Submodule Level Power Loss Balancing Control for Modular Multilevel Converters

This paper investigates the power loss imbalance in Modular Multilevel Converters (MMCs) with Nearest Level Modulation (NLM) resulting from the low switching frequency operation and the parameter mismatch. The imbalance might pose a challenge to the cooling system design as well as the reliability of the MMC. To address this problem, a submodule-level power loss balancing control (PLBC) is proposed. Compared with the normal control strategy without the thermal balancing, this method is able to decrease the degree of power loss imbalance among submodules (SMs) to at least half without deteriorating the performance of the converter efficiency and the capacitor voltage ripple. The effectiveness of the proposed control is validated by simulations.