具备故障电流阻断能力的改进型子模块及特性

Improved Sub-module with Fault Current Blocking Capability and Its Characteristics Analysis

实际工程中如何实现直流故障电流的阻断是基于模块化多电平换流器(multilevel modular converter, MMC)的柔性高压直流输电(flexible high voltage DC transmission based on MMC, MMC-HVDC)系统中亟须研究与解决的关键问题之一。在分析已提出的子模块拓扑的基础上,提出一种带有双向开关的钳位双电容子模块(clamp double capacitor bidirectional switch sub-module, CDCBSSM)。该子模块拥有双电容,可以输出3个电平,发生故障时将电容反向串联进故障回路中,利用电容的反向电压在抑制故障电流的同时迫使钳位二极管处于偏置状态从而快速切断故障电流且闭锁后电容电压较为稳定。与其他子模块拓扑相比,该子模块单位电容下所需功率器件的数量最少,具有良好的经济性。在MATLAB仿真平台上对该子模块的故障阻断特性进行验证,仿真结果证实该子模块在阻断直流故障电流方面有效,且各功率器件的电压应力也和理论分析相吻合。

How to realize the blocking of DC fault current in practical engineering is one of the key problems that need to be studied and solved urgently in the flexible high voltage DC transmission based on MMC(MMC-HVDC)system based on modular multilevel converter(MMC).Based on the analysis of the proposed sub-module topology,a clamp double capacitor bidirectional switch sub-module(CDCBSSM)with a bidirectional switch was proposed.This sub-module has dual capacitors that can output three levels.When a fault occurs,the capacitor was connected in reverse series into the fault circuit,and the reverse voltage of the capacitor was used to suppress the fault current while forcing the clamp diode to be in a bias state to quickly cut off the fault current and the capacitor voltage is relatively stable after blocking.Compared with other sub-module topologies,this sub-module requires the least number of power devices per unit capacitance,and has good economic efficiency.The fault blocking characteristics of this sub-module were verified on the MATLAB simulation platform.The simulation results confirm that the sub-module is indeed effective in blocking DC fault current and the voltage stress of each power device is also consistent with the theoretical analysis.