Submodule Control Strategy and DC Fault Ride Through Strategy for Battery Energy Storage System-Based Hybrid MMC

The hybrid modular multilevel converter (HMMC) is a promising topology that can be used in flexible DC transmission system because of its capacity of blocking DC fault. However, renewable energy sources connected to the AC side of HMMC will lead to fluctuation of DC transmission power. To solve this issue, a battery energy storage system (BESS) is proposed to be embedded in submodule (SM) of HMMC, serving as the energy buffer unit. Based on this structure, SM control strategy and DC fault ride through (FRT) strategy are proposed in this paper. The former is aimed at eliminating low frequency component in battery current, accelerating battery current response and balancing SM voltage without additional voltage balance methods, and the latter ensures the continuous operation ability of system without blocking IGBTs in DC fault state. The validity of the proposed method is verified by the full-scale simulations extensively.