中文摘要：

在交直流互联系统中,交流电网故障引发的直流换相失败可导致交流电网保护不正确动作。分析建立了换相失败情况下逆变器的开关函数模型和直流电流暂态变化模型;根据调制理论及卷积定理,推导出了换相失败情况下直流系统注入交流电网的等值工频及工频变化量电流的动态相量模型;通过分析表明该等值工频及工频变化量电流的变化特性有别于纯交流系统,可能造成交流电网故障引发换相失败时交流电网保护的不正确动作;最后,结合两种具体的交流电网保护,分析了直流换相失败导致交流电网保护不正确动作的机理,为交直流系统继电保护策略研究提供了理论基础。

英文摘要：

In the AC/DC interconnection system, the DC commutation failure caused by AC power network fault can lead to maloperation of AC power network protection. In this paper, under the commutation failure condition, a switching function model of inverters and a transient change model of DC current were established. According to modulation theory and convolution theorem, the dynamic phasor model of DC system equivalent current of power-frequency component variation was deduced. The analysis shows that the variation characteristics of the equivalent current of power-frequency component variation are different from those of pure AC system, which may lead to maloperation of AC power network protection under the DC commutation failure caused by AC power network fault. At last, combining the two specific AC power network protection, the mechanism for maloperation of AC power network protection caused by DC commutation failure was analyzed, which provided a theoretical basis for research on protection strategy of AC/DC interconnection system.