适用于直流配网的故障自清除型电力电子变压器

基于MMC-ISOP电力电子变压器结构的直流配电系统发生中压直流母线双极短路故障后，若采用常规半桥型MMC子模块，交流母线会与故障点构成三相短路而产生较大故障电流损坏功率器件，后级ISOP变换器输入侧若采用直接串联方式同样无法避免输入电容对地放电问题。提出具有故障电流自清除能力MMC子模块拓扑，未提高器件数量、电容耐压等级，且保证了阻断能力。提出DAB变换器输入侧混合串联型ISOP拓扑，可有效切断故障后电容放电通路，降低电容电压应力及电感电流脉动，缩短故障后系统恢复时间。利用Simulink软件搭建了直流配网稳态及故障状态仿真模型，仿真结果验证拓扑结构有效性及理论分析准确性。

Power Electronics Transformer with Fault Self-clearing Ability for DC Distribution Network

After the bipolar short circuit fault of the medium voltage DC bus in the DC distribution system based on MMC-ISOP PET structure, the AC bus will form a three-phase short circuit with the fault point when the conventional half bridge type MMC sub module is adopted, which will cause a large fault current to damage the power devices. Moreover, when the input side of the later stage ISOP converter is direct series connection, the short circuit discharge of the input capacitor cannot be avoided as well. In this paper, an MMC sub-module topology with DC fault self-clearance capability is proposed at first, and the blocking ability is guaranteed without increasing the number of devices and voltage withstand level of capacitors. A input side hybrid series type ISOP topology of DAB converter is proposed, which can not only effectively block the discharge of the input side capacitor after the fault, but also reduce the low voltage stress of the capacitor and the ripple of the inductance current. Moreover, the system recovery time after fault will be shortened. Then the simulation models of DC distribution network under steady state and fault state are built by Simulink software, and the simulation results verify the validity of the topology structure and the accuracy of the theoretical analysis.