The construction of new power system with high proportion of new energy and high proportion of electronic power is in urgent need of new DC transmission technology with strong network construction and active support capability. modular multilevel converter (MMC) is a widely used topology in medium voltage DC distribution networks, but the large number of switching devices and the number of submodules lead to increased costs and losses. Equipment volume and space constraints and other factors restrict the further development of MMC. To solve these problems, this paper proposes a topology of HVDC converter main circuit based on diagonal bridge structure with energy-consuming devices. The new converter topology consists of two key components: The diagonal H-bridge dissipative arm (Unidirectional current H-bridge SM, UCH-SM) and BUCK inverter unit (unit internal devices in series) are connected in parallel to the main converter circuit, in which the dissipative arm is used to deal with faults and improve redundancy capability, and the function of the converter is buck and inverter. According to the calculation and simulation analysis (MATLAB/Simulink), the new commutation topology has the advantages that attract researchers more: 1) smaller volume; 2) Lower loss (low heat); 3) More stable and secure (topology design security). Finally, the new topology can be used not only for DC commutation, but also for energy storage and motor control.