含故障限流器投入的MMC-HVDC系统直流短路故障电流解析计算

DC Fault Current Analytical Calculation of MMC-HVDC System Including Fault Current Limiter

基于模块化多电平换流器的高压直流(high voltage direct current based on modular multilevel converters,MMC-HVDC)系统发生直流短路故障时,故障电流上升速度快,这对系统保护提出了极大的挑战。对于采用半桥子模块拓扑的MMC-HVDC系统,通常会在直流线路两端加装故障限流器(fault current limiter,FCL)来抑制故障电流。在对FCL进行优化设计以及进行故障保护时,需要考虑含FCL投入的故障电流的演化规律。因此,含FCL投入的故障电流计算具有重要的意义。通过研究并联金属氧化物避雷器(metal-oxide arrester,MOA)的电感型FCL的特性,建立了FCL的暂态等效模型,将含FCL投入的故障电流演化划分为3个阶段:FCL未投入阶段、FCL投入的过渡阶段和FCL完全投入后阶段。对3个阶段的故障电流的解析表达式分别进行了推导,最后得到全过程的故障电流解析表达式。通过在PSCAD/EMTDC中搭建的两端MMC-HVDC系统的仿真模型对解析结果进行了验证,结果表明:故障后10ms内解析结果与仿真结果的最大偏差在3.5%以内,可以满足实际工程应用的需要。

The rapid rise of the fault current brings about great challenges to the protection of the system when a DC short circuit fault occurs in a high voltage direct current system based on modular multilevel converters(MMC-HVDC).Usually, the fault current limiters(FCL) are installed at both the ends of the DC line to suppress the fault current for a half-bridge-based MMC-HVDC system. When optimizing the design of FCL and performing the fault protection, the calculation of the fault current including the FCL input is of great significance. In this paper, an equivalent transient model of the impedance-based FCL in the action stage is derived in terms of the characteristics of the metal oxide arrester(MOA),in which the evolution of the fault current after a fault is divided into three stages. The analytical expressions of the fault current in the three stages are derived respectively, and the analytical expression of the fault current in the whole process is obtained. The electromagnetic transient model for a double-terminal MMC-HVDC system built in PSCAD/EMTDC is used to verify the analysis results. The simulation results show that the maximum deviation is smaller than 3.5% between the analysis results and the simulation results within 10 ms after the fault, which meets the actual engineering application needs.