基于半桥型MMC和混合式DCCB的柔直系统直流故障自适应重合闸技术

Research on Adaptive Reclosing Technology for the Half-bridge MMC and Hybrid DC Circuit Breaker Based on HVDC Systems

架空柔性直流输电是进行大规模新能源远距离并网的有效方案。考虑到架空线瞬时性故障概率较大,需配置有效的重启方法来进行系统恢复。传统的自动重合闸方案在重合于永久性故障时,会对系统造成二次过流危害,且需再次跳开直流断路器,加大了断路器的制造难度。为此,该文提出一种基于换流站主动注入信号的故障性质判别方案。该方法通过换流站和断路器的主动配合实现电压信号的注入,并利用行波折反射和低压判据识别瞬时性与永久性故障,进而实现故障测距与自适应重合闸。该方案耐过渡电阻能力强,且不受故障类型的影响,具有较高的可靠性。最后,在PSCAD/EMTDC平台下搭建半桥型MMC直流系统的电磁暂态模型,通过大量仿真,验证所提方法在故障性质判断以及故障测距方面的有效性。

The overhead MMC-HVDC system is an effective solution for large-scale renewable energy integration over long distance. Considering that the occurrence probability of nonpermanent faults of overhead lines is large, it is necessary to recover power transmission subsequent to DC fault isolation quickly. The traditional automatic reclosing scheme will cause a second strike to the system when it recloses to a permanent fault. Therefore, this paper proposed an adaptive reclosing method based on the active injection signal from the converter. By the coordination control of the converter and DC circuit breaker(DCCB), the voltage signal was injected into the faulted line. And the criterion using the traveling wave theory was employed to discriminate the instantaneous and permanent faults, thereby achieving adaptive reclosing and fault location. The method is robust to resistance and fault type. Finally, the electromagnetic transient model of half-bridge MMC-HVDC system was built under PSCAD/EMTDC. The effectiveness of the proposed method in fault identification and fault location was verified by a large number of simulation cases.