新型双降压式模块化多电平直流变压器

为保证直流配电网稳定运行，直流变压器起到了至关重要的作用。针对半桥和全桥型模块化多电平直流变压器存在的直通和死区问题，本文提出了一种新型双降压式模块化多电平直流变压器，详细阐述了其拓扑结构和工作原理。基于类方波调制方法，分析了在不同外移相角和桥臂子模块内移相角的情况下该拓扑的变压器漏感电流变化以及功率传输特性。并提出了结合子模块电容电压变化量与当前电容电压值的排序算法，实现了桥臂内的电容电压平衡。基于PSIM平台对比了传统桥式模块化多电平直流变压器（HB-MMDCT）与本文所提出的双降压式模块化多电平直流变压器(DB-MMDCT)在类方波调制方法下的运行特性，验证了本文所提拓扑和控制方法的可行性和有效性。

A novel modular multilevel DC transformer based on dual buck submodule

DC transformer plays an important role in maintaining the stable operation of the DC distribution grid. This paper proposes a novel modular multilevel DC transformer based on dual buck structure (DB-MMDCT) in order to address the shoot through and dead time issue in the half/full-bridge based modular multilevel DC transformer (HB-MMDCT). The topology and the operation principles are discussed. The leakage inductor current and the active power transmission property with different outer phase shift angles and inter-submodule phase shift angles per arm under the quasi square wave modula-tion scheme are illustrated. Furthermore, a capacitor voltage balancing algorithm is given by sorting the capacitor voltages and their charge differences. At last, comparative simulation waveforms between the HB-MMDCT and the proposed DB-MMDCT are illustrated in PSIM when the quasi-square wave modulation is adopted, thus validating the priority of the proposed topology and the effectiveness and validity of the corresponding control methods.