基于模糊聚类与识别的特高压混合级联直流系统过电流抑制方法

基于电网换相换流器(LCC)和模块化多电平换流器(MMC)的特高压混合级联直流(HC-UHVDC)系统受到工程和学术界的广泛关注.文中建立了整流侧采用双12脉动LCC、逆变侧采用LCC串联3个并联MMC的HC-UHVDC系统模型,分析了逆变站交流故障LCC换相失败导致直流过电流的产生机理,并提出了一种基于模糊聚类与识别的HC-UHVDC系统过电流抑制方法.该方法首先通过仿真对系统逆变侧交流故障时整流站多电气量进行模糊聚类,根据聚类结果识别的逆变站不同暂态阶段特征来提前设计分阶段的触发角指令值;当系统发生交流故障时再基于整流站本地信息及时调节整流站直流电压,从而快速抑制直流过电流.在PSCAD/EMTDC上的详细电磁暂态仿真结果表明,在逆变侧三相和单相金属性短路故障工况下,所提方法在一定程度上可以抑制逆变站LCC换相失败后的直流过电流和过电压,且可以显著改善HC-UHVDC系统的动态特性.

Overcurrent Suppression Method for Hybrid Cascaded UHVDC System Based on Fuzzy Clustering and Identification

The hybrid cascaded ultra-high voltage DC (HC-UHVDC) system based on the line commutated converter (LCC) and the modular multilevel converter (MMC) has received extensive attention from engineering and academic circles. This paper establishes a model for the HC-UHVDC system in which the rectifier adopts a dual 12-pluse LCC and the inverter is composed of one LCC and three paralleled MMCs in series. And the generation mechanism of the DC overcurrent due to the commutation failure of LCC caused by the AC fault at the inverter station is analyzed. Then this paper proposes an overcurrent suppression method for HC-UHVDC system based on fuzzy clustering and identification. In this suppression method, the fuzzy clustering of multiple electric parameters at the rectifier station is carried out through the simulation in the case of AC fault on the inverter side. According to the characteristics of different transient stages at the inverter station identified by the clustering result, the staged firing angle instruction value is designd in advance. When an AC fault occurs in the system, the DC voltage of the rectifier station is adjusted in time based on the local information of the rectifier station, to quickly suppress the DC overcurrent. The results of the detailed electromagnetic transient simulation in PSCAD/EMTDC show that, under the three-phase and single-phase metallic short-circuit fault conditions on the inverter side, the proposed approach can suppress the DC overcurrent and overvoltage after the commutation failure of LCC at the inverter station to some extent, and can significantly improve the dynamic characteristics of the HC-UHVDC system.