柔直电网站内单相接地故障分析及过电压抑制

柔直电网换流站内单相接地故障的电磁暂态过程复杂且易产生过电压,严重影响系统的安全稳定运行。文中将换流站内单相接地故障分成交流故障区和直流故障区,首先采用复合序网络定量分析交流侧过电压机理及零序电压特征。然后,基于换流器控制器方程推导得到故障序分量从交流侧向直流侧传播的规律,得出零序电压是导致直流侧和其他换流站过电压的主要因素。此外,为了抑制直流侧过电压,提出一种零序过电压控制方法,并给出控制器参数的选择方案。最后,基于PSCAD搭建柔直电网仿真模型,仿真结果验证了故障机理推演的正确性及过电压抑制策略的有效性,提升了站内单相接地故障后的安全稳定运行能力。

Single-phase-to-ground fault analysis and overvoltage suppression in the converter station of flexible DC grid

The electromagnetic transient process of single-phase grounding fault in converter station of flexible DC power grid is complex and prone to overvoltage, which seriously affects the safe and stable operation of the system. In this paper, the converter station is divided into AC fault area and DC fault area by single-phase grounding fault. The complex sequence network is first used to analyze the mechanism of AC overvoltage and characteristics of fault zero-sequence components. Then, the propagation law of fault sequence components from AC side to DC side is deduced based on the control equation of converter, which reveals the fault zero-sequence components are the main factor leading to overvoltage at the DC side and other converters. In addition,, a DC over-voltage suppression strategy is also proposed, and the selection method of controller parameters is also given . At last, a study system is built by PSCAD software, and the simulation results prove the correctness of fault mechanism deduction and the effectiveness of overvoltage suppression strategy, which effectively improves the safe and stable operation ability of the system after a single-phase ground fault in converter station.