直流故障下MMC-HVDC的两段式限流保护策略

Two-stage Current Limiting Protection Strategy for MMC-HVDC Under DC Fault

如何对直流故障电流进行有效抑制是实现柔性直流电网大规模发展的关键。为此,研究模块化多电平变换器(modular multilevel converter,MMC)的控制方法,提出一种针对半桥型MMC的两段式限流保护策略,通过减少子模块的投入数目来降低换流站直流出口电压,达到限制短路电流的目的。首先,介绍MMC的拓扑结构及基于MMC的高压直流输电(MMC based high voltage direct current,MMC-HVDC)系统控制策略;其次,分析两段式限流保护策略的原理与直流故障电流特性,介绍MMC-HVDC系统的直流故障保护策略;最后,通过双端MMC-HVDC系统仿真实验,对所提限流保护策略的有效性进行验证。仿真结果表明,两段式限流保护策略可以有效降低断路器开断电流和吸收能量,节约成本。

It is crucial to realize large-scale development of the flexible DC grid effectively suppressing DC fault current.Aiming at this problem,this paper studies the control method of modular multilevel converter(MMC)and proposes a two-stage current limiting protection strategy aiming at the half-bridge MMC which could reduce the DC output voltage by reducing the numbers of sub-modules so as to reach a purpose of limiting the short-circuit current.Firstly,the paper introduces the topology of the MMC and the control strategy of the MMC-HVDC.Then it analyzes the principle of two-stage current limiting protection strategy and DC fault current characteristics,and introduces the DC fault protection strategy of the MMC-HVDC.Finally,by means of simulated experiment of the double terminal MMC-HVDC system,it verifies the effectiveness of the current-limiting control strategy.The simulation results show that the proposed two-stage current limiting protection strategy could effectively reduce the breaking current and absorbed energy of the DCCB,and save the investment costs obviously.