同步调相机对分层接入特高压直流输电系统的暂态过电压抑制作用研究

目前已有特高压直流工程采用分层接入方式，同时随着新能源发电占比的提高，送端电网面临着暂态过电压的问题，同步调相机可以抑制过电压，有必要深入研究同步调相机对分层接入特高压直流输电系统暂态过电压的抑制效果。建立了含同步调相机的分层接入特高压直流输电系统模型，理论分析了同步调相机对暂态过电压的抑制机理，针对降功率运行、双极运行双极闭锁、双极运行单极闭锁和高低端换流器同时换相失败4种不同工况，研究了不同台数同步调相机对暂态过电压的作用效果，最后提出了基于暂态过电压的短路比增量指标，定量评估了同步调相机对暂态过电压的作用效果。结果表明所提指标可有效定量评估同步调相机抑制暂态过电压的作用效果，当分层接入特高压直流输电系统整流侧交流系统短路比在3~8变化，投入1台同步调相机后整流侧交流系统基于暂态过电压的短路比增量为0.106~0.396，投入2台同步调相机后基于暂态过电压的短路比增量为0.251~0.788，因此，投入同步调相机可等效提高交流系统短路比，有效抑制送端暂态过电压。

Suppressing Effect of Synchronous Condenser on Transient Overvoltage of UHVDC System under Hierarchical Connection Mode

At present, hierarchical connection mode has been adopted in UHVDC projects, and with the increasing proportion of new energy generation, the power grid at the sending end is facing the problem of transient overvoltage (TOV), which can be restrained by installing synchronous condensers, so it is necessary to study the suppressing effect of synchronous condensers on the TOV of UHVDC system under hierarchical connection mode. A model is established for the UHVDC system under hierarchical connection mode with synchronous condensers, and the suppression mechanism of synchronous condensers for TOV is analyzed theoretically. The effect of different number of synchronous condensers on TOV is studied under four different working conditions, including power-down operation, bipolar blocking fault, unipolar blocking fault and simultaneous commutation failure of both high-end and low-end inverters. Finally, the TOV-based short circuit ratio increment (SCRI) is proposed, and the suppressing effect of synchronous condenser on TOV is quantitatively evaluated. The results show that the proposed index can be used for quantitative evaluation of the suppressing effect of synchronous condensers on TOV. When the short circuit ratio of AC system on the rectifier side of UHVDC system under hierarchical connection mode varies from 3 to 8, the TOV-based SCRI at the rectifier side AC system is between 0.106 and 0.396 after one synchronous condenser is put into operation, and between 0.251 and 0.788 after two synchronous condensers are put into operation. Therefore, the implementation of synchronous condensers can effectively enhance the short circuit ratio of AC system and effectively restrain the TOV at the sending side.