向无源网络供电的MMC-HVDC送端交流故障穿越策略

向无源网络供电的模块化多电平换流器型高压直流输电(MMC-HVDC)系统的送端交流系统发生故障时,功率传输的不平衡会使MMC-HVDC直流电压严重跌落直至系统崩溃。首先分析了送端交流系统发生故障时MMC电容放电的机理,然后设计了一种向无源网络供电的MMC-HVDC送端交流故障穿越策略,该策略的核心思想是在送端故障期间降低无源网络吸收的功率从而使MMC-HVDC直流侧功率尽量平衡。最后在PSCAD/EMTDC仿真平台上搭建了向由感应电动机和静态特性负荷组成的无源网络供电的MMC-HVDC系统,验证了送端系统故障时MMC电容放电机理。仿真结果表明,在所设计的故障穿越策略的作用下,MMC-HVDC在送端交流系统故障期间能够遏制直流电压跌落而保持稳定运行,提高了系统的故障穿越能力。

AC Fault Ride-Through Strategy of MMC-HVDC Connected to Passive Networks

When there is a severe ground fault in AC grid,the modular multilevel converter high voltage direct current( MMC-HVDC)system connected to passive networks will collapse due to the continuous decline of the DC voltage caused by the imbalanced power transfer. Firstly,the discharging mechanism of the capacitors in the MMC is analyzed. Then an AC fault ride-through strategy of the MMC-HVDC system connected to passive networks is proposed,the key of which is to make a balance between the DC power flowing into and out of the MMC-HVDC system through reducing the power absorbed by the passive networks during the fault. Finally,an MMC-HVDC system connected to passive networks, including induction motors and static load models, is established in the PSCAD/EMTDC software, based on which the discharging mechanism of capacitors in the MMC under the condition of ground fault in AC grid is verified. The simulation results demonstrate that,with the help of the proposed fault ride-through strategy,the drop of the DC voltage is mitigated and the MMC-HVDC system operates steadily during the ground fault in the AC system.