In the uncontrolled charging stage of hybrid modular multilevel converter, the inconsistency of charging states between full bridge submodules and half bridge submodules will lead to the problem of capacitor voltage imbalance, which makes all traditional AC side controlled start-up schemes unavailable. To solve this problem, a hybrid modular multilevel converter AC side start-up strategy based on orthogonal decomposition of bridge arm voltage is proposed. In this strategy, the start-up process of hybrid modular multilevel converter is divided into three stages. In the third stage, the half bridge submodule is charged while the full bridge submodule voltage is kept unchanged by orthogonal decomposition of bridge arm voltage. The basic principle of the strategy is analyzed in detail, and a complete control strategy is proposed. Finally, the effectiveness of the proposed strategy is verified by simulation.

control strategy hybrid, modular multilevel converter, orthogonal decomposition, start-up process