and the uneven voltage of the capacitor will greatly affect the stable operation of the MMC system. This paper studies the multi-terminal flexible DC transmission system (MMC-MTDC) based on modular multi-level converters. The multi-terminal MMC-MTDC system model is established through the MMC-MTDC converter station level and the MMC-MTDC system level controller, and then according to the shutdown process of MMC-MTDC system, several optimal control methods are proposed to realize energy feedback and sub-module discharge to achieve capacitor voltage balance. Finally, the effectiveness of the proposed method is verified by building a simulation model.